TL;DR

Swimming rewards patience and punishes aggression. Small increases in swim speed create disproportionately large increases in drag and effort. The fastest swimmers are rarely the ones who surge the most; they are the ones who maintain the most stable rhythm. 

In the first article we saw that pool length matters less than we think. In the second we explored how tools like the Tempo Trainer help swimmers find rhythm. This final piece explores the deeper reason rhythm matters so much in water.

The Early Sprint Trap

Watch the start of almost any open water race. The horn sounds and the first few hundred meters look like a sprint. Arms churn, kicks explode, and swimmers fight for clear water. For a brief moment, it looks impressive.

Then something predictable happens. A few minutes later, many of those early attackers begin to fade. Their strokes shorten, breathing becomes frantic, and the rhythm that looked powerful at the start begins to unravel.

Meanwhile another group, the swimmers who started slightly more controlled, begin moving steadily forward through the field. By the halfway point, they are often swimming faster than the athletes who attacked the start.

What changed? Not fitness. Physics. Water punishes impatience.

The Universal Set Collapse

The same pattern appears in the pool. Every coach has seen a swimmer start a set of 400s like this:

First repeats:

• 1:27

• 1:29

Later repeats:

• 1:45

• 1:50

At first glance, it looks like fitness collapsed. Usually, it did not. The swimmer simply attacked the water too early, paid a large energy cost, and spent the rest of the set trying to recover.

Swimming Is Not Like Running

On land, increasing your speed usually leads to a fairly predictable increase in energy cost. In the water, the relationship is much harsher because you are moving through a medium 800 times denser than air.

This creates a "Power Tax" that escalates rapidly. Because water resists you more the faster you try to move through it, small increases in speed require disproportionately large leaps in effort. If you try to swim just 10% faster, you do not simply work 10% harder; you actually need roughly 33% more power to overcome that extra resistance.

To visualize this, imagine sliding your hand gently through the water. It moves aside smoothly and the resistance feels manageable. Now, imagine trying to shove your hand forward suddenly. The water immediately "hardens" against you, piling up in front of your palm.

This is why swimmers who surge early almost always pay for it later. Even a small, impulsive surge that feels harmless in the moment dramatically spikes your metabolic cost. Over the course of a set, those "mini-taxes" accumulate until your technique eventually collapses under the debt.

A Simple Way to Picture Drag

Think about riding a bike into the wind. At an easy pace, the wind resistance is noticeable but manageable. Increase your speed and the wind suddenly feels much stronger. Your legs burn much faster even though you only increased speed a little.

Swimming behaves the same way, except the "wind" is water. In water, small increases in speed cause a massive increase in resistance. That extra resistance must be paid for with energy. This is why pacing errors are so expensive in swimming.

Swimming fast is not only about producing more power. It is about avoiding unnecessary resistance.

The Hidden Cost of Surging

When swimmers accelerate suddenly, three things usually happen at once: drag rises immediately, technique begins to deteriorate, and rhythm breaks.

Stroke length shortens. The catch loses pressure: you begin slipping the water rather than holding it. Breathing becomes irregular. What looked like a small increase in speed quickly becomes an unsustainable effort. The swimmer is no longer moving efficiently through the water; they are simply fighting it.

When Does Technique Actually Break Down?

There is an important nuance here. Experienced swimmers often feel the opposite sequence to the one described above. For them, fatigue begins to accumulate first, and technique gradually fades as the metabolic system approaches its limit. In other words, fitness and form fail together.

Swimmers with less technical background often experience a different pattern. Because swimming is extremely sensitive to alignment and drag, small mechanical errors can appear before the aerobic system is fully stressed.

The mechanical system fails first. Stroke length shortens, rhythm breaks, and drag rises even though aerobic capacity is still available.

Both patterns are real and widely observed in swim coaching. Less experienced swimmers are often mechanically limited. More experienced swimmers are often metabolically limited. But the objective is the same for both groups: preserve efficient movement for as long as possible.

Why the Best Swimmers Look Calm

Watch elite swimmers during long sets or distance races. They rarely look aggressive. Their strokes appear relaxed, their breathing controlled, and their rhythm remarkably stable.

This is not because they are working less. It is because they understand that swimming fast is about managing resistance rather than overpowering it. Instead of attacking the water, they settle into a rhythm that allows them to maintain speed without triggering the collapse that impatience creates.

Rhythm Is the Real Skill

This is where the ideas from the earlier articles in this series come together. The first article showed that pool length does not matter as much as we think. The second article explained how tools like the Tempo Trainer help swimmers calibrate rhythm and pace.

But the deeper lesson is this: speed in swimming is rarely produced by sudden acceleration. It is produced by a stable rhythm sustained over time. Swimmers who surge repeatedly create drag, lose pressure on the water, and destroy efficiency. Swimmers who hold rhythm preserve both technique and energy.

The Open Water Lesson

This principle becomes even clearer in open water racing. The swimmers who exit the water fastest are rarely the ones who sprint the first few hundred meters the hardest. They are the ones who settle into rhythm early and maintain it with remarkable consistency from buoy to buoy. Their speed is not built through aggression; it is built through patience.

A Practical Coaching Cue

When swimmers begin to surge or lose rhythm, a simple cue often helps. Instead of thinking about swimming harder, think about swimming longer.

Longer strokes stabilize rhythm, maintain pressure on the water, and prevent the sudden accelerations that increase drag. Patience in the stroke often produces speed without extra effort. Another useful cue during longer sets is this: protect the rhythm. If the rhythm stays intact, speed usually follows.

Rhythm, Relaxation, Range (Swim Mantra of Brett Sutton)

The Final Insight

Swimming rewards a very different mindset than most athletes expect. In many sports, success comes from attacking harder. In water, the opposite is often true.

The swimmers who move fastest are not those who fight the water the hardest. They are the ones who learn to work with it. And that almost always begins with patience.

The fastest distance swimmers are rarely the ones who accelerate the most. They are the ones who slow down the least.

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TL;DR

Swimming is one of the few endurance sports where athletes receive almost no real-time feedback about pace. The Tempo Trainer solves this by providing a constant auditory metronome that can provide a precise timing signal for stroke rate, length pacing and interval cycles. Over time, swimmers internalize this rhythm and develop the ability to pace accurately using feel and the pool clock.

The Pacing Problem in Swimming

Most swimmers do not struggle to swim hard; they struggle to swim at the right speed. If you ask a runner to run 5:00/km, they will usually land within a few seconds of that target. However, if you ask a swimmer to hold 1:35 per 100 meters, their splits might look like this: 1:29, 1:40, 1:43, and 1:34. The problem is not effort; it is feedback.

If you watch an elite swim squad, you will notice something remarkable: swimmers can hold long sets within a second or two of their target pace, without wearing a watch. While that ability looks like talent, it is actually a learned skill. Running and cycling provide constant sensory information, including ground contact, cadence, visual movement relative to surroundings, and power output. Swimming removes most of these signals because water dampens movement feedback and swimmers have limited visual reference points. As a result, swimmers often only discover their pacing error every 25 or 50 meters.

Why Watches Do Not Solve the Problem

Many swimmers try to solve pacing with technology, but watches only provide feedback after the fact. You swim the length and then you look at the time. By the time you see the number, the pacing error has already happened. This is why many swimmers wearing sophisticated watches still produce wildly inconsistent splits.

The Elegance of the Tempo Trainer

The Tempo Trainer solves the pacing problem in a very simple way. Instead of giving feedback after the swim, it provides a continuous timing signal. Swimmers naturally drift faster when fresh and slower when fatigued; the Tempo Trainer removes that bias by fixing the rhythm externally.

For example, if your CSS (Critical Swim Speed) is 1:40 per 100 meters, you might set the Tempo Trainer to beep every 25 seconds per length. Each beep represents one 25-meter length:

• Arrive early: You are swimming too fast (missing the training stimulus).

• Arrive late: You are swimming too slow (missing the training stimulus).

• Arrive exactly on the beep: You are at the correct pace for the intended training stimulus.

The swimmer immediately knows whether they are on target, creating a real-time feedback loop between effort, stroke rhythm, and speed.

The Neurological Connection

The human brain is extremely good at synchronizing movement to sound: a process known as 'auditory-motor entrainment'. It is the same mechanism that allows musicians to play to a metronome or rowers to maintain stroke rate. When swimmers repeatedly hear the beep at a fixed interval, the nervous system begins linking stroke rhythm and effort to the moment they arrive at the wall.

From Beeper to Instinct: A Swimmer's Journey

After enough training with a Tempo Trainer, swimmers stop needing it. They develop what coaches call 'internal pacing'.

Swimmer Spotlight: One of our intermediate swimmers, Sarah, struggled for months with fly-and-die pacing (starting too fast and fading badly). She would start a 400-meter set at a 1:30 pace and finish at 1:55. After six weeks of using the Tempo Trainer in Mode 1, she found she could feel the 1:40 pace in her shoulders and lats. She eventually stopped using the device because the rhythm was so deeply ingrained that her body naturally rejected going any faster or slower.

Alongside pacing, elite swimmers develop a second skill: reading the pace clock. In most swim squads, the pace clock is the only timing tool available. Swimmers learn to process several things simultaneously: where the clock hand was when they pushed off, where it is when they arrive, and how that difference translates into a split time. In open water races, the swimmers who exit the water fastest are rarely the ones who start the hardest: they are the ones who hold the most stable rhythm from the first buoy to the last.

For developing swimmers, the Tempo Trainer acts like training wheels until they can reliably confirm their speed using the clock alone.

Integration with CSS and 'Red Mist' Training

The Tempo Trainer is the primary tool for CSS (Critical Swim Speed) training. CSS sets teach swimmers what the correct pace actually is, while Red Mist (RM) cycles train pace durability.

The Psychology of the Red Mist: Developed by Paul Newsome and Swim Smooth, Red Mist sessions are designed to be mentally grueling. While the turnaround intervals remain fixed, the effective rest diminishes as physical fatigue begins to slow your pace or your effort increases to hold it. The 'Red Mist' refers to the psychological state where exhaustion and frustration cloud a swimmer's judgment and erode their sense of timing. This is where the Tempo Trainer is most valuable: when the mind wants to quit or the stroke rhythm starts to falter, the beep remains an objective, unemotional guide that forces you to maintain accuracy under duress.

Overcoming Resistance: Why Precision Matters

Many swimmers resist using a pacing device because they feel they are "not fast enough" to justify that level of data, or they worry the math will be "too complicated". In reality, precision is most important for the developing swimmer because water is a dense, unforgiving medium where small margins define your effort.

Because of this density, swimming pace zones are much more compressed than those in running. A difference of just 0.25 seconds per 25 meters equates to one second per 100 meters. To put that in perspective, a one-second change per 100 meters in the pool is equivalent to a ten-second change per kilometer in running. While a runner would celebrate a ten-second-per-kilometer breakthrough, a swimmer often ignores the one-second-per-100-meter gain. In the water, these small numbers represent massive shifts in performance and efficiency.

How to Use the Three Modes

Pro-Tip for Beginners

If you find yourself constantly "chasing the beep" and getting frustrated, try setting the Tempo Trainer 0.25–0.50 seconds (1 to 2 s per 100) slower than your target CSS. Use the extra time to focus on a long, relaxed stroke. Once you can hit that slower beep consistently, gradually increase the speed until you reach your true CSS pace.

The Takeaway

The Tempo Trainer does not on its own make you fitter: it teaches you to swim at the right speed. By narrowing the gap between effort and feedback, it turns pacing from a guessing game into a predictable science. Once you master that rhythm, you carry it with you into every practice and that precision rewards itself with results.

If you’d like to hear from the father of beeper swimming himself; Mr Paul Newsome at Swim Smooth check out his blog 3 Quick Tips on How to Use the FINIS Tempo Trainer PRO and Why It Makes Sense for Your Swimming!

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I recently received an email from a swimmer in India who was getting incredibly frustrated with his swim sessions. His local pool was 24 meters long, which meant every workout required constant mental arithmetic. He was trying to follow the CSS-based Red Mist endurance sets (Swim Smooth), and looking at his data, you could see the struggle. He was trying to program complex "48 m" and "96 m" intervals into his Garmin, wrestling with "CSS-based send-off" settings mid-pool, and getting demotivated when the watch missed a turn or miscalculated his rest.

If you have ever felt this way, here is the key insight: Your heart and lungs do not care how long the pool is!

The Gym Weight Analogy

Imagine walking into a gym where every plate actually weighed 5% less than was marked. Would you stop training? Of course not. You would still lift the weights, you would still feel the burn, and most importantly, you would still get stronger.

As long as the weights are consistent, you can progressively increase the load. Swimming is exactly the same. Whether you are in a 24 m pool in India or a 25-yard pool in the US (22.86 meters) or a long-course meters pool, the goal is exactly the same.

Calibrating Your "Power Meter"

To train effectively in a "short" pool, you just need to calibrate your local CSS. Think of it like calibrating a power meter on a bike. Whether you are dealing with meters or yards, you simply adjust your target time to match the pool length.

Example Conversion

• Standard CSS: 2:00 / 100 m (120s)

• Pool ratio: 24 ÷ 25 = 0.96

• Local CSS: 120 × 0.96 = 115.2s

• Per-length pace: 115.2 ÷ 4 = 28.8s

Once you make this one-time adjustment, stop doing math during the workout. Treat every four lengths as a "100" and follow your training plan exactly as written. You aren't "losing" 4 meters; you are simply training at the correct intensity for your environment.

The reason this works is that CSS is not really about distance; it is about intensity. CSS represents the fastest pace your aerobic system can sustain without progressively draining your anaerobic reserves. As long as the pace and time match the intended effort, your body experiences the same training stimulus, regardless of whether the pool is 24 m, 25 m, 25 yds or 50 m.

Note: If you actually perform your CSS test in your 24 m pool, you don't need to calibrate anything. Use those results directly. Calibration is only necessary when "importing" a pace from a standard pool.

The "Watch vs. Water Bottle" Dilemma

One of the biggest hurdles swimmers face is trying to program the entire workout into their watch. When you are in an odd-sized pool, many smartwatches struggle. Features like auto-lap and auto-rest rely mainly on accelerometers that try to detect the push-off from the wall. When the pool length is unusual, the algorithms can miscount turns or miscalculate rest intervals.

Interestingly, some modern watches (like those from Coros and newer Suunto models) handle this better by combining a gyroscope with an internal compass. This approach is often more reliable because the watch can detect the 180-degree change in direction during a turn. The important point is that your training does not depend on your watch measuring the distance perfectly.

Our advice? Go low-tech for the workout plan and higher-tech for pacing.

Instead of programming your watch, try taping your session list to a water bottle at the end of the lane (or put it on a kickboard). It is splash-proof, easy to read, and requires zero button-pressing.

For the watch itself, adopt the "set and forget" approach:

1. Set your watch to a standard m or yd pool length.

2. Start it at the beginning of the session and stop it only when you finish.

3. For specific quality sets (like CSS paced or RM blocks), use your Tempo Trainer for live pacing feedback.

If you are checking your wrist every 25 meters, you aren't focusing on your catch or your feel for the water. You are just chasing a number.

The Jedi Skill: Reading the Analogue Clock

While the Tempo Trainer is great, there is a "Jedi Skill" that many great swimmers eventually learn: reading the pool pace clock.

We all know that one swimmer with no watch and no beeper, yet always knows exactly what their splits were. This isn't magic; it is "internalized pacing." By glancing at the big four-handed pace clock as you turn or finish a set, you develop a strong connection between your effort and the actual time.

Using a swimmer with a 1:40 CSS which is 25s per length:

• Length 1: Start at 0s – arrive at 25s.

• Length 2: arrive at 50s.

• Length 3: arrive at 15s.

• Length 4: arrive at 40s (the finish).

Learning to read the clock removes the digital distraction. It forces you to stay aware of your surroundings, and develop a "clock in your head." For those who think swimming is boring, you can turn it into a high-speed math lesson!

The Secret Advantage: The Turn Bonus

There is actually a hidden benefit to these "odd" pools: The Turn Bonus.

Because you turn more often, you get more practice with push-offs and streamlines. You also spend slightly more time in the low-drag streamline phase after each turn. This briefly reduces drag and can make holding pace slightly easier than in a longer pool.

One warning: Do not "cheat" the pace with an oversized push-off. Use the wall to practice your technique, but ensure you are earning that beep (or that clock time) through the swimming itself. If you can hold a calibrated pace in a shorter pool, you are building the exact same aerobic engine needed to hold your true CSS in a 50 m pool.

Three Rules for Non-Standard Pools

1. Calibrate Once: Use the ratio of your pool vs. a standard 25 pool (e.g., 24/25 to find your local CSS.

2. Chase the Beep (Selectively): Use a Tempo Trainer for your quality sets. Set it to your local length split (example from my Indian friend 28.8 s in a 24 m pool) and forget about the distance.

3. Ignore the Watch: Your watch and Strava might get the distance slightly wrong. Let it. Your progress in your local pool is just as valid for tracking improvement.

The Bottom Line

Stop worrying about exact meters and start focusing on consistent pacing and rhythm. Whether the pool is 24 meters, 25 yards, or 33.3 meters, the goal remains the same.

Find your threshold. Progress it over time.

Remember, we don't just "hold" one speed: we use your CSS as a baseline to work at precise percentages of effort. Whether we are adding four seconds for a Red Mist endurance block or chasing two seconds faster for an anaerobic sprint set, we are targeting a specific physiological stimulus. By having a calibrated local CSS, you can hit these targets with laser precision, regardless of what pool you are in.

Next time you find yourself in a weird pool, don't change the workout. Just calibrate your “power-meter” and get to work.

See you at the wall!

FWDMOTIONSTHLM – A Page for all things SwimRun, Training & more.

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TL;DR

Peak Divide Classic is a two-day, self-navigated crossing of the Peak District from Manchester to Sheffield, 80 km in total, with an overnight camp in Edale. It is deliberately framed as not being a race, but that does not make it soft. You still need to move well, manage yourself, carry kit, eat enough, and get up to do it again the next morning.

The Vimto Statue Start - photo: @clorroe_cam

What surprised me was not the format but the meaning it took on. The event became more than a long weekend of shuffling. It became a journey through landscape and personal geography, not just distance: through the north of England, toward my father in Sheffield, and back toward the places and histories that still shape how I think about home.

Why This One Mattered

There are plenty of trail events built around speed, splits, and ranking. Peak Divide is trying to do something else. The organisers describe it as a hosted point-to-point crossing, an anti-clock event for the ultra-curious.

That appealed to me immediately, but the timing and geography gave it extra weight.

I had persuaded two Swedish friends, Ingela and Niklas, to join me, neither of whom had been to the North of England before. Part of the pleasure was not just in doing the event, but in showing them a corner of the world that still feels deeply tied to my own story. I flew into Manchester, then would head east to Sheffield where my father now lives. After that we would travel north to Shipley and on to my mother’s in Baildon, where I grew up.

Very soon I will have lived 30 years in Sweden, more than half my life, and that fact had begun to land in a way I had not expected. What really is the relationship of an expat with their mother country: nostalgia, a false sense of belonging, maybe even a sense of guilt, with three generations now separated by a real geographic divide?

So when Peak Divide said this is a journey, not a race, that line landed more heavily than it otherwise might have. This was going to mean more than simply crossing the Peak District. It would take me through the north of England toward my father in Sheffield, and then on toward Baildon and the places where my own story began.

What Peak Divide Actually Is

Peak Divide Classic 2026 took place over 18–19 April, with 293 shufflers and five riders. The route ran from Manchester to Edale on day one, then Edale to Sheffield on day two, 42 km plus 38 km, for a total of 80 km.

Photo @joshbrown_799

The event starts from Track Brewing Co in Manchester, camps overnight at Newfold Farm in Edale, and finishes in Neepsend in Sheffield. There is bag transfer, food, checkpoints, beacon runners, and a proper hosted camp, so this is not a full mountain self-sufficiency exercise. But neither is it a sealed-off, fully managed race experience. You still have to navigate, manage the day, and move through the route with some responsibility.

That balance is what makes it work. The format lowers the pressure without lowering the seriousness. It feels accessible, but still real.

And in practice it did feel different. There was still anticipation, still the arithmetic of pace, weather, fuelling, and terrain. But the atmosphere was not performance anxiety. It was more like curiosity, about who you would meet, how the route would unfold, and what kind of weekend this would become.

What the Route Felt Like

One of the most interesting things about Peak Divide is the shape of the route itself. It is not just a line on a map, but a movement across different kinds of place.

Day one began gently enough with roughly 18 km of tarmac and concrete towpaths along the Ashton Canal, easy enough that small groups formed and dissolved naturally and conversation came easily. After that the pace dropped sharply as the route steepened and the terrain became more serious. The weather kept changing, sun, rain, wind, then sun again, but never for long enough to become oppressive.

Day two was different again. After the steep climb out of Edale the running was excellent, with flowing trails across magnificent countryside and green hills lit by sunshine. Ladybower Reservoir stood out, as did the line of crags along Burbage. Although day one had the higher average pace because of the canal section, day two felt more naturally runnable. The rhythm of the trails was easier to read and I could feel the progression towards Sheffield more clearly.

Ingela put it nicely. To her, the event felt like a civilised form of wilderness: perfect for city people who enjoy the outdoors but do not necessarily know how to navigate with an analogue compass. That is playful, but accurate. It gives you a real taste of distance and terrain, but in a way that still feels welcoming rather than doctrinaire.

Navigation, Friction, and the Real Challenge

Peak Divide is self-navigated, which changes the feel of the whole thing. You are not just running, you are moving through a route that you need to understand and manage.

For me, that generally improved the experience. I bought a COROS Pace Pro, my first watch with true mapping capability, specifically for this event, and it was excellent. Often you could see runners ahead, but not always, and having the route on the watch meant I could settle into the day rather than constantly second-guess where I was.

Photo @joshbrown_799

The one exception came after lunch on day two, when I had missed that the organisers had changed the route. My watch told me to go left while everyone else went straight. In fiddling with the watch, convinced something had gone wrong, I managed to turn off the navigation altogether. For a while I had to follow others more than I wanted to, which was mildly irritating.

That small episode was also a reminder of what the event really asks. Not speed in isolation, but steadiness: move for a long time, manage stops well, eat and drink enough, handle terrain changes, arrive at camp with something left, and then get up and do it again. That is a different kind of endurance test.

The hardest part of the whole event was not a remote moorland section but the final 8 km or so through Sheffield. The organisers had done their best to keep the route on park paths for as long as possible, but the urban environment felt grinding after two days on the move. With around 7 km left I hit a low point. There were two remedies: more carbs, and attaching myself to a small group of other shufflers so the final struggle could at least be shared.

As the kilometres passed my mood lifted again. I had shared my live location with my father and he said he would be at the finish. He appeared twice on the way in, each sighting a small emotional and physical boost.

The Shoe Question

Peak Divide is the kind of event that makes footwear feel less like a gear preference and more like a philosophy.

I keep returning to the idea that we should be careful about using technology to solve a problem the body may need to adapt to itself. Minimal shoes ask a different question. Instead of asking how much cushioning, stability, and protection I can add between myself and the ground, they ask how well I can move, absorb load, stabilise, and stay connected to the terrain with less interference.

That made them an interesting choice here. As this was not a race, I was not optimising for performance. I wanted to test my limits another way. So even though the opening terrain might not have been ideal for it, I chose the Vivobarefoot Primus Flow Trail for day one.

Subjectively, I think it worked, up to a point. It felt as though shifting more of the load to the feet and lower legs on day one preserved the quads, hamstrings, and hip flexors for day two, some form of accidental load management. The one worrying sign on Sunday morning was sore heels. I normally run midfoot to forefoot, but the combination of walking, descending, and limited cushioning had clearly loaded tissues in a way I was not used to. Thankfully that sensation disappeared as I warmed up and did not return.

For day two I switched to Altra Mont Blanc Carbon, a shoe I had used successfully at ÖTILLÖ the previous September and trusted over the distance.

What the experience did was make the philosophy more precise. I still believe minimalist shoes have a place. For swimruns and for the forests of Sweden, they fit both my mechanics and my idea of what footwear should allow. But this distance, on these legs, may simply have been a step too far. Less shoe can be a useful teacher, but not necessarily the answer to every terrain profile, every accumulated hour on foot, or every ageing body.

Atmosphere, Access, and Why It Worked

One of the strongest things about Peak Divide is that atmosphere is treated as part of the event, not as decoration. The merch, the venues, the camp, the food, and the general tone all felt younger, cooler, and less doctrinaire than many endurance events, though not in a superficial way.

Camp in Edale was one of the best parts. We arrived in sunshine, checked in, pitched the tent, went to the local pub to rehydrate, and came back to a campsite that felt closer to a festival than a holding pen. There was DJ music, people mingling, massage, ice baths, and enough shared downtime for the event to develop an actual social life.

Photo @joshbrown_799

That warm tone carried through to the finish as well. Ingela described it perfectly: a very warm welcome at the finish line, hugs, love, beer, and pulled pork. She also noticed something else that felt true. Not everyone wanted to chat, which in itself was part of the event’s generosity. You could keep yourself to yourself if you wanted, but still feel held inside a warm and friendly atmosphere.

At the start of day two one of the organisers sang Ewan MacColl’s The Manchester Rambler. One line stayed with me: I may be a wage slave on Monday, but I am a free man on Sunday. It made me smile, but it also reminded me that these hills have not always been open in the way they are now. We were there on the weekend of the Peak District National Park’s 75th birthday, which made the whole crossing feel even more connected to the longer story of access, wandering, and what these hills have come to mean.

Niklas responded strongly to that wider setting. He liked the relaxed running culture, the pub culture, and the constant historical references. His phrase was that this part of the UK felt like a forgotten gem. He was right. Peak Divide does not happen in a vacuum. Part of its appeal is that it sits inside a landscape and a culture that still feel distinct.

What Stayed With Me

My real verdict is that Peak Divide succeeds because it understands that endurance events do not always need more intensity, more spectacle, or more performance theatre. Sometimes they just need a better premise.

That premise is simple: move across a meaningful landscape, in good company, with enough support to make the challenge accessible and enough freedom to make it feel personal. In my case, that movement turned out to be geographical in more than the obvious sense.

What I expected was a good long weekend of running across the Peak. What I got was something broader: movement through landscape and personal geography, through the northern cities that shaped my life, toward the father who now stands near the far end of his, and onward to the places that still hold some part of me however long I have lived away.

We came through the finish arch into beer, noise, and the buzz of happy runners. My 82-year-old father shuffled in shortly after to greet us. The access to these hills opened up in his lifetime and was never really questioned in mine. His father had lived in Bolton. I found myself wondering how he had experienced the Kinder Trespass and the eventual right to wander. Peak Divide had begun as a route across the Peak District, but by the finish it also felt like a route across inheritance.

This could yet become a yearly pilgrimage to my roots. Next year, perhaps with my children. Later, if time allows, with grandchildren. I will be 70 when my oldest granddaughter is 18. That, too, feels worth keeping in view, though before I get too carried away I should probably check the age limits.

And before I disappear too far into philosophy, a proper thank you is due: to the organisers, the crew, the volunteers, the sponsors, and everyone else who helped create the route, the atmosphere, and the strange little moving community that made the weekend what it was.

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TL;DR Super shoes improve running economy. The disagreement is not about the physics, but about the priority: maximizing performance now, vs building capacity over time. For slower runners, this trade-off is sharper, not smaller.

The Question We Are Actually Asking

Most discussions about super shoes ask the wrong question. I recently read a post on the topic of: "Should slower runners use them?" That question is binary. It is simplistic. It ignores the fact that every runner is a complex biological system in a constant state of adaptation.

The real question is: Are you trying to reduce the metabolic cost of running, or increase your capacity to handle it?

One is an act of optimization, getting the most out of what you have right now, while the other is an act of development, building a more resilient, powerful version of yourself for the future. We are really asking whether we are optimizing for today's performance, or long-term development and robustness.

For the elite runner, whose foundation is already built through years of high-volume training, this trade-off is negligible. But for the slower runner (the mid-to-back of the pack athlete), the trade-off is the entire game.

The "Maximalist" Effect (Stack Height and Cushioning)

Before we even discuss carbon plates or energy return, we have to talk about the platform. Many of the arguments against super shoes are actually arguments against high-stack, maximalist cushioning. These effects exist regardless of whether a plate is present.

1. The Stability Tax

Most modern foams (PEBA-based) are extremely soft. When you stack 40mm of this material underfoot, you create an inherently unstable platform. While a fast runner skims over this foam with very precise, short ground contact times, the slower runner experiences something very different.

The Nuance: Faster runners spend very little time on the ground. Slower runners spend significantly more time in the "stance phase": the period when the foot is on the ground.

The Result: A slower runner stays on that unstable foam for longer during every stride. This forces stabilizing muscles (such as the glute medius and peroneals) to work harder to maintain balance. Because the foam is compliant, the ankle is constantly searching for stability. For many runners, the metabolic gain of the foam is partially canceled out by the metabolic cost of the stabilization required to stay upright.

2. Mechanical Bypass of the Windlass Mechanism

This is a core argument from perspectives like Squat University and Vivobarefoot. The human foot is designed to be a "dynamic tripod" that transitions from a shock absorber to a rigid lever.

• The Mechanism: As the big toe extends during push-off, it pulls the plantar fascia tight, arching the foot and turning it into a stiff, efficient spring. This is known as the Windlass Mechanism.

• The Rocker Effect: The aggressive "rocker" geometry of modern shoes does the rolling for you. Because the shoe is pre-curved, the big toe never has to extend fully to create that rigid lever.

• The Consequence: You are bypassing the foot's primary biological engine. Over time, the intrinsic muscles of the foot atrophy, the plantar fascia loses its elastic quality, and the big toe loses its functional range of motion. You are trading a biological spring for a mechanical one.

3. Proprioceptive "Muting"

Thick foam acts as a filter between the foot and the ground. This reduces sensory feedback, or proprioception. The foot is one of the most nerve-dense areas of the human body, designed to tell the brain exactly how to adjust the rest of the kinetic chain based on the surface it meets.

When you remove that signal with 40mm of foam, the brain is forced to approximate. For a developing runner, this can smooth the signals the brain receives, making it harder to learn efficient, natural movement patterns. Over many kilometers, you learn to run on a platform rather than with your body. This sensory deprivation can lead to a less precise foot strike that lacks the robustness required for long-term health.

4. Load Redistribution and Transformation

High-stack shoes naturally shift stress away from the lower leg (feet and calves) and move it higher up the chain to the knees and hips. While this can protect a sore Achilles or a fussy plantar fascia, it does not remove the load; it transforms it. It can expose weak links in the hips or lower back that are not prepared for the increased workload. The body is an expert at finding the path of least resistance, and maximalist shoes provide a very tempting detour that can lead to unexpected proximal issues.

The "Super" Effect (The Carbon Plate and Energy Foam)

The Super designation refers to the interaction between ultra-responsive foam and a stiff carbon plate. This is where the physics of the shoe begins to interfere with the biology of the runner in fascinating (and potentially detrimental) ways.

1. The Biomechanical "Dead Zone"

Carbon plates act like levers, designed to behave like a spring, but require a specific force threshold to load. A carbon plate is not active by default; it must be loaded. It requires a certain amount of energy (in the form of vertical oscillation and forward velocity) to compress the foam and engage the lever arm.

The Threshold: If a runner does not produce enough force (due to a slower pace, lower cadence, or a softer landing), they may not be compressing the foam enough to engage the plate's spring effect.

The Result: The runner carries the extra weight and instability of a super shoe without reaching the critical velocity required to get the mechanical pop. In this dead zone, the runner is paying the stability tax without receiving the economy refund.

2. The Step Count Paradox

This is perhaps the most overlooked nuance in the entire debate. We must look at the total mechanical work over a set distance.

A slower runner takes more steps over a marathon because total steps are determined by distance divided by average step length, or equivalently cadence multiplied by time. Since slower runners usually move at a lower speed without proportionally lower cadence, they accumulate more steps across the race. A marathon example ~25,000 steps for an elite versus ~35,000–45,000 for slower runners.

The Multiplier: From an execution lens, a 4% economy gain is a powerful protective tool against "death by a thousand cuts." Over 40,000 steps, that efficiency adds up to a massive amount of saved energy.

The Stimulus: From a development lens, the runner is outsourcing 40,000 opportunities for their tendons and muscles to stiffen and adapt. If you use a super shoe for every run, you are effectively missing thousands of training signals every single week. You are running more, but your tissues are learning less.

3. The Race Day Trap

Many runners save super shoes for race day to get the boost. However, plated shoes change how forces are applied through the body. Because the plate is stiff, it forces the foot into a specific rocker motion. If a runner has not trained in this specific geometry, race day becomes a novel stimulus under maximal load, often leading to local fatigue or cramping in tissues that are not prepared for the load, as the shoe imposes a gait cycle the runner’s muscles are not conditioned to support.

Part 3: The Psychology of "Aerobic Drift"

There is a hidden danger in how these shoes feel. Because super shoes lower the Rate of Perceived Exertion (RPE), they can distort a runner's relationship with intensity.

When an easy run feels bouncy and effortless, it is very easy to drift into a pace that is 10 seconds faster per km than intended. While this feels great in that moment, it can quietly undermine the specific goals of low-intensity training. While Zone 3 is still aerobic, it shifts the metabolic stimulus away from the fat-oxidation and mitochondrial efficiency gains of Zone 2. If every recovery run accidentally becomes a moderate-intensity session because the shoes made it feel easy, the runner accumulates systemic fatigue without building the deep aerobic base they actually need. The shoes mask the effort, but the heart and mitochondria still have to do the work.

Where the Debate Lands: Two Models

To understand the stakes, we have to look at two hypothetical runners over a 12-week training block for a 10 km race.

Runner A (The Optimizer): Runs 40 km per week using super shoes for almost every session. They love the feeling of speed. They hit faster splits in their workouts and feel less sore the next day. However, they are building performance on a system that relies on the shoe to stabilize the ankle and propel the center of mass. Their feet may be getting weaker, and their tendons less resilient because the shoe is doing the stiffening work for them.

Runner B (The Developer): Runs 40 km per week in traditional, lower-profile trainers, using super shoes only for the final two weeks of the block and the race itself. They have to work harder for every mile. They feel more natural fatigue in their calves and feet. But in doing so, they build foot strength, tendon resilience, and a visceral understanding of pacing.

After 12 weeks, Runner B has improved the biological system. Runner A has improved their ability to use the technology. On race day, both might run the same time, but Runner B has a higher ceiling for the next season. Runner A has already used their multiplier.

My View: Match the Shoe to the System

This is a systems problem, not a belief problem. Super shoes and maximalist shoes change the expression of your fitness, but not the underlying engine. They are a performance filter that allows you to express your current fitness at a lower cost.

I almost exclusively run in minimalist shoes, or to be precise, I choose the least amount of cushioning I can get away with for the run type and distance. This is not out of an ideological attachment to the barefoot movement, but because it provides the clearest possible signal to the biological system. When you strip away the tyres, you have no choice but to upgrade the suspension.

If the system is strong, the shoes amplify performance.

If the system is fragile, the shoes amplify the gap between what you can do and what your body can sustain.

All said, there is also a practical reality here. The market has already voted! Walk into any mainstream running store and you will struggle to find a true racing flat, let alone a genuinely minimal shoe. The industry has moved decisively toward more cushioning, more stack, more assistance, because that is what sells. In that environment, minimalism is often portrayed as a fringe position, almost a sect, rather than a legitimate training approach. That makes it harder to push back, even if the underlying principles are sound. For me, paradoxically, I enjoy the feeling of minimalist shoes for the same reason many runners love super shoes. You can feel the spring. The difference is that in one case, the spring comes from the foam and the plate. In the other case, it comes from your own tendons and technique. I promise the sensation is not so different!

A Simple Rule

Do not use technology to solve a problem you need to adapt to. If your feet are weak, do not buy a shoe that replaces their work. If your stability is poor, do not buy a shoe that hides it. Use technology when the problem is no longer adaptation, but execution.

Do the work first. Then use the tool.

The Final Synthesis

Performance = biological capacity × shoe efficiency.

Capacity constitutes the architecture; the shoe is merely the leverage applied to it.
Engineer the runner first, then apply the mechanical multiplier.
Utilize the tool to express your latent potential, rather than to circumvent your biological foundation.

The error is not found in the adoption of the technology.
The error is the cognitive trap of confusing external amplification with innate ability.

Most runners are preoccupied with increasing the brightness of the beam, when the priority should be manufacturing a more powerful bulb.

The Prescription: integrate a minimalist trail shoe into your training rotation. On technical, uneven terrain, the clinical precision of carbon plates and specific heel-to-toe drops becomes secondary. The ground itself is the disruptor. What matters is the integrity of the kinetic chain—your ability to stabilize, adapt, and modulate force.

Train the biological system to its peak, then use the technology to amplify the result.

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A Personal Encounter: Why This Matters

As a swim coach, I’ve witnessed the incredible highs and occasional hazards that come with endurance sports. At two separate events; the Vansbro 10k (Sweden) and the Montenegro Ultraswim 33.3, I saw two of my stronger swimmers pull out mid-swim due to a frightening and unfamiliar condition: sudden breathlessness, a rattling cough, and intense fatigue.

It turned out both had experienced Swimming-Induced Pulmonary Edema (SIPE) - the second case suspected but unconfirmed. At the time, I didn’t know much about it, but seeing it firsthand at these prestigious endurance races made me realize how vital this knowledge is. This article explores the science of SIPE, why it happens, and how we can keep our athletes and support crews safe.

SIPE: At-a-Glance

• What it is: Fluid leaking into the lungs from the bloodstream during immersion.

• Key Trigger: Combination of cold water, high exertion, and hydrostatic pressure.

• Smoking Gun: A persistent cough, sometimes with pink or frothy sputum.

• Immediate Action: Exit the water immediately and stay in an upright position.

• Prognosis: Usually resolves in 24–48 hours, but requires medical follow-up due to high recurrence rates.

What Is SIPE?

Swimming-Induced Pulmonary Edema (SIPE) is a condition where fluid abnormally leaks from the pulmonary capillaries into the airspaces (alveoli) of the lungs during immersion.

Unlike a panic attack or exercise-induced asthma, SIPE is a physiological event where the lungs are essentially being "flooded" from the inside out. It typically strikes during strenuous open-water swimming (or diving), especially in cold conditions, and can affect even the fittest, most elite athletes.

Recognizing the Warning Signs

Early recognition is critical. Look for:

• Sudden shortness of breath: Feeling "out of air" despite a manageable pace.

• Rapid or Uneven Breathing: Gasping for air even when moving slowly.

• The "SIPE Cough": A persistent cough, often producing frothy or pink/blood-tinged sputum (hemoptysis).

• A "Full" Feeling: A sensation of crackling or fluid in the chest.

• Disproportionate Fatigue: Feeling exhausted even though your muscles still feel strong.

The Science: Why the Lungs "Leak"

SIPE is driven by capillary stress failure. To understand it, think of your circulatory system like a plumbing system under sudden, extreme pressure:

1. Hydrostatic Pressure & The Squeeze: When you enter water, the pressure of the water itself (hydrostatic pressure) and the cold-induced constriction of peripheral blood vessels "squeezes" blood from your limbs toward your core. This can shift up to 700ml of blood into the chest cavity.

2. Increased Pulmonary Pressure: Intense physical exertion spikes your cardiac output. In SIPE-prone individuals appear to have an exaggerated pulmonary artery pressure response. Therefore the pressure in the pulmonary capillaries can reach a breaking point.

3. The Leak: Under this immense pressure, the delicate blood-gas barrier in the lungs suffers "stress failure." Fluid (and sometimes red blood cells) is forced out of the vessels and into the air sacs causing an impairment in oxygen exchange.

Risk Factors: Who is Most Vulnerable?

Evidence-based research points to several specific triggers:

• Colder Water: Temperatures below 20°C (68°F) exacerbate peripheral vasoconstriction.

• Overhydration (The "Preload" Trap): Pre-race hyperhydration increases total blood volume, which raises the baseline pressure in your "pipes" before you even hit the water.

• Tight Gear: A restrictive wetsuit can increase the work of breathing and further compress peripheral vessels, aiding the central blood shift which anecdotally has been reported to increase the incidence of SIPE.

• Exertion without Warm-Up: A sudden sprint in cold water causes a massive, uncompensated spike in pulmonary artery pressure.

• Hypertension and Heart Health: High blood pressure or underlying heart conditions significantly raise susceptibility by increasing the baseline pressure in the pulmonary system.

• Asthma: Researchers suggest that asthma may not only increase the risk of an episode but also prolong the recovery time and increase the likelihood of recurrence.

• Anxiety and Panic: While SIPE is physiological, anxiety can exacerbate vascular constriction and increase heart rate, potentially acting as a secondary trigger that worsens an event.

• Gender and Biology: Data suggest a higher incidence among female athletes, possibly due to differences in pulmonary vascular response, lung size, or hormonal influences on fluid regulation.

• History: A previous SIPE episode is the strongest predictor, with recurrence rates estimated near 28%.

• Current Respiratory Viral Infection: Data from military divers in the US points to a close association between respiratory infection and SIPE.

The "Silent" SIPE: Is it just Fatigue?

Many swimmers experience a "post-race cough" that they dismiss as "lake lung." It is crucial to distinguish a "silent" or sub-clinical SIPE episode from normal fatigue:

• The Deep Breath Test: If you have a lingering cough after a race, lie flat on your back. If the cough worsens or you hear a "crackling" sound (rales) during a deep breath, fluid is likely present in your lungs. Lying flat increases the return of blood to the heart, which can worsen the symptoms of a sub-clinical SIPE.

• Pink Sputum: Any amount of pink or "rusty" tinged phlegm is a definitive sign of capillary leakage and should be treated as a medical warning.

Athlete Action Plan: The 3-Step Protocol

If you suspect you are experiencing SIPE mid-swim, follow this immediate protocol:

1. Signal for Help: Do not try to "tough it out" to the shore alone. Roll onto your back, raise an arm, or signal your support kayak immediately.

2. Exit and Stay Upright: Once you reach land or a boat, do not lie down. Keep the swimmer warm but upright. Sitting or standing helps use gravity to keep fluid in the lower parts of the lungs, making it easier to breathe.

3. Seek Medical Review: Even if you feel better within minutes of exiting, you must be evaluated. SIPE can cause secondary inflammation or mask underlying cardiac issues. Administer oxygen if available.

Recovery Protocol: What Happens Next?

• The 48-Hour Window: Avoid all strenuous activity for at least 24–48 hours. Your lungs need time to reabsorb the fluid and for the capillary "leaks" to heal. Be aware that in some cases, symptoms or inflammation can linger beyond the 48-hour mark.

• Monitor Oxygen: If you have access to a pulse oximeter, monitor your oxygen saturation. If it stays below 94% at rest, seek emergency care.

• Cardiology Follow-up: Because SIPE has a high recurrence rate (up to 28%), you should consult a sports cardiologist.

Prevention and Safety Tips

For Support Crews: Spotting Distress

Crews on kayaks or boats (essential at events like the Ultraswim 33.3) must watch for:

• Vertical Swimming: A swimmer who suddenly stops their horizontal stroke and treads water vertically.

• Frequent Mask/Goggle Clearing: They may be stopping to cough or try to "clear" their airway.

• Speech Impediment: If a swimmer cannot speak a full sentence (e.g., "I am okay, I will continue") without stopping for breath, they are in respiratory distress.

Recent Research & Medical Stance

• Medications: Sildenafil (Viagra) and Nifedipine are pulmonary vasodilators being studied to prevent recurrence.

• WADA/World Aquatics: Sildenafil is currently not on the WADA Prohibited List. However, athletes should only use these under the guidance of a medical professional.

References & Further Reading

1. Moon, R. E., et al. (2016). "Sildenafil Inhibits Altitude-Induced Hypoxemia and Pulmonary Hypertension." Circulation.

2. Miller, C. C., et al. (2010). "Swimming-induced pulmonary edema in triathletes." Clinical Journal of Sport Medicine.

3. West, J. B., et al. (1991). "Stress failure of pulmonary capillaries." Journal of Applied Physiology.

Disclaimer: This article is for informational purposes only and does not replace professional medical advice. If you suspect you have experienced SIPE, consult a physician before returning to strenuous swimming.

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I received a question from a leading swimrunner a few weeks back. It was not about intervals, volume, or strength: it was about rotation.

As swim coaches we talk a lot about technique, long strokes, hip drive, reach, and glide. But swimrun is not normal swimming. The equipment changes the physics, and when the physics change, the optimal technique may change with it.

The question was simple and sharp: If rotation improves efficiency in normal freestyle, what happens when you add a pull buoy, paddles, and shoes? Does rotation still give a net gain, or does the added drag and instability make a large roll mechanically expensive?

I am not aware of any paper that has studied rotation in swimrun swimming, but that does not mean we are guessing. We can reason from mechanics, and when you do, something interesting emerges. This is not just about rotation: it is about how swimrun forces us to evolve beyond copying no-gear technique and instead adapt to a different physical system.

Step 1. What Do We Mean by Rotation?

All freestyle rotates around the long-axis (an imaginary line running from your head to your toes, like a rotisserie spit). The real question is how much, and where that rotation originates. There are two primary archetypes:

1. Hip-driven swimming

   • Larger roll, often 30 to 50 degrees at the hips.

   • Hips initiate the rotation.

   • Modest, often two-beat kick, mostly for timing.

   • Longer stroke length and lower cadence (the speed or "tempo" of your arm turnover).

   • This style is the gold standard for efficiency in calm, predictable water. It relies on a long glide phase and using the "cylinder" of the body to generate torque. Role models include elite distance swimmers like Sun Yang, who utilize massive hip drive to maintain a rhythmic, low-cadence glide.

2. Shoulder-driven swimming

   • Smaller visible hip roll, around 20 to 30 degrees.

   • Shoulders and ribcage initiate the movement.

   • Higher cadence.

   • A stronger kick stabilizes the body in no-gear swimming.

   • This pattern is the engine of open-water dominance. While it is used for sprinting, it is also the preferred archetype for elite distance swimmers (like Lucy Charles-Barclay) who need to maintain a high tempo to navigate turbulent conditions like chop and current.

Step 2. What the Pull Buoy Changes

The kick stabilizes roll, yaw (the side-to-side swinging of your legs), and timing. Remove the kick and the system becomes less stable. Add a buoy and its primary effect is not just buoyancy, but transverse stability and a shift in pivot points.

It is important to distinguish between a "standard" buoy and a "swimrun" buoy. A standard buoy provides modest lift, but a modern swimrun buoy (like the Ark Keel Mega) provides massive buoyancy, often three to four times that of its traditional counterpart. This extreme lift creates a powerful restoring torque (a force that aggressively pushes you back to a flat, horizontal position). It effectively pins the hips to the surface like a rigid stabilizer.

Because the hips are locked to the surface, the swimrun buoy acts as a yaw fulcrum (a fixed pivot point). In no-gear swimming, the body can "snake" slightly to absorb energy, but the buoy creates a rigid point. If the torso rotates too violently, this pivot point forces the legs to swing out like a compass needle. The buoy translates messy roll into lateral drag.

Step 3. What Shoes Change: The Self-Correction Trap

Shoes sit at the end of a long lever relative to the axis of rotation. Rotational inertia (the resistance to being turned) increases with mass times the square of the radius. That "radius squared" term matters: a small mass far from the center of rotation dramatically increases the effort required to rotate or stop a rotation.

Consequently, shoes amplify the cost of the "compass needle" effect. When uncontrolled rotation causes the legs to swing laterally, the shoes present a large surface area to the water.

There is a subtle psychological trap here. Because the drag on the shoes is so high, the water actually "pushes" your feet back into line almost as soon as they swing out. This is a self-correcting system, but it comes at a massive cost. It is like tapping the brakes in your car every time you turn the steering wheel.

Because the shoes snap back into position so quickly, you might not even realize your legs are wiggling. To the swimmer, it does not feel like a "wobble," it just feels like a heavy, constant drag. You feel like you are swimming in a straight line, but you are wondering why other athletes are gliding past you with half the effort.

Put simply, shoes turn a small hip wiggle into an invisible, automatic brake.

Step 4. The Mobility "Cheat Code": Scapular Movement

In no-gear swimming, you can "fake" reach by rotating the whole cylinder. If you lack thoracic (mid-back) or shoulder flexibility, you simply roll your hips further to get your hand forward. This works because there is less penalty for a large, slow roll.

In swimrun, that strategy breaks down. Because the gear punishes large-amplitude rotation, you must find reach elsewhere. This is where scapular protraction (the ability of the shoulder blade to slide forward around the ribcage) becomes the ultimate advantage.

If your shoulder blades and mid-back move well, you can achieve a long stroke without a massive pelvic roll. This allows you to "project" forward from the ribcage while keeping your hips and legs perfectly quiet. If you lack this mobility, you will be forced to choose between a short, inefficient stroke or a large, high-drag roll.

As a curiosity, I have excellent shoulder mobility and I would argue I punch above my weight in pull paddle swimming: is it correlation or causation? Based on these mechanics, I would argue causation. My mobility profile matches the constraints of the gear, allowing me to maintain length without the instability that plagues less flexible swimmers.

Step 5. Angular Momentum and The Torque Trigger

When you rotate, you generate angular momentum (the "momentum of a turning object"). In no-gear freestyle, the kick helps dampen excess rotation. In buoy plus shoes swimming, the legs cannot counterbalance and increased inertia resists rapid changes in direction.

Because angular momentum must be conserved unless an external force is applied, and the kick is gone, the primary corrective force available to stop your roll is the opposite arm pull. This is often triggered by the hand entry and amplified by paddles.

To find balance, swimrunners often reach across their midline (the center of their body). This is a "cross-over." With the added surface area of a paddle, this cross-over creates a lateral force that initiates the very leg sway we want to avoid. A wider, "tracks-on-a-rail" entry is a prerequisite for maintaining a stable, low-rotation platform.

Step 6. The Rhythm Trap: Paddles and the "Dead Spot"

Paddles naturally slow down your Strokes Per Minute (SPM) because of the increased resistance. This creates a timing trap. If a swimmer has poor timing, they often fall into one of two errors that destroy the stability of the system:

1. The Early Pull: Pulling before the weight shift of the recovering arm has "triggered" the rotation. This creates a disconnected stroke where the arms and hips are out of sync, leading to a jerky, unstable roll.

2. The Dead Spot: Leaving the lead hand "parked" at the front for too long while waiting for the other arm to recover.

In no-gear swimming, you can survive a "dead spot" in propulsion. In swimrun, you cannot. The moment propulsion stops, the massive buoyancy of the buoy and the drag of the shoes take over. Without the "tension" of constant forward motion, the body begins to snake or sink. To stay stable, a swimrunner needs a continuous, front-quadrant rhythm where one hand begins the catch just before the other enters. You are not just pulling for speed; you are pulling to keep the platform taut.

The Shoulder-Driven Disadvantage Natural shoulder-driven swimmers often have more difficulty adapting to paddles than hip-driven swimmers. Because their engine is built for a high-turnover rhythm, the forced drop in stroke rate caused by large paddles can feel like "stalling" a car engine. This is fundamentally a problem of optimizing the DPSxSPM equation (Distance Per Stroke multiplied by Strokes Per Minute).

For a naturally high-cadence swimmer, bigger paddles are often not worth the trade-off. Since they rely more on high-frequency turnover than on the deep rotational torque generated by the core and hips, oversized paddles can quickly overload the smaller stabilizing muscles of the shoulder. This leads to rapid fatigue and a breakdown in that vital continuous rhythm, ultimately decreasing their speed despite the increased surface area of the paddle.

Swimrun Reality Check

In race conditions (cold water, high heart rate, and fatigue) stability becomes your primary performance limiter. In a pool, you are limited by how much power you can generate (propulsion). In swimrun, you are limited by how much of that power is lost to misalignment.

When your core fatigues, the gear actively tries to pull you out of a straight line. If you cannot maintain a stable platform, any extra effort you put into the pull simply increases your lateral sway. Because shoes turn even a small wiggle into a massive brake, your speed is effectively capped by your stability, not your strength.

This also changes breathing mechanics. In a low-amplitude stroke, the window for breathing is shorter. You can no longer rely on a big hip roll to "carry" your head to the air. It requires much more precision to peek for air without lifting the head and destroying your body position.

So Is Rotation Still Important?

Yes, but the optimal amplitude (the size of the movement) decreases. The goal becomes minimal effective rotation. This should be enough to load the catch, protect the shoulder, and clear the breath.

However, we must be careful: flattening the stroke too much shifts load back toward the shoulder joint. This is where scapular mobility and control save the day: they allow you to maintain a long, healthy stroke on a stable, flatter platform.

A Working Hypothesis

As gear increases, the mechanical cost of large hip-led rotation increases. Therefore:

• Optimal rotation amplitude decreases.

• Rotation origin shifts toward the torso and scapula rather than the pelvis.

• The better your thoracic and scapular mobility, the less you need to rely on high-drag whole-body rolls.

• A wider entry and a continuous, connected rhythm are essential to maintain the platform.

• Stability becomes more valuable than maximal reach.

No-gear technique often maximizes reach; swimrun technique minimizes waste.

Test It Yourself

To understand your baseline, try these dry land mobility tests before your next swim.

The Mobility Baseline (Dry Land)

1. Thoracic Rotation: Sit on a chair with your back straight and feet flat. Cross your arms over your chest and rotate your torso as far as possible to each side without moving your hips. If you cannot rotate comfortably past 45 degrees, you are likely using hip roll to "fake" rotation in a no-gear context.

2. Scapular Slide: Stand with your back against a wall. Keeping your elbows and the back of your hands against the wall, slide your arms up into a "Y" position. If your back arches or your hands lift off the wall, your shoulder blade is not moving independently of your spine.

3. Protraction Reach: Stand sideways to a wall and reach forward with one hand. Try to "punch" the wall forward without rotating your hips or chest. This is your "usable rotation" from the shoulder blade.

If you fail any of these tests, large hip-driven rotation is not a style choice: it is a compensation.

The Stability Challenge (In the Water)

• 6 x 50: Pull buoy only.

• 6 x 50: Pull buoy and shoes (natural rotation).

• 6 x 50: Pull buoy and shoes (minimal effective rotation, focusing on scapular reach and a wide entry).

Pro tip: For an even greater challenge, try using an ankle band in combination with your paddles and pull buoy. This dramatically increases your proprioception (your body's awareness of its position) and will make any lateral movement or "snaking" instantly noticeable.

Compare your stroke rate, pace, and perceived stability. You may find that the fastest option is not the biggest roll, but the most controlled one.

Swimrun does not reward aesthetic amplitude.

It rewards economy under constraint.

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TL;DR: Autonomic fitness is the ability to shift efficiently between activation and recovery. Performance is not defined solely by how powerfully you can engage stress, but by how deliberately you can exit it. Chronic activation without conscious downshift erodes adaptation, regardless of talent or willpower.

Two athletes. Same training plan. Same life load. One adapts; the other breaks.

More often than not, the difference is stress processing capacity: the ability to engage stress fully and then exit it deliberately.

We measure VO2max. We track lactate. We watch RHR. We analyze splits and power curves. Yet we rarely discuss the variable that determines how training is actually absorbed: autonomic fitness.

You can build the engine. The question is whether you can shift gears.

What Is Autonomic Fitness?

Autonomic fitness is the physiological ability to move efficiently between two states:

• Sympathetic activation: effort, focus, mobilization, fight or flight.

• Parasympathetic recovery: repair, digestion, hormonal regulation, sleep.

Both states are essential. Performance requires one. Adaptation requires the other.

Sympathetic activation sharpens attention, mobilizes glucose, increases cardiac output, and prepares you to act. Parasympathetic recovery restores glycogen, supports immune function, regulates hormones, and allows deep sleep.

The problem is not stress. It is the inability to exit it. Chronic activation without downshift quietly and persistently erodes adaptation. In simple terms:

1. How hard can you switch on?

2. How quickly can you switch off?

High performers are not calm all the time; they are simply excellent at exiting stress quickly. As performance coach Steve Magness argues, resilience is not suppression; it is regulation under pressure. The best performers engage fully and then disengage deliberately. That ability is a decisive competitive advantage.

The Cost of Being "Always On"

Endurance athletes are particularly vulnerable to chronic activation. Training is a stressor. Work is a stressor. Family responsibility is a stressor. Competition is a stressor.

When these stack without clear downshift periods, the nervous system remains in a low-grade sympathetic state. This often looks like:

• Elevated resting heart rate.

• Blunted HRV rebound.

• Delayed sleep onset or fragmented sleep.

• Irritability and reduced appetite regulation.

• Slower heart rate recovery between intervals.

• Morning heart rate drift over weeks.

• Loss of enthusiasm for sessions that once energized you.

It rarely feels dramatic. It usually feels like ordinary fatigue. But physiologically, adaptation is compromised. You cannot out-train a nervous system that cannot downshift. More intensity does not restore regulation.

Cognitive Load Is Physiological Load

Stress is not exclusively physical; it leaves a mental residue. Two cognitive habits strongly influence autonomic regulation.

Compartmentalization

Healthy compartmentalization allows you to focus fully on the session and park unresolved issues temporarily. Work stays at work. Training stays in training. A mistake in a race does not contaminate the rest of the event.

Focus is not just a performance tool: it is a recovery tool.

However, healthy compartmentalization is not emotional avoidance. It is temporary and flexible. You return to what you parked. The nervous system knows the difference. If you never return to the parked issue, background activation lingers. That load accumulates like junk training volume: invisible but costly.

High performers park issues. Elite performers close the loop.

Control and Release

The stress response amplifies under uncertainty and perceived lack of control. Athletes who repeatedly rehearse uncontrollable scenarios (weather forecasts, selection decisions, or competitors’ tactics) maintain low-grade activation.

The body does not distinguish between a physical threat and a rehearsed one. Cortisol and adrenaline respond either way. The highest performers focus on what is controllable and release the rest.

This is not indifference: it is energy management.

Energy spent worrying is energy unavailable for adaptation, and in endurance sport that margin matters. The Stoics reduced this to a simple rule: focus on what is yours to influence and release what is not. Performance improves when attention is directed only toward the former.

Physiology follows attention.

In The Comeback Quotient, endurance coach Matt Fitzgerald describes resilient athletes as ultrarealists. They see reality clearly, without denial or catastrophizing, and then act decisively on what can be influenced. Physiology stabilizes when perception is accurate.

The Foundations of Autonomic Fitness

Autonomic fitness is not a personality trait. It is a trainable physiological capacity. Like aerobic fitness, it responds to consistent exposure. It rests on four foundations.

• Fuel: Low energy availability elevates cortisol and sympathetic tone. When intake does not match output, recovery becomes secondary. You cannot regulate a nervous system that is underfed.

• Sleep Anchors: A consistent wake time, morning light exposure, and a deliberate evening downshift stabilize circadian rhythm. Circadian stability strengthens autonomic stability.

• Training Design: Intensity is not the enemy. Chronic, unstructured activation is. Intentional stress builds capacity. Unintentional accumulation erodes it.

• Breath: Breathing is a mechanical lever into the nervous system. Longer exhales and deliberate pauses accelerate recovery kinetics. Few tools are as immediately accessible.

Deliberate Exposure

Autonomic fitness is not trained only in intervals and recovery runs. It is trained in conversations you would rather avoid, uncertainty you cannot eliminate, and moments when your identity feels exposed to judgment.

The nervous system does not distinguish between physical and social threat. It responds to perception.

Avoidance strengthens activation. Deliberate engagement strengthens regulation.

Markers to Watch

Autonomic fitness is observable:

• Heart rate recovery after hard intervals.

• HRV rebound following training blocks.

• Sleep latency and depth.

• Mood stability under load.

• How quickly you let go after a mistake.

When these trend poorly, the issue may not be fitness. It may be regulation.

The Closing Frame

If aerobic fitness is your engine, autonomic fitness is your gearbox.

A powerful engine is an advantage. Remaining in one gear is a liability.

Targeted tempo work, hard intervals, and competitive stress are all valuable. The essential question is whether you can shift cleanly back to recovery. Can you exit activation as deliberately as you enter it?

The Stoics believed strength was not the absence of pressure, but the ability to respond well under it. The most resilient athletes are rarely the most optimistic. They are the most realistic.

Enter stress deliberately. Exit it deliberately. That is autonomic fitness.

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TL;DR: Western endurance training, French or otherwise, was built around a shared model that prized effort and fatigue as proof of progress. Modern physiology has not rejected that model, but refined it: controlling intensity density and working just below critical boundaries leads to more repeatable training and better long-term gains.

In a previous article, we explored the tectonic shift occurring in modern endurance training. Building on those concepts, this piece examines why the language we use to describe performance has become the final bottleneck for progress.

If you grew up running in the US, the UK, Australia, or most of the English-speaking world, you probably assume that endurance training has always been fragmented. Different coaches. Different models. Different definitions of threshold, tempo, or speed.

That assumption is understandable. It is also incomplete.

In France, distance running has operated for decades with something that most English-speaking countries never really had: a shared national training language. In the thousands of clubs affiliated with the Fédération Française d'Athlétisme (FFA), you will often hear the same terms, regardless of the region:

• endurance fondamentale (easy aerobic running).

• séance seuil (threshold work).

• VMA (maximal aerobic speed intervals; standing for Vitesse Maximale Aérobie).

• sortie longue (the long run).

These are not casual labels. They represent a codified system, taught through coaching education and tradition. Most club runners broadly agree on what each session is for, where it fits in the week, and how it should feel. For many readers, this alone is surprising.

But here is the more important point: France did not invent a unique way of training. It formalized what most of the Western endurance world was already doing.

1. A shared Western model, not a French anomaly

When people refer to "the French system", it is often with the assumption that France developed a uniquely rigid or idiosyncratic way of training endurance athletes. In reality, the opposite is closer to the truth.

From the late 1970s through the early 2000s, endurance programmes across France, the US, the UK, Australia, and much of Europe shared the same underlying structure:

• A large volume of easy aerobic running.

• One weekly session targeting VO2 max.

• One weekly session near "threshold" or tempo.

• Pace-based prescriptions derived from track tests or race performances.

• A belief that fatigue was a necessary and visible sign of effective training.

The labels differed; the logic did not. France called this VMA + seuil. The US talked about intervals and tempo. The UK spoke of speedwork and threshold.

France’s real contribution was not inventing a new model, but making the existing one explicit and scalable. Clear terms allowed thousands of recreational runners to train with a shared understanding of intent. Group training became easier to organise. Expectations were clear. For its time, this was a genuine strength.

2. Why the traditional model worked (for a long time)

It is important to be fair: the traditional Western model worked, and worked well, for decades. It was simple and intuitive. It matched the tools runners had available: a stopwatch, a track, perhaps a heart-rate monitor. Hard sessions felt hard, easy sessions felt easy, and progress was easy to explain.

For recreational runners, it provided structure and motivation. For competitive athletes, it produced high aerobic capacities and mental toughness. Crucially, it offered a form of psychological validation: in an era without precise metabolic monitoring, feeling "shattered" was the most reliable proof of a productive session. Visible, undeniable effort became the primary proxy for future results. It also aligned with how success was measured at the time: race results and the sheer capacity to suffer. In short, it did what it was designed to do.

But success can hide limitations.

3. Where the cracks appeared

Over time, patterns began to emerge. Many runners trained hard, often very hard, yet struggled to improve consistently. Injuries became common and fatigue accumulated. Training weeks became a cycle of big efforts followed by compromised recovery.

The problem was not intensity itself: it was intensity density. This density was created by two primary factors: the unmanaged accumulation of time spent in the "inter-threshold" space (the middle ground between the first and second metabolic boundaries, often entered unintentionally through pace drift and group dynamics), and, more critically, an excessive volume of work performed above the second threshold (Zone 4 and Zone 5).

While drifting into the middle ground is a common inefficiency, the real systemic failure often came from over-prescribing high-intensity intervals that exceeded the body's ability to clear metabolic by-products. The traditional model often prioritised near-maximal effort in every hard session. This meant threshold sessions frequently drifted upward into race-pace efforts, and VO2 max sessions were performed at an intensity that stunted subsequent recovery.

The Norwegian model eventually turned this concept on its head: instead of avoiding the inter-threshold space or red-lining every interval, they made this middle ground deliberately powerful through a highly controlled threshold focus. By keeping "hard" efforts strictly anchored below the second threshold (LT2), they were able to accumulate far more total volume without the systemic "crash" associated with the older club models.

At the recreational level, the lack of control showed up as stagnation or burnout. Fatigue became normalised and even celebrated as a marker of commitment. At the time, there was no clear language to describe the issue. The default explanation was often psychological rather than physiological: not tough enough, not committed enough, not disciplined enough.

4. The institutional anchor vs. the open debate

The training model itself was shared across countries. The reaction to its limitations was not.

In English-speaking coaching cultures, questioning established practice has long been part of the ecosystem. Coaches write books, publish blogs, host podcasts, and debate ideas publicly. There is no single authority or national curriculum. As endurance science evolved, these cracks were challenged out loud.

This is why figures such as Steve Magness have spoken openly about how the way they trained as young runners contributed to stagnation in US distance running through the 1990s and early 2000s. The issue was not effort, but how that effort was distributed and recovered from.

In France, debate is just as vibrant and endless. However, the difference lies in the institutional anchor: the FFA. While freelance coaches and social groups in France frequently "do their own thing," the official coaching certification pathways and club structures create a formalized baseline that the English-speaking world lacks.

But this can also create a form of "knowledge debt," where official manuals may lag five to ten years behind what elite practitioners or independent coaches are already doing. In a centralized system, updating a national curriculum requires bureaucratic consensus and long-term administrative cycles. This means that while an elite coach at the INSEP (the National Institute of Sport) may be using the latest lactate-shuttle science, the volunteer coach at a local club is still following the 2015 manual. Consequently, official language often stays fixed even as day-to-day practice evolves underneath it to match modern evidence..

5. Elite practice moved first (and quietly)

One reason this debate can feel confusing is that elite training has rarely matched simplified club language. Elite runners, regardless of nationality, have long managed intensity carefully. Lactate was controlled. Easy days were genuinely easy. Hard days had ceilings. Large volumes of sub-threshold work were accumulated without constant exhaustion.

What changed over the last decade was not elite behaviour, but visibility. Better data, better measurement tools, and better communication made these practices easier to see, explain, and eventually adopt outside the elite bubble.

6. Modern physiology reframes the model, it does not reject it

Modern endurance science has not overturned the foundations of training. Zone 2 remains non-negotiable. Aerobic volume still underpins everything. Threshold still matters. High-intensity work still has a place. What has changed is how these elements are used, and how they are controlled.

A key development has been a better understanding of lactate. Rather than viewing lactate simply as a waste product or a marker of suffering, it is now understood as a normal by-product of aerobic metabolism and a useful signal of internal load.

At intensities below the critical boundary, lactate production and clearance remain in balance. This is often associated with the Aerobic Threshold (LT1), typically observed around 2.0 mmol/L of blood lactate (though individual values vary). Above it, lactate accumulates rapidly and fatigue accelerates. This upper boundary is commonly associated with the Anaerobic Threshold or maximal lactate steady state (LT2 or MLSS), often cited around 4.0 mmol/L. This boundary matters far more for training adaptation than any single race pace.

In laboratory settings, lactate measurements help identify this line. In daily training, however, we need a practical, repeatable proxy. This is where Critical Speed (CS) comes in.

CS acts as an external output marker for that internal metabolic boundary. It tells us, in pace terms, where sustainable aerobic work ends and non-sustainable effort begins. For context, Critical Speed typically sits at roughly 88% to 92% of VO2 max velocity for most trained runners, making it a far more stable anchor for aerobic development than maximal-speed metrics. For recreational athletes, the effective ceiling is often lower than expected; running slightly slower than instinctively feels "right" is often more specific for aerobic development.

By working just below CS, athletes accumulate large amounts of high-quality aerobic work while keeping lactate stable and recovery manageable. Threshold, in this framework, is no longer a target to attack but a ceiling to respect. VO2 max work remains useful, but it is applied sparingly. Large volumes of training now sit just under the lactate tipping point, where efficiency improves without excessive systemic stress.

7. When systems outgrow their language

The words did not change as quickly as the practice. Terms like seuil, tempo, or threshold began to cover too much ground. They described everything from controlled aerobic work to near-maximal efforts, depending on context.

Even within France, the language is beginning to fray. Many social groups and freelance coaches have pivoted away from the formal VMA scripts, opting instead for labels like fractionné court or fractionné long (short and long intervals). This shift toward more descriptive labels is often a reaction to the difficulty of implementing precise metrics like VMA in a group setting.

Furthermore, the rising divide between road and trail running has added a new layer of complexity. While road groups might focus purely on pace-based metrics for 10k or marathon training, trail groups incorporate hill sessions and varying terrain that don't always fit neatly into a standardized pace-based language. This fragmentation is a sign of a system trying to find a more flexible vocabulary for the modern runner.

The result for many runners is a paradox: training feels easier, yet performance improves. Fatigue decreases, yet consistency increases. This was not because they were doing less: it was because the signal-to-stress ratio improved.

What this means for your week (practical takeaways)

• Make easy days truly easy: If you are slightly unsure whether an easy run is too fast, it probably is. Err on the side of comfort.

• Treat threshold as a ceiling, not a test: You should finish threshold sessions feeling controlled, not depleted.

• Reduce accidental hard running: Be wary of runs that feel "moderately hard" without a clear purpose. This is where intensity density quietly accumulates.

• Use pace as feedback, not a command: On tired days, slower execution is often better training.

• Judge success by repeatability: If you can stack weeks of consistent training without feeling run-down, the system is working.

8. What happens next

Most club structures will remain familiar. Easy runs, long runs, threshold sessions, and faster work are not disappearing. What will change is execution. Threshold will become calmer. High-intensity work will become shorter and more deliberate. Easy running will become easier. Progress will be measured in weeks and months, not in how shattered a single session feels.

Language will lag. Physiology will not.

From bravery to precision

This is not a story about France versus Norway, or tradition versus science. It is a story about a shared European and Western endurance model reaching the limits of its original language.

The goal remains unchanged: to get faster. The method has evolved. Repeatability has replaced exhaustion as the marker of effective training. And that shift is not national. It is generational.

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You do not need to become obsessed with physiology to train well. Mostly easy, sometimes hard, still takes most athletes a very long way. But it does help to understand what coaches and scientists actually mean when they use terms like threshold, LT2, Critical Speed, Critical Power, or CSS.

• “Hour pace” is not a physiological rule.

• True threshold = the highest pace/power you can hold without progressively draining your anaerobic battery (W').

• For most runners, that’s 30–45 minutes, not 60.

• Critical Speed (CS) and Critical Power (CP) find this point better than guessing based on race distance.

• If your TrainingPeaks Threshold value is wrong, your workouts quietly drift from the intended intensity.

The Catalyst: A Great Question from the Group

"How do I use Citicial Speed (CS) run pace in Training Peaks? Currently, I have my hour-long threshold pace in there rather than CS."

Why this question matters

This question reflects one of the most common misconceptions in endurance training: the idea that threshold is defined by how long you can sustain it, rather than by the physiological state itself, whether that is Critical Speed (CS), Functional Threshold Power (FTP), or Critical Swim Speed (CSS). When an athlete anchors threshold to an hour-long pace, they often end up training below the intensity needed to drive the intended metabolic adaptations. The rest of this article explains why that gap exists and how to correct it.

To be completely open, this confused me for a long time. Swimming seemed to treat 1500m pace as threshold pace, even though for competitive swimmers that will mean less than 20 minutes of work. Cycling was heavily anchored to hour power (even here it was being clarified and refined). Running, meanwhile, appeared to be shifting from half-marathon or 15 km pace toward something closer to 10 km pace through Critical Speed and Critical Power testing. It all felt inconsistent, and for a long time I struggled to understand how such different anchors could all be pointing to the same underlying physiological intensity.

So first, let’s define what threshold is.

Physiologically, threshold is often described in relation to Maximal Lactate Steady State (MLSS), the highest intensity at which blood lactate remains relatively stable over time. Lactate is best understood here as a useful marker of the underlying metabolic strain, rather than the sole cause of fatigue.

Once you move above that intensity, the disturbance begins to build progressively and the effort becomes far less sustainable. Stay at or just below it and you can maintain the effort for a substantial period.

The "Hour" Shorthand

In the early days of cycling power meters, Functional Threshold Power (FTP) was widely popularised as “the power you can hold for one hour.” That was a useful shorthand, not a biological rule. The real idea was always the highest power an athlete can sustain in a steady or near-steady physiological state, not a fixed 60-minute performance for every rider.

Some elite cyclists can hold that boundary for close to an hour, but that reflects exceptional durability, economy, and training status, not the definition itself. The clock is only a rough guide. The physiology is the real anchor.

Bottom line: whether you use pace or watts, the goal is to identify the same metabolic red line, the highest intensity at which internal strain remains relatively stable rather than progressively rising. In running and swimming, Critical Speed, Critical Power, and Critical Swim Speed are practical field estimates of that same boundary, giving you a useful proxy for MLSS without needing a lab test.

The "Hour Power" Trap

If you anchor your training on an "hour power" model across all three sports, you risk using a performance outcome as your reference point instead of the physiological boundary you actually want to target.

A 60-minute effort is highly aerobic, but it is not defined by aerobic steady-state metabolism alone. It is also shaped by W′, your finite work capacity above critical intensity, along with pacing, fatigue resistance, and sport-specific durability. That means an hour pace or power can sit slightly above or below your true metabolic threshold depending on the athlete and the sport.

When training is prescribed from that anchor, the aerobic stimulus often becomes less precise than intended. To drive the right adaptation, training should instead be anchored to your actual metabolic aerobic limit: MLSS, CP, CS, or CSS.

Why We Anchor Zones on LT2 (and Its Proxies)

In previous articles, we explored how training systems drift when intensity is not clearly bounded. That same logic applies here.

We anchor training zones to LT2 (MLSS), or to practical field proxies such as Critical Speed (CS), Critical Power (CP), or Critical Swim Speed (CSS), rather than to maximal outputs like vVO₂max or race-based heuristics.

VO₂max defines your ceiling. LT2 defines the boundary between sustainable and non-sustainable work. For training purposes, that boundary matters more, because it determines how much quality work you can accumulate and repeat without progressively depleting W′, your finite reserve of work above critical intensity.

Anchoring zones to LT2 does not make training easier, it makes training repeatable. It keeps threshold work honest, reduces accidental intensity drift, and ensures each session targets the intended metabolic system rather than slipping into a no man’s land between zones.

The Cellular "Why" Durations Differ

If Threshold is a metabolic steady state, why can't we maintain it for the same duration in every sport? The reason lies in metabolic clearance vs. mechanical occlusion.

In Swimming (The Occlusion Problem): Water drag requires high force throughout the stroke. High muscular tension compresses the capillaries within the muscle (venous occlusion). This creates a "local" environment where Hydrogen ions (H+) and metabolic byproducts cannot be "washed out" into the bloodstream effectively. You reach cellular failure faster because the waste products are trapped in the muscle fiber.

In Running (The Membrane Problem): The "pounding" of running causes eccentric muscle damage. This microscopic tearing of the cell membranes leads to "calcium leakage." This leak disrupts the electrical signal required for muscle contraction, meaning your "battery" (W') drains due to structural breakdown, even if your aerobic engine is still "steady."

In Cycling (The Clearance Advantage): Cycling has a very high "duty cycle" efficiency. There is a clear "off" phase in the pedal stroke where tension drops and blood can flow freely to clear byproducts. This allows the cellular environment to stay cleaner for longer, which is why cycling threshold duration is typically the longest.

Stryd & Running Power: CP vs. CS

If you use a Stryd power meter, you will be familiar with Critical Power (CP). CP and CS are two sides of the same coin:

Critical Speed (CS): Measures your metabolic limit in terms of Pace (min/km).

Critical Power (CP): Measures your metabolic limit in terms of Work Output (Watts).

The Stryd Advantage

Power accounts for external variables like hills, wind, and terrain.

The 10km Anchor: In practice, your CP will often land close to your best 35–45 minute effort (often around 10k race intensity). This is why your Stryd "Auto-CP" often looks "aggressive" compared to a 1-hour power estimate; it is finding your actual physiological limit, not a theoretical clock-based duration.

The "Battery" (W') and Your Phenotype

Think of your fitness as a battery-powered engine. The relationship between your Engine (Threshold) and your Battery (W') defines your Phenotype.

1. The Engine (MLSS/Threshold): Your sustainable cruising speed/power.

2. The Battery (W'): Your anaerobic reserve—a fixed amount of "emergency" energy (measured in Joules).

Nerd Note: W' vs D' You may see some articles refer to D' (D-prime). This is the exact same concept as W', just measured in meters (distance) rather than Joules (energy). While Stryd uses W', pace-based systems often use D' to tell you how many "bonus meters" you have in the tank when you sprint.

Diesel vs. Rocket

The Diesel (High Threshold / Small Battery): Massive engine, tiny battery. Can cruise at a high pace all day but has no "kick." Surging just 5% above threshold causes rapid failure (within minutes).

The Rocket (Lower Threshold / Massive Battery): Smaller cruising engine, huge "emergency reserve." Can surge, sprint, and attack repeatedly. Dangerous in a finish-line sprint but struggles with 40-minute steady-state grinds.

Bottom line: Understanding your phenotype is a powerful diagnostic tool. While it helps you decide where to place "matches" in a race, its primary value is identifying if a low speed ceiling (small battery) is the bottleneck preventing your threshold from moving higher.

The Recreational Athlete Challenge

Most recreational athletes without a sprint background present as accidental "Diesels." Because they lack high-intensity background, their W' (Battery) is often severely underdeveloped. For these athletes, raising the "speed ceiling" through specific speed work is essential. Making your top-end speed faster makes your threshold pace feel comparatively easier.

Durability: The "Third Pillar"

Your Critical Power/Speed is not a fixed number; it is a perishable one. In sports science, this is called Durability. Your CS at the start of a race is different from your CS after you have burned 2,000 calories. High-level endurance training isn't just about moving your "fresh" threshold higher; it’s about making your threshold durable so it’s still there in the final hour of a race.

Bottom line: This is why we don’t just test CS, we build the ability to hold it when tired.

Zone Compression: The Mark of the Elite

As you become more advanced, your Power-Duration Curve flattens out significantly, narrowing the gap between "Easy Pace" (Zone 2) and "Threshold Pace" (Zone 4/CS).

The Elite Profile: A world-class marathoner's Zone 2 pace might be only 15 to 20 seconds per km slower than their Threshold pace.

The Recreational View: Don't try to force this by running easy days too fast. True Zone Compression is a result of fitness, not a method of training. You want your easy pace to naturally "drift" toward your threshold over years of consistency.

The Battery in Real Life: Surges and recovery

When you go above threshold, you are "spending" your W' battery.

The Drain: In swimming, drag is so high that W' disappears almost instantly if you surge. In cycling, you can "meter" the drain precisely.

The Recharge: To refill the battery, you must drop below threshold. It is easiest to "recharge" in cycling (coasting). It is hardest in swimming and running (constant work/impact), which is why recovery intervals in those sports feel less "refreshing."

The "Slower Threshold" Debate: 15 km Pace vs. CS/CP

The No-Man’s Land Trap

If your “threshold” is anchored to something like 15 km pace, short threshold sessions can miss the mark. They may be too slow to create a strong ceiling-raising stimulus, yet still hard enough to generate meaningful fatigue and consume recovery capacity. The result is a kind of no-man’s land: not hard enough to target the intended upper boundary of steady-state fitness, but not easy enough to be low-cost aerobic volume either.

The CS/CP Scalpel

Critical Speed and Critical Power solve that problem by anchoring training to the boundary that actually matters. They let you place threshold work right on the limit of sustainable metabolism, where the stimulus is both repeatable and specific.

That does not make hour pace or 15 km pace useless, it simply means they should be used deliberately as session intensities, not as the reference point for the whole system.

Practical Application: TrainingPeaks (TP)

1. For Run Pace: Enter your CS Pace in the "Threshold Pace" field and for the zone model I use Joe Friel for Running (7)

2. For Run Power (Stryd): Enter your Stryd CP in the "Threshold Power" field. For the zone model I use Stryd.

3. For Swim Pace: Enter your CSS pace in the “Threshold Pace” field. For auto-calculation choose Threshold Speed and for the zone model I use MyProCoach Swimming (5).

Summary Table: Threshold by Sport

The mechanical demands of each sport dictate how long you can hold that engine at its limit:

• Cycling (FTP): ~40–60 mins. High efficiency, sitting down, zero impact. Muscles handle the "burn" longer before mechanical fatigue becomes limiting.

• Running (CS/CP): ~30–45 mins. High impact (eccentric loading). Mechanical load accelerates fatigue, meaning the threshold expresses at a shorter duration than in cycling.

• Swimming (CSS): ~20–30 mins. Water is 800x denser than air. As technique slips, drag increases exponentially. This doesn’t mean lower physiological strain; it means the curve reaches its ‘steady’ region (asymptote) sooner because drag punishes even small speed increases.

Bottom line: Set CS/CP correctly, and your training stops drifting.

Final Thoughts: From Clock-Watching to Metabolic Intent

You do not need to become obsessed with physiology to train well. Mostly easy, sometimes hard, still takes most athletes a very long way. But it does help to understand what coaches and scientists actually mean when they use terms like threshold, LT2, Critical Speed, Critical Power, or CSS.

That understanding helps you cut through jargon. It helps you recognise when different terms are describing the same underlying idea, and when they are not.

It helps you become your own best coach, because you are less reliant on borrowed rules of thumb and better able to judge the purpose of a session for yourself. And it helps you avoid hype, because you are less likely to be distracted by labels, trends, or false precision.

In the end, the value is not complexity, but clarity. Understanding the physiology helps you cut through the jargon, avoid the hype, and make better decisions about your own training. That does not replace simple training. It just helps you understand why simple training works.

FWDMOTIONSTHLM – A page for all things swimrun, training & more.

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Last week we talked about Critical Swim Speed CSS. If you haven’t read that post I suggest you go back and read it first <here>.

If you want to use CSS more effectively, this post helps to understand how the testing works and what additional information you can extract from it.

I’ve created a calculator you can use here:

CSS_Calculator_Any_Distances_Aligned_v2

Unlike most online calculators, this one allows different test distances and multiple data points. Make your own local copy, and let me know if you find any bugs or have suggestions on how to improve it.

Two Distances vs Three Distances

Most athletes are familiar with the traditional 400 + 200 test. This works well, but it has a limitation: it forces a straight line through only two points. Any pacing error or sprint bias can distort the result. Using three distances improves accuracy because it calculates a best-fit line across multiple efforts.

In simple terms:

• Two tests: Good estimate

• Three tests: More robust estimate

For many endurance athletes, three data points produce a CSS that better reflects sustainable performance.

What Distances Should You Test?

Rather than prescribing fixed distances, it is often more useful to choose test efforts based on duration. This allows faster and slower swimmers to select distances that target similar physiology. A practical guideline is to include efforts lasting approximately:

• 2 to 3 minutes

• 4 to 6 minutes

• 8 to 10 minutes

The goal is to include efforts across different durations that allow you to estimate threshold speed, rather than prescribing identical distances for everyone.

Examples of test protocols:

• Swimmer A (Faster): Might use 200, 400, and 800 meters to hit those time brackets.

• Swimmer B (Developing): Might use 100, 200, and 400 meters to stay within the same physiological windows.

Whatever protocol you choose, consistency matters more than perfection. Always repeat the same test format when tracking progress.

What Does D' Tell Me?

D' describes how much speed you have above threshold, while CSS describes how fast you can sustain. It helps explain why athletes with similar CSS can perform differently over shorter distances.

Low D' is very common in endurance athletes and is not always a weakness. It often reflects strong fatigue resistance and efficiency.

Higher D' athletes typically show:

• Bigger difference between 200 and 400 times

• More ability to accelerate and surge

• Greater sprint capacity

Lower D' athletes typically show:

• Smaller pace differences across distances

• Strong pacing stability

• High endurance durability

For most training decisions, CSS remains the more important number. D' mainly provides insight into your athlete profile.

How to Use the Calculator

The calculator provides several outputs. Here is how to interpret them and how to use them in practice.

Two Data Points vs Three Data Points

If you enter two test distances, the calculator gives you a CSS based on those two performances. This is the traditional approach and works well when pacing is good. If you enter three distances, the calculator also provides a regression CSS. This uses all available data to calculate a best-fit line across your efforts.

In practice:

• Two points: Simple estimate

• Three points: More robust estimate

If you have three good maximal efforts, the regression value is usually the better number to use.

Which CSS Should I Use to Anchor My Zones?

Use the number that best reflects what you could repeat in training. For many endurance athletes with low D’ values, raw CSS slightly overestimates threshold pace. In these cases, it can be useful to anchor training zones on CSS + 2 to 3 seconds per 100 meters. This is not changing your fitness; it is aligning training intensity with physiology. The objective is repeatable quality, not validating the test result.

What Is the Manual Adjustment?

The calculator includes a manual adjustment factor so you can modify the pace slightly if needed. This exists because testing conditions vary, athlete profiles differ, and sustainable pace is not identical to test pace.

• If your repeats consistently fall apart at raw CSS, you might add +2 to +3 seconds

• If the pace feels hard but repeatable, you may not need any adjustment.

Think of this factor as a coaching correction, not a mathematical one.

A Final Thought on Testing

Testing is not about producing the perfect number. It is about creating a consistent reference point that helps guide training. Used correctly, CSS becomes a tool for understanding your physiology, not judging it.

The number matters far less than how you use it.

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Many endurance athletes have had this experience. You do a CSS test, you get a number, and then you try to train at that pace. It feels too hard. You cannot hold it across repeats, or the pace falls apart after a few intervals.

That frustration is extremely common. The natural conclusion is usually: "I must just need to get fitter." Very often, however, the problem is not fitness. It is understanding what CSS actually represents.

CSS Is a Model, Not a Measurement

Critical Swim Speed (CSS) is an estimate of the fastest pace you can sustain aerobically without continually accumulating fatigue. It is similar to:

• Lactate threshold (LT2)

• Critical Speed (CS) in running

• Functional Threshold Power (FTP) in cycling

But here is the important part: CSS is not a direct physiological measurement; it is a model derived from performance. That means it reflects more than just fitness. It reflects aerobic capacity, technique efficiency, fatigue resistance, and pacing skill. Two athletes with identical physiology can produce different CSS numbers simply because they move differently in the water.

CSS comes from the relationship between how far you swim and how long it takes. The slope of this line represents your sustainable speed.

A Maximal Test Is Not a Sprint

This is one of the most common mistakes athletes make. A maximal effort does not mean exploding off the wall as hard as possible. It means the fastest pace you can sustain for the entire distance.

If you sprint the first part of the test:

• Lactate accumulates early

• Stroke mechanics deteriorate

• Oxygen delivery lags behind demand

Starting too hard usually produces a slower overall time. A well-paced maximal swim usually feels like:

• A controlled first quarter

• A strong middle

• A very hard final quarter

The goal of a CSS test is not to prove toughness; it is to reveal an threshold anchor speed.

The Hidden Variable: Your Speed Reserve

Some athletes have a large gap between short and long distances, while others do not. This difference comes from anaerobic capacity, often represented as D' (D-prime). In simple terms: D' is your speed reserve above threshold.

Athletes with large speed reserves often have:

• A significant difference between 200 and 400 times

• Strong sprint ability

• A larger pace drop-off over distance

Athletes with small speed reserves often have:

• A 200 pace that is not much faster than their 400 pace

• A strong endurance profile

• High fatigue resistance

Neither profile is necessarily better or worse; they are simply different physiological signatures.

Physiology is curved. CSS is the straight-line approximation that helps us estimate threshold.

The Technical Dimension: Why Better Swimmers Have More Accurate CSS

Critical Swim Speed (CSS) is a mathematical model applied to a mechanically complex sport. Unlike running or cycling, swimming mechanics can change significantly with intensity. Small alterations in body position or coordination can dramatically increase resistance, which affects how accurately the model predicts performance.

CSS tends to be more reliable for technically stronger swimmers because they behave more like stable hydrodynamic systems. Developing swimmers often do not, at least not consistently. There are three primary reasons.

1. Stable Hydrodynamics

Water resistance increases with the square of velocity for all swimmers. However, stronger swimmers maintain a consistent body position across intensities, including high hips, narrow alignment, and controlled rotation. Because their shape in the water remains stable, increases in effort translate predictably into increases in speed.

2. The Technique Penalty

When less experienced swimmers increase effort, they frequently create additional resistance rather than additional propulsion. Common patterns include slipping water during the pull, increasing stroke rate while losing stroke length, or losing alignment through the kick. This creates a disproportionate rise in drag relative to speed, making pacing relationships non-linear and introducing noise into CSS calculations.

3. Propulsion Consistency

Advanced swimmers maintain similar stroke mechanics, timing, and coordination across intensities. They are essentially performing the same movement pattern at different speeds. Developing swimmers often change coordination strategies between moderate and hard efforts, meaning the test distances may reflect different movement patterns rather than different intensities of the same system. This reduces reliability of the model.

Practical Implication

If CSS feels inaccurate or difficult to sustain, the limitation is not always physiological fitness. Technique stability, pacing skill, and coordination under fatigue are often the primary factors. Improving technique does not only increase speed; it also improves the reliability of training metrics.

Fitness determines potential. Technique determines whether that potential can be expressed consistently. CSS works best when both are present.

Training Zones (CSS-Based)

These zones are organized around your CSS and align broadly with commonly used swimming intensity scales. They are guidance ranges, not strict boundaries.

How to Interpret the Zones

Most endurance training happens in Z1 to Z3. Z4 is typically performed in shorter intervals rather than continuously. It is designed to create a strong aerobic stimulus that can be repeated with recovery. Z5 is used sparingly for intensity and speed development.

Zones are tools, not rules.

Why CSS Sometimes Feels Too Hard

Several factors can make raw CSS feel unrealistic: testing pacing errors, small anaerobic capacity, fatigue from training load, or technique breakdown under intensity.

For many endurance athletes, raw CSS slightly overestimates sustainable pace for different reasons. In athletes with a low D', the pace is often too fragile because they lack a speed buffer. In contrast, athletes with a high D' often have mathematically inflated results because their sprint speed tricks the model into overestimating their aerobic floor. For developing swimmers, results are often noisy and inconsistent because speed is limited by technical volatility and high drag.

Because of this, many athletes anchor their training zones slightly slower than a raw CSS test result. A practical guideline is to use CSS + 2 to 4 seconds per 100 meters for sustained work. Developing swimmers may find that a wider adjustment of +4 to 6 seconds is necessary to prioritize form over raw numbers. This adjustment does not change your fitness; it improves training quality and repeatability. The goal is consistent adaptation, not chasing a number.

Same CSS, different physiology. D′ explains why athletes respond differently to training.

The Biggest Mistake Athletes Make

The biggest error is treating CSS as a target instead of a reference. CSS is not a pace you must prove you can hold; it is a calibration point to organize training intensity. Effective training includes multiple intensities around that mark:

• Easy aerobic: Slower than CSS

• Tempo: Slightly slower than CSS

• Threshold: Around CSS

• High intensity: Faster than CSS

Trying to sit exactly on CSS all the time often leads to stagnation and fatigue.

What Really Matters: Durability

Performance is not determined by how fast you can swim once. It is determined by how fast you can swim repeatedly without breaking down. That quality is called durability. Durability improves when training is paced correctly, not heroically.

Practical Takeaways

• A maximal test is not a sprint

• CSS is an estimate, not a truth

• Consistency beats intensity

• Most endurance swim sessions are slower than CSS

The Bigger Lesson

Endurance sport rewards restraint. The athletes who improve the most are rarely the ones who push hardest in tests. They are the ones who learn to sit on the edge of sustainable effort, again and again, until the edge moves. When that edge moves, CSS moves with it.

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At a Glance

• The Core Thesis: In swimming, you don't build a bigger engine to go faster; you build a more hydrodynamic swim form.

• The Methodology: Progressive overload in the water is not about piling on volume. It’s about maintaining technical integrity as fatigue rises.

• The Outcome: Speed emerges when efficiency improves, not just when effort increases. If running rewards work, swimming rewards control.

Note: This framework is primarily designed for adult-onset swimmers, triathletes, and swimrunners, for whom technical efficiency is the primary bottleneck to performance.

The Plateau Problem

I recently received a question that perfectly captures why so many swimmers feel stuck:

The problem isn't the app or the watch. The problem is that most adults treat swimming like running: they assume that adding more distance or more heart rate is the only way to get faster.

Swimming doesn’t work like that.

Progressive overload is one of the most fundamental principles in endurance training. In running and cycling, it’s almost intuitive: you add time, distance, or power, and performance improves. The relationship between effort and output is reasonably linear, and progress is easy to see.

In the water, the usual levers of overload behave differently. Sessions are often time‑limited, technique collapses before fitness, and intensity doesn’t scale in a neat, predictable way. This is why many swimmers feel stuck; even when they’re training consistently and working hard.

Why Swimming Breaks the Usual Overload Rules

Time Is Usually Fixed

Most swimmers don’t have unlimited training time. In most squads, sessions are fixed at 60 or 90 minutes. Unlike running, you can’t simply extend a session to create overload. The total volume is capped before you even start. This forces a different question: If I can’t train longer, what exactly am I progressing?

Technique Is the Primary Limiter

For the majority of adult-onset and sub-elite swimmers, fitness is rarely the first thing to fail. Technique is. As intervals get longer, stroke mechanics degrade. Once that happens, the swimmer is no longer training the intended system; they’re rehearsing inefficiency; adding fatigue without adding speed.

In most adult-onset swimmers, simply trying harder usually results in "fighting the water"; creating more turbulence rather than more propulsion.

Intensity Behaves Differently in Water

Water is approximately 800 times denser than air. In fluid dynamics, drag force is proportional to the square of velocity. However, the power required to overcome that drag increases with the cube of velocity.

Why this matters:

• To swim just 10% faster, the drag force increases by roughly 21%, but the power required to overcome that drag increases by over 33%.

• Because resistance scales so aggressively, progress is often "invisible" on the clock. A 0.5s improvement on 100m pace may look like noise on a watch, but it represents 5 seconds per kilometer; a massive gain in efficiency and energy cost.

Many swimmers are improving long before the clock confirms it. In water, small time gains are massive physiological wins.

Progressive Overload: A Different Lens

Instead of thinking in terms of time or distance, progressive overload in swimming should be framed around control.

Progress Interval Structure, Not Session Length

Structure training blocks by progressing interval length, not total volume. However, there is a golden rule here: Your intervals should map to your technical ability, not your fitness.

Even if you have the cardio to swim 1km straight, if your "form" falls apart after 50m, you should stop at 50m. By resting for 15 seconds, you reset your stroke so you're always "practicing" being fast and efficient, rather than practicing survival mode.

• The Rule of Thumb: If your pace decays or your stroke feels "mushy," the interval is too long.

• Permission to Break the Set: If a plan says 400m, don’t feel bad about breaking them into 4 x 100m or 8 x 50m. Only good strokes count! As you get faster and more efficient, you will feel more "flow," and the ability to hold those longer intervals will follow naturally.

Equipment as Overload (The Swimrun Factor)

For swimrunners, paddles and pull buoys are not just "toys"; they are tools for specific force production and hydrodynamic proprioception.

• Don't use equipment to hide flaws: If you can only hold a 1:40 pace with paddles but drop to 1:55 without them, the paddles are masking a mechanical collapse.

• The "Cadence Trap": Be wary of oversized paddles. While they allow for more force to be generated, they often force a significant drop in stroke rate. This triggers timing flaws like over-gliding, where the swimmer develops a "dead spot" at the front of the stroke.

• Load the surface area, not just the distance: Progress from smaller paddles to larger paddles only if and when you can maintain power through the stroke with correct stroke timing.

• The "Buoy as Teacher": Don't view the pull buoy as a "cheat" for low legs. Use it to teach your body what a horizontal, slippery profile feels like. For a swimrunner, the buoy is race-specific kit; the goal is to build a massive aerobic engine (the "lungs") without the metabolic drain of an inefficient kick (the "anchor").

Use Intensity Anchors—With Judgment

For swimmers faster than roughly 1:45 / 100m, use Critical Swim Speed (CSS) as a reference point. For swimmers slower than ~1:45 / 100m, RPE (Rate of Perceived Exertion) and "relaxed speed" are more effective. At this pace, chasing a clock time often leads to "thrashing," which increases drag and reinforces poor mechanics. Focus on finding a "slippery" sensation instead.

A Proof Point from Swim History

Legendary coach Brett Sutton explains why this "broken" approach to distance is the secret to real speed:

There is a well-known story from the early career of Sutton. As a young coaching assistant, he was sent to observe a rival club that kept winning state championships. He expected to see complex, constantly changing workouts. Instead, week after week, he watched them do the exact same session. He eventually realized that champions aren't built on "variation" but on repetition under control. That "monotonous" set used by this world-dominating club was a Broken 500 Metres:

10 × 50 m on a fixed, tight start time, as:

• 4 × build from steady to hard from 3/4 distance.

• 3 × build from steady to hard from 1/2 distance.

• 2 × build from steady to hard from 1/4 distance.

• 1 × maximum effort for the full 50 m.

The Marathon Myth: Training for 10k and Multi-Day Swim Events

A common misconception among amature marathon swimmers and multi-day athletes is that they must prove their readiness by swimming a very high percentage of their target distance in a single, continuous session. Many believe that if they cannot swim 8 km or 9 km straight in training, they are not ready for a 10 km event.

In reality, readiness for marathon distances is not determined by any single workout. It is primarily driven by consistent weekly volume. For most amateur athletes, weekly mileage will typically peak somewhere around 1.5 to 2 times the longest swim distance, depending on experience and training time.

In long-distance swimming, the greatest limiter is rarely aerobic stamina alone. It is the accumulation of drag caused by technical breakdown under fatigue. High-percentage simulation swims often become “death marches,” where the final kilometres are spent reinforcing slow, inefficient movement patterns.

Effective overload comes from accumulating large volumes of high-quality swimming across the week. Sessions broken into repeats with short rest allow swimmers to reset posture, maintain a horizontal profile, and preserve an effective catch. This results in better mechanics, higher average speed, and a stronger aerobic stimulus than a single continuous effort performed in a fatigued state.

Long continuous swims still have a role, particularly for nutrition practice, cold adaptation, and psychological preparation. However, they are tools for specificity, not the foundation of your training program.

The Fourth Variable: Mental Overload

When most swimmers plateau, they assume they need a different app or a more complex plan. In reality, the plateau is often mental.

Swimming requires a level of constant proprioceptive focus that running doesn't. You have to think about your hand entry, your hip rotation, and your kick timing simultaneously. As you get tired, your "mental bandwidth" shrinks. You stop "swimming" and start "surviving."

Progressive overload is also the training of focus. Holding your form for 200m instead of 100m isn't just a cardiovascular win; it’s a cognitive win. It means you've automated the movements well enough that they no longer require 100% of your conscious attention.

The Swimmer’s Audit — Use This After Your Next Session

• Stroke Count & Rate: Did my strokes per length and my rhythm (SPM) stay consistent?

• Split Consistency: Was my final 100m within ~1 second of my first?

• Breath Management: Did I maintain my planned breathing pattern?

• The "Slip": Did I feel like I was moving through a small hole in the water, or pushing a wall of water?

• Hand or Paddle Pressure: Did I feel equal pressure throughout the entire stroke?

The Takeaway

Progressive overload in swimming is not about doing more. It’s about doing better.

1. Interval structure matters more than session length.

2. Technical stability precedes speed gains.

3. Focus fatigue is as real as muscular fatigue.

Swimming rewards patience and precision. The work often looks boring. The gains often feel invisible. Until one day, you realise you’re swimming faster than ever; without trying harder.

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How sleep changes the "operating system" and physics of your training tomorrow

If Part 1 was about the "Maintenance Crew" fixing the damage from today, Part 2 is about the "Operating System" you run on tomorrow. Most athletes treat sleep as a passive bank account; in reality, it is an active performance variable that shifts the goalposts of your fitness.

Most athletes understand that sleep helps recovery. What’s less understood is that sleep directly changes how training feels; how accurately you pace and how well you access your fitness under load.

Perceived Effort Is Not Fixed

Perceived exertion (RPE) is often treated as purely subjective, but research shows sleep loss increases RPE at any given workload.

Same pace. Same power. Higher effort. The body works harder to produce the same output when restricted. This is why threshold work "drifts" and why endurance days feel heavier than they should.

Neurological Pacing

Pacing is a cognitive skill. It relies on internal feedback and decision‑making. Sleep loss degrades both. Athletes short on sleep are more likely to start too fast or abandon pacing plans mid‑session. This is not a willpower issue; your brain simply loses the ability to fine‑tune the engine when the battery is low.

The Cellular Energy Factor: Creatine and Sleep

Emerging research suggests that sleep quality isn't just about "lifestyle"; it's about cellular energy. During hard training, your cells burn through ATP faster than it can be rebuilt. When reserves are depleted, energy sensors flag a crisis, keeping the sympathetic nervous system firing. This is the biological signature of being “tired but wired.”

A 2024 study showed that athletes (specifically women) taking 5g of creatine daily slept 48 minutes longer on training nights than those on a placebo. By buffering cellular energy stores, creatine may help switch off that "crisis" signal, allowing the body to transition into deep sleep more effectively.

The "Mystery" Niggles

The link between short sleep and injury risk is undeniable. Athletes sleeping under 7 hours are significantly more likely to develop overuse injuries. Sleep loss impairs tendon repair and makes movement subtly less precise. Small errors accumulate until something hurts "out of nowhere."

Durability as You Age

As we move into our 40s and beyond, recovery margins narrow. Connective tissue remodels more slowly. Sleep becomes your cheapest and most effective durability tool. 

A Simple Framework to Take Away

If 6:30 is your current wake‑up time, aim for 7 hours first. When that sticks, add 15 minutes. Small gains compound.

Core Principles:

• Environment: The bedroom is for sleep. No scrolling.

• Caffeine: Cut it 6 hours before bed. It lingers longer than you think.

• The Brain Dump: If your mind races, write tomorrow’s to‑do list before bed to "unload" the stress.

• Morning Light: Even in a Swedish winter, get outside for your morning coffee. It’s the strongest circadian signal we have.

• Creatine Buffer: Consider 5g of creatine monohydrate daily. It helps buffer cellular energy, potentially silencing the "tired but wired" signal on hard training days.

• Downshift: If you train late, use a warm shower and slow breathing to signal to your nervous system that the session is over.

• The "Pinot" Clause: Enjoy a good glass of wine if you like; just don’t pretend the science backs the recovery benefit.

The Takeaway

Hard training feels easier not because you’re tougher; but because your system is prepared to absorb the work.

Consistency beats perfection. Sleep makes consistency possible.

A Note on Women and Sleep

After the last newsletter, several women replied with something like “Sleep more… easy for you to say.” That is fair. Women are more prone to sleep disruption, not because of life load, but because of specific physiological shifts.

Progesterone has a calming effect on the brain. It enhances GABA signalling, which supports sleep onset. At the same time, progesterone raises core body temperature by around 0.3–0.5°C in the luteal phase. For some women, particularly during perimenopause when hormones fluctuate unpredictably, this can make sleep feel lighter or more fragmented.

Iron deficiency, common in women, can also impair sleep quality even when haemoglobin levels appear “normal”.

And if you are under-fuelling your training, low energy availability can increase evening cortisol and sympathetic activation, both associated with poorer sleep. In endurance sport, this sits on the same spectrum as Relative Energy Deficiency in Sport, where disrupted sleep is often an early signal rather than a late one.

So sometimes the issue is not just better habits. It is biology. The practical step — If sleep is consistently poor:

• Track it alongside your menstrual phase.

• Check ferritin, not just haemoglobin (many sports physicians prefer levels above ~50 ng/mL in active women).

• Review fuelling: ensure energy intake matches training load.

• Magnesium bisglycinate may help some individuals.

• Speak to a GP or gynaecologist if patterns persist, ideally someone familiar with active women/endurance athletes.

As coaches, we adjust training when data changes. Sleep deserves the same respect.

FWDMOTIONSTHLM – A Page for all things SwimRun, Training & more.

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Why the most powerful training tool in your arsenal is the one you’re probably ignoring

I recently received my Coros Year in Review, and one number stood out immediately: an average of 8 hours and 39 minutes of sleep per night over the past year.

When I shared this with my training group after a dark Saturday morning session, the reaction was telling. A few of the others still smelled faintly of chlorine from an early indoor pool workout. There were a few low whistles. Some disbelief.

Out of a dozen dedicated runners, swimmers, and swimrunners, no one else came close. Most were hovering somewhere in the high sixes or low sevens.

And I get it.

In endurance sport, there’s often a quiet badge of honor attached to doing it all on very little rest. The 5:00 a.m. alarm for a pre‑work swim. The long run before the city wakes up. Strength work squeezed into whatever gap remains. We admire the grind.

But sitting there over coffee, it struck me that we often have the problem backwards.

We obsess over carbon plates, pull buoys, paddle size, and wetsuit model; while quietly undercutting all that work by neglecting the one window where we actually get better.

Training Is the Signal. Sleep Is the Adaptation.

This is a truth I regularly remind athletes:

• You don’t get fitter during the run.

• You don’t get stronger during the swim set.

• You don’t adapt while you’re suffering through threshold work.

In those moments, you are breaking things down. Muscle fibers are stressed. Glycogen is depleted. The nervous system is loaded. Training is simply the signal; the message to your body that says, “This version of me isn’t robust enough yet.”

Sleep is when the upgrade happens. If you send a massive training signal but don’t provide enough sleep to support the adaptation, you’re not training. You’re just accumulating fatigue.

“I Function Fine on Six Hours” — A Subtle Trap

I hear this a lot:

“Coach, I’ve always been a low‑sleep person. I function fine on six or seven hours.”

I believe you. Humans are remarkably resilient. We can function under all sorts of sub‑optimal conditions. But there’s a big difference between functioning and thriving as an endurance athlete.

General sleep recommendations, 7 to 8 hours are designed for the average person. If you’re training an hour or more per day, stressing your cardiovascular system, connective tissue, and nervous system, you’re no longer average. Your recovery requirements are higher.

One of the most consistent findings in sports science is that increasing sleep duration reduces injury risk and lowers perceived effort.

• On 8.5 hours of sleep, a threshold swim feels like a controlled 6 out of 10.

• On 6.5 hours, the same session feels like an 8 out of 10; even at an identical pace.

Sleep doesn’t just help you recover. It makes the work feel easier.

Your Overnight Maintenance Crew

Think of sleep as your body's essential service window:

• Tissue Repair: Deep sleep is the primary window for growth hormone release. When sleep is cut short, the window for physical repair narrows.

• Refueling: Glycogen restoration accelerates while you sleep. Nutrition provides the raw material, but sleep governs how effectively that fuel is stored for the next day’s work.

• Neurological Filing: Endurance training is as much neurological as it is muscular. Coordination, rhythm, and technical efficiency are all brain‑dependent. Sleep is when motor patterns are consolidated. The improvements you chase in the pool are not truly "saved" until you sleep.

Tracking Tools vs. Truth Machines

Most of us now wear something that tracks sleep. Used correctly, these tools are genuinely helpful for pattern recognition. They reliably show:

• Consistency of your routine.

• Duration trends (up or down).

• The impact of lifestyle stressors.

Where these devices fail is the details. Sleep stages (REM vs. Deep) require brain‑wave measurements in a lab. Wrist‑based devices estimate these via movement and heart rate, making them "noisy" day‑to‑day.

Many athletes wake up, see a poor sleep score, and subconsciously decide the day is doomed. Use sleep data as feedback, not judgment. If your resting heart rate is trending up, that’s a coaching signal; not a verdict.

Sleep trackers should help you sleep more — not worry better.

The Anchor Rule

In the middle of a Swedish winter, the lack of daylight can wreak havoc on your internal clock. Your body’s circadian rhythm loves predictability, and the most important part of that rhythm is your wake‑up time.

Think of it as your physiological anchor. Even if you have a late night, try to wake up at the same time the next morning. Consistency at 7:00 AM every day is far more powerful than catching up on weekends and inducing "social jet lag."

A Gentle Challenge

What would change if you aimed for just 30 more minutes of sleep tonight? Not perfection. Not two hours. Just thirty minutes. Move the bedtime up. Close the laptop. Let the adaptation happen.

But sleep doesn’t just dictate how you recover from yesterday's work. In the next post, we’re going to look at the hidden side of the equation: why the exact same session can feel like a breeze or a death march depending entirely on what happened while your eyes were closed. It turns out, sleep isn't just a recovery tool; it's a performance enhancer that changes the very physics of your training. This is what we will look into next week.

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In last week’s article, The New Evolution of Speed, we explored the science of internal load and why metabolic stability; staying in the "sweet spot" is the true engine of progress. But to apply those scientific principles to daily training, we need a common language for intensity. In practice, this shift means we no longer chase exhaustion as proof of effectiveness; we chase repeatability.

Before we dive into the "gears" of high performance, we must acknowledge the foundation. Regardless of your model; Zone 2 (Aerobic Base) remains the non-negotiable bedrock. Volume is still the king of endurance; the following shifts are about how we layer quality on top of that foundation.

The Foundation: Understanding the 7-Zone Model

To dose training stress precisely, we use a framework based on Joe Friel’s intensity zones, mapped against both internal metabolic markers (Lactate) and external output (Critical Speed).

• Zone 1 (Recovery): Very easy (< 1.5 mmol/L). Active recovery between hard days.

• Zone 2 (Aerobic Base): The foundation (1.5–2.0 mmol/L). Build endurance and fat-burning efficiency.

• Zone 3 (Tempo): "Extensive" aerobic work (2.0–3.0 mmol/L). Lower end of the heavy domain; roughly 90–94% of Critical Speed.

• Zone 4 (Threshold / CS): "Intensive" aerobic gear (~3.0–4.0 mmol/L, individual MLSS-dependent). This is your Critical Speed (CS)—the highest steady-state pace you can maintain without a rapid "drift" in lactate or fatigue.

• Zone 5 (VO2 Max): High-intensity "ceiling" work (> 5.0 mmol/L), roughly 3km to 5km race effort.

• Zone 6 [5b] (Anaerobic Capacity): High-intensity bursts (30–60s) for power and lactic capacity.

• Zone 7 [5c] (Neuromuscular Power): Maximum "all-out" effort (sprints/hills) under 20 seconds.

Note on Notation: While traditional Friel models use "5b" and "5c," we label them as distinct Zones 6 and 7. They target mechanical power and neuromuscular snap, requiring different recovery strategies than the "metabolic storm" of Zone 5.

1. The Traditional Model vs. The “Modern” Model

For decades, the Traditional Model focused on "Raising the Ceiling" via a binary approach: lots of Zone 2 and hard Zone 5 intervals. The logic is simple: work your heart and lungs at their absolute limit. This builds "mental callusing" but often ignores the metabolic middle ground.

The Modern Model (championed by researchers like Alejandro Casado and coaches like Marius Bakken) focuses on "Filling the Engine." We prioritize controlled Zones 3 and 4, using Critical Speed (CS) as our primary anchor to manage lactate levels. Instead of 15 minutes in Zone 5, we do 45–60 minutes in the Z3/Z4 "Heavy Domain." This is a "surgical" approach designed to maximize efficiency with minimal systemic fatigue.

2. The "Hollowed Out" Zone 4 & Zone 5

We effectively "hollow out" Zone 5 and the higher end of Z4; not by removing them entirely, but by using them sparingly and strategically.

• Working Below (CS / Zone 4): Builds your "aerobic floor." The key is staying sub-critical (95-100% of CS), which corresponds to the high-efficiency lactate range of 2.5–3.5 mmol/L.

• Working Above (Zones 6 & 7): Develops the "chassis" (tendons, stiffness, force application). This is "free speed"; high power with zero acid. It prevents the "wet noodle" chassis that leads to plateaus. While much of the recent hype centers on controlled "double threshold" sessions, very little focus is placed on sessions like the Ingebrigtsen 20 x 200m hill repeats. For most recreational runners, this type of mechanical stimulus is severely underused.

Why keep any Zone 5? As Steve Magness points out, we don't eliminate Z5 because we still need to recruit high-threshold motor units and teach the brain to stay composed in a "metabolic storm." We just no longer use it as our primary workhorse.

3. Critical Speed: The Athlete’s Practical Dashboard

While Lactate (mmol/L) is the internal signal telling us if the engine is overheating, Critical Speed (CS) is your external dashboard. It is the mathematical boundary between "sustainable" and "unsustainable" effort.

How to Find Your CS (Testing Best Practices)

Since we aren't using daily blood tests, we calculate CS using a three-point mathematical model. This requires three max-effort time trials on fresh legs:

1. 1000m (All-out max effort).

2. 1500m (All-out max effort).

3. 3000m (All-out max effort).

By using three distances instead of two, we create a more robust "line of best fit." This statistical redundancy helps filter out daily variations (bad sleep, heat, or pacing errors on a single test) and provides a much truer metabolic map of your engine.

All tests must be performed on separate days, fully recovered, or the calculation will underestimate your true Critical Speed. The relationship between these three data points defines your CS; roughly the pace you could race for 45–60 minutes. For more details on testing and critical speed see this guide.

CS Training Rules

• The "Sub-CS" Volume Play (Lactate 2.0–3.5): Most of our work is done at 95–98% of CS. This allows for massive quality volume because you never "tap too far into" your anaerobic reserves or spike your lactate into the red.

• The "Over-CS" Exposure (Lactate > 4.0): When we work at 102–105% of CS, we are intentionally draining your "Anaerobic Tank" (D'). This is used sparingly to build race-specific toughness.

4. The Performance Spectrum: A 10km Analysis

The 30-Minute Runner (Sub-Elite / Elite)

Pace: 3:00/km

• The Nuance: These runners have a narrow gap between CS and VO2 Max. Precision is mandatory.

• Verdict: They would use CS (and probably lactate testing) to ensure morning sessions stay strictly at ~2.5 mmol/L, protecting their legs for the afternoon session.

The 40-Minute Runner (Competitive Amateur)

Pace: 4:00/km

• The Nuance: "Life Stress" is the biggest variable. A Z5 "soul-crusher" can spike cortisol levels in a way that derails an entire week.

• Verdict: Shifting to CS-based intervals (96-98% CS / ~3.0 mmol/L) allows them to stack "quality minutes" without the cortisol spikes of traditional VO2 max repeats.

The 50-Minute Runner (Recreational / Club)

Pace: 5:00/km

• The Nuance: Simplicity is enough for the heart, but precision may be needed for safe peripheral adaptations (tendons, connective tissue).

• Verdict: Using CS ensures they don't accidentally "race" their workouts. Training near CS (~3.0-3.5 mmol/L) is mechanically safer and builds the structural foundation needed to reach the 40-minute mark.

5. Understanding the "6-Minute Max" (The Gordo Byrn Approach)

Coaches like Gordo Byrn prescribe intervals at "the maximum pace you can sustain for 6 minutes." In the CS model, this is a point on the curve above your Critical Speed. We use this strategically for:

1. Maximum Stimulus: The strongest signal for heart stroke volume.

2. Mental Callusing: Teaching the brain to handle the chaos above the CS boundary.

3. The Efficiency Wedge: If your 6-minute max pace is 3:30/km, then your 10km race pace (near CS) of 4:00/km feels mechanically effortless.

In other words, the 6-minute max becomes a spice; not the base of the meal.

Summary: The New Training Hierarchy

Final Words

Since you’re a regular reader of this newsletter, I know you’re fascinated by the nuances of training physiology, and rightly so! But it’s important not to let that complexity cloud your actual approach. As Steve Magness puts it with almost haiku-like simplicity: 'Mostly easy, occasionally hard, vary it up, and very seldom, go see God.' Let that be your north star next time you lace up.

We aren't asking you to work less hard; we are asking you to be more intentional. Critical Speed gives us the line in the sand, while Lactate explains why that line matters. Stay just below it to build the engine; step above it to sharpen the sword. Stop chasing exhaustion; start chasing repeatability.

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For decades, world‑class distance running looked like a blend of feel and grit. Training diaries were personal, hard to compare, and even harder to copy. What has changed is not the athlete; but our ability to dose training stress precisely. We can now apply enough physiological signal to drive adaptation without crossing the line where fatigue erodes consistency.

One of the clearest expressions of this shift is the approach associated with Norwegian distance running and popularized by athletes like Jakob Ingebrigtsen: Lactate‑Guided Threshold Interval Training (LGTIT). What appears new is largely a refinement of long-standing endurance principles, made visible through better measurement and tighter control. It is a method that uses internal load to keep “hard days” hard enough to matter, but controlled enough to repeat.

This article draws on the 2023 review by Casado, Foster, Bakken, and Tjelta on LGTIT and cross‑references it with broader endurance science and coaching practice to explain the logic behind high‑performance training design.

Part 1 — What the Science Says: Internal vs. External Load

Most runners manage training by external load (pace, watts, distance). That’s useful, but incomplete. The modern evolution is to prioritize internal load: how the body is responding right now; metabolically, ventilatorily, and mechanically.

Two athletes can run the same pace on the same day and accumulate very different physiological stress depending on sleep, life stress, heat, terrain, fueling, or training background.

The Two Big Cellular Signals

The review highlights the logic behind combining high-volume, low-intensity work with precisely controlled work near the second threshold. At a cellular level, this approach leverages two primary pathways:

1. Calcium‑Related Signaling (The Aerobic Builder): Long, easy running creates sustained muscle contractions with relatively low metabolic disturbance. This supports increased mitochondrial function, capillarization, and improved fat oxidation.

2. AMPK / Energy-Stress Signaling (The Efficiency Optimizer): Work near the boundary of heavy exercise; often near LT2/Critical Speed—creates a stronger energy‑stress signal. This improves carbohydrate metabolism and the "Lactate Shuttle"; your body's ability to use lactate as a fuel source.

Coach Translation: In practice, this means easy volume builds the machinery, while controlled threshold work teaches that machinery to run efficiently under load.

The Key Target - Stability: The goal is not suffering; it's a steady state where production and clearance remain in balance. This allows you to spend more "quality" minutes in a productive zone without turning the session into a recovery‑destroying race.

Part 2 — What Great Coaches Do: Controlled Intensity Beats Maximal Effort

The best training is the training you can repeat. One of the counter‑intuitive lessons in the Norwegian approach is that the best runners often "hold back" on their hard days to protect the repeatability of the training week.

Why “Volume” Really Means Repeatable Work

Recreational athletes often ask: “If I only have 5–8 hours a week, shouldn't I make every minute hard?” The answer is typically no. Volume is about repeatability, not just mileage.

• Consistency over Intensity: For non-elites, "volume" means stacking months of training without injury or burnout. Hammering workouts feels productive but often leads to the pattern of big days followed by missed days.

• More Truly High‑Quality Minutes: A single 20‑minute maximal tempo is brutally expensive. But breaking that into controlled intervals (e.g., 5×6 min) allows you to accumulate 30–50 minutes near the target intensity with less total stress.

• Life‑Stress Management: For athletes with jobs and families, maximal efforts amplify stress hormones. Controlled intensity gives you a way to gain fitness while protecting sleep, mood, and motivation; the key determinants of long‑term progress. This isn’t “soft.” It’s strategic.

Part 3 — Bridging the Lab to Your Plan (The Proxy Guide)

Since most of us aren't taking blood samples mid‑run, we use surrogates that track the same underlying idea: staying in the right internal‑load domain.

1. Breathing and Speech: This is your real-time guardrail. If you can only get out clipped words and breathing feels chaotic, you’ve drifted too high. If breathing is rhythmic and you can speak short phrases, you are in the "steady hard" zone.

2. Critical Speed (CS) as a Proxy: CS represents the highest sustainable steady‑state intensity before fatigue accelerates non‑linearly (roughly a 30–40 minute maximal effort running). Training just below CS overlaps strongly with the intended LGTIT domain: high aerobic stress and manageable recovery.

3. The Treadmill as a Standardization Tool: As emphasized by Dr. Marius Bakken, the treadmill reduces "noise" (wind, terrain, surface). It allows for precise pacing and reduces impact stress, making it an ideal tool for hitting exact internal-load targets.

4. Rest Ratios that Prevent Drift: We use short rests (e.g., 4:1 work-to-rest) to prevent "upward drift." The aim is not to recover fully, but to ensure each rep remains in the intended metabolic domain.

5. RPE as the Meta-Proxy: All of these proxies ultimately converge on perceived exertion; when they disagree, RPE is often the tie-breaker. This reinforces athlete autonomy over blind metric dependence.

Part 4 — Polarized vs. Pyramidal: A False Dichotomy

Much confusion comes from treating Polarized (80/20) and Pyramidal systems as competing ideologies. They are actually built on the same physiological constraints. The real distinction is not distribution models, but how well intensity is controlled relative to recovery capacity.

Lactate-guided work fits both. The shared success factor is simple: Easy days are truly easy. Hard days are purposeful. And nothing is allowed to quietly become unsustainably hard.

The Synthesis: From Theory to the Training Week

How do we take these high-level scientific models—polarized, pyramidal, and lactate-guided—and distill them into a schedule you can follow?

Whether you are self-coached, working with me, or another coach, the common thread is Intensity Discipline. It doesn’t matter which "distribution model" you choose if you cannot control the physiological effort on any given day. By shifting the focus from the pace on the watch to the stability of the internal system, any runner can design a week that targets every cellular pathway without overwhelming their ability to recover.

When I design a plan for my athletes, I use this synthesis to create a "training bridge." This bridge uses high-volume principles to build your "floor" and precise threshold principles to optimize your "engine," all while protecting you from the "grey zone" of uncontrolled fatigue. On top of this I add very short neuromuscular stimuli. This approach ensures that every kilometer has a purpose, whether you're chasing an Olympic standard or a personal best.

The Anatomy of a Performance Plan

A well‑structured training plan applies one core principle: Maximize signal, minimize unnecessary stress.

• Z1/Z2 Easy Days: Build the aerobic foundation and the weekly durability that allows you to handle quality work.

• Threshold Intervals: Designed to drive high aerobic adaptation and efficiency while staying controlled enough to repeat.

• High‑Output Strides: Short bursts that preserve neuromuscular coordination and "top-end" economy without stealing recovery from the engine.

The Goal: We aren't training you to tolerate suffering. We are teaching your physiology to solve the problem of speed more elegantly. By respecting the ceiling and building durability through volume, we raise your floor, expand your sweet spot, and turn the ceiling from a limit into a variable.

FWDMOTIONSTHLM – A page for all things swimrun, training & more.

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The Big Idea

• The Problem: Most training is viewed as a purely physical tax.

• The Science: Swimming induces a unique "Goldilocks zone" of cerebral blood flow and neuroplasticity.

• The Result: A smarter, more resilient brain that can handle higher training loads and cognitive stress.

Ever notice how problems feel smaller after a swim?

Why your thoughts feel quieter but clearer?

Why you leave calm—yet alert—not flattened?

That isn’t just mood. It’s neurobiology.

Why Swimming Feels Different

Swimming produces a unique state that many athletes struggle to describe but instantly recognize. Unlike a hard run or bike session, swimming rarely leaves you wired. Unlike passive rest, it doesn’t dull you either.

It occupies a "Goldilocks zone" between recovery and high-performance training: physically worked, yet mentally reset.

That combination matters more than we usually acknowledge—especially in high-load training weeks, high-stress lifestyles, or as we get older.

What’s Actually Happening in the Brain

Regular aerobic exercise increases levels of BDNF—Brain-Derived Neurotrophic Factor.

BDNF is often described as "fertilizer" for the brain. It:

• Supports the survival of existing neurons.

• Promotes the growth of new ones (neurogenesis).

• Strengthens learning, memory, and long-term brain health.

Swimming does this in a particularly efficient way. Because you are submerged, hydrostatic pressure naturally pushes blood from your extremities toward your heart and brain.

Research shows that chest-deep water immersion can measurably increase cerebral blood flow—meaning more oxygen and nutrients delivered to the brain.

Rhythm, Breath, and Cognitive Load

Swimming is one of the few activities that demands rhythmic, bilateral movement while simultaneously restricting oxygen intake in a controlled way.

That matters.

Coordinating stroke, timing, and breathing forces a level of presence that “zone-out” cardio simply can’t match. You can’t scroll. You can’t multitask. You have to be here.

In simple terms: Swimming trains attention without overwhelming the nervous system.

Stress, Cortisol, and the "Internal Brake"

The moment your face hits the water, your heart rate slows and your nervous system begins to recalibrate—an evolutionary shortcut to calm known as the mammalian dive reflex.

While a hard run triggers a "fight or flight" response, the dive reflex acts as a parasympathetic brake.

Swimming allows you to perform high-intensity work while maintaining a baseline of physiological calm.

Add to that:

• Water immersion (weightlessness)

• Steady, repetitive movement

• Controlled breathing

• Reduced impact and threat

This is why swimming often feels grounding rather than draining. An athlete who can down-regulate recovers faster and adapts better. Not because they train less—but because their system is better regulated.

The Quiet You Can’t Replicate Elsewhere

One reason swimming feels so mentally restorative is what isn’t there. No gravity pounding joints. No traffic noise. No screens. Sound is muffled. Sensory input is reduced.

In a world of constant stimulation, swimming provides what psychologists call "Attention Restoration." By stripping training down to movement, breath, and rhythm, you allow the brain’s directed-attention filters to rest.

That reduction in sensory noise is a feature, not a bug. It’s why swimming doesn’t just tire you out—it resets you.

Brain Resilience and Training Longevity

After 50, maybe the most important adaptation from training isn’t VO₂max. It’s brain resilience.

Aging is associated with gradual brain volume loss and declining cognitive flexibility. Aerobic exercise slows this process. Regular movement preserves brain tissue, protects memory centers, and maintains mental sharpness.

The goal isn’t just to stay physically fit—it’s to stay mentally sharp for the long haul.

Swimming stands out because it is low impact, highly repeatable, and sustainable across decades. It’s one of the few modalities you can use hard when you’re young, gently when you’re injured, and still benefit from when you’re 70 and beyond.

What This Means for Your Training

A few coaching takeaways:

• Swimming isn’t “just training” — it is an active stimulus for brain health.

• Easy, rhythmic swims still stimulate blood flow and BDNF production.

• Clear the decks: By inducing a parasympathetic state, swimming may also support the brain’s glymphatic system—the network responsible for clearing metabolic waste.

• High cognitive-stress days often benefit more from swimming than high-intensity land work.

Sometimes the most productive session isn’t the one that hurts. It’s the one that resets you.

Coach’s Note

If you’re struggling with consistency, motivation, or mental fatigue—don’t automatically add more work. Add more rhythm.

Good training doesn’t just make you fitter. It makes you more capable—physically, mentally, and emotionally.

FWDMOTIONSTHLM – A page for all things swimrun, training & more.

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Stroke Timing and Propulsive Force

This kind of graph plots propulsive force over time for each arm during freestyle, showing not where the arms are in space, but when each hand is actually producing forward drive. In this figure, the original author uses the terms “catch-up” and “opposition” in a force-based, not stylistic, sense, so it’s worth being precise. By catch-up, the author means a timing pattern where one arm completes its propulsive phase before the other arm begins to generate meaningful force, producing a clear gap or “dead spot” in propulsion. By opposition, the author does not mean strict 180-degree arm opposition — true opposition would also create a dead spot. Instead, the solid curves represent a front-quadrant overlap, where the recovering hand has entered and begun setting the catch before the opposite arm has fully finished its push. This overlap prevents propulsive force from dropping to zero, creating a continuous pressure wave that maintains momentum and body support. The key distinction the author highlights is therefore not stroke length or patience at the front, but whether propulsion is overlapping or interrupted.

Before I get into my own reflections, I want to start by pointing you to a blog post that’s genuinely worth your time.

Paul Newsome from Swim Smooth recently published an article called “The Hardest Swim Type to Correct and Why.” If stroke timing has ever felt hard to see, hard to feel, or hard to explain to athletes, this is one of the clearest frameworks I’ve come across.

Why this matters: Stroke timing is often the invisible wall that stops fitness from turning into speed. Swimmers can get stronger, fitter, and more committed—yet still feel stuck—because momentum leaks away at the front of the stroke.

Paul introduces a simple timing spectrum based on his Swim Types system that places swimmers not by talent or fitness, but by when propulsion happens at the front of the stroke:

• Bambinos and Arnies: Sit on the early / unstable timing side, often dropping the lead arm too soon.

• Kicktastics, Swingers, and Smooths: Generally show good timing (front quadrant)—but they arrive there and maintain it through very different mechanisms.

• Over-gliders: Sit on the late-timing, paused side.

If you coach or train swimmers regularly, I’d strongly recommend reading Paul’s article first. Everything below builds on his model, exploring how these types react when we add variables like cadence and gear.

The Big Idea: Timing Is Directional, Not “Good vs Bad”

What I really like about Paul’s spectrum is that it removes judgment. Swimmers don’t suddenly become “bad.” They drift. Often, a real problem is fixed—just taken a step too far.

The Fix-to-Fault Pipeline

The Flaw: Dropping the lead arm too early -> Instability at the breath.

The Fix: Holding the lead arm longer ->  Improved support and confidence.

The Drift: The hold becomes a pause -> Momentum stalls and over-gliding appears.

Nothing broke. A sensible fix just overshot the middle of the spectrum.

The "Implicit" Timing of Swingers and Kicktastics

In Paul’s model, Swingers and Kicktastics are not timing-fault swimmers. They have rhythm and continuity. However, there is a key difference in how they sustain that timing:

• Swingers: Maintain timing through rotation and a natural, higher cadence.

• Kicktastics: Maintain timing through a high-energy kick. That kick creates a "propulsive bridge" that connects one arm stroke to the next.

For both types, good timing is often implicit—it happens as a byproduct of their rhythm rather than through conscious control of the lead arm. This distinction is vital for Swimrun.

Why Stroke Timing Is Often Under-Coached

In my own coaching, I've observed that stroke timing is often under-emphasized, especially by experienced swimmers and coaches. Why? Because good swimmers tend to self-solve timing with stroke rate.

When cadence is higher:

• Time at the front compresses.

• Pauses are harder to sustain.

• The hands tend to pass naturally.

In simple terms: Higher stroke rates hide timing problems.

At higher cadence, propulsion overlaps more smoothly from one arm to the other. This creates a near-continuous pressure wave through the stroke, masking the brief loss of lift that would otherwise be obvious during a pause.

Learner Swimmers Live in “Stretched Time”

With adult learners and developing swimmers, I regularly see stroke rates in the low-to-mid 50s. At those rates:

• Small pauses become full stops.

• Delayed catches kill momentum.

• Timing faults become the main limiter.

Paul’s spectrum explains what the swimmer is doing wrong. Stroke rate explains why it feels so hard.

Why This Explains Paddle Performance in Swimrun

This framework explains something many swimrun coaches notice intuitively: two swimmers can look identical in no-gear swimming—then become worlds apart once paddles and pull buoys are added.

The "Timing-Fragility" of the Kicktastic and Swinger

In Swimrun, the Kicktastic and the Swinger are uniquely vulnerable to a timing collapse. Why? Because the gear systematically removes their primary timing mechanism.

• For the Kicktastic: Their "propulsive bridge" is the legs. When that kick is neutralized by a pull buoy or restricted by a wetsuit and shoes, the bridge vanishes.

• For the Swinger: Their "timing mask" is high cadence. When large paddles artificially reduce their stroke rate and lengthen their time at the front, their natural rhythm is disrupted.

In no-gear swimming, both types look great. But under the constraint of gear, if they haven't learned to consciously maintain that front-quadrant connection using their arms alone, they drift instantly rightward on the spectrum. They become accidental over-gliders because the mechanisms they usually rely on (kick and cadence) have been taken away.

Paddles Change the Timing Game

Especially with the current trend toward larger paddles:

• Stroke rate drops.

• Time at the front increases.

• Any timing error is magnified.

Without realizing it, swimmers are pushed rightward along the timing spectrum.

What Paddles Really Reveal

When stroke rate slows, over-gliders lose momentum and delayed catches become obvious because the legs can’t "rescue" the stroke. Meanwhile, swimmers with solid timing maintain continuity and stay fast even at low cadence.

Paddles don’t create the difference. They expose it.

There is also a double whammy here. When an over‑glider uses large paddles, they’re not just losing momentum — they’re placing significant torque on the shoulder as they try to accelerate the paddle from a dead stop.

But it often doesn’t stop there. Because the swimmer is eager to restart momentum, the pull frequently begins too early — before the recovering hand has passed the head and before the natural weight shift has occurred.

That means the catch is no longer set up by the body moving past an anchored hand. Instead, the arm tries to do the work in isolation. Elbow position drops, the shoulder takes the load, and what should have been a high‑elbow, forward‑set catch becomes a forced pull against the water.

So paddles amplify two timing problems at once: restarting from zero and pulling before the body is in position to support the catch. Over time, that combination isn’t just inefficient — it’s a clear durability risk.

The Swimrunner’s Trap: Why No-Gear Swimming is Your Timing Lab

Many swimrunners fall into the trap of training exclusively with pull buoys and paddles. While the sport is gear-intensive, skipping no-gear training is a mistake for one primary reason: Gear is a crutch that masks dead spots.

The False Buoyancy of the Pull Buoy

A pull buoy artificially raises the hips, making it "safe" to pause at the front because the back end isn't sinking. Without gear, that same pause causes the legs to drop immediately. No-gear swimming provides the instant feedback you need to realize that your timing is stalling.

The Artificial Momentum of Paddles

Large paddles create a massive burst of propulsion that can "carry" a swimmer through a dead spot in their timing. This creates a "pulse-and-coast" rhythm that is ineffective over long distances. In no-gear swimming, that momentum evaporates the second you pause.

Owning the Flow

If you can’t maintain a continuous, fluid rhythm without gear, you don't actually "own" your stroke timing—you are simply renting it from your equipment. To achieve optimal timing with gear on, you must first master the ability to remove dead spots when you have nothing but your own rhythm to keep you moving.

Coaching Takeaways

• Stroke timing deserves to be a primary coaching focus.

• Low stroke rates are a stress test for timing.

• No-gear swimming is the diagnostic lab; paddles are the final exam.

• Kicktastics and Swingers are "Timing-Fragile"—they must learn to maintain flow when gear removes their natural rhythm.

• Bigger paddles magnify timing issues if continuity isn't solid.

If you can’t maintain flow when time stretches, you don’t fully own your stroke timing yet.

Final Thought

Paul’s article explains how swimmers drift into timing problems. Stroke rate and equipment explain when those problems become obvious. Together, they offer a practical, non-judgmental way to understand one of the most misunderstood parts of freestyle.

If stroke timing has ever felt slippery—either to feel or to coach—start with Paul’s piece. Everything else builds from there.

FWDMOTIONSTHLM – A page for all things swimrun, training & more.

coach_t@outlook.com

fwdmotionsthlm.blog

We often assume that better decisions come from better logic:

• More data.

• Better plans.

• Smarter tools.

And yet, in endurance sports today, something strange is happening. Athletes have unprecedented access to “best practice.” Training theory, physiology, session design, and recovery protocols are instantly available through AI tools and large language models.

And still, many athletes:

• Push when they should hold back

• Add volume when they need patience

• Turn “optimal” plans into chronic fatigue

• Make the wrong call at the exact moment it matters most

The question isn’t why athletes lack information. The question is why athletes still make bad decisions when the logic is clear.

Game Theory: The Missing Lens

Game theory studies decision-making when outcomes depend on interaction, not just individual effort. Its most uncomfortable insight is this: Rational individuals, acting alone, often create irrational outcomes.

In endurance training, this shows up as a quiet race to the bottom. The classic Prisoner’s Dilemma illustrates why:

• Cooperation (following the plan) produces the best long-term outcome.

• Uncertainty and fear push individuals toward short-term, self-defeating choices.

Each training session becomes a decision made under uncertainty, where the fear of falling behind outweighs the logic of restraint.

Training as a Repeated Game

Training is a repeated game played between:

• Today vs. Tomorrow

• Ambition vs. Restraint

• Ego vs. Patience

Each decision subtly reshapes the environment in which the next one is made. The “correct” answer is rarely a mystery. What’s unclear is whether you can trust that answer when you are under pressure. Without an external anchor, the “safe” bet feels like doing more — even when that bet leads to physical bankruptcy.

Why Perfect Information Leads to Bad Decisions

AI is extremely good at logical optimization. It can explain zones, structure blocks, and translate science into sessions with flawless precision. But training decisions are not made in a vacuum. They are made:

• When you are exhausted

• When you are emotionally invested

• When your identity is tied to the result

From a psychological perspective, this is predictable. Under fatigue and stress, humans rely more heavily on System 1 thinking — fast, emotional, heuristic-driven decision-making — rather than slow, analytical reasoning. Even when we know the correct choice, our nervous system biases us toward actions that reduce immediate discomfort or uncertainty.

In game-theory terms, athletes don’t default to the best move. They default to the move that alleviates their current anxiety. This aligns with research on loss aversion and temporal discounting: the pain of potentially losing fitness now outweighs the abstract benefit of protecting performance later. As a result, we choose the virtuous exhaustion of a hard workout over the quiet discipline of a rest day — even when the data screams for restraint.

The Biological Layer: Co-Regulation

This is where insights from physiology, neuroscience, and developmental psychology converge. Coaching is not just cognitive. It is biological.

Human coaches don’t simply provide instructions; they facilitate co-regulation — the physiological process by which one person’s stable nervous system helps regulate another’s.

From a nervous-system perspective, performance decisions are filtered through threat detection. When an athlete is stressed, under-recovered, or identity-threatened, sympathetic arousal increases and perceptual bandwidth narrows. Effort feels harder. Risk feels larger. Urgency rises.

Two nervous systems interacting can:

• Lower threat responses

• Stabilize arousal

• Change how perceived effort feels

Presence, tone, timing, and shared history all alter how an athlete processes stress. This is why a calm, confident coach can materially change how a session feels, even when the external workload is unchanged.

AI can simulate empathy, but it cannot embody it. It has no nervous system to offer. It cannot slow its breathing with you, soften its tone, or transmit safety through shared history. It cannot “hold the space” when you are vibrating with the stress of a taper or a performance slump.

Coaching Isn’t Better Answers — It’s a Better System

Another useful lens here comes from systems theory: complex adaptive systems cannot be optimized through linear control.

The human body is not a machine that responds proportionally to inputs. It adapts non-linearly, with delays, thresholds, and emergent behavior. Small changes in stress, sleep, or emotion can produce disproportionate changes in performance. This is why rigid optimization often fails in endurance sport — and why coaching is fundamentally about steering, not controlling.

The future of coaching is not a binary choice between human or machine. It is a hierarchy of intelligence.

• AI provides Computational Intelligence: High-volume data analysis, general theory, and what works for most athletes, most of the time.

• Coaches provide Contextual Intelligence: Clinical intuition, pattern recognition across non-linear progress, and insight into the data that never fits neatly into a spreadsheet.

The coach doesn’t just provide information. They curate infinite noise into a singular, actionable truth. LLMs can design excellent plans, but they cannot:

1. Synthesize soft data — when life stress is quietly eroding capacity.

2. Filter the noise — when the “optimal” session is wrong today.

3. Embody strategy — using presence itself to steady an athlete who is spiraling.

A Note on Using AI Well

A quiet tension sits underneath all of this. Some view AI as “cheating.” Others assume it flattens expertise. In practice, the opposite is true.

AI does not replace coaching judgment — it amplifies it.

The quality of output depends entirely on the quality of the questions being asked and the discernment applied to the answers. An experienced coach can use AI to stress-test ideas, refine principles, and pressure-check decisions in ways that are simply unavailable to less experienced users.

The tool is the same. The lens is not. This mirrors every advance in sport science. Data never made better coaches by itself. It rewarded those who already understood what mattered.

The Real Advantage

Across psychology, neuroscience, and performance science, the same conclusion appears again and again: the quality of decisions under stress matters more than the quality of plans made at rest.

The athletes who thrive in the AI era won’t be the ones with the most data. They’ll be the ones who can:

• Make good decisions when tired

• Stay patient when progress is slow

• Choose restraint when effort feels virtuous

AI knows what works for most people, most of the time. You, through cooperation with a coach, know what works for you, right now.

That isn’t a knowledge problem. It’s an interaction problem. Which is why, even in an age of perfect answers, human coaching remains not just relevant — but biologically, psychologically, and strategically essential.

Images created with Nano Banana Pro

FWDMOTIONSTHLM – A Page for all things SwimRun, Training & more.

coach_t@outlook.com

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