UTMB Workshop: Taking Ventilatory Measurement Out of the Lab and Into Training
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A year ago, breathing was still a fringe idea in endurance training. It showed up around Team Visma | Lease a Bike, a UCI debate, and then the Tour de France. Most athletes had never seen their own ventilation outside a lab.
That has changed. Tymewear has now delivered more than 9,000 threshold tests and hundreds of thousands of workouts with breathing data. The people in that set are not only elites. Their average VO₂max is 52, and the range runs from the low 30s to the low 90s.
Arnar Larusson, Tymewear's co-founder, walked through what that data and those athletes are showing, in a talk you can watch above.
Three patterns keep coming back.
Individual zones start the progress again
The first is what happens when zones stop being a formula.
Again and again, athletes who had been flat for months or years do a threshold test and find that VT1 or VT2 was higher or lower than a percentage of max heart rate, or a time-trial estimate, had suggested. They move the training to the threshold they actually have. The test numbers move. Then the racing does, including how well the effort holds up late.
One rider described the change in a single comparison. Once he knew where VT1 actually was, he was riding those sessions around 180 to 190 watts, with a heart rate more than 20 beats per minute lower than before. Another watched VT1 climb 40 watts, a shift a generic ramp estimate would have missed, because the whole block of endurance work under VT1 had been aimed at the wrong place.
The mechanism is not mysterious. A prescription based on a percentage of max heart rate, VO₂max, or FTP misses a large share of people. In threshold studies, that miss shows up as a non-responder rate of roughly 40 to 60 percent, even in untrained groups you would expect to improve from twelve weeks of almost anything. When the same program is anchored to each person's ventilatory or lactate thresholds, the non-responders disappear and the gains are larger. The work is finally landing where that body responds.
Pace the cost, not only the output
The second pattern is pacing.
Heart rate drifts with heat, dehydration, fueling, fatigue, and elevation. Power and pace record what you did. They are a weaker record of what that work did to you.
Ventilation is closer to the cost.
A group at Auckland University of Technology looked at this directly. Fourteen trained cyclists and triathletes rode for two hours at 90 percent of the power at VT1, then repeated the threshold assessment. Heart rate at VT1 rose by 9 beats per minute on average, from 142 to 151. Power at VT1 fell by 21 watts, from 217 to 196. Inside the group that power drop was individual: some athletes lost none, others lost about 40. Minute ventilation at the same threshold held, about 72 liters per minute before and 69 after. What shifted underneath it was the pattern of the breath: breathing rate rose about 16 percent and tidal volume fell about 16 percent. The air moved per minute stayed put. Heart rate and power did not.
That is the decision on a long ride or run. Heart rate is up. Do you slow down, or is the drift just heat and fluid? Power is down. Are you undercooking the session, or has the power you can hold at the same internal cost fallen? If ventilation is still sitting on the target, you have an answer that heart rate and power cannot give you by themselves. Get it wrong and you either stack fatigue you did not mean to, or you leave the adaptation on the table.
The extreme version is an ultra. Arnar showed lap-by-lap data from a backyard ultra run by one of Stephen Seiler's PhD students. Pace fell. Heart rate fell with it. Read on those two alone, he was easing off. Breathing rate did the opposite: it climbed, which matches what the effort felt like from the first lap to the last. Minute ventilation showed he had gone out too hard, then settled into a steady internal workload for the rest of the event. Tidal volume dropped so breathing rate could rise while the air moved per minute stayed about the same. The pace drop, against a stable internal cost, is one way to see durability: how much external output you lose while the physiological work stays constant. That drop is trainable, and it is also a race-execution problem. Going out too hard makes it worse.
Trail running and races like UTMB push the same point further. Elevation, temperature, sleep, dehydration, and uneven fueling all move pace and heart rate for reasons that are not "you are working harder." Ventilation is the line that stays attached to the work.
VT1 is the foundation almost nobody has measured
The third pattern is VT1 itself.
Arnar's estimate is that almost everyone either does not know VT1 or has never had it tested. The result is a foundation that is either undertrained or overtrained. Once the marker is visible, the easy work has a ceiling that belongs to that athlete. Raise it, and the rest of the profile has more room: the top end can come up, and late-race durability improves, because the early hours were not spent above the point where carbohydrate use accelerates.
Knowing VT1 and VT2 as a percentage of VO₂max also tells you where the next training block should go. A low VT1 relative to VO₂max is a base problem. A profile that is already strong underneath and thin on top is an interval problem. Plenty of athletes have repeated the same week for years because nothing in heart rate, pace, or power exposed the neglected piece. The thresholds do. Shift the stimulus and progress starts again.
Why breathing shows the threshold
Breathing is a window into the working muscle. Its job in exercise is to bring oxygen in and clear the carbon dioxide the muscle produces.
During hard work, CO₂ is the main driver, not oxygen. Carbohydrate breakdown produces CO₂. The body is highly sensitive to the pH change that follows, and it raises ventilation to clear it. As the muscle shifts from mostly fat toward more carbohydrate, CO₂ production rises and breathing has to rise with it. Those shifts are the ventilatory thresholds: breakpoints in how steeply ventilation climbs. Below the first one, the rise is relatively stable. Above it, ventilation has to work harder to keep up with the CO₂.
Tymewear is a chest strap that measures that ventilation along with heart rate. A threshold test estimates VO₂max and locates VT1 and VT2. Those two points are the definition of the training zones, and they also show where improvement is available. From there, daily workout recommendations and training plans keep the next session tied to the current thresholds, and the same signals can run live on most bike computers and watches.
The same system, further down the spectrum
The athletes who can finish UTMB are one end of a fitness spectrum. The other end is low fitness, cardiovascular disease, and metabolic disease. It is the same system, measured the same way and improved the same way.
Existing zone methods often fail the people who need the improvement most. If a large share of exercisers are non-responders because the prescription missed their thresholds, then making those thresholds measurable outside a lab is not only a performance tool. It is a way to make endurance improvement more reliable for people who will never race in the mountains.
That is the larger point of the talk. The Tour, the elites, and the 9,000 tests are evidence that the signal works. The use of it is anyone whose training is still being guided by a formula.
See how a Tymewear threshold test works
References
Stevenson, J. D., Kilding, A. E., Plews, D. J., & Maunder, E. (2022). Prolonged cycling reduces power output at the moderate-to-heavy intensity transition. European Journal of Applied Physiology, 122, 2673-2682. https://doi.org/10.1007/s00421-022-05036-9
Stevenson, J. D., Kilding, A. E., Plews, D. J., & Maunder, E. (2023). Prolonged exercise shifts ventilatory parameters at the moderate-to-heavy intensity transition. European Journal of Applied Physiology. https://doi.org/10.1007/s00421-023-05285-2
Wolpern, A. E., Burgos, D. J., Janot, J. M., & Dalleck, L. C. (2015). Is a threshold-based model a superior method to the relative percent concept for establishing individual exercise intensity? A randomized controlled trial. BMC Sports Science, Medicine and Rehabilitation, 7, 16. https://doi.org/10.1186/s13102-015-0011-z