You head out on a Saturday morning. Two-by-twenty at threshold. Three-eighty watts. The legs feel honest. Perceived effort is a seven and a half. The interval is hard, but you finish it knowing exactly why it was hard and where the upper edge is.
Three days later you sit down for the same session. Same bike. Same numbers on the screen.
Four minutes in, the lights are out. Power sliding. Heart rate stuck up at a number that does not belong on a Tuesday. Perceived effort already at nine and a half. You stop.
Same wattage. Same intervals. Same engine. Two completely different days.
If you have ever lived inside that contradiction — and most of us have — you have already met the problem that Team Visma–Lease a Bike has spent the last twelve months trying to solve.
Listen to the full conversation on the Roadman Cycling Podcast →
What Visma Is Actually Doing
Visma's men's and women's World Tour teams are now riding with a wearable sensor strapped to the chest. It is not a heart rate monitor. It is not a chest-strap power tool. It does not measure lactate or core temperature.
It measures the rise and fall of your ribcage. Tens of thousands of times a ride.
The kit is from a company called Tymewear, and the founder, Arnar Larusson, came on the podcast to walk through what is going on. He has had the device on a number of teams now and has spent two embedded camps with Visma. The athletes wear it in training. The coaches read the data after.
Why does that matter? Because what the sensor measures is the one number every other cycling metric is secretly built on — and almost nobody is reading directly.
The Bit Nobody Tells You About Your Power Meter
Here is the line that should make every serious amateur sit up.
Heart rate is a proxy for oxygen. Power is a proxy for workload. Ventilation — the literal volume of air you push through your lungs — is the signal that both of those metrics are calibrated against in the lab.
Arnar said it plainly. In a physiology lab, when researchers want to define your zones, they do not start with watts. They start with breathing. They watch where your ventilation kicks up against your workload and they call those points your ventilatory thresholds. Then they hand you the heart rate and power numbers that match. Those numbers are the proxies. The breathing was the original.
Take that one step further. Every formula you have ever used for your zones — the seventy-five percent of FTP rule, the heart rate band based on age, the Karvonen method — is a population average sitting on top of someone else's lab assessment of someone else's ventilation. The error margins are wide. The fit to your body is approximate.
Ventilation is the underlying signal. Everything else is an educated guess about it.
Why The Saturday-Tuesday Problem Goes Away
Back to the four-minute blow-up.
There is a study Arnar referenced — Manders and Plews — where riders did a long endurance session at the top of zone two. The researchers checked their first ventilatory threshold before and after. The result is the bit you want to remember.
Ventilation stayed stable. Heart rate climbed ten to fifteen percent. Power dropped ten to fifteen percent.
The body had moved. The proxies recorded the shift. The underlying signal did not budge.
That is the whole problem with riding to a fixed wattage on a fatigued day. The number on the head unit is telling you about the workload you are producing. It is not telling you what that workload is doing to you. The same three-eighty watts on Tuesday after a brutal commute and a poor night's sleep is a different physiological taxation to the same number on a fresh Saturday morning. You already knew this in your legs. The lab now confirms it in writing.
If you train to ventilation, you stop chasing a wattage your body cannot afford to pay. You ride to the breathing. The power is allowed to drop. The heart rate is allowed to drift. The training stress lands where you actually wanted it to land — in zone two — instead of accidentally creeping into zone three because you were too proud to back off the watts.
The Pro Calibration Creep
Here is where it gets really interesting.
Arnar said the most surprising thing about working with Visma was not the physiology. The pros respond to training the same way you do, just at higher numbers. The surprise was that the World Tour riders also lose calibration.
"Easy" creeps. Eight-hour rides at what is meant to be endurance pace gradually nudge ten percent above where they should be. Across a season that adds up. The pros are riding harder than their plan because their internal sense of "easy" is slowly drifting up. The breathing sensor catches it before the season unravels.
Now translate that to your week. You are not riding eight hours. You are riding six or eight or ten total, with a job and a family and a winter that drags. The chance of your own "easy" creeping is higher, not lower. You have less margin. Fewer sessions to course-correct. The Saturday club spin that should be a recovery ride is actually a tempo effort because the group has slowly normalised faster. The Wednesday endurance hour has crept up because the legs felt good last week.
This is fixable. And it is fixable without a Tymewear sensor on your chest.
Stephen Seiler's Bow Tie
When I spoke to Professor Stephen Seiler about what he was excited about over the next twelve months of cycling research, he named two things. Continuous lactate monitors. And respiratory sensors. The Visma rollout is the second one already happening.
Seiler's framing for stress and adaptation is what he calls the bow tie. A whole spectrum of stressors — long easy rides, short hard sessions, life pressure, sleep, calories — feeds into the middle of the bow tie. Out the other side comes a smaller spectrum of adaptations. Fitness. Durability. Resilience.
The job is not to maximise any single input. The job is to manage what arrives at the middle of the bow tie so the body keeps adapting week after week, month after month. Burnout, injury and stalled progress all live in the version where the inputs are uncontrolled.
Ventilation is the cleanest measurement we have ever had of what is actually arriving in the middle.
Where TrainingPeaks Fits
A reasonable question at this point. If ventilation is the truer signal, do all the existing tools — TrainingPeaks, the performance management chart, training stress score — get thrown out?
Not at all. Arnar made the point on the podcast and it is worth holding on to.
TrainingPeaks gave the sport a shared language. Chronic training load. Acute training load. Training stress balance. The performance management chart. None of that disappears. It is the framework most coaches and serious amateurs already think inside, and it does the job of stopping you from accidentally ramping load by thirty percent week-on-week. It tells you what you did.
What ventilation adds is a measurement of what was done to you. The two are not in conflict. Ventilation tightens the input side. TrainingPeaks tracks the cumulative effect. A coach reading both gets a clearer picture than a coach reading either alone.
If you are already living inside TrainingPeaks, you do not need to rip it up. You need to layer a better intensity signal underneath it.
What You Can Actually Do This Week
You are not buying a chest sensor and a coach next to you on every ride. The good news is the principle here is portable.
Three things drop straight into your week without any new kit.
1. Recalibrate "easy." On your next zone two ride, do the conversation test. Can you speak in full, settled sentences without gasping at the punctuation? If not, you are not on a zone two ride. Drop the watts until you can. The wattage is the proxy. The breathing is the truth.
2. Stop chasing the number on a tired day. If your Tuesday session is supposed to hit threshold and you are blowing your lights inside four minutes, the session is over. Not because you are weak. Because the underlying signal has already told you the workload your body could afford today is somewhere lower. Ride home easy. Keep the next two days clean. The interval will still be there on Saturday.
3. Audit your easy days for creeping calibration. Pull the last four weeks of your endurance rides. Are the average heart rates trending up at the same wattage? That is the creep. Pull the watts back down. Let the heart rate fall back into where zone two actually lives for you right now, today, with the sleep and stress you actually have.
Each of these is the practical version of what Visma is doing with a sensor on the chest. You do not need the sensor to do the thinking.
The Bigger Pattern
The story behind this episode is not really about a wearable.
It is about the slow process of cycling waking up to the fact that the metrics most amateurs train to are simplifications. Power is not effort. Heart rate is not stress. Both are useful. Neither is the underlying truth. And the gap between the proxy and the truth is where most stalled training plans go to die.
Arnar's view on what happens next is the bit worth holding on to. He thinks we are looking at year one of breathing data the way the late nineties were year one of power meters. The framework around it has not been built yet. The norms, the analytics, the way of folding it into a season. That work is happening now, on World Tour teams, in real time.
By the time it filters down to the rest of us, the cyclists who are already paying attention to how they feel — and who are honest about it — will be ahead of the cyclists who only believe what the head unit tells them.
You are not done yet. The kit is catching up to what the best riders have always done by feel. The trick now is to stop arguing with your own body when it tells you the truth.
Listen To The Full Conversation
The full episode with Arnar Larusson is on the podcast. For more on why intensity discipline matters more than volume, see our 80/20 cycling reset and our zone 2 complete guide. The breathing technique side — diaphragmatic patterns, nasal versus mouth, inspiratory muscle training — is in our breathing techniques piece and the cycling breathing techniques guide.
If you want help building a year that compounds the way the pros' do, the Roadman coaching system is the place to start. If you want a fast answer to a specific question, ask the AI coach.
