The WattPlan Podcast · Episode 4 · 10 min
How quickly do you lose cycling fitness?
Read the transcript
James. This is the WattPlan Podcast, and I'm James. Somewhere between family, the day job and the occasional podium, I'm building WattPlan and reading sports science papers I really should have skipped. This one's close to home, because the season's ending and I fancy a fortnight off the bike. So how quickly do you actually lose cycling fitness, and is two weeks on the sofa a disaster? Lyra's with me, our AI research voice, and every study she mentions is linked in the show notes.
Lyra. Ha, the end of season question. Straight answer, a fortnight off costs you far less than you'd fear. In the best study on short breaks, trained men lost about six percent of their VO2max, the most oxygen your body can use, after two to four weeks off. And most of that loss was blood, not muscle. It's past about a month that the losses get properly bigger.
James. Six percent. Okay, that's less scary than I expected. But what do you mean, it's blood?
Lyra. Right, so here's the thing. The study is Coyle and colleagues, 1986, in the Journal of Applied Physiology. They took eight endurance trained men and stopped them training for two to four weeks. Blood volume fell nine percent, mostly plasma, the watery part of the blood, which fell twelve. With less blood filling the heart, each beat pushed out twelve percent less, VO2max dropped six percent, and heart rate at a steady, easier effort went up eleven percent. [3]
James. Hang on, hang on. So that's why my heart rate looks awful on the first ride back?
Lyra. That's a big part of it, yes. And here's the clever bit. When the researchers topped the men's blood volume back up with a dextran and saline infusion, their VO2max came back to within two to four percent of where it had been. So the early loss really is mostly plumbing. The muscle side changes more slowly. The capillaries around the fibres are slow to go, and the engine underneath hangs on for longer than the first numbers suggest.
James. Oh, that's brilliant. So what about longer breaks? Say a month, or one of those winters where life just gets in the way.
Lyra. That's where it changes. Zheng and colleagues published a meta-analysis in 2022 in BioMed Research International. It pooled 21 studies of trained people and compared short breaks with long ones. VO2max fell after both, but the effect after long breaks was much bigger. The odd bit is that past about a month it didn't keep getting worse. Thirty to ninety days off and more than ninety days off looked much the same. [1]
James. Really? So once you're a month off, you've basically taken the hit?
Lyra. In that pooled data, roughly, yes, though I wouldn't lean on it too hard, because the long break studies varied a lot. Two more details matter. The people with the highest VO2max to start with lost the most over long breaks. And people under twenty lost more than adults did. So the fitter you are, the further you've got to fall.
James. Okay, now the bit that really gets me. I take a week off and my Fitness line in the app falls off a cliff. Is it lying to me?
Lyra. Not lying, just measuring something different. Fitness in WattPlan is a 42 day weighted average of your daily Load. A day off adds a zero to that average and takes about 2.4 percent off whatever Fitness you had, and over a break that compounds. Take a made up rider at a Fitness of 60. After a week off the chart reads about 51. After two weeks, about 43. After four weeks, about 31, almost half. Over similar spans, the studies measured VO2max six to seven percent lower.
James. So the chart says I've lost more than a quarter after two weeks, and my body's lost maybe six percent.
Lyra. Exactly. The chart tracks how much training you've absorbed recently, and during a break that number really is falling. It just has no way of knowing that the first weeks cost you mostly blood volume while your muscle hangs on. Fatigue drains even faster than Fitness, so your Form swings into the Fresh band within a few days. That's the maths of a six week average, not a verdict on your legs.
James. Right. But surely the honest answer is just don't stop? Keep riding all winter and you never lose anything.
Lyra. You could, and plenty of riders do. But our view at WattPlan is that a week or two off at the end of a season is worth taking if you want it. The cost is small. And if the break runs longer than that, you need surprisingly little to hold on to most of it. This is the study I love. Hickson and colleagues, 1982, back in the Journal of Applied Physiology.
James. Go on then, I'm listening. What did Hickson actually do?
Lyra. Thirteen people trained by cycling and running, forty minutes a day, six days a week, for ten weeks. Then for fifteen more weeks they cut each session to either twenty six or thirteen minutes, at the same intensity and the same number of days a week. VO2max held in both groups. But endurance in a test lasting two hours or more only held in the twenty six minute group. The thirteen minute group lost ten percent, from 139 minutes down to 123. [5]
James. So the short sessions kept the top end but not the long ride legs.
Lyra. That's it. Keep the effort and you can cut the time a lot, but long rides need some long riding. The catch is who they were. These were people who'd trained for only ten weeks, not riders with years in their legs. The Zheng meta-analysis points the same way, though. Keeping some exercise going during a break reduced the drop in VO2max.
James. Okay, let's split it out by who's listening. If you're new to this, what should you take from all of it?
Lyra. If you're new to structured training, don't panic about a break. Take your week or two off without the guilt, and when you come back, start from where you are, not where you were. The first rides will probably feel harder than they should, and your heart rate may sit higher for the same effort. That's the blood volume story from the 1986 study, not lost talent.
James. And if you train with power or heart rate?
Lyra. If you train with power, the trick is the intensity, not the hours. If the break runs past two weeks, ride twice a week and make part of each ride as hard as your in season sessions. The sessions can get shorter, but the effort shouldn't drop. And if your next goal is a long sportive, keep one longer ride a week, because that's exactly what Hickson's thirteen minute group lost.
James. And if you race, or you're chasing a big target next season?
Lyra. If you race, you've probably got the most to lose, because the fittest people dropped furthest over long breaks. So keep the full stop short, a week or two, then move to reduced training rather than none. Two hard sessions a week through the off season, plus a longer ride, and you should start the winter block a lot closer to where you finished.
James. I've got to ask, though. Where does all this run out? Because some of these studies are from the eighties.
Lyra. Fair. Most of it is old and small. Eight men in one study, thirteen people in another. Hickson's group had only trained for ten weeks, so how well it carries over to riders with years of training is genuinely uncertain. In the meta-analysis the long break studies varied widely. And here's the big gap. None of these studies measured how quickly the fitness comes back once you start again. Nobody has tested that properly yet.
James. Which is the question everyone actually wants answered.
Lyra. It is, and it's why I'd be wary of anyone who gives you a neat number for it. What we can say is what the losses look like and how little it takes to slow them. The comeback curve is still guesswork, so it's worth watching your own numbers rather than trusting a rule of thumb.
James. Okay. So what's the homework?
Lyra. Three things. One, if your season's done, take one to two weeks fully off, and expect your Fitness line to fall far more than your legs do. Two, if the break runs longer, ride twice a week and keep part of each ride hard, plus one longer ride if a sportive is next. Three, start your next block from the Fitness you have now, not the Fitness you had. A new WattPlan plan starts from your current Fitness, and the plan wizard shows you that number before it builds anything.
James. Okay, in my words. Take the fortnight, ignore the scary chart, then two short hard rides a week and one long one. And start again from where I actually am, not where my ego says I am.
Lyra. That's exactly it. And if you only remember one line, the first weeks off mostly cost you blood, not engine. Keep the intensity, and you keep most of what you built.
Lyra. The full article and every study we mentioned are on the WattPlan blog, linked in the show notes.
James. And if you want a plan that's built around the time you've actually got, that's what WattPlan does. Thanks for listening.
Voices produced with ElevenLabs. James's voice is a clone of his own, Lyra is an AI voice, and James reviews every script before it is published.
Endurance-trained men lost 6% of their VO2max after two to four weeks without training, mostly because their blood volume fell, in a 1986 study by Coyle and colleagues. A 2022 meta-analysis of 21 studies found breaks longer than four weeks had more than double the effect of shorter ones, so a fortnight off costs far less than a month.
How much fitness do you lose in two weeks off?
None of the studies here tested a single week, so the closest evidence comes from breaks of two to four weeks. Coyle's group stopped seven endurance-trained people training and tested them 12, 21, 56 and 84 days later, and VO2max fell 7% over the first 21 days. In the 1986 study, eight trained men tested after two to four weeks of inactivity had lost 9% of their blood volume and 12% of their plasma volume, and their VO2max was down 6%.
Most of that early loss is blood. With less blood filling the heart, stroke volume fell 12%, and heart rate while cycling at 50 to 60% of VO2max rose 11%. When the researchers restored the detrained men's blood volume with a dextran and saline infusion, stroke volume and VO2max came back to within 2 to 4% of their trained values.
Muscle changes more slowly. In the 1984 study the muscles' aerobic enzymes lost half of their eventual drop in 12 days, then settled 50% above untrained levels, and the capillaries around the muscle fibres didn't decline at all over 84 days. After 84 days off, the group still had a higher VO2max than people who had never trained, 50.8 against 43.3 ml/kg/min.
The numbers from each study
| Time without training | Who was tested | What changed | Study |
|---|---|---|---|
| 2 to 4 weeks | 8 endurance-trained men | VO2max down 6%, blood volume down 9%, heart rate at a steady effort up 11% | Coyle and colleagues, 1986 |
| 21 days | 7 endurance-trained people | VO2max down 7% | Coyle and colleagues, 1984 |
| 5 weeks | 10 young top-level road cyclists | VO2max per kg down 10.8%, power at the second lactate threshold down 11.5%, peak power down 6.5% | Maldonado-Martín and colleagues, 2017 |
| 56 to 84 days | 7 endurance-trained people | VO2max down 16%, still above people who never trained | Coyle and colleagues, 1984 |
What happens after a month off?
The loss grows once a break passes four weeks. Zheng and colleagues pooled 21 studies of trained people in 2022 and split the breaks at four weeks. VO2max fell after both, with a moderate standardised effect after shorter breaks (-0.62, 95% CI -0.94 to -0.31) and a large one after longer breaks (-1.42, 95% CI -1.99 to -0.84). Breaks of 30 to 90 days and breaks longer than 90 days didn't differ, and the people with the highest VO2max to begin with lost the most over long breaks. The same paper summarises earlier reviews by Mujika and Padilla, which put the loss in highly trained people at 4 to 14% after a short break and 6 to 20% after a long one.
A cycling study fits that picture. Maldonado-Martín and colleagues tested 10 young top-level road cyclists, average age 20, before and after a five week off-season break taken with almost no exercise. Their body mass went up, VO2max fell 8.8% in litres per minute and 10.8% per kilo, and power at the first and second lactate thresholds fell 12.9% and 11.5%. Peak power fell less, 6.5%, and haemoglobin fell 5.4%. The authors suggest shorter stoppages for riders at that level, with reduced training in place of a full break.
Why does your Fitness chart drop faster than you do?
WattPlan's Fitness is a 42-day weighted average of your daily Load, and Fatigue is the same calculation over 7 days. A day off adds a zero to the average and takes about 2.4% off whatever Fitness you had, and over a break that compounds. Take a made-up rider at a Fitness of 60. After 7 days off the chart reads 50.7, which is 15.5% lower. After 14 days it reads 42.8, 28.6% lower, and after 28 days it reads 30.6, almost half. Over similar spans the studies above measured VO2max 6 to 7% lower.
Fatigue drains faster than Fitness, so Form moves into the Fresh band within a few days of stopping. The chart is doing its job, because it measures how much training you have absorbed recently, and during a break that number is falling. Load is its only input, so it has no way of showing that the first weeks cost you mostly blood volume while your muscle capillaries hold. Our guide to Fitness, Fatigue and Form covers how the three lines relate.
Our view at WattPlan is that a break of one to two weeks at the end of a season is worth taking when you want one, and the drop in the Fitness line during it reflects the maths of a six-week average more than what you lose on the bike.
How little training keeps your fitness?
In the trials, two sessions a week or much shorter sessions were enough to hold VO2max, as long as the intensity stayed the same. In Hickson's 1982 trial, 13 people trained by cycling and running 40 minutes a day, six days a week, for ten weeks, then carried on for 15 weeks with sessions cut to 26 or 13 minutes at the same intensity and frequency. VO2max held at its trained level in both groups, but long endurance, measured as how long they could keep going in a test lasting two hours or more, held only in the 26 minute group and fell 10% in the 13 minute group, from 139 to 123 minutes.
A 2021 review by Spiering, Mujika and colleagues reached the same conclusion across the research. Endurance held for up to 15 weeks on as few as two sessions a week, or with each session cut by a third to two thirds, as long as the intensity stayed the same. The review adds that there isn't enough data to give trained competitors specific numbers. The 2022 meta-analysis points the same way, finding that some exercise during a break reduced the drop in VO2max.
What to do with an end-of-season break
- Take one to two weeks fully off if your season is over and you want the rest. Expect the measured losses over that span to be smaller than the 6 to 7% seen at two to four weeks, while your Fitness line falls by between 15.5% and 28.6%.
- If the break runs past two weeks, ride twice a week and make part of each ride as hard as your in-season sessions. In the trials that held VO2max, the sessions got shorter but the effort didn't drop.
- If your next goal is a long sportive, keep at least one longer session each week. In Hickson's trial the 26 minute sessions held two hour endurance and the 13 minute ones didn't.
- If you can't ride for a while, other exercise still helps. The 2022 meta-analysis found that keeping some exercise going reduced the loss.
- Start the next block from the Fitness you have now, not the Fitness you had before the break. A new WattPlan plan starts from your current Fitness, which you confirm in the plan wizard, and sets its opening hours from it. Our winter training guide covers what to build once you're back.
What we don't know yet
Most of this evidence is old and small. The two Coyle studies tested seven and eight people, the cycling study ten young men, and Hickson's trial people who had trained for only ten weeks, so how far the results carry over to riders with years of training behind them is uncertain. In the 2022 meta-analysis the studies of long breaks varied widely, and its test for publication bias was significant for them. People under 20 lost more over long breaks than adults did in the pooled data, and the cycling data here come only from men. None of the studies above measured how quickly the losses come back once training restarts.
Sources
- Effects of Short- and Long-Term Detraining on Maximal Oxygen Uptake in Athletes: A Systematic Review and Meta-Analysis, BioMed Research International
- Time course of loss of adaptations after stopping prolonged intense endurance training, Journal of Applied Physiology
- Effects of detraining on cardiovascular responses to exercise: role of blood volume, Journal of Applied Physiology
- Effects of long-term training cessation in young top-level road cyclists, Journal of Sports Sciences
- Reduced training duration effects on aerobic power, endurance, and cardiac growth, Journal of Applied Physiology
- Maintaining Physical Performance: The Minimal Dose of Exercise Needed to Preserve Endurance and Strength Over Time, Journal of Strength and Conditioning Research