On Saturday 10 October the peloton leaves Bergamo for Il Lombardia, 239 kilometres to Como and the last of the season's five Monuments. Whoever wins, a quieter decision follows in the days afterwards, and it belongs to any endurance athlete whose season is winding down: how long to stop, and how much of the fitness built since winter to pay for the privilege. Coaching folklore answers with slogans, either "a week off does nothing" or "a month off ruins you". The laboratory literature is more specific than both, even though some of its best-known numbers come from studies of seven or eight men and are four decades old. Later reviews, Iñigo Mujika and Sabino Padilla's among them, have kept the broad picture intact, and you should know it before you plan your own break.
What the first fortnight takes
The early drop in VO2 max after stopping training is a plumbing problem before it is a muscle problem.
In a 1986 paper in the Journal of Applied Physiology, Edward Coyle and two colleagues, M. K. Hemmert and Andrew Coggan, tested eight endurance-trained men before and after two to four weeks of complete inactivity. Blood volume fell 9%, from 5,177 to 4,692 ml, and plasma volume fell 12%. Stroke volume, the amount of blood the heart pumps per beat, dropped 12% and VO2 max dropped 6%, while heart rate at a fixed submaximal workload climbed 11% as the heart beat faster to make up for pumping less each time. The most telling part came next: when the researchers expanded blood volume back to its trained level with an infusion of a dextran solution, stroke volume and VO2 max returned to within 2–4% of their trained values. That was a laboratory demonstration of where the loss sat, not a method anyone should copy, and the authors concluded that the decline after a few weeks of detraining was largely down to reduced blood volume. Mujika and Padilla's review of breaks shorter than four weeks describes the same pattern in highly trained athletes and adds a lower lactate threshold, a heavier reliance on carbohydrate during exercise and reduced oxidative enzyme activity in muscle. Strength, in the review's own words, shows only "limited" declines over that window.
Where the decline levels off
Stopping for two weeks and stopping for three months are different experiments, and Coyle's earlier study, published in 1984, ran the longer one. Seven endurance-trained subjects were retested 12, 21, 56 and 84 days after they stopped training, and VO2 max fell 7% in the first 21 days before settling, by day 56, at 16% below the trained value. Even at 84 days the group still out-measured eight sedentary controls, 50.8 against 43.3 ml per kilogram per minute. The authors tied the early fall to stroke volume and the later one to a narrower arteriovenous oxygen difference, which is the muscle's ability to pull oxygen out of the blood. Capillarisation in the muscle did not decline at all and stayed about 50% above the controls, while two oxidative enzymes, citrate synthase and succinate dehydrogenase, fell with a half-time of 12 days and then levelled off, again about 50% above sedentary levels.
The picture is not unanimous. Mujika and Padilla's second review, which covers breaks longer than four weeks, lists capillarisation among the things that decline in athletes and says recently acquired VO2 max gains are lost completely. Read together, the two sets of findings suggest that an athlete with years of base behind them will look more like Coyle's volunteers than someone who built their fitness this summer. And Coyle's volunteers did nothing at all, which very few athletes manage; the same review notes that cross-training in a mode similar to the main sport can help hold adaptations in trained athletes.
A rough clock for each quality
Vladimir Issurin's work on block periodisation puts numbers on how long different qualities persist once the specific training behind them stops. The version summarised by the reference site ExRx.net reads as follows.
| Quality | Residual effect (days) |
|---|---|
| Maximal speed | 5 ± 3 |
| Strength endurance | 15 ± 5 |
| Anaerobic glycolytic endurance | 18 ± 4 |
| Aerobic endurance | 30 ± 5 |
| Maximal strength | 30 ± 5 |
Treat these as planning numbers rather than constants, because the ranges are part of the message. The ordering is still useful: top-end speed fades within days, repeated-effort capacities within a few weeks, and the aerobic base and maximal strength hold for about a month. A two-week break therefore lands on or beyond the first three entries and well short of the last two, which is roughly the pattern the football data below shows.
Two weeks of nothing in a football squad
A 2018 study by Chang Hwa Joo in PLOS ONE is the cleanest recent test of that idea. It followed 20 male semi-professional players from South Korea's K3 League for five weeks starting immediately after the last match of the season. For the first two weeks, half of them did high-intensity aerobic work, three sets of 12 minutes at 80–90% of maximum heart rate, three times a week, while the other half abstained from exercise entirely. Both groups then trained at high intensity four times a week for three weeks. After the fortnight of rest, performance in the Yo-Yo Intermittent Recovery Level 2 test and in a repeated-sprint test was significantly lower; the group that had kept training held both. The Yo-Yo score was back at baseline after two weeks of retraining, while repeated-sprint performance took three weeks to recover. Isokinetic strength, 30-metre sprint times, agility and body composition showed no significant differences between the groups at any point.
Twenty players is a small sample, and the paper's own introduction notes that elite footballers normally stop or cut training for more than two weeks after a season, for physical and mental recovery. The trade is then easy to state: a fortnight of rest cost these players some repeated-sprint ability and about three weeks of rebuilding. On strength, a 2013 meta-analysis led by Laurent Bosquet, covering 103 studies, found that stopping resistance training lowered every measure of muscular performance, with the loss growing as the break lengthened, and that inactive people lost more maximal force and power than recreational athletes did.
What a pro-team coach prescribes
Nate Wilson, performance manager and coach at EF Pro Cycling, told the team's website last October that a proper break has two parts. "Ten to 14 days of physical rest is a must," he said, followed by "at least another two weeks of mental rest", which adds up to about a month away from the sport. His argument is a budget, not a mystique: "You don't want to go from eight rungs up the ladder down to two," he said, and the aim is to rest enough to drop from eight rungs to six while the body makes some positive adaptations along the way. That is a coach's judgement rather than trial evidence, but it fits the physiology above, where the early losses are mostly blood volume and enzyme activity and strength declines stay limited.
Wilson's warning is about what athletes do with the time. "Hyperactive cross training is the biggest pitfall that athletes fall into," he said, and his example is an athlete who has run once a week all year and jumps to 120 kilometres of running in seven days. The advice that follows from the evidence is plain enough.
- Take the first ten to fourteen days with no structured exercise at all, and walk if you want to.
- For the next fortnight, choose activities you enjoy and do not normally have time for, without a plan attached.
- Plan about three weeks to rebuild, as the footballers needed, and ease in the way they did, with a couple of moderate-intensity days before any hard sessions.
- Sleep and eat properly, because Wilson's example of a bad break is alcohol-impaired sleep six nights a week, and other habits of that kind.
Athletes who cannot stop completely, such as a footballer in the middle of a congested fixture list, are better served by the conclusion of Mujika and Padilla's second review: the negative effects of reduced training can be limited as long as intensity is kept and frequency is cut only moderately, while volume can fall sharply. Put the restart date in the diary before the break begins. Coyle's seven men were still 16% below their trained VO2 max after 56 days, and the longer a break runs past four weeks, the closer it gets to that number.