How little training keeps your VO2max

Building and keeping are different jobs

Most training advice is written for people trying to improve. Once you have the fitness you wanted, the question changes: what is the least you can do and still hold on to it? That turns out to have a clear answer, and it comes from a set of experiments run in the same lab in the early 1980s.

The design was the same each time. Subjects trained hard for 10 weeks, cycling and running 40 minutes a day, six days a week, which raised VO2max by roughly 10 to 25%. Then one variable was cut for a further 15 weeks while the other two were held constant. Running the experiment three times, once per variable, is what makes the answer unusually clean.

Cut how often you train: it holds

When 12 subjects dropped from six days a week to four days or two days, keeping intensity and duration the same, VO2max stayed at trained levels when checked every five weeks for 15 weeks. The authors concluded that more exercise is needed to raise VO2max than to maintain it¹.

Two sessions a week is a third of what built the fitness in the first place. That is the headline most people need.

Cut how long each session is: it mostly holds

The second study cut session length instead. Thirteen subjects went from 40 minutes a day to either 26 or 13 minutes, holding intensity and frequency. VO2max remained at trained levels in both groups².

There is a caveat worth keeping. Long-term endurance, meaning the ability to keep going for a long time, fell in the 13-minute group even though VO2max did not. So a very short session protects your ceiling but not necessarily your staying power. If you care about both, cutting to around 26 minutes is the safer trim.

Cut how hard you go: it does not hold

The third study is the one that matters most. Same setup, but this time intensity was cut by a third or by two thirds while frequency and duration stayed at six days a week for 40 minutes. VO2max was not maintained with even the one-third reduction, and fell further with the two-thirds reduction. Calculated left ventricular mass, which had grown about 15% with training, returned to its starting level in both groups³.

That last detail is the mechanism in miniature. The heart adaptation that drives a higher VO2max is a response to hard work specifically, so when the hard work goes, the adaptation goes with it, no matter how many easy hours you log.

The modern version of the rule

A 2021 review pulled this literature together and reached a generalized version: endurance performance can be maintained for up to 15 weeks when training frequency drops to as little as two sessions per week, or when volume drops by 33 to 66%, going as low as 13 to 26 minutes per session, provided exercise intensity is maintained⁴. Forty years on, the conclusion has not moved.

This is not the same as stopping

Reduced training and no training behave very differently, and it is worth not confusing the two. Stopping completely costs about 7% of VO2max in three weeks and around 16% by eight weeks. We covered that, and how it should shape your testing schedule, in how often to take the Cooper test. The maintenance findings here all depend on continuing to do something hard, just less of it.

What a maintenance week looks like

The minimum

Two quality sessions a week, each with a genuine hard component. That could be one interval session, for example the 4 x 4 minute format covered in running to increase VO2max, plus one shorter, sharper session. Keep the hard intervals at the effort you used when you were building, not a comfortable version of it.

If you have slightly more time

Add easy aerobic work around those two sessions. It will not defend your VO2max by itself, as the intensity study shows, but it supports general health, keeps the habit alive and makes returning to full training easier when your schedule opens up again.

How to tell it is working

Retest rather than assume. A field test repeated under the same conditions is enough to catch a real decline before it becomes a large one.

The decade view

Over five or ten years the opponent is not a busy month, it is age. VO2max falls throughout adult life, by about 3% to 6% per decade in your 20s and 30s, accelerating to more than 20% per decade from your 70s⁵. That decline happens in the background whether or not you train.

This is what makes maintenance worth the trouble rather than merely tidy. Holding your current fitness is not standing still, it is actively offsetting a loss that would otherwise compound. And the thing being defended has measurable value: in a meta-analysis of 33 studies and roughly 100,000 people, each one MET higher fitness, about 3.5 ml/kg/min of VO2max, was associated with 13% lower risk of death from any cause and 15% lower risk of heart disease events⁶.

Two hard sessions a week for a decade is a modest standing cost against that. It is also a far easier commitment to keep than the block of training that built the fitness, which is the practical point: the version of training you can sustain for ten years is not the version that got you here.