How to improve your VO2 max: about 5 points, intervals or steady

Both hard intervals and steady endurance work improve your VO2 max, and by a similar amount. Pooling 28 controlled trials of 723 healthy adults aged 18 to 45, endurance training, meaning a sustained effort at one moderate pace, added about 4.9 points compared with people who did not train, and high-intensity interval training, repeated bursts of hard effort with recovery in between, added about 5.5 [14].

Participants averaged 40.8 points before training, so a five-point gain is a rise of about an eighth [14].

Head to head, intervals finished about 1.2 points ahead of continuous training, a difference the reviewers rated as small [14]. A physiology review of interval training gets to the same place from the other side: for the same volume of training, hard intervals raise VO2 max more than moderate continuous work, while sprint intervals, very short all-out efforts, match continuous training on far less total exercise [12]. So intervals win narrowly, and their bigger advantage is the time they save.

Sessions that move the number share one feature: minutes spent near the ceiling. Programming reviews put the target at several minutes per session above 90% of VO2 max, close to the hardest the oxygen system can work [13], built from hard bouts lasting anywhere from under 45 seconds to 2-4 minutes with recovery between them [15]. In footballers, 8 to 12 weeks of running above 85% of maximum heart rate, the fastest the heart beats at full effort, raised VO2 max by 5% to 11% and improved running economy, the oxygen cost of running at a set speed, by 3% to 7% [1].

Two things predicted a bigger gain. From interval training, people who started less fit gained about 3.2 points more than fitter participants, and longer programmes added about 3.0 points over shorter ones; the same directions showed up for endurance training in smaller amounts [14]. None of it happened in days. The pooled trials ran from two weeks upwards [14] and the football programmes ran 8 to 12 weeks [1].

Non-response looks more like under-dosing than bad luck with genes. A review of the biology of VO2 max concludes that every previously untrained person improves, provided the training passes a threshold of volume or intensity [6].

The limit sits in how much oxygen the blood carries and how much of it the heart can move. Training-driven rises in VO2 max come mostly from a bigger volume of red blood cells, the cells that carry oxygen around the body, and a larger stroke volume, the amount of blood the heart pushes out with each beat [6].

Inside the muscle, the target is the mitochondria, the compartments in a cell that burn fuel with oxygen. Exercise switches on PGC-1 alpha, a signalling protein that starts the building of new mitochondria, and a 2025 meta-analysis of randomised trials found large increases in it after endurance training, with interval and continuous work coming out about the same [10]. When trials match the amount of work done, mitochondrial content rises more after intervals, though that evidence is thin [12].

The trigger is a fuel shortage in the working muscle. AMPK, an enzyme that senses when a cell is running low on energy, is switched on by exercise and starts the programmes that build mitochondria and grow new blood vessels [7]. Muscle mitochondria are built and broken down continuously, and that turnover is what lets their volume and capacity shift with training [8].

How much of this you get is set by how much, how hard and how often you train, and part of the adaptation is specific to the type of exercise trained, which is why the gain shows up most in the movement you actually did [11].

The pooled numbers come from healthy adults aged 18 to 45, average age 25 [14]. That young sample is the main limit on everything above.

Who this evidence does not cover:

• older adults, since the pooled trials stopped at 45 [14]
• people with heart or lung disease, since the trials recruited healthy volunteers [14]
• people with a muscle disease, where a review of 14 trials found the evidence uncertain and a possible gain in aerobic capacity only in facioscapulohumeral muscular dystrophy, one inherited muscle-wasting condition [3]
• people already highly trained, who gained less than participants with lower starting fitness [14]

There is also a ceiling. A review of marathon physiology argues that how far training can push VO2 max is limited by genetics, and that above a certain weekly mileage runners stop getting better at holding a high fraction of their maximum [2]. More is not endlessly better.

Hard interval work carries a cost the reviews track separately. High speeds and power outputs load the muscles and joints, and the programming literature treats that strain as something to plan around rather than ignore [15].

One measurement caveat: every number here came from an exercise test run inside a study [14], not from a wrist device's estimate.

The trials describe a shape rather than a prescription. In the football studies, players spent 8 to 12 weeks running above 85% of maximum heart rate, and their VO2 max rose 5% to 11% [1]. In the interval reviews, sessions were built backwards from one target, several accumulated minutes above 90% of maximum oxygen uptake, by choosing how long the hard bouts run, how long the recoveries run, how many of each, and which exercise is used [13].

The same reviews add two practical points. They count the exercise mode as one of the variables you pick rather than a fixed requirement [13], and they treat the load on muscles and joints as a reason to build up gradually [15]. Anyone with a heart or lung condition, or who has been inactive for years, falls outside the group these trials studied, and that is a conversation for a doctor rather than a plan copied out of a paper.