Training raises VO2 max, but how much varies widely
High confidence
Training raises VO2 max (the most oxygen the body can use), but the size of the gain depends on where you start. New and recreational runners often add 5 to 20 percent. Well-trained runners gain less, usually 1 to 5 percent. And a few people barely respond, even after training hard and staying consistent.
Why it works
Gains come as the heart pumps more blood per beat, total blood volume rises, and the muscles get better at using oxygen. Genetics influence both the ceiling and how fast the body adjusts.
What it means in practice
Don't promise a fixed number. Treat training as setting up the conditions for the body to adjust, not a guarantee of a specific gain. And when a runner isn't seeing the progress they expected, don't assume they're doing something wrong. Some of the variation is simply biological.
The evidence
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Joyner and Lundby argue that fixed individual differences in trainability have been overstated. Under more intense or progressive training, such as interval work and longer programs, VO2max rises in essentially all participants. That undercuts earlier reports of a substantial 'non-responder' fraction seen at modest training doses, where under-dosed protocols produce small mean responses with high apparent variability. The authors read this as a stimulus problem more than a genetic one, and call for new twin-study designs that separate true genetic limits from inadequate training.
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Joyner modeled marathon performance as the product of three physiological factors: VO2max sets the ceiling on aerobic energy, lactate threshold fixes the fraction of that ceiling sustainable over the race, and running economy sets the oxygen cost of a given speed. Feeding physiologically plausible upper bounds for each factor into the model yielded a theoretical optimum of roughly 1:57:58, about 8 minutes under the world record at publication (near 2:06). This is theory rather than data. It extrapolates from elite male values, pushes running economy to the extreme low end of observed values, and does not account for pacing, environment, or fatigue durability. The three-factor framing still anchors endurance physiology and later informed the Nike Breaking2 and INEOS 1:59 projects.
Why we call confidence high
Joyner's 2018 review pulls together decades of training studies. They show VO2 max is trainable but that responses vary widely, including a notable fraction of low responders. The HERITAGE family studies found a substantial genetic component to how trainable it is.
Where it applies
Adult runners at every training level. Beginners and detrained adults see the largest gains.
Does not apply to: children, where growth-related changes confound training adaptation; elite athletes near their physiological ceiling.
Last reviewed Apr 30, 2026. See how we score.