Recreational Runners Hit Higher VO2 Max With Less Work From Their Hearts

The work is a cross-sectional observational study. That means it compared two groups of people at one point in time. It included 85 healthy men: 44 recreational half-marathon and marathon runners (average age 32.6) and 41 untrained men of similar age and body size. It cannot show that running caused any of the differences.

Every participant did a maximal exercise test on a stationary bike. Resistance started at 40 watts and rose by 15 watts each minute until the person could not continue. Researchers measured the gases people breathed in and out. They also estimated heart output with a non-invasive method called bioreactance.

The runners reached a maximal oxygen consumption, or VO2 max, of 53.2 mL per kilogram per minute. The untrained men reached 38.7. VO2 max is the standard measure of aerobic fitness. It reflects how well the body takes in oxygen, moves it around and uses it.

The heart numbers went the other way. At peak effort, the runners had lower cardiac output (the amount of blood the heart pumps each minute), lower stroke volume (the amount per beat) and lower cardiac power output, a measure that combines blood flow and blood pressure. The authors report cardiac output was 19% lower in runners. Their heart rates were higher, which the authors link to the runners reaching an 18% higher workload on the bike.

The likely explanation is oxygen extraction, which the study measured as the difference in oxygen content between arterial and venous blood. In plain terms, it shows how much oxygen the muscles pull out of the blood passing through them. Runners showed higher extraction at maximal effort. The authors say this lets them meet greater oxygen demands with less cardiac work, and that peripheral adaptations in the muscles appear to play a dominant role.

The authors say these findings may suggest a potential cardioprotective role of endurance training, since the heart works less hard at maximal effort. That is their interpretation. The study did not follow anyone over time or measure heart disease outcomes. The authors also point to known cellular changes with endurance training, such as more mitochondria and capillaries in muscle, but this study did not measure them.

There are other limits. Only men took part, all runners were recreational, and cardiac output was estimated rather than measured directly. At rest, the runners also had higher heart rate and mean arterial blood pressure than the controls. The paper does not say whether this matters.

The finding adds a different angle to The Arising's October 18 report on UK Biobank data linking higher VO2 max to lower depression and anxiety risk. That was a separate, large observational study of health outcomes. This one looks at how fitter bodies handle oxygen under maximal stress.

The authors say that, for people with compromised heart function, it remains to be worked out which type of exercise training can improve it. Studies that follow people over time, and include women, would be the next step.

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