Which of the following is a structural/physiological reason why VO2 max may be greater in an elite athlete than a recreational runner?

• A. Increased maximum cardiac output
• B. Increased blood glucose stores
• C. Higher resting heart rate
• D. Increased capillary density

Answer: (A)

VO2 max is the maximal rate at which oxygen can be delivered to and used by the working muscles. The most direct way to raise this ceiling is to increase how much blood can be pumped around the body at maximal effort. Cardiac output (the amount of blood the heart can move per minute) is the key limiter here, because VO2 max in the Fick equation is the product of cardiac output and the muscles’ oxygen extraction. Elite athletes often develop a larger stroke volume through heart adaptations, so their maximal cardiac output is higher, allowing more oxygen to reach the muscles and be used, which raises VO2 max. While other factors like capillary density and diffusion improvements help utilisation, they don’t increase the maximal rate of oxygen delivery as directly as boosting maximum cardiac output.