VO2max Versus VO2peak

VO2max applies strictly to the highest oxygen consumption value attainable for the whole body. VO2peak on the other hand is contextual. For example, during small muscle mass exercise (like on arm ergometer) your highest attainable VO2 value is much lower than your VO2max. As a result, we would refer to this as a VO2peak. However, during whole body exercise VO2peak often equals VO2max.

The attainment of a true maximum VO2 value requires a certain percentage of total muscle mass be engaged. Interestingly, once a ‘critical mass’ of total muscle is used, the engagement of more muscle mass may not increase VO2 further. This is due to the intricacies of cardiovascular control.

Because the vasodilator capacity of skeletal muscle can outstrip the maximal pumping capacity of the heart, we can only deliver oxygenated blood to so much skeletal muscle. As you transition from a local (arm ergometer) to regional (cycling) to systemic (XC Skiing) exercise the brain selectively restricts blood flow to the skeletal muscle in order to maintain arterial blood pressure. As a result, you can no longer rely on progressive increases cardiac output to drive blood flow up further. Instead, athletes in ‘whole body’ endurance sports rely on extraction based strategies to increase their rate of energy turnover.

In these individuals the difference in oxygen concentration between mixed venous and pulmonary artery blood flow widens with increasing oxygen consumption, and it’s not uncommon for >85% of available oxygen in the blood to be extracted as it moves through the capillaries of the working muscle. In elite athletes with very high maximal cardiac outputs we may even see a compression of this arteriovenous oxygen concentration difference due to a lowering of the arterial oxygen saturation (SpO2) since pulmonary diffusion limitations may be present.

In these cases we can’t rely on increased oxygen extraction to improve performance. Instead we need to improve the maximal pumping capacity of the heart (which will primarily come through extrinsic influences on the heart like increased ventricular filling pressure) as well as the fatigue resistance of the respiratory muscles. Collectively these two factors will lead to functional sympatholysis, which is a blunting of the sympathetic vasoconstrictor response that limits skeletal muscle blood flow during maximal effort exercise.