The different relationship of VO2max to muscle mitochondria in humans and quadrupedal animals.

Abstract

The relationship of VO2max to muscle oxidative capacity (estimated morphometrically as the volume of mitochondria of the entire musculature) was analyzed by compiling data on 8 species of mammals varying widely in VO2max. Over a five-fold range of weight-specific VO2max, a linear relationship between VO2max and muscle mitochondria was found. As an exception, humans seem to have 'excess' mitochondrial volume for their VO2max. However, the rate at which mitochondria operate in vivo at VO2max is found to be very similar for humans and quadrupedal animals. A larger total mitochondrial volume thus accounts for the well known finding that humans are capable of reaching VO2max with a subset of their body musculature. In quadrupedal animals the oxygen delivery system is geared to supply the entire musculature while in humans, possibly as a consequence of the upright posture, the cardiovascular system is designed to supply only a fraction of the total muscle oxidative capacity at VO2max.