Sex differences of physical working capacity in normoxia and hypoxia

Abstract

A balanced Latin square design examined sex differences in working capacity for four endurance tasks involving different volumes of muscle (two-leg, one-leg, arm plus shoulder and arm ergometry) in eight women and eight men under normoxic and hypoxic (12% oxygen) conditions. There was a substantial (30-40%) sex difference in maximum oxygen intake during two-leg ergometry. Much of the difference was size related. The discrepancy was reduced by expressing data per litre of active leg muscle, and (more simply) was largely eliminated if expressed per kilo of skinfold-estimated fat-free body mass. However, a part of the sex discrepancy in the performance of two-leg ergometer work arose from a limitation of oxygen transport in the female. The balance thus shifted progressively in favour of the women in tasks that involved a smaller proportion of the total body mass. Likewise, hypoxia exacerbated the female disadvantage in large muscle but not in small muscle tasks. From the viewpoint of physical employment, the female is at little disadvantage in light activities; indeed, because of small hands and light bones, the working capacity of the arms per unit volume of muscle is greater for a woman than for a man. However, if body mass must be displaced against gravity, as in walking, the average woman has a disadvantage of some 10%, and if maximum aerobic power must be exerted against an external machine, the handicap rises to 30-40%. Nevertheless, inter-individual differences in working capacity are large, and in most types of industrial task some women will be able to out-perform some men.

Keywords:

• Sex differences
• Work capacity
• Maximum oxygen intake
• Muscle volume
• Hypoxia