Sex differences in endurance capacity and metabolic response to prolonged, heavy exercise

Summary

In order to test for possible sex differences in endurance capacity, groups of young, physically active women (n=6) and men (n=7) performed bicycle ergometer exercise at 80% and 90% of their maximal oxygen uptakes ($\dot V_{{\text{O}}_{\text{2}} {\text{max}}}$). The groups were matched for age and physical activity habits. At 80%$\dot V_{{\text{O}}_{\text{2}} {\text{max}}}$ the women performed significantly longer (P<0.05), 53.8±12.7 min vs 36.8±12.2 min, respectively (means ± SD). Mid-exercise and terminal respiratory exchange ratio (R) values were significantly lower in women, suggesting a later occurrence of muscle glycogen depletion as a factor in their enhanced endurance. At 90%$\dot V_{{\text{O}}_{\text{2}} {\text{max}}}$ the endurance times were similar for men and women, 21.2±10.3 min and 22.0±5.0 min, respectively. The blood lactate levels reached in these experiments were only marginally lower (mean differences 1.5 to 2 mmol·l⁻¹) than those obtained at$\dot V_{{\text{O}}_{\text{2}} {\text{max}}}$, suggesting high lactate levels as a factor in exhaustion. The changes in body weight during the 80% experiments and the degree of hemoconcentration were not significantly different between men and women.