Sex differences in the maximal metabolic steady state of fitness matched women and men.

We tested the hypothesis that power at maximal metabolic steady state is similar between fitness matched men and women. Eighteen participants (9 men, 9 women) performed a cycling graded exercise test for maximal oxygen consumption (V̇O). Men and women were matched for V̇O normalized to fat free mass (FFM), which was 50.4±4.7 ml·min·kg FFM and 52.1±8.2 ml·min·kg FFM, respectively (P=0.62). Participants completed a muscle oxygenation (%SmO) zero-slope prediction trial and a 3-min trial (3MT). The %SmO zero-slope trials included three, 5-min cycling bouts (30 sec rest) spanning intensity domains. Linear regression of trial work rate and %SmO slope over the final three minutes established the work rate occurring at the predicted zero slope in %SmO2. The 3MT requires all-out cycling, where end test power (ETP) was calculated as the mean power output over the last 30 sec and work above end test power (WEP) as the power-time integral above ETP. Independent of method, mean (±SD) absolute power at the maximal metabolic steady state was similar between fitness matched women and men (P=0.72), yet became higher in women when expressed relative to FFM (P=0.02). V̇O at the power associated with %SmO2 zero-slope represented a significantly higher fraction of V̇O for women compared to men (P=0.03). Normalized WEP (Watts/kg FFM) remained higher in men (P<0.01). Although highly correlated (r=0.88, P<0.01), ETP was ~8% higher than %SmO zero-slope power (P=0.03). Compared to fitness matched men, women displayed higher FFM normalized power associated with the heavy-severe exercise domain boundary.