No sex differences in oxygen uptake or extraction kinetics in the moderate or heavy exercise intensity domains

The integrative response to exercise differs between sexes, with oxidative energy contribution purported as a potential mechanism. The present study investigated whether this difference was evident in the kinetics of oxygen uptake (Vo(2)) and extraction (HHb + Mb) during exercise. Sixteen adults (8 males, 8 females, age: 27 +/- 5 yr) completed three experimental visits. Incremental exercise testing was performed to obtain lactate threshold and Vo(2peak). Subsequent visits involved three 6-min cycling bouts at 80% of lactate threshold and one 30-min bout at a work rate of 30% between the lactate threshold and power at Vo(2peak). Pulmonary gas exchange and near-infrared spectroscopy of the vastus lateralis were used to continuously sample Vo(2) and HHb + Mb, respectively. The phase II Vo(2) kinetics were quantified using monoexponential curves during moderate and heavy exercise. Slow component amplitudes were also quantified for the heavy-intensity domain. Relative Vo(2peak) values were not different between sexes (P = 0.111). Males achieved similar to 30% greater power outputs (P = 0.002). In the moderate- and heavy-intensity domains, the relative amplitude of the phase II transition was not different between sexes for Vo(2) (similar to 24 and similar to 40% Vo(2peak), P >= 0.179) and HHb + Mb (similar to 20 and similar to 32% ischemia, P >= 0.193). Similarly, there were no sex differences in the time constants for Vo(2) (similar to 28 s, P >= 0.385) or HHb + Mb (similar to 10 s, P >= 0.274). In the heavy-intensity domain, neither Vo(2) (P >= 0.686) or HHb + Mb (P >= 0.432) slow component amplitudes were different between sexes. The oxidative response to moderate- and heavy-intensity exercises did not differ between males and females, suggesting similar dynamic responses of oxidative metabolism during intensity-matched exercise.