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 (V̇O₂) and extraction (HHb+Mb) during exercise. Sixteen adults (8 males, 8 females, age: 27±5 years) completed three experimental visits. Incremental exercise testing was performed to obtain lactate threshold and V̇O_2peak. Subsequent visits involved three six-minute cycling bouts at 80% of lactate threshold and one 30-minute bout at a work rate 30% between the lactate threshold and power at V̇O_2peak. Pulmonary gas exchange and near-infrared spectroscopy of the vastus lateralis were used to continuously sample V̇O₂ and HHb+Mb, respectively. The phase II V̇O₂ kinetics were quantified using mono-exponential curves during moderate and heavy exercise. Slow component amplitudes were also quantified for the heavy intensity domain. Relative V̇O_2peak values were not different between sexes ( p=0.111). Males achieved ~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 V̇O₂ (~24 and ~40% V̇O₂peak, p≥0.179) and HHb+Mb (~20 and ~32% ischemia, p≥0.193). Similarly, there were no sex differences in the time constants for V̇O₂ (~28 s, p≥0.385) or HHb+Mb (~10s, p≥0.274). In the heavy intensity domain, neither V̇O₂ ( p≥0.686) or HHb+Mb ( p≥0.432) slow component amplitudes were different between sexes. The oxidative response to moderate and heavy intensity exercise did not differ between males and females, suggesting similar dynamic responses of oxidative metabolism during intensity-matched exercise.