RESUMO
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 (VÌo2) 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 VÌo2peak. 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 VÌo2peak. Pulmonary gas exchange and near-infrared spectroscopy of the vastus lateralis were used to continuously sample VÌo2 and HHb + Mb, respectively. The phase II VÌo2 kinetics were quantified using monoexponential curves during moderate and heavy exercise. Slow component amplitudes were also quantified for the heavy-intensity domain. Relative VÌo2peak values were not different between sexes (P = 0.111). Males achieved â¼30% 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 VÌo2 (â¼24 and â¼40% VÌo2peak, P ≥ 0.179) and HHb + Mb (â¼20 and â¼32% ischemia, P ≥ 0.193). Similarly, there were no sex differences in the time constants for VÌo2 (â¼28 s, P ≥ 0.385) or HHb + Mb (â¼10 s, P ≥ 0.274). In the heavy-intensity domain, neither VÌo2 (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.NEW & NOTEWORTHY This study demonstrated no sex differences in the oxidative response to moderate- and heavy-intensity cycling exercise. The change in oxygen uptake and deoxyhemoglobin were modeled with monoexponential curve fitting, which revealed no differences in the rate of oxidative energy provision between sexes. This provides insight into previously reported sex differences in the integrative response to exercise.