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 (V{square}O2) 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 V{square}O2peak. 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 V{square}O2peak. Pulmonary gas exchange and near-infrared spectroscopy of the vastus lateralis were used to continuously sample V{square}O2 and HHb+Mb, respectively. The phase II V{square}O2 kinetics were quantified using mono-exponential curves during moderate and heavy exercise. Slow component amplitudes were also quantified for the heavy intensity domain. Relative V{square}O2peak 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 V{square}O2 ([~]24 and [~]40% V{square}O2peak, p[≥]0.179) and HHb+Mb ([~]20 and [~]32% ischemia, p[≥]0.193). Similarly, there were no sex differences in the time constants for V{square}O2 ([~]28 s, p[≥]0.385) or HHb+Mb ([~]10s, p[≥]0.274). In the heavy intensity domain, neither V{square}O2 (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. New and NoteworthyThis study demonstrated no sex differences in the oxidative response to moderate and heavy intensity cycling exercise. The change in oxygen uptake and deoxyhaemoglobin were modelled with mono-exponential 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.