Grant: Travel Awards - Institute Community Support

Recently, the plateau in the near-infrared spectroscopy (NIRS)-derived deoxyhemoglobin ([HHb]) signal (ie. oxygen (O2) extraction) observed towards the end of a ramp incremental (RI) exercise test has been linked to an increase in local blood flow despite the existence of a reserve in the upper limit of O2 extraction. Although this observation was made in male participants, sex-related differences in O2 extraction have been previously been observed. The purpose of this study was to assess whether the existence of a "reserve" in O2 extraction immediately at the end of a RI cycling test to exhaustion was affected by sex. Twenty-one participants (12M, 9F; 27±3 yrs; 177.4±8.3 cm; 75.0±11.1 kg) performed a RI (25-30W·min-1) test to exhaustion on a cycle ergometer to determine the O2 uptake (VO2) and the [HHb] responses. The [HHb] signal was measured on the Vastus Lateralis (VL) muscle of the quadriceps. An automatic rapid inflation cuff was used to occlude blood flow to the leg (300 mmHg), at the upper portion of the thigh, for two minutes immediately at test failure. A repeated measures ANOVA was used to compare the normalized (0-100% of the response during RI test) [HHb] signal (plateau and peak value obtained during occlusion) at different time points. Post-exercise peak [HHb] (following occlusion) was higher compared to its plateau value (p<0.05), in both women (52.0±39.6%) and men (31.8±19.3%). No differences were found between groups. This study confirmed the existence of "reserve' in O2 extraction at the end of a RI test, despite a continuous increase in the VO2, which indicates that the plateau in the [HHb] response is not related to O2 extraction reaching its upper limit. Importantly, sex does not influence the size of the O2 extraction "reserve".