Effect of pedal cadence on the heterogeneity of muscle deoxygenation during exercise
Résumé
This study examines the effect of pedal cadence on the heterogeneity of muscle deoxygenation during exercise of moderate intensity. Twelve healthy subjects performed six minutes of cycling at 40 and 100 rpm at 80% of the workload corresponding to the gas exchange threshold. Gas exchanges were measured breath-by-breath during each exercise. Muscle deoxygenation (HHb i.e. O2 extraction) and blood volume (tHb) were monitored continuously by near-infrared spectroscopy at eight sites on the vastuslateralis. The heterogeneity of HHb and tHb was assessed using the relative dispersion of the signal measured at the eight sites (i.e. 100 x standard deviation/mean). HHb and tHb were not altered by the pedal cadence, while pulmonary V ̇ O2 was higher at 100 than at 40 rpm (p < 0.001). The relative dispersion of HHb was significantly higher at 100 rpm compared to 40 rpm (p < 0.001) whereas no significant difference was shown for the relative dispersion of tHb. These results indicate that the pedal cadence has no effect on O2 extraction but that an elevated cadence would increase muscle V ̇ O2, suggesting an increase in muscle blood flow. Elevated cadence also induced greater heterogeneity of the muscle’sV ̇ O2/Q ̇ O2 delivery ratio, suggesting impairment in the adequacy between O2 demand and O2 delivery in some regions of active muscle