Sex-related differences in muscle deoxygenation during ramp incremental exercise.

Sex-specific differences in the temporal profiles of fractional O2 extraction during incremental cycling were examined using changes in near-infrared spectroscopy (NIRS)-derived muscle deoxygenated hemoglobin concentration (Δ[HHb]) and breath-by-breath pulmonary O2 uptake ( .VO2p ) measurements. Subject's (men: n=10; women: n=10) Δ[HHb] data were normalized to 100% of the response, plotted as a function ( .VO2p, % .VO2p), power output (PO), and % PO, and fit with a piecewise double-linear regression model. The slope of the first segment of the double linear model was significantly greater in women compared to men when %Δ[HHb] was plotted as a function of .VO2p, % .VO2p and PO (p<0.05). Both sexes displayed a near-plateau in the %Δ[HHb] which occurred at an exercise intensity near the respiratory compensation point. Thus, young women display a poorer ability to deliver O2 to the exercising tissue compared to men and oxidative demands must be supplemented by a greater fractional O2 extraction.