Sex-related differences in muscle deoxygenation during ramp incremental exercise

- Local O2 extraction was larger in women than in men during ramp incremental exercise.
- The HHb signal breaking point was associated with the respiratory compensation point.
- Results suggest poorer microvascular perfusion in women than men during ramp tests.

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 (V˙O2p) measurements. Subject's (men: n = 10; women: n = 10) Δ[HHb] data were normalized to 100% of the response, plotted as a function V˙O2p, %V˙O2p, 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 V˙O2p, %V˙O2p 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.