Caitlin Hubbard, Angelina Curiel, Rebecca Larson, J. Mikhail Kellawan, Hugo Pereira and Christopher Black

University of Oklahoma, Norman, OK

Women typically show longer time to task failure than men during low to moderate intensity isometric exercise. It has been suggested higher intramuscular pressures, due to the greater muscle mass and absolute strength of men leads to greater reductions in skeletal muscle perfusion during a fatiguing contraction. PURPOSE: This study sought to investigate potential changes in oxygen saturation during low-intensity isometric exercise in men and women and determine if task failure occurs at a similar level of oxygen desaturation. METHODS: Twenty-three participants (11 men and 12 women) completed four visits consisting of two familiarization visits and two experimental visits consisting of a normal flow control condition (CON) and proximal blood flow occlusion (OCC), randomly assigned. Isometric elbow flexion of the non-dominant arm was performed at 20% of MVC until task failure (TTF). Changes in oxygen saturation during exercise were assessed using near-infrared spectroscopy (NIRS). Mitochondrial function was also assessed using NIRS to determine its relationship with TTF. RESULTS: TTF in the CON condition was shorter for women compared to men (906 ± 553 sec vs 514 ± 260 sec; p= 0.04) but not during the OCC (207 ± 28 sec vs 225 ± 47 sec; p = 0.29). There were no differences between men and women in oxygen desaturation at the end of exercise (46 ± 32%Δ vs. 68 ± 44%Δ; p=0.17) or at 20, 40, 60, and 80% of TTF (p ≥ 0.33). A main effect for time (p < 0.001) and condition (p = 0.02) were found demonstrating significant oxygen desaturation over time during exercise and greater desaturation during OCC (52 ± 45%Δ vs. 77 ± 37%Δ for CON and OCC, respectively). There were also no differences in mitochondrial function between men and women (time constant of 15.1 ± 5.5 sec vs. 20.1 ± 8.4 sec; p = 0.10). CONCLUSIONS: Women exhibited greater TTF than men during an elbow flexion isometric task. This difference was not present when blood flow was occluded during exercise. When expressed relative to TTF, similar levels of oxygen desaturation were observed between men and women during and at the end of exercise. This study provides further evidence that sex differences in TTF may be partially explained by faster oxygen desaturation in men that is not related to mitochondrial function.

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