Contributions to forearm desaturation during transient ischemia in healthy adult males and females across the lifespan.

This study investigated skeletal muscle tissue oxygenation (StO₂) desaturation in males and females across the adult lifespan. One hundred-two individuals (51 females) of 41 young, 34 midlife, and 27 older adults completed a vascular occlusion test with near-infrared spectroscopy (NIRS + VOT). This included five minutes of arterial occlusion, inducing transient ischemia in the forearm flexor muscle group while recording StO_2. The magnitude of desaturation (StO_2mag) was quantified as the difference between baseline StO₂ and the minimum StO₂ value observed during ischemia. The rate of desaturation was also examined. Forearm adipose tissue thickness (ATT), forearm lean mass, and handgrip muscular strength were measured. A p ≤ 0.05 was considered significant. Two-way between factor Analysis of variance (ANOVAs) indicated that males exhibited significantly (p < 0.001) less ATT than females (collapsed across age) and that forearm lean mass (p < 0.001) and muscular strength (p < 0.001) decreased across the lifespan independent of sex. Bivariate analyses revealed significant (p < 0.05) associations for sex, age, ATT, forearm lean mass, and muscular strength with the desaturation metrics. The ATT values demonstrated the strongest relations with StO_2mag and desaturation rate (r = -0.620 and 0.618). Using a model comparison approach, ATT plus age offered the best predictive power for StO_2mag and desaturation rate (R² = 0.456 and 0.438) such that the inclusion of sex did not improve the models. These findings suggested differences in desaturation were primarily explained by variations in ATT and, to a lesser extent, age, but biological sex had no meaningful effect. Future studies must determine what other factors influence desaturation during ischemia.