Sex-Differences in the Oxygenation Levels of Intercostal and Vastus Lateralis Muscles During Incremental Exercise

This study aimed to examine sex differences in oxygen saturation in respiratory (SmO 2 - m.intercostales ) and locomotor muscles (SmO 2 - m.vastus lateralis ) while performing physical exercise. Twenty-five (12 women) healthy and physically active participants were evaluated during an incremental test with a cycle ergometer, while ventilatory variables [lung ventilation ( V. E), tidal volume (Vt), and respiratory rate (RR)] were acquired through the breath-by-breath method. SmO 2 was acquired using the MOXY ® devices on the m.intercostales and m.vastus lateralis . A two-way ANOVA (sex × time) indicated that women showed a greater significant decrease of SmO 2 - m.intercostales , and men showed a greater significant decrease of SmO 2 - m.vastus lateralis . Additionally, women reached a higher level of ΔSmO 2 - m.intercostales normalized to V. E (L⋅min –1 ) ( p < 0.001), whereas men had a higher level of ΔSmO 2 - m.vastus lateralis normalized to peak workload-to-weight (watts⋅kg –1 , PtW) ( p = 0.049), as confirmed by Student’s t -test. During an incremental physical exercise, women experienced a greater cost of breathing, reflected by greater deoxygenation of the respiratory muscles, whereas men had a higher peripheral load, indicated by greater deoxygenation of the locomotor muscles.