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

Abstract

This study aimed to examine sex differences in oxygen saturation in respiratory (SmO₂-<i>m.intercostales</i>) and locomotor muscles (SmO₂-<i>m.vastus lateralis</i>) 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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mtext>V</mml:mtext> <mml:mo>.</mml:mo></mml:mover> </mml:math> E), tidal volume (Vt), and respiratory rate (RR)] were acquired through the breath-by-breath method. SmO₂ was acquired using the MOXY^® devices on the <i>m.intercostales</i> and <i>m.vastus lateralis</i>. A two-way ANOVA (sex × time) indicated that women showed a greater significant decrease of SmO₂-<i>m.intercostales</i>, and men showed a greater significant decrease of SmO₂-<i>m.vastus lateralis</i>. Additionally, women reached a higher level of ΔSmO₂-<i>m.intercostales</i> normalized to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mtext>V</mml:mtext> <mml:mo>.</mml:mo></mml:mover> </mml:math> E (L⋅min^-1) (<i>p</i> < 0.001), whereas men had a higher level of ΔSmO₂-<i>m.vastus lateralis</i> normalized to peak workload-to-weight (watts⋅kg^-1, PtW) (<i>p</i> = 0.049), as confirmed by Student's <i>t</i>-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.