LAUSR

INTRODUCTION The female diaphragm develops less fatigue following high intensity exercise compared to males. Diaphragm fatigability is typically defined as a decrease in transdiaphragmatic twitch pressure (Pdi,TW) and represents the contractile function of the muscle. However, it is unclear whether this sex difference persists when examining changes in voluntary activation, which represents a neural mechanism contributing to fatigability. PURPOSE To determine if high intensity cycling results in a decrease in diaphragm voluntary activation (D-VA) and to explore if the decrease in D-VA is different between sexes. METHODS Twenty-five participants (15 females) completed a single bout of high intensity constant load cycling. D-VA and Pdi,TW were measured before and after exercise using cervical magnetic stimulation of the phrenic nerves to assess diaphragm fatigability. RESULTS Participants were of similar aerobic fitness when expressed relative to predicted values (Females: 114 ± 25, Males: 111 ± 11%predicted; p = 0.769). Pdi,TW decreased relative to baseline to 85.2 ± 16.7 and 70.3 ± 12.4%baseline (p = 0.012) in females and males, respectively, immediately after exercise. D-VA also decreased in both females and males immediately after exercise. The decrease in D-VA was less in females compared to males (95.4 ± 4.9%baseline vs. 87.4 ± 10.8%baseline, respectively; p = 0.018). CONCLUSIONS D-VA decreases after whole body exercise in both females and males although the magnitude of the decrease is not as large in females compared to males. The findings of this study suggest the female diaphragm is more resistant to both contractile and neural mechanisms of fatigability after whole body exercise.