Sex Differences in Diaphragm Voluntary Activation after Exercise

Introduction The female diaphragm develops less fatigue after high-intensity exercise compared with males. Diaphragm fatigability is typically defined as a decrease in transdiaphragmatic twitch pressure (P-di,P-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 This study aimed 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 P-di,P-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% predicted, males: 111% +/- 11% predicted; P = 0.769). P-di,P-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 with 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 with males. The findings of this study suggest that the female diaphragm is more resistant to both contractile and neural mechanisms of fatigability after whole-body exercise.