UBC Theses and Dissertations
Sex differences in voluntary activation of the diaphragm Ramsook, Andrew Harry
Purpose: Three studies were performed to examine how voluntary activation of the diaphragm changes after fatiguing tasks in young, healthy males and females. The change in diaphragm voluntary activation (D-VA) was also compared to the change in contractile function, assessed by the change in transdiaphragmatic twitch pressure (P¬DI,TW). Methods: Study 1 (Chapter 2) investigated the within- and between-session reliability of D-VA using cervical magnetic stimulation (CMS) to evoke twitches. Study 2 (Chapter 3) examined changes in D-VA after high intensity, whole-body exercise between sexes. Study 3 (Chapter 4) examined changes in D-VA after inspiratory pressure threshold loading (IPTL) between sexes. Conclusions: CMS can be used to reliably assess D-VA, measured via intraclass correlation coefficients (ICC) both within- (ICC: 0.76) and between-session (ICC: 0.88). After exercise, D-VA decreased in males and females. The decrease in D-VA was greater in males compared to females (87.4±10.8 vs 95.4±4.9%basline, respectively, p=0.036). The magnitude of the decrease in D-VA was less than the decrease in PDI,TW (Males: 70.3±12.4, Females: 85.2±16.7%baseline, p=0.024). After IPTL, both males and females showed a decrease in D-VA and PDI,TW. While males showed a greater decrease in PDI,TW (73.3±12.1 vs 87.1±15.0%baseline, respectively, p=0.016) compared to females, the decrease in D-VA was similar between sexes (88.2±10.5 vs 91.4±7.6%baseline, respectively, p=0.432). After IPTL, the decrease in PDI,TW correlated with the total respiratory work performed whereas the decrease in D-VA correlated with time until task failure. The magnitude of the decrease in PDI,TW was greater than the decrease in D-VA after IPTL. Collectively, the results of this thesis suggest that there are sex differences in the change in D-VA after exercise but not IPTL. This thesis provides a foundation for future work to investigate how diaphragm fatigability can affect exercise performance in humans.
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