Reduction in respiratory muscle strength following a series of preparatory and maximal static, dry breath-holds

Breath-hold diving poses significant physiological challenges to maintaining O₂ homeostasis. During a maximal breath-hold, numerous, subsequently augmenting, involuntary respiratory muscle contractions against a closed glottis (i.e., involuntary breathing movements, IBMs) may elicit respiratory muscle fatigue, especially under conditions of arterial hypoxemia. Thus, the purpose of this study was to determine whether respiratory muscle fatigue occurs following a series of static breath-holds in 14 trained male divers. To do so, we measured transdiaphragmatic twitch pressure (P_DI,TW), maximal inspiratory pressure (MIP), and maximal expiratory pressure (MEP) before and 8 min after three preparatory breath-holds (separated by 2.5 min; average duration = 185 ± 69 s and range = 62-309 s) and three maximal breath-holds (separated by 5 min; average duration = 308 s and range = 179-733 s). We calculated a pseudo O₂ delivery as heart rate × peripheral O₂ saturation. There was a significant reduction of P_DI,TW following the breath-hold series (-8.5 ± 13.7%; range: +7 to (-37)%; <i>P</i> = 0.03). Similarly, we found that MIP and MEP decreased by 6.3 ± 10.6% (<i>P</i> = 0.04) and 8.6 ± 10.4% (<i>P</i> = 0.002), respectively. Using an individualized means of determining the presence of fatigue, we observed that some (∼50%), but not all divers incurred respiratory muscle fatigue. Those who developed fatigue had a lower pseudo O₂ delivery during the struggle phase than those who did not (<i>P</i> = 0.01). Our findings suggest that respiratory muscle fatigue was more common in those divers who experienced a greater severity of arterial hypoxemia during the breath-holding protocol.<b>NEW & NOTEWORTHY</b> Respiratory muscle fatigue could occur following involuntary breathing movements during maximal breath-holds. We measured respiratory muscle strength pre and post three preparatory and maximal breath-holds. We found significant reductions in diaphragm strength and total inspiratory and expiratory strength in some, but not all, divers. Divers that had respiratory muscle fatigue had a lower pseudo O₂ delivery (HR × [Formula: see text]) during the struggle phase. This suggests that reduced oxygen delivery may contribute to respiratory muscle fatigue during a breath-hold.