Evaluating the physiological and perceptual responses to inspiratory muscle training in males and females

Abstract

Background: Although the respiratory system is often considered “overbuilt” for the ventilatory demands of exercise in healthy individuals, respiratory muscle fatigue can limit exercise tolerance by increasing the work of breathing, activating the respiratory muscle metaboreflex, and exacerbating exertional dyspnoea. Inspiratory muscle training (IMT) improves inspiratory muscle strength and reduces respiratory muscle fatigue; however, whether males and females adapt differently remains unclear. Objective: To determine whether sex influences physiological (inspiratory muscle strength, exercise performance) and perceptual (exertional dyspnoea) responses to IMT in physically active adults. Methods: Twenty-five healthy, physically active adults (12 males, 13 females; 20–60 years) completed a 5-week IMT program (two daily sessions of 30 breaths, 5 days/week) at 60% of maximal inspiratory pressure (MIP), with weekly workload adjustments. Before and after training, participants completed pulmonary function testing, MIP assessment, incremental and constant-load exercise tests, and ratings of dyspnoea intensity and unpleasantness (modified Borg CR10 scale). Two-way repeated-measures analysis of variance were performed and if significant F ratios were detected, Tukey’s or Bonferroni-adjusted post hoc tests were performed. Multiple linear regression analyses examined whether sex and relative change in inspiratory muscle strength (% change in MIP) independently predicted changes in perceptual and physiological exercise outcomes. Results: Relative MIP increased significantly following IMT in both sexes (43.7 ± 23.9% vs. 40.7 ± 36.4%; p < 0.0001), with no sex-by-time interaction, although males exhibited greater absolute increases (p = 0.01). Peak oxygen uptake, constant-load exercise endurance time, and dyspnoea during incremental exercise were unchanged after IMT, with no sex differences in training responses. Oxygen uptake at the same submaximal workload decreased following IMT (p < 0.05). During constant-load exercise at isotime, dyspnoea intensity and unpleasantness demonstrated significant sex-by-time interactions (both p = 0.02). Changes in MIP were not associated with exercise performance or dyspnoea, whereas sex was associated with dyspnoea intensity changes (p = 0.038), with greater reductions in females. Conclusion: In physically active adults, IMT increased inspiratory muscle strength similarly in males and females but did not translate into improved exercise performance. Sex-specific differences were observed only in perceptual responses during constant-load exercise, suggesting limited sex-related effects of IMT.