Impact of High-Intensity Inspiratory Muscle Training on Inspiratory Muscle Strength in Healthy Adults

Background: Previous research has demonstrated that moderate-intensity inspiratory muscle training (IMT) improves inspiratory strength and exercise performance in athletes, but the impact of high-intensity IMT on inspiratory strength in healthy adults is unclear. The purpose of this study was to compare the effects of high-intensity versus moderate-intensity IMT on inspiratory strength and VO 2 peak in healthy adults. Methods: Twenty-six adults enrolled in this double-blinded randomized controlled trial. Participants completed an inspiratory strength assessment through S-Index and VO 2 peak testing before randomization into a moderate-intensity or high-intensity group. Participants in both groups performed IMT to 40 repetitions or task failure once per day, 5 times per week for 8 weeks. IMT intensity was 50% and 80% of pretraining S-Index for the moderate-intensity and high-intensity groups, respectively. S-Index and VO 2 peak testing were repeated at the end of the trial. Repeated measures ANOVA were used to assess differences of pretraining and post-training S-Index and VO 2 peak between groups. Results: A significant increase in mean (SD) S-Index from pretraining to post-training was present for both moderate-intensity (7.6% (8.9), P = .001) and high-intensity (10.8% (11.7), P < .001) groups. No significant group ( P = .88) or interaction ( P = .44) effects existed for S-Index. There were no significant main effects for group, time, or interaction for VO 2 peak ( P > .05 for all). Conclusions: Both moderate-intensity and high-intensity IMT to task failure in healthy adults led to significant improvements in inspiratory strength. No effects were observed in either group on changes in VO 2 peak. Given that moderate-intensity and high-intensity IMT to task failure were both effective at improving inspiratory strength in healthy adults, training intensity at less intense, moderate levels can be used to achieve similar strength gains.