Effects of Pressure-Threshold Versus Dynamic Flow-Resistive Inspiratory Training on Respiratory Strength in Healthy Adults: A Randomized Controlled Trial

Purpose: Inspiratory muscle training (IMT) strengthens the muscles of inspiration, improves maximal inspiratory pressure (MIP), and can be performed using pressure-threshold or dynamic flow-resistive devices. Varying costs and complexity between devices may limit accessibility for use. Although both devices have been used in IMT research, it is unclear if 1 device provides superior results. This study compared the effectiveness of matched-volume IMT delivered by pressure-threshold and dynamic flow-resistive loading on inspiratory strength in healthy adults. Methods: Twenty healthy adults were enrolled in this single-blinded randomized controlled trial. Baseline inspiratory strength by S-index was assessed before randomization into a pressure-threshold or dynamic flow-resistive IMT group. Participants in both groups performed IMT 5 days per week for 5 weeks, 30 maximal inhalations per session with resistance of 50% baseline S-index. Inspiratory strength testing was repeated at the end of the trial. Repeated-measures ANOVA assessed differences of pre-training and post-training S-index values between groups. Results: Both pressure-threshold and dynamic flow-resistive IMT produced significant improvement in S-index ( P < .01) by mean (SD) 15.5% (7.9) and 18.9% (15.5), respectively. No group by time interaction existed ( P = .41). Conclusions: Both pressure-threshold and dynamic flow-resistive IMT are effective at improving inspiratory strength in healthy populations. Comparable gains across modalities suggest that the magnitude of imposed resistive load, rather than specific valve or aperture mechanics, is the primary driver of diaphragmatic and accessory muscle adaptation. As both devices are equally effective, device selection for patients can be guided by cost, portability, and patient preference without compromising efficacy. Five weeks of IMT significantly improved inspiratory strength in healthy adults, independent of device type.