Moderate- and High-Intensity Inspiratory Muscle Training Equally Improves Inspiratory Muscle Strength and Endurance-A Double-Blind Randomized Controlled Trial

Background and Objective: Inspiratory muscle training (IMT) produced outstanding results in the physical performance of active subjects; however, little is known about the best training intensity for this population. The objective was to investigate the impact of an IMT of high intensity, using the critical inspiratory pressure (CIP), on inspiratory muscle strength (IMS), inspiratory muscle endurance (IME), peak power, and oxygen uptake of recreational cyclists; and to compare these results with moderate-intensity IMT (60% of maximal inspiratory pressure [MIP]). Methods: Thirty apparently healthy male recreational cyclists, 20-40 years old, underwent 11 weeks of IMT (3 times per week; 55 min per session). Participants were randomized into 3 groups: sham group (6 cmH(2)O; n = 8); 60% MIP (MIP60; n = 10) and CIP (n = 12). All participants performed the IMS test and incremental IME test at the first, fifth, ninth, and 13th weeks of the experimental protocol. Cardiopulmonary exercise testing was performed on an electromagnetic braking cycle ergometer pre-IMT and post-IMT. Data were analyzed using a 2-way repeated measures ANOVA (group and period factors). Results: IMS increased in CIP and MIP60 groups at the ninth and 13th weeks compared with the sham group (P < .001; beta = 0.99). Regarding IME, there was an interaction between the CIP and MIP60 groups in all periods, except in the initial evaluation (P <.001; beta = 1.00). Peak power (in watts) increased after IMT in CIP and MIP60 groups (P =.01; beta = 0.67). Absolute oxygen uptake did not increase after IMT (P = .49; beta = 0.05). Relative oxygen uptake to lean mass values did not change significantly (P = .48; beta = 0.05). Conclusion: High-intensity IMT is beneficial on IMS, IME, and peak power, but does not provide additional gain to moderate intensity in recreational cyclists.