Effects of inspiratory muscle training on exercise responses in normoxia and hypoxia

The purpose of this study was to determine the effects of inspiratory muscle training (IMT) on exercise in hypoxia (H) and normoxia (N). A 4-week IMT program was implemented with 12 healthy subjects using an inspiratory muscle trainer set at either 15% (C; n = 5) or 50% (IMT; n = 7) maximal inspiratory mouth pressure (PImax). Two treadmill tests (85% V˙O2max) to exhaustion and measures of diaphragm thickness (Tdi) and function were completed before and after training in H and N. Significant increases of 8–12% and 24.5 ± 3.1% in Tdi and PImax, respectively, were seen in the IMT group. Time to exhaustion remained unchanged in all conditions. Inspiratory muscle fatigue (↓PImax) following exercise was reduced ∼10% (P < 0.05) in IMT after both N and H. During H, IMT reduced (P < 0.05) V˙O2 by 8–12%, cardiac output by 14 ± 2%, ventilation by 25 ± 3%; and increased arterial oxygen saturation by 4 ± 1% and lung diffusing capacity by 22 ± 3%. Ratings of perceived exertion and dyspnea were also significantly reduced. These data suggest that IMT significantly improves structural and functional physiologic measures in hypoxic exercise.