The Effect Of Inspiratory Muscle Training On Hypoxic Exercise

Abstract

The effect of inspiratory muscle training (IMT) on exercise performance remains unresolved. PURPOSE To determine if greater effects of IMT on exercise would occur in hypoxia where there is a greater pulmonary contribution compared to normoxia. METHODS Twelve healthy subjects (20 ±1 yrs) were randomly divided in an experimental group (IMT; n = 7) and a control group (C; n = 5). A 4-week IMT program was implemented using an inspiratory muscle trainer set at either 15% (C) or 50% (IMT) maximal inspiratory pressure (PImax). Two treadmill (85% VO2max) tests to exhaustion (F1O2: 0.21 (N); 0.14 (H)), and measures of respiratory muscle (RM) structure (diaphragm thickness via ultrasound; tdi) and function (PImax) were performed pre and post IMT. Breath by breath data was collected throughout exercise. Cardiac output (Q) and lung diffusing capacity (DLCO) were determined via single breath exhalation. RESULTS Significant increases of 8–12% and 25% in tdi and PImax, respectively, were seen in the IMT group but not in C. Time-to-exhaustion was not different between groups or training. RM fatigue (PImax) following exercise was reduced ∼10% (p < 0.05) in IMT after both N and H. During H, IMT reduced (p < 0.05) VO2 at min 3 (39.7±1.0 vs. 35.2±1.8 ml/kg/min) and 6 (41.6±1.0 vs. 38.6±1.0 ml/kg/ min), VE at min 3 (99.4±8.2 vs. 75.0±5.3 l/min), and increased SaO2 at min 3 (78.1±1.5 vs. 82.4±1.9%) and 6 (77.1±1.0 vs. 81.4±1.8%). At min 5, Q (16.0±2.3 vs. 13.9±1.8 l/min), RPE and dyspnea ratings were reduced (p < 0.05) and lung diffusing capacity (DLCO) significantly increased (42.6±1.5 vs. 52.0±5.1 ml/min/mmHg) in H with IMT. No changes (p > 0.05) during exercise were seen in C. CONCLUSIONS These data suggest that IMT leads to significant hypertrophy of the diaphragm, increased RM strength, reduced ventilatory demand and RM fatigue, and improved gas exchange and subject perception of effort during heavy exercise in hypoxia. Supported by Howard Hughes Medical Institute and American Lung Association RG-039-N