Endurance and Resistance Respiratory Muscle Training and Aerobic Exercise Performance in Hypobaric Hypoxia

INTRODUCTION: Hypoxia-induced hyperventilation is an effect of acute altitude exposure, which may lead to respiratory muscle fatigue and secondary locomotor muscle fatigue. The purpose of this study was to determine if resistive and/or endurance respiratory muscle training (RRMT and ERMT, respectively) vs. placebo respiratory muscle training (PRMT) improve cycling performance at altitude. METHODS: There were 24 subjects who were assigned to PRMT (N = 8), RRMT (N = 8), or ERMT (N = 8). Subjects cycled to exhaustion in a hypobaric chamber decompressed to 3657 m (12,000 ft) at an intensity of 55% sea level maximal oxygen consumption ((V) over dot(O2max)) before and after respiratory muscle training (RMT). Additionally, subjects completed a (V) over dot(O2max), pulmonary function, and respiratory endurance test (RET) before and after RMT. All RMT protocols consisted of three 30-min training sessions per week for 4 wk. RESULTS: The RRMT group increased maximum inspiratory (P-Imax) and expiratory (P-Emax) mouth pressure after RMT (P-Imax: 117.7 +/- 11.6 vs. 162.6 +/- 20.0; P-Emax: 164.0 +/- 33.2 vs. 216.5 +/- 44.1 cmH(2)O). The ERMT group increased RET after RMT (5.2 +/- 5.2 vs.18.6 +/- 16.9 min). RMT did not improve (V) over dot(O2max) in any group. Both RRMT and ERMT groups increased cycling time to exhaustion (RRMT: 35.9 +/- 17.2 vs. 45.6 +/- 22.2 min and ERMT: 33.8 +/- 9.6 vs. 42.9 +/- 27.0 min). CONCLUSION: Despite different improvements in pulmonary function, 4 wk of RRMT and ERMT both improved cycle time to exhaustion at altitude.