INSPIRATORY MUSCLE TRAINING AND ENDURANCE PERFORMANCE IN HYPOXIA

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2017-04

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Ventilation is higher at any submaximal workload in hypoxia as compared to normoxia. Whether or not training the respiratory muscles helps to improve exercise performance in hypoxia is unclear. Purpose: To determine if improvements in ventilatory strength with chronic inspiratory muscle training (IMT) improves 20km cycling time trial (TT) performance in hypoxia (FIO2 = 16.1%). Methods: Thirteen highly-trained men were pair-matched based on pre-exercise values of maximal inspiratory pressure (MIP) and randomly placed into either a sham (n = 5, V̇O2max = 61.7 ± 2.0 ml∙kg-1∙min-1) or an IMT (n = 8, V̇O2max = 63.5 ± 3.4 ml∙kg-1∙min-1) group. Subjects completed 6 weeks of flow resistive IMT (80% of MIP) or a sham protocol (30% of MIP), with each session consisting of up to 6 sets of 6 MIP maneuvers performed to failure with descending rest intervals 3 times per week. Pre- and post-training, subjects performed tests of pulmonary function, lung volume, MIP, maximal expiratory pressure (MEP), lung diffusion capacity (DLCO), and a 20km cycling TT in hypoxia (FIO2 = 16.1%). Results: After 6 weeks of IMT or sham, the IMT group significantly improved MIP (127.6 ± 13.4 cmH2O vs 159.0 ± 15.3 cmH2O, p < 0.05), while MIP in the sham group remained unchanged. MEP, DLCO, lung volumes, and pulmonary function values remained unchanged in both groups post-training. 20km TT mean ventilation was significantly higher post-IMT (99.6 ± 5.5 l∙min-1 vs 110.4 ± 6.8 l∙min-1, p < 0.05) and unchanged in sham. 20km TT mean breathing frequency was also significantly increased post-IMT (41.4 ± 2.8 b∙min-1 vs 45.1 ± 2.9 b∙min-1, p < 0.05) and unchanged in sham. 20km TT mean V̇O2 was significantly increased post-IMT (3.41 ± 0.19 L∙min-1 vs 3.61 ± 0.21 L∙min-1) and unchanged in sham. In the IMT group, 20km TT performance time pre-training was 36.77 ± 1.40 (min) and post-training was 36.28 ± 1.24 (min) (-1.4 ± 1.9%, p = 0.06). 20km TT performance time was unchanged in the sham group. 20km TT heart rate and SpO2 were unchanged in both groups post-training. Conclusion: In a small cohort, IMT-induced improvements in respiratory muscle strength which resulted in greater ventilation and oxygen uptake during a 20km time trial in hypoxia. IMT should be explored as a useful strategy for improving the quality of cycle exercise training and/or endurance exercise performance at altitude.

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