Purpose We hypothesized that respiratory muscle endurance training (RMET) in hypoxia induces greater improvements in respiratory muscle endurance with attenuated respiratory muscle metaboreflex and consequent whole-body performance. We evaluated respiratory muscle endurance and cardiovascular response during hyperpnoea and whole-body running performance before and after RMET in normoxia and hypoxia. Methods Twenty-one collegiate endurance runners were assigned to control (n = 7), normoxic (n = 7), and hypoxic (n = 7) groups. Before and after the 6 wk of RMET, incremental respiratory endurance test and constant exercise tests were performed. The constant exercise test was performed on a treadmill at 95% of the individual`s peak oxygen uptake (V.O2peak). The RMET was isocapnic hyperpnoea under normoxic and hypoxic conditions (30 min/d). The initial target of minute ventilation during RMET was set to 50% of the individual maximal voluntary ventilation, and the target increased progressively during the 6 wk. Target arterial oxygen saturation in the hypoxic group was set to 90% in the first 2 wk, and thereafter it was set to 80%. Results Respiratory muscle endurance was increased after RMET in the normoxic and hypoxic groups. The time to exhaustion at 95% V.O2peak exercise also increased after RMET in the normoxic (10.2 ± 2.4 to 11.2 ± 2.6 min) and hypoxic (11.5 ± 2.6 to 12.6 ± 3.0 min) groups, but not in the control group (9.6 ± 3.2 to 9.4 ± 4.0 min). The magnitude of these changes did not differ between the normoxic and the hypoxic groups (P = 0.84). Conclusion These results suggest that the improvement of respiratory muscle endurance and blunted respiratory muscle metaboreflex could, in part, contribute to improved endurance performance in endurance-trained athletes. However, it is also suggested that there are no additional effects when the RMET is performed in hypoxia.
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