Effect of respiratory muscle training on maximum aerobic power in normoxia and hypoxia

To assess the effects of respiratory muscle training (RMT) on maximum oxygen uptake ((V) over dot(O2max)) in normoxia and hypoxia, 9 healthy males (age 24 +/- 4 years; stature 1.75 +/- 0.08 m; body mass 72 +/- 9 kg; mean +/- SD) performed on different days maximal incremental tests on a cycle ergometer in normoxia and normobaric hypoxia (FIo(2) = 0.11), before and after 8 weeks of RMT (5 days/week). During each test, gas exchange variables were measured breath-by-breath by a metabolimeter. After RMT, no changes in cardiorespiratory and metabolic variables were detected at maximal exercise in normoxia. On the contrary, in hypoxia expired and alveolar ventilation ((V) over dotE and (V) over dotA, respectively) at maximal exercise were significantly higher than pre-training condition (+12 and +13%, respectively; P<0.05). Accordingly, alveolar O(2) partial pressure (PAo(2)) after RMT significantly increased by similar to 10%. Nevertheless, arterial Po(2) and (V) over dot(O2max) did not change with respect to pre-training condition. In conclusion, RMT improved respiratory function but did not have any effect on (V) over dot(O2max), neither under normoxic nor hypoxic condition. In hypoxia, the significant increase in ((V) over dotE and (V) over dotA at maximum exercise after training lead to higher alveolar but not arterial Po(2) values, revealing an increased A-a gradient. This result, according to the theoretical models of (V) over dot(O2max), limitation, seems to contradict the lack of (V) over dot(O2max) increase in hypoxia, suggesting a possible role of increased ventilation-perfusion mismatch. (C) 2010 Elsevier B.V. All rights reserved.