Respiratory muscle endurance training in humans increases cycling endurance without affecting blood gas concentrations

Abstract.

Isolated respiratory muscle endurance training (RMT) can prolong constant-intensity cycling performance. We tested whether RMT affects O₂ supply during exercise, i.e. whether the partial pressure of oxygen in arterial blood (P _aO₂) and/or its oxygen saturation (S _aO₂) are higher during exercise after RMT than before. A group of 28 sedentary subjects were randomly assigned to either an RMT (n=13) or a control group (n=15). The RMT consisted of 40×30 min sessions of normocapnic hyperpnoea. The control group did not perform any training. Breathing and cycling endurance time as well as P _aO₂ and S _aO₂ during cycling at a constant intensity of 70% maximum power output were measured before and after the RMT or the control period. Mean breathing endurance increased significantly after RMT compared to control [RMT 5.2 (SD 2.9) vs 38.1 (SD 6.8) min, control 6.5 (SD 5.7) vs 6.4 (SD 7.6) min; P<0.01], as did mean cycling endurance [RMT 35.6 (SD 11.9) vs 44.0 (SD 17.2) min, control 32.8 (SD 11.6) vs 31.4 (SD 14.4) min; P<0.05]. The RMT did not affect P _aO₂ which ranged from 11.6 to 12.3 kPa (87–92 mmHg), and S _aO₂ which ranged from 96% to 98% throughout all tests. In conclusion, RMT substantially increased breathing and cycling endurance in sedentary subjects. These changes, however, cannot be attributed to increased O₂ supply, as neither P _aO₂ nor S _aO₂ were increased during exercise after RMT.