Respiratory muscle training increases cycling endurance without affecting cardiovascular responses to exercise

We tested whether the increased cycling endurance observed after respirator y muscle training (RMT) in healthy sedentary humans was associated with a t raining-induced increase in cardiac stroke volume (SV) during exercise, sim ilar to the known effect of endurance training. Thirteen subjects underwent RMT by normocapnic hyperpnea, nine underwent aerobic endurance training (c ycling and/or running) and fifteen served as non-training controls. Trainin g comprised 40 sessions performed within 15 weeks, where each session laste d 30 min. RMT increased. cycling endurance at 70% maximal aerobic power ((W )over dot(max)) by 24% [mean (SD) 35.6 (11.9) min vs 44.2 (17.6) min, P<0.0 5], but SV at 60% (W)over dot(max), was unchanged [94 (21) ml vs 93 (20) ml ]. Aerobic endurance training increased both SV [89 (24) ml vs 104 (32) ml, P<0.01] and cycling endurance [37.4 (12.8) min vs 52.6 (16.9) min, P<0.01] . In the control group, no changes were observed in any of these variables. It is concluded that the increased cycling endurance that is observed afte r RMT is not due to cardiovascular adaptations, and that the results provid e evidence for the role of the respiratory system as an exercise-limiting f actor.