Effect of inspiratory muscle-loaded exercise training on peak oxygen uptake and ventilatory response during incremental exercise under normoxia and hypoxia

Background Although numerous studies have reported the effect of inspiratory muscle training for improving exercise performance, the outcome of whether exercise performance is improved by inspiratory muscle training is controversial. Therefore, this study investigated the influence of inspiratory muscle-loaded exercise training (IMLET) on peak oxygen uptake (VO2peak), respiratory responses, and exercise performance under normoxic (N) and hypoxic (H) exercise conditions. We hypothesised that IMLET enhances respiratory muscle strength and improves respiratory response, thereby improving VO2peak and work capacity under H condition. Methods Sixteen university track runners (13 men and 3 women) were randomly assigned to the IMLET (n = 8) or exercise training (ET) group (n = 8). All subjects underwent 4 weeks of 20-min 60% VO2peak cycling exercise training, thrice per week. IMLET loaded 50% of maximal inspiratory pressure during exercise. At pre- and post-training periods, subjects performed exhaustive incremental cycling under normoxic (N; 20.9 +/- 0%) and hypoxic (H; 15.0 +/- 0.1%) conditions. Results Although maximal inspiratory pressure (PImax) significantly increased after training in both groups, the extent of PImax increase was significantly higher in the IMLET group (from 102 +/- 20 to 145 +/- 26 cmH(2)O in IMLET; from 111 +/- 23 to 127 +/- 23 cmH(2)O in ET; P < 0.05). In both groups, VO2peak and maximal work load (W-max) similarly increased both under N and H conditions after training (P < 0.05). Further, the extent of W-max decrease under H condition was lower in the IMLET group at post-training test than at pre-training (from - 14.7 +/- 2.2% to - 12.5 +/- 1.7%; P < 0.05). Maximal minute ventilation in both N and H conditions increased after training than in the pre-training period. Conclusions Our IMLET enhanced the respiratory muscle strength, and the decrease in work capacity under hypoxia was reduced regardless of the increase in VO2peak.