Effects of respiratory muscle training versus placebo on endurance exercise performance.

We evaluated the effects of a 5 week (25 sessions); (30-35 min/day, 5 days/week), respiratory muscle training (RMT) program in nine competitive male cyclists. The experimental design included inspiratory resistance strength training (3-5 min/session) and hyperpnea endurance training (30 min/session), a placebo group which used a sham hypoxic trainer (n=8), and three exercise performance tests, including a highly reproducible 8 km time trial test. RMT intensity, measured once a week in terms of accumulated inspiratory pressure and the level of sustainable hyperpnea increased significantly after 5 weeks (+64% and +19%, respectively). The RMT group showed a significant 8% increase in maximal inspiratory pressure (P<0.05) while the placebo group showed only a 3.7% increase (P>0.10). RMT and placebo groups both showed significant increases in the fixed work-rate endurance test performance time (+26% and +16%, respectively) and in the peak work-rate achieved during the incremental maximal oxygen consumption (V(O2)max) test (+9 and +6%). The 8 km time trial performance increased 1.8+/-1.2% (or 15+/-10 sec; P<0.01) in the RMT group with 8 of 9 subjects increasing; the placebo group showed a variable non-significant change in 5 of 8 subjects (-0.3+/-2.7%, P=0.07). The changes observed in these three performance tests were not, however, significantly different between the RMT and placebo groups. Heart rate, ventilation, or venous blood lactate, at equal work-rates during the incremental exercise test or at equal times during the fixed work-rate endurance test were not changed significantly across these exercise trials in either group. We propose that the effect of RMT on exercise performance in highly trained cyclists does not exceed that in a placebo group. Significant placebo and test familiarization effects must be accounted for in experimental designs utilizing performance tests which are critically dependent on volitional effort.