Inspiratory muscle fatigue in trained cyclists: effects of inspiratory muscle training

This study evaluated the influence of simulated 20- and 40-km time trials upon postexercise inspiratory muscle function of trained competitive cyclists. In addition, we examined the influence of specific inspiratory muscle training (IMT) upon the responses observed.

Using a double-blind placebo-controlled design, 16 male cyclists (mean +/- SEM VO2max 64 +/- 2 mL.kg-1.min-1) were assigned randomly to either an experimental (IMT) or sham-training control (placebo) group. Maximum static and dynamic inspiratory muscle function was assessed immediately pre- and <2, 10, and 30 min post-simulated 20- and 40-km time trials before and after 6-wk of IMT or sham-IMT.

Maximum inspiratory mouth pressure (P0) measured within 2 min of completing the 20- and 40-km time trial rides was reduced by 18% and 13%, respectively, and remained below preexercise values at 30 min. The 20- and 40-km time trials induced a reduction in inspiratory flow rate at 30% P0 by 14% and 6% in the IMT group versus 13% and 7% for the placebo group, and also remained below preexercise values at 30 min. There was also a significant slowing of inspiratory muscle relaxation rate postexercise; these trends were almost completely reversed by 30 min postexercise. Significant improvements in 20- and 40-km time trial performance were seen (3.8 +/- 1.7% and 4.6 +/- 1.9%, respectively; P < 0.05) and postexercise reductions in muscle function were attenuated with IMT.

These data support existing evidence that there is significant global inspiratory muscle fatigue after sustained heavy endurance exercise. Furthermore, the present study provides new evidence that performance enhancements observed after IMT are accompanied by a decrease in inspiratory muscle fatigue.