Differential effects of exercise intensity and tolerable duration on exercise-induced diaphragm and expiratory muscle fatigue.

ABSTRACT

We investigated the effect of exercise intensity and tolerable duration on the development of exercise-induced diaphragm and expiratory muscle fatigue. Ten healthy adults (25 ± 5 yr; 2 females) cycled to intolerance on three separate occasions 1) 5% below critical power (ramp-incremental power (Δ25; severe intensity "longer"); and 3) ∼50% Δ (Δ50; severe intensity "shorter"). Diaphragm and expiratory muscle fatigue were quantified as a pre- to 5 min postexercise reduction in magnetically evoked transdiaphragmatic (Pditw) and gastric (Pgatw) twitch pressures, respectively. Exercise time was 34.5 ± 6.2 min, 10.2 ± 2.6 min, and 4.9 ± 0.7 min for Oxygen uptake (V̇o2) at end-exercise was lower during 0.05). In conclusion, the magnitude of exercise-induced diaphragm fatigue was greater after longer-duration severe exercise than after shorter-duration severe and heavy exercise. By contrast, the magnitude of exercise-induced expiratory muscle fatigue was unaffected by exercise intensity and tolerable duration.NEW & NOTEWORTHY Exercise-induced respiratory muscle fatigue contributes to limiting exercise tolerance. Accordingly, better understanding the exercise conditions under which respiratory muscle fatigue occurs is warranted. Although heavy-intensity as well as short- and long-duration severe-intensity exercise performed to intolerance elicit diaphragm and expiratory muscle fatigue, we find, for the first time, that the relationship between exercise intensity, exercise duration, and the magnitude of exercise-induced fatigue is different for the diaphragm compared with the expiratory muscles.