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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 (tw) 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 2) at end-exercise was lower during 2peak) relative to Δ25 (97 ± 4% V̇ o 2peak) and Δ50 (99 ± 4% V̇ o 2peak) (P < 0.001). The pre- to postexercise decrease in Pditw was greater after Δ25 (−22 ± 12%) versus tw from pre- to postexercise was not different between trials ( 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. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "The Two-Hour Marathon: Who and When?" by M. J. Joyner and colleagues.