Chadwick, Matt R.

During severe exercise, expiratory and inspiratory muscle fatigue develops by ∼50% of the tolerable exercise duration. The magnitude of expiratory and inspiratory muscle fatigue increases progressively toward exercise intolerance but is not different between muscle groups; this is despite the expiratory muscles being less fatigue-resistant. Inspecting esophageal and gastric twitches via cervical stimulation, we speculate that the progressive magnitude of exercise-induced inspiratory muscle fatigue is a function of recruitment and fatigue of the accessory inspiratory muscles.

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.