Expiratory muscle fatigue impairs exercise performance

High-intensity, exhaustive exercise may lead to inspiratory as well as expiratory muscle fatigue (EMF). Induction of inspiratory muscle fatigue (IMF) before exercise has been shown to impair subsequent exercise performance. The purpose of the present study was to determine whether induction of EMF also affects subsequent exercise performance. Twelve healthy young men performed five 12-min running tests on a 400-m track on separate days: a preliminary trial, two trials after induction of EMF, and two trials without prior muscle fatigue. Tests with and without prior EMF were performed in an alternate order, randomly starting with either type. EMF was defined as a >= 20% drop in maximal expiratory mouth pressure achieved during expiratory resistive breathing against 50% maximal expiratory mouth pressure. The average distance covered in 12 min was significantly smaller during exercise with prior EMF compared to control exercise (2872 +/- 256 vs. 2957 +/- 325 m; P = 0.002). Running speed was consistently lower (0.13 m s(-1))throughout the entire 12 min of exercise with prior EMF. A significant correlation was observed between the level of EMF (decrement in maximal expiratory mouth pressure after resistive breathing) and the reduction in running distance (r(2) = 0.528, P = 0.007). Perceived respiratory exertion was higher during the first 800 m and heart rate was lower throughout the entire test of running with prior EMF compared to control exercise (5.3 +/- 1.6 vs. 4.5 +/- 1.7 points, P = 0.002; 173 +/- 10 vs. 178 +/- 7 beats min(-1), P = 0.005). We conclude that EMF impairs exercise performance as previously reported for IMF.