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Effects of respiratory muscle fatigue on exercise performance in healthy females Shoemaker, Andrea Paula

Abstract

The respiratory system has not been traditionally considered a limiting factor in exercise performance however, several studies have demonstrated that respiratory muscle fatigue (RMF) occurs following high-intensity exercise as well as prolonged submaximal exercise. In order to investigate RMF as a limiting factor in exercise performance fatigue was induced in ten healthy female participants (Age = 26.8 ± 2.0 yrs; height = 165.7 ± 4.5 cm; weight = 57.3 ± 7.6 kg; VO2 max 43.3 ± 4.7 mL-kg-1 min-1, range 35.8 to 49.5 mL-kg-1-min-1). Subjects were required to visit the lab on six separate occasions. Three test days served as control conditions where RMF was not induced and baseline measures of spirometry and exercise performance were measured. On the remaining three test days, RMF was induced and the subsequent effects on exercise performance were measured. Maximal test of aerobic capacity was performed on two of the six test days and on the remaining 4 test days participants performed tests of endurance performance. Subjects were instructed to breathe at 70% of their maximal voluntary ventilation (MVV) for 15-minutes to induce RMF. Following induction of RMF exercise performance was measured on an electronically braked cycle ergometer. Ventilation during the hyperpnea task equaled 72 to 75% MVV on the three days that RMF was induced. The induction of RMF did not significantly alter maximal aerobic power (p = 0.111), although, exercise was ceased at a significantly lower peak heart rate (p = 0.002) and peak minute ventilation (p = 0.013). Ratings of perceived exertion for the respiratory muscles muscles were significantly increased following the induction of RMF (p = 0.003). Endurance performance (time to exhaustion) was reduced from 408.0 ± 84.9 seconds to 320.3 ± 71.5 seconds following the induction of RMF (p = 0.002) without any associated changes in VO2, heart rate, or minute ventilation. The reduction seen in endurance performance time supports the hypothesis that a decreased time to exhaustion is seen with the induction of RMF. Maximal oxygen consumption did not decrease and therefore cannot support the hypothesis that VO2max will be reduced following RMF induction. Respiratory muscle fatigue appears to be a limiting factor in exercise performance in healthy females.

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