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This Article Full Text Full Text (PDF) All Versions of this Article: 104/5/1442    most recent 00428.2007v1 Submit a response View responses Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Taylor, B. J. Articles by Romer, L. M. PubMed PubMed Citation Articles by Taylor, B. J. Articles by Romer, L. M.

Effect of expiratory muscle fatigue on exercise tolerance and locomotor muscle fatigue in healthy humans

Centre for Sports Medicine and Human Performance, School of Sport and Education, Brunel University, Uxbridge, United Kingdom

Submitted 19 April 2007 ; accepted in final form 3 March 2008

High-intensity exercise (90% of maximal O₂ uptake) sustained to the limit of tolerance elicits expiratory muscle fatigue (EMF). We asked whether prior EMF affects subsequent exercise tolerance. Eight male subjects (means ± SD; maximal O₂ uptake = 53.5 ± 5.2 ml·kg^–1·min^–1) cycled at 90% of peak power output to the limit of tolerance with (EMF-EX) and without (CON-EX) prior induction of EMF and for a time equal to that achieved in EMF-EX but without prior induction of EMF (ISO-EX). To induce EMF, subjects breathed against an expiratory flow resistor until task failure (15 breaths/min, 0.7 expiratory duty cycle, 40% of maximal expiratory gastric pressure). Fatigue of abdominal and quadriceps muscles was assessed by measuring the reduction relative to prior baseline values in magnetically evoked gastric twitch pressure (Pga_tw) and quadriceps twitch force (Q_tw), respectively. The reduction in Pga_tw was not different after resistive breathing vs. after CON-EX (–27 ± 5 vs. –26 ± 6%; P = 0.127). Exercise time was reduced by 33 ± 10% in EMF-EX vs. CON-EX (6.85 ± 2.88 vs. 9.90 ± 2.94 min; P < 0.001). Exercise-induced abdominal and quadriceps muscle fatigue was greater after EMF-EX than after ISO-EX (–28 ± 9 vs. –12 ± 5% for Pga_tw, P = 0.001; –28 ± 7 vs. –14 ± 6% for Q_tw, P = 0.015). Perceptual ratings of dyspnea and leg discomfort (Borg CR10) were higher at 1 and 3 min and at end exercise during EMF-EX vs. during ISO-EX (P < 0.05). Percent changes in limb fatigue and leg discomfort (EMF-EX vs. ISO-EX) correlated significantly with the change in exercise time. We propose that EMF impaired subsequent exercise tolerance primarily through an increased severity of limb locomotor muscle fatigue and a heightened perception of leg discomfort.

abdominal muscle fatigue; quadriceps muscle fatigue; dyspnea; leg discomfort; exercise performance