Source: Annual Congress 2007 - Pathophysiology of respiratory muscles
Disease area: Airway diseases

Abstract

High-intensity (≥90% VO_2max) sustained exercise elicits expiratory muscle fatigue (EMF). We asked whether prior EMF affects subsequent exercise performance. Eight male subjects cycled at ≥90% VO_2max to the limit of tolerance with (EMF-EX) and without (CON-EX) prior induction of EMF. The subjects also exercised for a time equal to that achieved in EMF-EX 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). Abdominal and quadriceps muscle function were assessed before and after exercise by measuring the changes in gastric twitch pressure (P_ga,tw) and quadriceps twitch force (Q_tw), respectively, in response to magnetic stimulation of the nerve roots supplying these muscles. EMF was not different after expiratory loading vs. after CON-EX (–27±13% vs. –26±6%; P>0.05). Exercise time was reduced by 33±10% in EMF-EX vs. CON-EX (411±176 s vs. 594±173 s; P<0.001). Exercise-induced abdominal and quadriceps muscle fatigue were greater after EMF-EX vs. ISO-EX (–28±12% vs. –12±9% for P_ga,tw, P=0.001; –28±14% vs. –14±8% for Q_tw, P=0.015). Perceptions of dyspnoea and leg discomfort were higher throughout EMF-EX vs. ISO-EX. Multiple regression analysis showed that 76% of the variance in exercise time after induction of EMF was accounted for by the exacerbation of quadriceps muscle fatigue and the heightened sense of leg discomfort. We propose that EMF plays a role in determining exercise performance both through its direct effect on locomotor muscle fatigue and through its indirect effect on effort perceptions.

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Citations should be made in the following way:
B. Taylor, L. Romer (London, United Kingdom). Expiratory muscle fatigue exacerbates exercise-induced locomotor muscle fatigue and impairs exercise performance. Eur Respir J 2007; 30: Suppl. 51, 3147

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