Effect of Expiratory Muscle Fatigue on the Respiratory Response during Exercise

Abstract

[Purpose] The aim of this study was to reveal the effect of expiratory muscle fatigue (EMF) on respiratory response under two different exercise conditions: exercise (EX) with EMF (EMF-EX) and control EX without EMF (CON-EX). [Methods] Nine healthy adult men performed cycle exercise with a ramp load, and a spirometer was used to measure forced vital capacity (FVC), forced expiratory volume in one second, percent of forced expiratory volume, maximal expiratory mouth pressure, and maximal inspiratory mouth pressure (PI_max) to evaluate respiratory functions immediately and at 15 and 30 min after exercise. To assess the respiratory response during exercise, an exhaled gas analyzer was used to measure minute ventilation (V_E), respiratory frequency (f), tidal volume (V_T), oxygen uptake, and carbon dioxide output. In addition, the Borg Scale was used to evaluate dyspnea, while electrocardiography was used to measure heart rate. [Results] The results showed that compared with the CON-EX condition, no change in V_E, an increase in f, or a decrease in V_T was observed under the medium-intensity EMF-EX condition, while high-intensity exercise reduced V_E and f without changing V_T. [Conclusion] These results suggest that during medium-intensity exercise, EMF modulates the respiratory response by inducing shallow and fast breathing to increase ventilation volume.