Effect of Expiratory Muscle Fatigue on the Respiratory Response during Exercise

[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.