Effect of Expiratory Muscle Training on Respiratory Muscle Fatigue in Healthy Adults: a Randomized Controlled Trial

[Purpose] This study examined the effects of expiratory muscle training on fatigue in individual respiratory muscles. [Participants and Methods] Healthy adult males (n=31) were randomly assigned to two groups: expiratory muscle training (n=15) and normal controls (n=16). In the expiratory muscle training group, training was performed once for 15 min at 50% load of the maximum expiratory mouth pressure twice daily for 4 weeks. Respiratory muscle fatigue indicators were measured using surface electromyography as the median power frequency of each respiratory muscle at the time of measuring the maximum inspiratory mouth pressure during 20 min of inspiratory muscle loading and maximum expiratory mouth pressure. [Results] In the expiratory muscle training group, the median power frequency values of the sternocleidomastoid, rectus abdominis, and internal oblique/external oblique before expiratory muscle training significantly decreased during inspiratory muscle loading. However, no difference was observed in the median power frequency values measured before and during inspiratory muscle loading after the expiratory muscle training. In the normal controls, the median power frequency values of the sternocleidomastoid and rectus abdominis significantly decreased during inspiratory muscle loading. [Conclusion] Expiratory muscle training increased fatigue tolerance of the sternocleidomastoid, rectus abdominis, and internal and external oblique muscles in healthy individuals.