Abstract
[Purpose] To investigate accessory respiratory muscle fatigue caused by expiratory load and its effects on accessory respiratory muscles during expiratory load. [Subjects] Eleven healthy adult males. [Methods] Maximum mouth pressures (PEmax, PImax) were measured during expiratory load and rest, and the trapezius, sternocleidomastoid, pectoralis major, rectus abdominis, and internal and external oblique abdominal muscle activities were assessed using electromyographic frequency analysis. [Results] The ratio of high to low frequency components of accessory respiratory muscle activity decreased by ≥20% in all muscles over 8 min. Furthermore, the time taken to reach the minimum PEmax was significantly greater for the external oblique than for the rectus abdominis, and the time taken to reach the minimum PImax was significantly longer for the sternocleidomastoid than for the external oblique. [Conclusions] The times taken to reach accessory respiratory muscle fatigue showed no differences, suggesting that expiration and inspiration barely fatigue the external oblique and sternocleidomastoid muscles, respectively.
