[Purpose] Considering that respiratory muscle fatigue is a cause of respiratory failure, we aimed to clarify the characteristics of respiratory muscle fatigue under inhalation load and investigate its impact on individual respiratory muscles. [Participants and Methods] The study included 14 healthy adult male volunteers. Maximal inspiratory and expiratory mouth pressures were measured under inhalation load and while at rest. The statuses of the trapezius, sternocleidomastoid, pectoralis major, diaphragm, rectus abdominis, and external and internal abdominal oblique muscles were also assessed using electromyographic frequency analysis. [Results] The maximal inspiratory and expiratory mouth pressures decreased over time and recovered after rest. The median power frequency decreased significantly in the sternocleidomastoid and rectus abdominis muscles at maximal inspiratory and expiratory mouth pressures, respectively, under inhalation load. [Conclusion] As a characteristic of respiratory muscle fatigue, there is a possibility that decreases in maximal inspiratory and expiratory mouth pressures as a result of the inhalation load affect muscle fatigue in the sternocleidomastoid and rectus abdominis muscles.
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