Background — Recurrent upper airway obstruction during the sleep is a key feature of obstructive sleep apnea (OSA). In patients with OSA, an intermittent upper airway obstruction yields an increase in inspiratory effort and, consequently, an augmented impact on inspiratory muscles (IM). However, the issue of IM fatigue development in OSA patients is still controversial. Objective — to investigate the functional condition of IM in patients with OSA of various degrees of severity. Material and Methods — Were examined 82 men (30-65 years old), who were distributed among four groups depending on the OSA severity. Cardiorespiratory monitoring was performed to detect OSA. IM electrical activity was detected via surface electromyography (EMG) while holding the breath (during the inhalation). Results — In the course of our study, we detected a reduction in the frequency of EMG of accessory IM, specifically sternocleidomastoid muscle (SCMM) and external intercostal muscles (EIM), accompanied by a simultaneous increase in the amplitude of EMG of SCMM, EIM, and diaphragm (D), while holding the breath (during the inhalation), in the group of patients without OSA. In patients with mild OSA, when holding the breath during the inhalation, the frequency of EMG of SCMM and EIM decreased, while the amplitude of SCMM and EIM increased. In patients with moderate OSA, when holding the breath during the inhalation, a decrease in the frequency of SCMM EMG with a simultaneous increase in the amplitude of the EIM EMG were revealed. Same maneuver in the group of patients with severe OSA yielded no significant changes in the frequency and amplitude of EMG of respiratory muscles. Conclusion — Periodic obstruction of the upper airways with OSA leads to the development of fatigue resistance in accessory IM.