Motor unit involvement in scalene, strenocleidomastoid, and rectus abdominis muscles during eupnea, tachypnea, and bradypnea of sedentary young male adults: an observational study

Background: It is well-established that extra-diaphragmatic muscles participate in respiration depending on the physiological situation. Even in clinical conditions where the diaphragm cannot act optimally, extra-diaphragmatic muscles can compensate for the breathing mechanics. Aim of the study: This study aims to determine the role of motor units in various respiratory conditions by monitoring the motor unit discharge in the scalene, sternocleidomastoid, and rectus abdominis during eupnea, tachypnea, and bradypnea using surface electromyography (sEMG). Material and methods: In this study, 28 healthy, sedentary males without a history of ailments participated. Using sEMG, the motor unit discharges from the scalene, sternocleidomastoid, and rectus abdominis were measured in three breathing patterns: normal breathing, hyperventilation, and intermittent breath retention. Results: The motor unit discharges of the rectus abdominis during eupnea, bradypnea, and tachypnea were significantly different, indicating that only the rectus abdominis' motor units were actively involved. Rectus abdominis muscle experienced changes in motor unit discharges that were highest and lowest during tachypnea and bradypnea, respectively [p<0.05]. Conclusions: This study has tried to evaluate the role of the motor units of three extra-diaphragmatic muscles in healthy sedentary young male adults with different respiratory conditions. This study has revealed that the rectus abdominis actively participates in the physiological conditions in young, sedentary healthy adult males. In scalene and sternocleidomastoid, active involvement of the motor unit has not been observed.