Electromyographic activity and coordination of accessory respiratory muscles during increased breathing effort in...

Intensified inspiration and expiration require recruitment of accessory respiratory muscles, whose activity is essential for generating appropriate pressure changes and ensuring efficient ventilation. The aim of this study was to evaluate their surface activity (sEMG) and analyze bilateral symmetry and coordination in healthy individuals during maximal inspiratory (PImax) and expiratory (PEmax) pressure maneuvers. Thirty healthy volunteers (mean age 49 ± 12 years) participated in the study. sEMG activity was recorded from the sternocleidomastoid (SCM), scalene (SCA), and external oblique abdominal (EOA) muscles. Signals were normalized to maximal voluntary contraction (%MVC). Bilateral symmetry and agonist-antagonist activity ratios were assessed. High bilateral symmetry was observed for all examined muscles (p > 0.05 for all R/L pairs). The greatest activity was noted for the EOA during forced expiration, reaching 100.74% MVC, whereas SCM and SCA exhibited peak activity during inspiration (53.23% MVC and 40.18% MVC, respectively). Coordination analysis revealed significant agonist dominance; however, the EOA maintained relatively higher activity during the antagonist phase (inspiration) compared to neck muscles during expiration. No significant correlations were found between PImax/PEmax values and sEMG activity of the accessory muscles. In healthy individuals, accessory respiratory muscles function with high bilateral symmetry. The EOA is a key force generator during forced expiration, likely contributing to trunk stabilization. The absence of a relationship between sEMG activity and generated pressure suggests that inspiratory and expiratory force in healthy subjects depends on mechanisms more complex than mere recruitment of accessory muscle motor units.