Differential regional pectoralis major activation indicates functional diversity in healthy females

Pectoralis major activation enables the performance of several upper extremity movements. Its regional activation, however, is not documented in healthy females. This work used high-density surface electromyography to investigate regional pectoralis major activation in twenty-nine healthy young females across two independent experiments in several ramp and hold isometric tasks and force levels. Regional mean root mean square amplitudes (normalized to the task-specific maxima) were quantified for the clavicular, superior, and middle sternocostal regions. Two-way ANOVAs were used to determine if differences in normalized regional activation exist within each task and force level. The middle sternocostal region activated 12-108% more than the clavicular and the superior sternocostal region in extension, adduction with external rotation, and high elevation internal rotation. In high elevation adduction, the middle sternocostal region activated more (7-22%) than the superior sternocostal region. In low elevation, internal rotation (60°), the clavicular and middle sternocostal regions activated more (9-13%) than the superior sternocostal region, while in adduction 60°, the clavicular region activated 9-19% more than the superior sternocostal region. Lastly, in forward and horizontal flexion, all three regions activated similarly irrespective of the force level, except at 25% MVF in forward flexion, where the clavicular region activated 21% more than the superior sternocostal region. This work provides a first comprehensive evaluation of the normalized regional pectoralis major activation in healthy females. The present findings indicate that the performance of isometric tasks in different directions activates different pectoralis major regions in healthy females, suggesting regional specificity to functional actions.