Standard bipolar surface EMG estimations mischaracterize pectoralis major activity in commonly performed tasks

The pectoralis major assists in several shoulder movements, such as humeral vertical and horizontal adduction, flexion, extension, and internal rotation. Despite its involvement in numerous functional activities, its role in typical shoulder function is ambiguous. Due to this, its purpose in arm movement is largely diminished. However, mounting evidence associates pectoralis major injuries to long-term debilitating arm disability. Therefore, a more deliberate investigation of its role in typical shoulder function is paramount. The purpose of this paper is to outline the current limitations in the acquisition and characterization of pectoralis major activation using standard bipolar surface electromyography. Macroscopic level analyses are used to investigate pectoralis major activation in eight tasks at low (15-25% of maximal voluntary effort (MVE) and moderate (50% MVE) efforts in healthy males. Virtually derived bipolar EMG amplitudes are quantified for the clavicular and the upper sternocostal regions based on the common locations used to acquire EMG signals from classic EMG. HD-sEMG amplitudes from three pectoralis major regions (i.e. clavicular, upper, and lower sternocostal) were compared to virtually derived bipolar EMG amplitudes (i.e. clavicular and upper sternocostal) to determine if current EMG methods misestimate pectoralis major activity. Current findings indicate that classic EMG recordings mischaracterize pectoralis major activation in several tasks and effort levels, highlighting the importance of acquiring signals from multiple pectoralis major regions.