An investigation of the surface electromyograms spatial distribution of the pectoralis major muscle during flat and inclined bench press exercises

Abstract

For the first study we use high-density surface electromyography (HD-EMG) to investigate the location of the innervation zone (IZ) on the pectoralis major muscle (PM) and how it displaces during bench press (BP) exercise. Eleven participants performed isometric BP at two conditions: elbow joint flexed at 100° and at 0°. Electromyograms (EMGs) were detected with a dry array of 16 electrodes parallel to the PM fibres. Shifts in IZ position ranged from 0.5 cm to 3.5 cm across all subjects over the detection sites. For the second study, we investigated the distribution of PM activity during the flat and inclined (45°) BP. Seven individuals performed two sets of flat BP and two sets of inclined BP. They used two different load levels, 70% of their one maximum repetition load (1MR) to perform 8 repetitions and 50% of 1MR for 15 repetitions. EMGs activity was recorded with an array of 16 electrodes placed parallel to the sternum and between IZ and PM tendon region. For each contraction, the root mean square (RMS) value was computed. Additionally, active channels were defined as EMGs with RMS amplitude greater than 70% of the maximum amplitude for each contraction. Considering the active channels, the barycentre coordinates were calculated indicating the mean position of the RMS distribution along cranio-caudal axis of PM. For all the volunteers, we identified for the inclined BP that the barycentre was located near to the clavicular region, and for the flat BP it was near to the sternocostal region.