Abstract
The purpose of this study was to illustrate the actions of the gluteus maximus (GM), medial hamstrings (MH), and lateral hamstrings (LH) during forward-reaching in a sitting position using electromyography (EMG). We found that as the distance of forward-reaching increased, EMG activity of the GM, MH, and LH muscles increased to maintain forward-bending of the trunk. In addition, lower GM activation increased at a shorter reaching distance than the upper GM. From the analysis of posture during this task, we also found that the distance covered during forward-reaching was increased by up to 15 cm mainly through flexion of the thoracic spine. This mechanism enhances the distance of forward-reaching achieved by flexion of the hip joint, but extension of the lumbar spine. From these results, we suggest that forward reaching is not simply caused by flexion of the hip joint and that each fiber of GM, MH, and LH muscles has a different function in the sequence of activities that leads to a change in posture.
