Siu A, Schinkel-Ivy A, Drake JD. Arm position influences the activation patterns of trunk muscles during trunk range-of-motion movements. Hum Mov Sci. 2016 Oct;49:267-76.
To understand the activation patterns of the trunk musculature during movement, it is important to consider the adjacent structures such as the arms and the muscles that act to move them. This study investigated the effects of arm positions on the activation patterns between the trunk musculature and upper back muscles that move the arm during trunk range-of-motion movements. Muscle activation data from six trunk muscles and two upper back muscles (latissimus dorsi and upper trapezius) were collected on 30 healthy young adults while performing three maximum trunk movements (trunk twisting, flexion, and side bend) with different arm positions (crossed and hanging loose for all movements, plus straight out to the side for axial twist). Results revealed greater muscle co-activation between the trunk musculature and upper trapezius when the arms were held out to the side during trunk twisting, suggesting increased synergy between the trunk musculature and upper trapezius. The effect of arm position on the relationships between trunk muscles and latissimus dorsi varied depending on the specific trunk muscles (either abdominal or back), the latissimus dorsi muscle (either right or left side), and the trunk movement. The findings highlight the influence of arm position on trunk musculature during movement in a healthy population asymptomatic for back pain. Future work comparing these results to those of individuals with back or shoulder conditions may help to identify factors contributing to those conditions.