Effects of Same-Sided and Cross-Body Load Carrying on the Activity of the Upper Trapezius and Erector Spinae Muscles

Effects of Same-Sided and Cross-Body Load Carrying on the Activity of the Upper Trapezius and Erector Spinae Muscles

Background The preference of the bag varies according to age, shoulder bag is mostly used by adults. Shoulder bag can result in an asymmetrical load that has negative impacts on the body. Purpose The purpose of this study was to investigate the effects of same-sided and cross-body carrying on the activity of the upper trapezius and erector spinae muscles in standing position. Study design Controlled laboratory study, with a pretest-posttest design. Methods 20 healthy students were asked to carry the shoulder bag, placing it either on a shoulder on the same side of the body as the bag (same-sided load) or in cross-body fashion in standing position. We used surface electromyography to measure the activities of both upper trapezius and erector spinae muscles. We analyzed the data by using paired t-test and compared muscle activity in two methods. The alpha level was set at 0.05. Results The activity of the right upper trapezius and left erector spinae muscles differed significantly between the two carrying methods (p<0.05), showing significantly less activity under the cross-body condition. The activity of the left trapezius and right erector spinae muscles did not differ significantly between the two carrying methods (p>0.05). Conclusions We suggest that proper carrying method for shoulder bag is needed to help prevent musculoskeletal pain caused by asymmetrical muscle activity.