Introduction: The aim of present study was to determine the effect of biofeedback training on electrical activity of trapezius muscles and range of motion in people with shoulder impingement syndrome. Martials and Methods: In this study, 20 patients with shoulder impingement syndrome in age range of 20-40 y were selected as the statistical sample and were divided into experimental (n=10) and control (n=10) groups. The experimental group trained by using EMG biofeedback for 8 weeks and 3 sessions per week. The control group was applied only for pre-test and posttest measurements. For data collection, surface electromyography was used to analyze the muscle activity patterns of trapezius muscles (upper, middle, lower), and a goniometer was executed to evaluate the flexion. Shapiro-Wilk test was used to confirm the normality of the data and covariance analysis test was applied to compare pre-test and post-test. Correlated t-test was used to examine within-group changes. Results: In this study, after 8 weeks of biofeedback training in the experimental group, a significant improvement in the electrical activity of the middle trapezius (P=0.000) and lower trapezius muscles (P=0.016) was observed. In addition, a significant improvement in the amount of flexion range of motion (P=0.000) was indicated in the experimental group compared to the pretest and also the control group (P=0.05). However, no significant difference was shown in the muscle activity of the upper trapezius muscle (P=0.776). Conclusion: The present study showed that biofeedback training is effective to improve the electrical activity of trapezius muscle and flexion in people with SIS.
