Purpose : The purpose of this study is to investigate the effect of each lower trapezius muscle exercise performed according to the abduction position (Y type - shoulder joint abduction 145°, T type - shoulder joint abduction 90°, and MPC type - shoulder joint 45° abduction) of the shoulder joint on the muscle activity of the round shoulder and lower trapezius muscle. Methods : This study was conducted on 31 adult men and women. Through random assignment, they were assigned to the Y group, T group, and MPC group. A 4-week intervention was performed for each group of 31 subjects who participated in the experiment, and shoulder height and lower trapezius muscle activity were measured before and after the intervention. Shoulder height measurement is a test to measure rounded shoulder posture. When the value is low, it means that rounded shoulder posture is improved. The muscle activity of the lower trapezius muscle was measured using the %MVIC method, and when the value is high, it means that the lower trapezius muscle is active. All measured data were verified using dependent t-tests for before and after comparisons and one-way analysis of variance for comparisons between groups. Results : The results of this study showed a significant decrease after intervention only in shoulder height. Muscle activity of the lower trapezius muscle decreased after intervention, but did not show a significant difference. Both variables showed no significant differences between groups. Conclusion : The results of this study show that three lower trapezius muscle exercises were performed on subjects in rounded shoulder posture. All three groups showed a significant decrease in the shoulder height value, a method of measuring rounded shoulder posture, and no significant differences between groups could be confirmed. Therefore, all three exercises can be considered effective in reducing shoulder posture.