Acute effects of lower trapezius activation exercises on shoulder muscle activation during overhead functional tasks in symptomatic and asymptomatic adults

Introduction Shoulder musculoskeletal disorders are associated with atypical kinematics and muscle activity. Exercises to activate weakened muscles may reduce pain and disability. The objectives of this study were to test the effectiveness of exercises for activating the lower trapezius and to compare changes in shoulder muscle activity during functional tasks before and after the exercises in symptomatic and asymptomatic groups. Methods Eighteen adults, nine with subacromial pain syndrome and nine asymptomatic controls, participated in this study. A within-session repeated measures case-control design was employed. Participants performed overhead functional tasks before and after completing lower trapezius activation exercises. Electromyography (EMG) data of scapular muscles were captured during the tasks and exercises. One-way analysis of variance (ANOVA) compared muscle activations during the exercises. Paired t-test statistical parametric mapping assessed changes in muscle activity after the exercises. Results Lower trapezius activation was highest during the Trapezius Muscle Exercise for both groups. Post-exercise, a transient increase in lower trapezius activation was observed in the pain group during the Comb Hair task ( p = 0.0012, d = 1.55) and the no pain group in the Overhead Reach task ( p < 0.001, d = 1.38) , but this effect did not persist in either group. Discussion The exercise protocol successfully increased lower trapezius activation immediately post-exercise, but the effects were short-lived. The findings suggest that while lower trapezius activation exercises can temporarily alter muscle activation, their efficacy for acute prevention or rehabilitation is limited. Further research is needed to explore the effects of longitudinal training programs on functional task performance.