Context: Scapular retraction exercises are often prescribed to enhance scapular stabilization.
Objectives: To investigate the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT) activities, and UT/MT and UT/LT ratios during scapular retraction exercise with elastic resistance at different shoulder abduction angles. Design: Descriptive laboratory study. Setting: Biomechanical analysis laboratory. Patients or Other Participants: Thirty-five asymptomatic individuals. Main Outcome Measures: Surface electromyography was used to evaluate UT, MT, and LT activities during the scapular retraction exercise at 0º, 45º, 90º, and 120º shoulder abductions. Results: The mean muscle activity ranged from 15.8%–54.7% maximum voluntary isometric contraction (MVIC) for UT, 30.5%–51.6% MVIC for MT, 21.4%–25.5% MVIC for LT. A significant "muscle×angle" interaction was found (p<0.001). Post hoc analysis revealed that the MT was significantly more activated than UT and LT during both retraction at 0º (p<0.001; p=0.01, respectively) and 120º (p=0.03; p=0.002, respectively). During retraction at 45º and 90º, the LT generated significantly lower activity than the UT (p=0.02; p=0.03, respectively) and MT (p<0.001; p=0.002, respectively). Besides, UT/MT and UT/LT ratios during retraction at 0º were significantly lower than 45º (p=0.03; p=0.001, respectively) and 90º (p<0.001; p<0.001, respectively). Retraction at 90º resulted significantly higher UT/LT ratio than 45º (p=0.004) and 120º (p=0.004).
Conclusions: Due to lower UT activity relative to MT, retraction at 0º, 45º, and 120º can be preferred in early shoulder training or rehabilitation. Additionally, retraction at 90º was the most effective exercise in activating entire trapezius muscle parts.