Shoulder-Abduction Angle and Trapezius Muscle Activity During Scapular-Retraction Exercise

Abstract

CONTEXT: Scapular-retraction exercises are often prescribed to enhance scapular stabilization. OBJECTIVE: To investigate upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) activities and UT/MT and UT/LT ratios during scapular-retraction exercises 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 MEASURE(S): Surface electromyography was used to evaluate UT, MT, and LT activities during the scapular-retraction exercise at 0°, 45°, 90°, and 120° of shoulder abduction. RESULTS: The mean muscle activity ranged from 15.8% to 54.7% maximal voluntary isometric contraction (MVIC) for UT, 30.5% to 51.6% MVIC for MT, and 21.4% to 25.5% MVIC for LT. A significant muscle × angle interaction was found (P < .001). Post hoc analysis revealed that the MT was more activated than the UT and LT during both retraction at 0° (P < .001 and P = .01, respectively) and 120° (P = .03 and P = .002, respectively). During retraction at 45° and 90°, the LT generated less activity than the UT (P = .02 and P = .03, respectively) and MT (P < .001 and P = .002, respectively). Further, UT/MT and UT/LT ratios during retraction at 0° were lower than at 45° (P = .03 and P = .001, respectively) and 90° (P < .001 and P < .001, respectively). Retraction at 90° resulted in a higher UT/LT ratio than at 45° (P = .004) and 120° (P = .004). CONCLUSIONS: Due to less UT relative to MT activity, retraction at 0°, 45°, and 120° can be preferable in early shoulder training or rehabilitation. Additionally, retraction at 90° was the most effective exercise in activating all parts of the trapezius muscle.

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