Relationship Between Middle Trapezius Muscle Activation and Acromiohumeral Distance Change During Shoulder Elevation With Scapular Retraction

Context: The scapular retraction exercises are widely used among clinicians to balance the activity of the scapular muscles as well as the rotator cuff muscles in different shoulder abduction positions. Objectives: The aim of this study was to investigate the relationship between scapular (middle and upper trapezius) and shoulder muscles (middle deltoid and infraspinatus) activation level differences and acromiohumeral distance changes during shoulder abduction with scapular retraction. Design: Cross-sectional study. Setting: University research laboratory. Participants: Nineteen asymptomatic individuals were included (mean [SD]: age = 22.4 [1.8] y). Main Outcome Measure: The acromiohumeral distance was measured at 0 degrees and 90 degrees shoulder abduction when the scapula was in nonretracted and retracted position with ultrasound imaging. The relationship between muscle activation level changes and acromiohumeral distance difference was analyzed with the Pearson correlation test. Results: Middle trapezius muscle activity change correlated with acromiohumeral distance difference (r = .55, P = .02) from 0 degrees to 90 degrees shoulder abduction when scapula was retracted. For both nonretracted and retracted scapular positions, no correlations were found between middle deltoid, infraspinatus, and upper trapezius muscle activity changes with acromiohumeral distance differences during shoulder abduction (P > .05). Conclusions: Active scapular retraction exercise, especially focusing on the middle trapezius muscle activation, seems to be an effective treatment option to optimize the acromiohumeral distance during shoulder abduction.