Shoulder muscle activation during scapular protraction exercise with arm rotation

BACKGROUND: The role of the serratus anterior is to maintain scapular stability. To strengthen this muscle, scapular protraction exercises are typically performed. Although the angle of arm rotation leads to changes in shoulder muscle activation, the arm rotation position is not normally determined. OBJECTIVE: To investigate if scapular muscle activations were changed by combining arm external rotation during scapular protraction exercises. METHODS: Thirty-four healthy men were enrolled in this study. Participants were instructed to perform scapular protraction exercises at 90 degrees and 120 degrees of shoulder flexion while in the standing and supine positions. Two different arm rotation angles were used: the thumb-up position (neutral position) and the maximum arm external rotation (ER) position. The percentages of maximum voluntary contractions (%MVCs) were measured, and %MVCs in the neutral and arm ER positions were compared. RESULTS: Muscle activities of the middle serratus anterior (MSA) and lower serratus anterior (LSA) in the arm ER position were significantly higher than those in the neutral position during all tasks. The highest MSA and LSA positions were observed with the arm ER position of 120 degrees while standing. CONCLUSIONS: Scapular protraction exercises with arm ER resulted in a higher serratus anterior activity.