Shoulder-muscle electromyography during shoulder external-rotation exercises with and without slight abduction.

ABSTRACT

CONTEXT Standing and side-lying external-rotation exercises produce high activation of the deltoid and infraspinatus. Slight shoulder abduction during these exercises may decrease deltoid activity and increase infraspinatus activity. OBJECTIVE: To determine if the addition of a towel under the arm during standing and side-lying external rotation affects infraspinatus, middle and posterior deltoid, and pectoralis major activation characteristics compared with a no-towel condition. DESIGN: Controlled laboratory study. PARTICIPANTS: 20 male volunteers (age 26 ± 3 y, height 1.80 ± 0.07 m, mass 77 ± 10 kg) who were right-hand dominant and had bilaterally healthy shoulders with no current cervical pathology and no skin infection or shoulder lesion. INTERVENTIONS: External-rotation exercises without a towel roll (0° shoulder abduction) and with a towel roll (30° shoulder abduction) were performed in a standing and side-lying. MAIN OUTCOME MEASURES: Maximal voluntary isometric contraction for the infraspinatus, middle and posterior deltoid, and pectoralis major and external rotation in standing and side-lying with and without a towel roll were performed. Normalized average and peak surface EMG amplitude were compared between the towel conditions during standing and side-lying external rotation. RESULTS: Both infraspinatus and pectoralis major activity had no significant differences between the towel conditions in standing and side-lying (P > .05). In standing and side-lying, posterior-deltoid activity was significantly greater with a towel roll (P < .05). Middle-deltoid activity had no significant differences between the towel conditions in standing (P > .05). However, in side-lying, middle-deltoid activity was significantly lower with a towel roll (P < .05). CONCLUSION: Middle-deltoid activity decreased with a towel roll during side-lying exercises. More data are needed to determine if a towel roll could be used to potentially reduce superior glide during external-rotation exercises.