Electromyographic activity in the shoulder musculature during resistance training exercises of the ipsilateral upper limb while wearing a shoulder orthosis.

BACKGROUND

Resistance training is usually postponed until 3 months after rotator cuff surgery to prevent the damaging effects of high muscle stress on the repaired tendon. After upper limb immobilization, noninjured muscles as well as the repaired muscles are affected by long-term inactivity. Exercises with minimal cuff activity may be appropriate in the early postoperative period, so we aimed to quantify the effect of resistance exercises on the muscle activity of a semi-immobilized upper limb.

METHOD: Fifteen shoulder muscles of the dominant limb of 14 healthy subjects were evaluated by electromyography, with 11 surface electrodes and 4 fine-wire electrodes in the rotator cuff muscles. While wearing an orthosis, the subjects completed resistance tests including elbow and wrist flexion/extension with 3 loads, maximal squeezing, and shoulder adduction against 3 different foams. The peak activity of each muscle was normalized to maximal voluntary contraction (% MVC).

RESULTS

Shoulder muscles were activated less than 20% MVC during elbow and wrist flexion/extension with 2-lb (907-g) and 4-lb (1814-g) loads. In the maximal squeezing test, rotator cuff activity exceeded 20% MVC in some cases. During shoulder adduction tests, subscapularis, latissimus dorsi, triceps, and pectoralis major had the highest activation levels; supraspinatus and infraspinatus were minimally activated.

CONCLUSION

Supported elbow and wrist flexion/extension in the horizontal plane, with weights of up to 4 lb (1814 g), minimally activates the rotator cuff muscles while potentially preventing muscle disuse of other upper limb musculature. Resisted shoulder adduction cannot be considered safe for all rotator cuff injuries.

LEVEL OF EVIDENCE: Basic science study, electromyography