Electromyographic Activity in the Immobilized Shoulder Girdle Musculature During Ipsilateral Kinetic Chain Exercises

Smith J, Dahm DL, Kotajarvi BR, Boon AJ, Laskowski ER, Jacofsky DJ, Kaufman KR. Electromyographic activity in the immobilized shoulder girdle musculature during ipsilateral kinetic chain exercises.

Objective

To quantify the electromyographic activity in the shoulder girdle musculature during ipsilateral kinetic chain exercises performed in a shoulder immobilizer in asymptomatic men.

Design

Descriptive.

Setting

Motion analysis laboratory at a tertiary care center.

Participants

Five asymptomatic male volunteers, ages 24 to 32 years.

Intervention

Fine-wire (supraspinatus, infraspinatus, upper subscapularis) and surface (deltoids, trapezii, biceps, serratus anterior) electrodes recorded electromyographic activity from each muscle during a split-stance cross-body rotation (twisting to the opposite side at high, mid, and low levels), split stance attempted ipsilateral floor touch, and attempted overhead reach. All movements were initiated from the immobilized scapula and were tested with and without a combined step.

Main Outcome Measure

Mean peak normalized (percentage of maximum voluntary contraction [%MVC]) electromyographic activity of each muscle during each exercise.

Results

For all exercises, biceps and infraspinatus activity remained low (<10% MVC), whereas upper subscapularis activity was moderate to very high (29%−68% MVC). Supraspinatus activity was low (<20% MVC) for all motions except the attempted overhead reach (23% MVC). Serratus electromyographic activity was less than 20% of MVC for all motions and was most responsive to added stepping (23%−136% MVC without stepping vs 24%−199% MVC with stepping). Cross-body rotation at lower heights progressively increased serratus activity while decreasing supraspinatus, upper trapezius, and anterior deltoid activity.

Conclusions

Based on these electromyographic data, selected kinetic chain exercises could potentially be implemented during periods of shoulder immobilization. All exercises examined could potentially be safe after superior labral anteroposterior repair, but not after subscapularis repair. All exercises, with the exception of the attempted overhead reach, could potentially be safe after supraspinatus repair, with or without concomitant infraspinatus repair. Early activation of the serratus anterior could potentially be achieved by performing cross-body rotations, particularly at lower heights.