Selective activation of intra-muscular compartments within the trapezius muscle in subjects with Subacromial Impingement Syndrome. A case-control study.

Neuromuscular control of the scapular muscles is important in the etiology of shoulder pain. Electromyographical (EMG) biofeedback in healthy people has been shown to support a selective activation of the lower compartment of the trapezius muscle, specifically. The aim of the present paper was to investigate whether patients with Subacromial Impingement Syndrome (SIS) were able to selectively activate the individual compartments within the trapezius muscle, with and without EMG biofeedback to the same extent as healthy controls (No-SIS). Fifteen SIS and 15 No-SIS participated in the study. Sessions with and without visual biofeedback were conducted. Surface EMG was recorded from four compartments of the trapezius muscle. Selective activation was defined as activation above 12% with other muscle parts below 1.5% or activation ratio at or above 95% of the total activation. Without biofeedback significantly fewer SIS subjects than No-SIS achieved selective activation (p=0.02-0.03). The findings of the study show that without biofeedback No-SIS had a superior scapular muscle control. However, when provided with visual EMG feedback the SIS group performed equally well as the No-SIS group. This indicated that individuals with SIS may benefit from biofeedback training to gain control of the neuromuscular function of the scapular muscle.