The influence of shoulder position during multi-joint exercises in the relative scapular muscles activity in symptomatic and asymptomatic conditions

Abstract

BACKGROUND:

Scapular muscles changes, as increased upper trapezius activity and decreased middle and lower trapezius and serratus anterior muscle activity, have been demonstrated in shoulder pain specific or non-specific conditions. Shoulder external rotation exercises have been recommended to improve scapular activity in shoulder pain.

OBJECTIVE:

To evaluate the relative scapular muscles activity during multi-joint exercises combining shoulder external rotation, trunk rotation and scapular squeeze.

METHODS:

Forty-one participants with and without shoulder pain were assessed in a cross-sectional study. They performed isometric multi-joint exercises at 0 ${}^{\circ }$ and 90 ${}^{\circ }$ of shoulder abduction with and without support. The relative activity of upper, middle, and lower trapezius and serratus anterior (upper/middle and lower portions) was measured through electromyography. The scapular muscular balance was assessed by the ratio between relative activity of the upper trapezius and the other muscles.

RESULTS:

Both groups presented similar results. The exercise at 90 ${}^{\circ }$ abduction led to increased relative muscle activity against maximal voluntary contraction in both groups for upper trapezius (with support: 4% MVIC, $p=$ 0.001 or 15% MVIC, $p<$ 0.0001; and without support: 11% MVIC, $p<$ 0.0001 or 13%, $p<$ 0.0001, for asymptomatic and symptomatic group, respectively) and lower trapezius (with support: 66% MVIC, $p<$ 0.0001 or 62% MVIC, $p<$ 0.0001, for asymptomatic and symptomatic group,