Adduction and Infraspinatus Activity in Shoulder Pain

Overview

The goal of this randomized crossover trial is to determine whether different levels of shoulder adduction pressure during an external rotation exercise change shoulder muscle activity in adults with chronic shoulder pain and adults without shoulder pain. The main question is whether adding a small amount of shoulder adduction pressure increases activity of the infraspinatus muscle without increasing activity of the deltoid muscles. Researchers will compare three levels of adduction pressure (0, 5, and 10 mmHg) during the same external rotation exercise. Participants will perform the three exercise conditions in a randomly assigned order while researchers measure shoulder muscle activity using surface electromyography.

Shoulder external rotation exercises are commonly used during shoulder rehabilitation to improve rotator cuff muscle function. Adding isometric shoulder adduction during external rotation may modify the activation of the muscles involved in the exercise, but the effect of different levels of adduction pressure has not been fully established in adults with shoulder pain. This study was designed to examine whether progressively increasing shoulder adduction pressure during external rotation changes shoulder muscle activation in adults with chronic shoulder pain and adults without shoulder pain. The study used a randomized crossover design, in which each participant performed the same external rotation exercise under three different levels of adduction pressure. The order of the experimental conditions was randomized and balanced to reduce potential effects related to the sequence of conditions. The study focused primarily on the activation of the infraspinatus muscle, while activity of the deltoid, latissimus dorsi, and middle trapezius muscles was also assessed. Muscle activity was recorded using surface electromyography during the experimental exercise. The study was conducted during a single laboratory session.