Four-week exercise program does not change rotator cuff muscle activation and scapular kinematics in healthy subjects

Rotator cuff and scapular muscle strengthening exercises are an essential part of shoulder rehabilitation and sports training. Although the effect of exercise training on pain and function have been widely investigated, few studies have focused on the changes in shoulder kinematics and muscle activity after exercise training. Therefore, the purpose of the present study was to investigate the effect of rotator cuff and scapular strengthening exercises on shoulder kinematics and the activation of rotator cuff and scapular muscles in healthy subjects. Thirty-six healthy subjects were recruited and randomly assigned into either a training or control group. Subjects in the training group were trained with rotator cuff and scapular strengthening exercises for 4 weeks. Scapular kinematics and shoulder muscle activity during arm elevation were measured before and after exercise training. After the 4-week training protocol, there was an increase in strength and a decrease in upper trapezius activation in the training group, which is consistent with previous studies. However, no difference was found in scapular kinematics and activation of rotator cuff muscles between the control and training groups after the training protocol. Although the exercise protocol resulted in strength gains for the rotator cuff, these gains did not transfer to an increase in muscle activation during motion. These results demonstrate the difficulty in changing activation patterns of the rotator cuff muscles. (c) 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2079-2088, 2016.