The effects of upper body posture and instructional cues on shoulder muscle activity and kinematics during elastic resistance exercise

The purpose of this study was to examine the effects of upper body posture on shoulder muscle activity and kinematics during shoulder exercises using TheraBand® elastic resistance. 12 healthy individuals performed 4 shoulder exercises using a TheraBand® CLX: 1) unilateral flexion to 90 degrees, 2) bilateral flexion to 90 degrees, 3) external rotation, 4) external rotation with a towel. All exercises were performed with either no postural cues, poor posture, or corrected posture. 3D kinematics and surface electromyography (EMG) from 16 upper extremity muscles were recorded. During unilateral and bilateral flexion there was a significant increase in muscle activity for almost all of the muscles tested during the poor posture condition. For the external rotation exercise, infraspinatus muscle activity was greatest during the poor posture condition. These results suggest a potential neuromuscular inefficiency during the poor posture conditions that may lead to muscle fatigue and/or overuse.