The Efficacy of Instability Resistance Training on Shoulder Muscle Firing Characteristics

PURPOSE: The glenohumeral joint is the most mobile joint in the body. Due to the anatomical makeup and range of motion demands, the shoulder is at risk for instability. The purpose of this research was to examine the effects of instability resistance training on muscle activation on the shoulder in healthy subjects. SUBJECTS: Fifteen adults (10 females, 5 males; 21.5 years ± 1.5) without previous shoulder injury were included. METHODS AND MATERIALS: D2 shoulder flexion/extension and wrist flexion/extension exercises were performed supine using a resistance device (unstable and stable). The unstable condition was a water-filled pipe device that caused dynamic resistance during exercise. The stable condition was a similar pipe device filled with stationary weights. The Biopac MP 150 EMG system was used to measure muscle activity for the middle deltoid (DELT), pectoralis major (MAJ), and latissimus dorsi (LAT). Subjects performed 10 repetitions of exercise following a metronome. Exercise and condition were randomly assigned. ANALYSES: Four separate repeated measures ANOVAs (Muscle x Condition) were performed to evaluate differences in the coefficient of variance for each exercise (D2 flexion, D2 extension, Wrist flexion, Wrist extension). RESULTS: No significant differences were identified across any exercise for muscle or condition, alpha \u3e 0.05. Despite no significant main or interaction effect being realized, higher EMG activity was noted for the unstable PEC and LAT (2.96±0.31 vs. 2.44±0.12, 2.6± 0.19 vs. 2.31±0.11). CONCLUSIONS: Data did not indicate significance, however, subjects experienced varied applications of load during D2 flexion. Further investigation is warranted to explore instability resistance training and potential benefits in the shoulder