Abstract
Introduction
Rehabilitation after shoulder arthroplasty is a fundamental in enabling patients achieve a good functional outcome. Therapists must consider the underlying diagnosis, operative technique employed and rotator cuff integrity, amongst other factors, in order to select the most appropriate exercise regime. There is an absence of comprehensive studies in the literature with regard to shoulder rotational exercises. Therefore, this study aimed to describe the shoulder girdle muscle activation strategies during eight commonly cited rotational shoulder exercises.
Method
Thirty healthy subjects with no history of shoulder problems participated in the study. EMG was recorded from 16 shoulder girdle muscles (surface electrodes: anterior, middle and posterior deltoid, upper, middle and lower trapezius, upper and lower latissimus dorsi, upper and lower pectoralis major; fine wire electrodes: supraspinatus, infraspinatus, subscapularis and rhomboid major) using a telemetry based EMG system. Five external and three internal rotation exercises were included (table 1). Signal acquisition and processing were in accordance with standardised guidelines. Amplitude normalisation was to external and internal rotation maximum voluntary contraction as appropriate. Mean EMG amplitudes between exercises were compared using repeated measures ANOVA. Data for muscle groups was calculated by averaging the activation of the component muscles.
Results
External Rotation Exercises: significantly higher levels of deltoid activation were seen in external rotation at 90° abduction compared to the other external rotation exercises (73.7% vs 12.4–27.2%; p < 0.001). Peri-scapular muscle activation was highest in external rotation at 90° abduction and prone external rotation (76.7–83.2% vs 28.2–45.5%; p = 0.013 − <0.001). Activation of latissimus dorsi and teres major was significantly higher during prone external rotation (64.1% vs 18.1–48.4%; p < 0.001). Activation of the rotator cuff muscles was similar across all exercises.
Internal Rotation Exercises: the highest deltoid activity was seen during internal rotation at 90°abduction, followed by zero-position internal rotation. It was lowest during internal rotation at 0°abduction (261.6% vs 190.1% vs 40.9%; p = 0.003 − <0.001). A similar activation pattern was also seen for peri-scapular muscles. The highest activation of pectoralis major was seen during zero-position internal rotation (25.4% vs 4.9–15.7%; p = 0.002 − <0.001). Significantly higher levels of rotator cuff activation were seen during internal rotation at 90° abduction (325.0% vs 94.0–188.3%; p = 0.005–0.017).
Discussion and Conclusion
This study provides a comprehensive description of muscles activation during common rotational shoulder exercises. It enables therapists to target specific muscles for rehabilitation following shoulder surgery, while minimising the activation of others. Understanding the activation profile of the shoulder girdle muscles during individual exercises forms the basis for exercise prescription and the development of tailored and individual physiotherapy protocols.
