It’s important for therapists to know the level of muscle activation during postoperative shoulder exercises. While most strengthening exercises are chosen based on higher levels of muscle activity measured by EMG, therapists may need to choose an exercise that produces lower levels of EMG activity. Postoperative shoulder patients, particularly those undergoing rotator cuff repair, often need to minimize stresses placed on healing tissue during range of motion (ROM) exercises. Early recovery exercises often include passive ROM and active assisted ROM to regain lost motion. Active ROM and isometric exercises are then incorporated to begin light muscle activation prior to performing progressive resistance exercises.
Most shoulder exercise EMG studies are performed on healthy, young subjects. While theses studies are beneficial in providing clinicians with muscle activation levels, they must be interpreted with caution. The reported values in studies using healthy subjects may not be representative of a post-operative patients expressing pain and muscle guarding, which may lead to higher levels of muscle activation, potentially damaging a surgical repair.
A paper in the Journal of Shoulder and Elbow Surgery examined the EMG levels of the supraspinatus and infraspinatus muscles of the rotator cuff, which are the most commonly injured. The researchers used fine-wire EMG while 26 patients performed 14 commonly prescribed post-operative exercises. The patients averaged 53 years old and underwent a subacromial decompression or resection of the distal clavicle bone, or both, one to 4 days prior to their EMG test.
In comparison to most EMG studies on shoulder rehabilitation exercise, this study used an older post-operative population, giving clinicians a better understanding of the activity levels in patient populations – thus improving the external validity of the study. As with any study involving a clinical population, the delicate balance of internal and external validity must be recognized.
The researchers compared EMG levels of the 2 muscles during the exercises to a resting baseline in quiet stance. They found that the supraspinatus remained passive in the 6 exercises (defined as 5 times baseline muscle activation by the authors):
• Therapist-assisted and self-assisted external rotation
• Therapist-assisted elevation
• Isometric Internal Rotation and Adduction
2 other exercises involving Thera-Band® products, the shoulder pulley and tubing for scapular retraction, elicited higher muscle activation of the rotator cuff than more passive exercises. Isometric external rotation and abduction produced the highest levels of activation, defined as 5 to 15 times resting EMG levels. The infraspinatus was found to have higher activation than the supraspinatus in all exercises.
In conclusion, this study suggests that Thera-Band scapular retraction and shoulder pulley exercises can be added to early post-operative rehabilitation after more passive and active-assisted ROM exercises have been performed.
REFERENCE: Murphy CA, McDermott WJ, Petersen RK, Johnson SE, Baxter SA. Electromyographic analysis of the rotator cuff in postoperative shoulder patients during passive rehabilitation exercises. J Shoulder Elbow Surg. 2013 Jan;22(1):102-7. doi: 10.1016/j.jse.2012.01.021. Epub 2012 May 3.