Pain Inhibits the Rotator Cuff
This study looked at 17 healthy adults without known shoulder pathology. Subacromial pain was experimentally elicited with a saline injection. Maximal isometric external rotation testing was done pre and post injection with the arm at the side and both (dynamometer) and Voluntary activation (VA) was measured (electrical activity of infraspinatus).
Initially after the injection there was a 32.8% decline in force and a 22.7% decline in VA. As pain resolved the force and VA both improved again.
Subacromial pain produces an inhitition of infraspinatus and external rotator function. In shoulder pathology this may become a self perpetuating pathology as poor mechanics produce more pain and further inhibition.
Clinically we need to be far more aware of assigning exercises that produce symptoms, as it may actually slow progress toward the goal.
Be very aware of tiny changes in resistance, position, amplitude and speed to help the client find a symptomless variation with a standard exercise. Practice normal movement, and be aware that normal movement is painless.
Reference: Stackhouse SK, Eisennagel, J, Lenker H, Sweitzer BA, McClure PW. Experimental pain inhibits infraspinatus activation during isometric external rotation. J Shoulder Elbow Surg. 2012 Aug (Epub).