ISOMETRIC ABDUCTION MUSCLE ACTIVATION IN PATIENTS WITH ROTATOR TENDINOSIS OF THE SHOULDER

Objective: To examine the influence of pain on activation in brief max imal and sustained submaximal isometric abduction in patients with rot ator tendinosis of the shoulder. Design: Randomized, controlled experi mental trial. Participants: Ten patients with complaints of at least 3 months' duration (median range, 1 to 2 years) and nine healthy contro ls. Intervention: Patients and controls were randomized into subacromi al local anesthetic injection on 2 different days. Methods: The uninvo lved shoulder was tested first, elbow flexed 90 degrees, shoulder abdu cted 45 degrees. The protocol consisted of three brief maximal volunta ry contractions (MVCs), followed by a sustained submaximal contraction until exhaustion and three MVCs during a 20-minute recovery period. E lectromyography (EMG) was obtained bilaterally from the supraspinatus, infraspinatus, upper trapezius, and middle deltoid muscles. Pain was scored on a visual analogue scale (0 to 100). Results: Mean pain ratin g on MVC of the involved side of patients was reduced from 28 to 10 by subacromial injection. Mean MVC force improved from 163N to 184N (95% confidence interval for the difference, 14 to 29N), The accompanying EMG amplitude during MVC increased significantly in three of the four muscles examined. Pain, force, and EMG of the uninvolved side and in c ontrols were unaltered. Endurance time and EMG (given as mu V) during the submaximal contraction were not influenced by pain. MVC did not fu lly recover during the postexhaustive period, while the corresponding EMG amplitudes were comparable to values in unfatigued muscle. Conclus ion: Pain reduced central motor drive during maximal efforts in the un fatigued state, but no additional reduction was seen after a sustained submaximal contraction. (C) 1997 by the American Congress of Rehabili tation Medicine and the American Academy of Physical Medicine and Reha bilitation.