Muscle activation during isometric contractions in workers with unilateralshoulder myalgia

Objective: To determine whether chronic unilateral shoulder myalgia pain in hibits maximal voluntary muscle activation or increased muscle activation d uring sustained submaximal contractions. To determine whether pain enhances fatigue development or slows recovery. Methods: Ten subjects with chronic unilateral shoulder myalgia and 10 match ed subjects without symptoms were studied. Unilateral maximal and sustained submaximal abduction contractions were performed with both arms and follow ed by a 20 minute rest period. Shoulder abduction torque and surface electr omyography from the muscles of upper trapezius, infraspinatus, and middle d eltoideus were recorded bilaterally. Results: No side or group differences were found for maximal abduction torq ue, muscle activation during maximal or sustained submaximal contractions. The sustained abduction contraction induced a marked increase in pain in th e contracting shoulder of the myalgia subjects, particularly in the afflict ed shoulder. Pain did not increase in the controls. Despite the pain differ ences, a similar loss of torque after the sustained submaximal contraction without recovery after 20 minutes rest were seen in both groups. Conclusions: A marked pain increase was induced by the sustained submaximal contraction in both the afflicted and unafflicted formerly painfree should er of the myalgia subjects, indicating sensitization of pain perception in these subjects. Chronic muscle pain did not influence muscle activation dur ing maximal or submaximal contractions.