Objective: To determine whether chronic unilateral shoulder myalgia pain inhibits maximal voluntary muscle activation or increased muscle activation during sustained submaximal contractions. To determine whether pain enhances fatigue development or slows recovery.Methods: Ten subjects with chronic unilateral shoulder myalgia and 10 matched subjects without symptoms were studied. Unilateral maximal and sustained submaximal abduction contractions were performed with both arms and followed by a 20 minute rest period. Shoulder abduction torque and surface electromyography from the muscles of upper trapezius, infraspinatus, and middle deltoideus were recorded bilaterally.Results: No side or group differences were found for maximal abduction torque, muscle activation during maximal or sustained submaximal contractions. The sustained abduction contraction induced a marked increase in pain in the contracting shoulder of the myalgia subjects, particularly in the afflicted shoulder. Pain did not increase in the con...