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 controls. Despite the pain differences, 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 shoulder of the myalgia subjects, indicating sensitization of pain perception in these subjects. Chronic muscle pain did not influence muscle activation [...]