Scapular muscle fatigue in athletes with shoulder impingement syndrome: an Emg analysis

Abstract

Background: Shoulder muscle fatigue is a common sequela of repetitive arm use and proposed as a possible link to explain the association between repetitive arm use and development of shoulder pain. Objective: To identify and compare the fatigue produced in scapular muscles in injured and non-injured side in athletes with impingement syndrome and also with athletes without impingement syndrome. Design And Methodology: Experimental study with different subject design. 20 overhead athletes from various sports participated in this study. 10 athletes had shoulder impingement syndrome and 10 were healthy athletes. Subjects performed submaximal contraction (40% - 80% of MVIC) for 30 seconds of four scapular muscles i.e. upper trapezius, middle trapezius, lower trapezius and serratus anterior. The fatigue was calculated by measuring the median frequency difference (frequency shift) between the first 10 seconds (0-10) contraction and last 10 seconds (20-30) contraction. Results: There was significant (p ≤ 0.05) increase in frequency shift (25% - 85% more fatigue) in the four scapular muscles on the injured side of impingement group as compared to the same side of control group. On comparing injured and non-injured side of impingement group, injured side showed significant (p ≤ 0.05) increase in frequency shift (30% - 90% more fatigue) in the four muscles. Conclusion: Athletes with shoulder impingement syndrome have more median frequency shift in UT, MT, LT, & SA muscles on injured side as compared to non-injured side as well as same side of control group.

Key words:

impingement, fatigue, frequency, electromyography