Background: Shoulder impingement syndrome is considered to be associated with an altered muscular activity, which is related to strategy changes in the movement plan. The present study aimed to investigate the differences in timing and intensity of activity of shoulder girdle muscles while performing a forehand topspin loop between elite table tennis players with and without shoulder impingement syndrome. The timing and activity amplitude of these shoulder girdle muscles have not been evaluated in other studies in table tennis elite athletes. Methods: Activation timing and activity levels of the upper trapezius, lower trapezius, and serratus anterior, anterior deltoid, supraspinatus, and biceps brachii muscles were measured in 30 table tennis players (Premier League tournament level or higher) with shoulder impingement syndrome and compared with 30 same-level healthy players while performing the forehand topspin loop. Results: The results indicated that the activity levels of the serratus anterior (P ¼ .007) and supraspinatus (P ¼ .001) muscles significantly decreased; however, the activity level of the upper trapezius significantly increased in the impingement compared with the healthy group (P ¼ .009). The serratus anterior (P ¼ .001) was activated significantly later, but the upper trapezius (P ¼ .004) was activated significantly earlier in the impingement group. Conclusion: Results of the present study support the theory that the activation and sequence of recruiting of the shoulder muscles are altered in people with impingement symptoms, suggesting that impingement syndrome may be associated with disturbed timing and activity level of shoulder girdle muscles.
