Timing and Movement Pattern of the Shoulder Muscles of the Elite Table Tennis Players with and without Shoulder Impingement Syndrome during the Performance of Forehand Topspin

Shoulder impingement syndrome is associated with alterations in scapulohumeral muscles activity in sports such as table tennis in which hands operate higher than shoulder level and these changes are theoretically related to a change in the motor program strategies. One of the important scales of investigating muscular coordination and motor control in shoulder muscles is the study of the timing of muscle activation. The aim of this study was to examine the difference between muscle activity and inactivity and the activation pattern of the shoulder muscles in the elite table tennis players with and without shoulder impingement syndrome. In this study, 30 male elite table tennis players (age: 20-28 years old) were purposively categorized into 2 groups: with syndrome (n=15, mean age=25.12±1.65) and without shoulder impingement syndrome (n=15, mean age=24.43±1.55). The timing of the activity of the supraspinatus, upper trapezius, lower trapezius, serratus anterior, anterior deltoid and biceps brachii muscles of the dominant upper limb were measured by surface electromyography during table tennis forehand topspin. Shapiro–Wilk test was used to check the normal distribution of the data; then, independent sample t test was used to compare the results of the two groups using SPSS 20 at P<0.05. The results of independent t test showed that serratus anterior (P=0.001) and upper trapezius (P=0.004) were significantly activated sooner and later in the patient group than the healthy group. Also, the muscle activation pattern changed in the patient group compared with the healthy group. These results showed that the function of scapular stabilizing muscles in athletes of overheard throwers fields who had should impingement symptoms is temporally disturbed, and confirms the assumption that shoulder impingement syndrome may be associated with dysfunction of timing and activity coordination of the scapulothoracic and glenohumeral muscles.