|（1.Graduate School，Beijing Sport University，Beijing 100084，China；2.School of Sport and Human Science，Beijing Sport University，Beijing 100084，China)
Abstract: In order to study the effects caused by tennis racket string diameters to the ball hitting speed, controllabil-ity and the elbow joint of the racket holding arm, and to reveal the cause for athletic injury of the elbow joint of the racket holding forearm, possibly caused during ball hitting, the authors selected 15 national level two tennis players as the testees, and tested their forehand ball hitting on the court with the use of tennis racket strings of different di-ameters (No. 18: 1.15mm and 16L: 1.25mm). Research results: racket string diameters would produce effects on the baseline ball hitting effect, in which they produced a significant effect on the ball hitting speed, the ball hitting speed of the No. 18 polyester string with a smaller diameter was significantly faster than that of the 16L polyester string with a bigger diameter, and the overall trend of the ball hitting controllability of the No. 18 polyester string was higher than the ball hitting controllability of the 16L polyester string; racket string diameters would caused certain effects on the racket holding arm, specifically showing their effects on the myoelectricity peak value, root mean square value and discharge duration of the racket holding arm, in which their effect on the brachioradialis was the most significant; when the 16L polyester string was used for ball hitting, in order to better realize control over the ball, the flexor carpi radialis, pronator teres and extensor carpi radialis longus of the racket holding arm were overly mobilized to involve in movement, the overuse of these muscles may cause the injury of the elbow joint of the racket holding forearm.
Key words: sports biomechanics；tennis racket string diameter；baseline ball hitting effect；myoelectricity peak value；root mean square amplitude；discharge duration；elbow joint of the racket holding arm