Epicondylitis is commonly called as ‘tennis elbow’, because it often appears in tennis players. It is one of the most well-known sports injuries and has been known for more than a century. It may be considered a degenerative disease caused by overuse of the wrist and elbow (Gruchow and Pelletier, 1979).
　Yoshizawa et al. reported that the total activity levels of the forearm muscles were somewhat lower in the highly skilled tennis players than in the moderately skilled ones (1987) and that the use of a racket that has lighter moment of inertia, a larger face area with a wider frame and softer gut tension showed a decrease in the high amplitude level of the forearm muscle activities during the strokes (1988).
　In the present experiments, electromyographical and kinesiological studies were done to elucidate various changes in muscular laod on the forearm of the player as seen during each basic tennis stroke and its variations. The subjects employed were 17 university students who belong to a tennis club and who had participated in official contests. Electromyograms (EMGs) with bipolar surface clectrodes were recorded from the extensor carpi radialis brevis and longus, the flexor carpi radialis and ulnalis muscles. EMGs, strain curves of the shaft of the test racket and video motion pictures were simultaneously recorded during forehand and backhand strokes, both single-handed and double-handed, with balls controlled so as to be thrown every four seconds by a tennis ball machine, and also during services which were performed at four-second intervals. The skilled players were also required to change the ball impact positions while they were making forehand strokes. They were asked to strike the ball near the peak of its bounce line and at lower points of it.
　The results obtained by the present experiments were as follows:
　(1) The forehand strokes at higher impact positions induced the higher amplitude level of EMGs in the forearm muscles, especially in the flexor, than those at lower points.
　(2) In the case of the double-handed strokes, the muscular load showed a tendency to decrease in the forearm extensor and flexor muscles during the forehand strokes, and especially in the extensor muscles during the backhand strokes.
　(3) When the services were performed at the same intervals as in making strokes, the muscular load was not as high as that in the single-handed forehand and backhand strokes.
　These results suggested that for prevention of tennis-elbow, beginners or players with weak muscle strength should keep the following in mind:
　(1) To try to hit the ball at lower points of its bounce line in forehand and backhand strokes.
　(2) To grip the racket with both hands for forehand and backhand strokes.
　(3) Not to serve continuously and without any pause, and to try to take the interval of at least four seconds between services.

DESCENTE SPORTS SCIENCE Vol.10/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE