In tennis, it's the shot that counts. For the recreational player, the proper execution of the maneuver -- precise aim, wrist position, correct grip on the racquet -- can result in injury.

Too much pressure on the muscles that straighten the wrist and fingers can cause tennis elbow -- a painful inflammation of the soft tissues surrounding the elbow.

There are 21.3 million Americans who play tennis, according to a 1989 survey by the American Tennis Industry Federation, a trade association. It is estimated that about 1 million people suffer from tennis elbow each year.

Playing tennis is not the only cause of the painful condition. Almost any activity that involves vigorous use of the wrist muscles -- gardening, carpentry, even politicians who shake too many hands -- may tear tendons, fibrous cords that connect muscles to bones or other muscles. The tendons that are attached to the elbow become inflamed and swell. "Tennis elbow is like a heart attack of the tendon," said Robert P. Nirschl, assistant professor of orthopedics at Georgetown University. "The blood vessels leading to the tendon get cut off, and the tendon looses its oxygen supply."

Although resting the arm or taking anti-inflammatory drugs may ease the pain, the injured tissue will not heal unless the blood supply is restored to the area, according to Nirschl. That means doing rehabilitative exercises specifically designed to strengthen and restore flexibility to the forearm. Tendon problems can linger for years, said Nirschl, because people go back to the same activity without strengthening their muscles first. Experts suggest a variety of rehabilitative exercises -- such as wrist curls using three-to-five-pound weights -- to condition the entire arm and shoulder. The idea is to improve other muscles and joints to take the stress off the elbow.

For tennis players, the most frequent cause of tennis elbow is a faulty backhand stroke. Other problems include using a tightly strung racquet, which increases the force against a player's arm, and hitting the ball with the wrong part of the racquet. According to Howard Brody, a professor of physics at the University of Pennsylvania who has studied the game, a player should aim to hit the ball with the center of the head of the racquet -- called the center of percussion.

Sports medicine experts suggest that people may want to condition their muscles first before playing a new sport. "People who take up a sport to get in shape rather than getting in shape to take up a sport run the high risk of injury," Nirschl said.