Fitness, like so many other things, has a price. When aerobics and running were the rage, physicians focused on treating knee and ankle injuries.

With the change in recreational habits -- more people are swimming, golfing and playing tennis -- new attention is focused on the shoulder as an area prone to injury.

"As people participate in sports later in life, when they retire and can play tennis or golf every day, they become fanatics about their recreation," said James R. Andrews, an orthopedic surgeon at the Alabama Sports Medicine and Orthopedic Center in Birmingham. "You can accelerate the wear and tear that would normally occur in your shoulder by doing a repetitive sport."

According to Marilyn Pink, director of the Biomechanics Laboratory at Centinela Hospital Medical Center in Inglewood, Calif., about 57 percent of professional baseball pitchers, 44 percent of college volleyball players, 29 percent of college javelin throwers and 7 percent of professional golfers will experience some type of shoulder problem.

A serious shoulder injury can prevent a person from exercising or playing a sport for six weeks or even longer. Pain is usually felt around the shoulder but can also radiate down the arm to the elbow.

The shoulder -- a combination of several joints, tendons and muscles -- is a complex unit capable of moving into an estimated 16,000 positions, said Pink. Three bones meet at the shoulder -- the scapula or shoulder blade, clavicle or collar bone and humerus or upper arm bone.

The range of motion is produced by part of the biceps muscle -- several small muscles called the rotator cuff -- various chest wall muscles and the deltoid muscle, located at the top of the upper arm and shoulder.

Most shoulder problems involve soft tissue areas -- muscles, ligaments and tendons -- and are often the result of chronic overuse. A professional swimmer who covers 10,000 to 14,000 meters daily for six days will experience 16,000 shoulder revolutions per week. Professional tennis players will rotate their shoulders about 1,000 times each week and golfers about 200.

Combine the number of revolutions with the force necessary to pitch a baseball or swing a golf club and the result over time is either tendinitis -- injury to the cords connecting muscles to bone or other tissues -- or instability -- when one of the bones in the shoulder moves out of its normal position.

Tears in the rotator cuff -- the muscles that help hold the shoulder joint in place -- have been serious enough to end professional careers. By strengthening the shoulder muscles, injuries can be minimized, according to sports medicine experts. Orthopedist Andrews recommends basic exercises to strengthen and improve flexibility in the shoulder. For flexibility, stretch the shoulder by pulling one arm across the body. To strengthen the rotator cuff, use one to five pound weights. Lying on one side, place the arm across the chest. Then raise the arm away from the chest toward the ceiling while holding a weight. Lift 10 times and repeat for a total of five sets.