If your favorite sport causes chronic pain or an injury that does not heal, you should probably switch to another sport. Two recent studies from the Argentine Tennis Association followed players with knee and shoulder problems (British Journal of Sports Medicine, May 2006).

In the first study, men who had anterior cruciate ligament tears showed a great drop in their tennis performance, difficulty landing after a smash, stopping and changing step direction, finishing three set singles, and playing on hard court surfaces. The knee is nothing more than two sticks held together by four bands, called ligaments. Two ligaments are located on the outside of the knee and two ligaments cross in the middle of the knee joint. The anterior cruciate ligament runs from the bottom of the upper bone of the knee joint forward to the top of the lower bone of the knee joint. It prevents the upper bone of the knee joint from slipping forward when your knee hits the ground. When this ligament is torn, each foot strike causes the upper femur bone to slide forward over the lower tibial bone, shears off cartilage in the process and hastens a knee replacement. It is downright dangerous for a person with a torn anterior cruciate ligament to play tennis or run until the ligament is replaced. Even then the surgical replacement is not as strong as the original anterior cruciate ligament and that person risks joint damage every time he runs, jumps and turns on his knee joint.

The second study followed older men who had played tennis for many years and had no shoulder pain, surgery or trauma to their shoulders. Even with no symptoms, thirty-three percent of these men had significant x-ray findings of joint damage called osteoarthritis in their dominant shoulder, and the older they were, the more likely they were to have this damage. X rays showed increased incidence of joint space narrowing, joint cysts, bone fragments, flattening of the joint cartilage, displacement of the upper arm bone and erosion of the joint cup. If you are a long-time tennis player and have shoulder pain, your doctor will probably recommend that you stop playing tennis.

The good news is that switching to a new sport is much easier than starting from inactivity. Training principles are the same for all sports. Give yourself time to learn new skills and build up the muscles you have not used before.