There’s good news and bad news about “Tommy John surgery,” a technique used to replace a damaged elbow ligament often suffered by athletes. The surgery has a high success rate, with most people going back to previous levels of activity, a study has found. However, more young athletes are having the surgery, leaving some experts concerned about the possible ill effects of overtraining.

“This is not a case of inadequate care,” says Dr. E. Lyle Cain Jr. of the American Sports Medicine Institute in Birmingham, Ala. Cain was lead author of the study. “I think many young athletes assume that the more they train and participate, the better they’ll become. The reality is that the body has to have a certain amount of time off.”

Tommy John surgery, or ulnar collateral ligament reconstruction, refers to the replacement of a damaged elbow ligament with a tendon from elsewhere in the body — usually the forearm, according to Cain. The ligament provides stability when doing any throwing motion but can fray, stretch or tear from overuse or without warning from one sudden movement. People with the injury usually experience a sharp pain while throwing, and for baseball players the injury can result in slower pitches and less control.

During surgery, the replacement ligament is woven through holes drilled in the humerus and the ulna. Cain says that healing usually takes about three to four months, but that complete recovery takes longer. The procedure was named for former major league pitcher Tommy John, the first pro athlete to have successful surgery. It was performed in 1974 by Dr. Frank Jobe, who pioneered the procedure.