Excess pounds put pressure on knees and hips. But fitness freaks are more likely to incur the kinds of injuries that lead to joint problems down the road. Doctors are replacing more than 200,000 hips a year now, and the number will nearly triple by 2030.

The surgeon swaps a metal ball for the top of the femur (the bone in the upper leg) and removes portions of the damaged socket. Full recovery, including physical therapy to restore mobility and balance, takes three to six months.

Cost: $20,000 to $40,000 for surgery; $3,000 fortherapy.

What's new: A less drastic procedure called resurfacing, for those with limited damage. Doctors reshape and cap the head of the femur with a prosthetic instead of removing it. The procedure is being tested at several U.S. hospitals.

"Resurfacing seems to offer more hip stability and less risk of dislocation," says Dr. Michael J. Grecula, an orthopedic surgeon in Galveston. "My patients say they feel better - more normal - after the surgery."

Advances in design and materials may make running and racquetball possible after a hip is fixed.