While moderate exercise helps keep bones strong, excessive exercise can cause cartilage damage that weakens joints. Doctors have long been aware that long-term intense exercise is related to joint damage, but a recent study found that it causes changes in cartilage cells. When viewed under a microscope, cartilage cells from joints exposed to heavy exercise show evidence of molecular changes, which could result in a failure of the cartilage. The changes are most noticeable in joints that are more stressed because of misalignment or injury.
Damaged cartilage can make it difficult or painful for the joints to function.
That's not an excuse for avoiding exercise, though. Doctors at UT Southwestern Medical Center at Dallas say moderate weight-bearing exercise, like walking, can strengthen bones to prevent loss of bone calcium. It's repetitive, intense exercise over a long period of time that can lead to damage. Varying your exercise routines and incorporating lower-impact exercise can help prevent damage. Damage is worse when joints are injured or misaligned, so if you have pain when exercising you might want to consult a physical therapist to see if there is something you can do to protect injured joints or keep joints in proper alignment.