Muscle weakness can both increase the risk for osteoarthritis and result from osteoarthritis. In the workings of a normal joint, muscles allow the joint to move and help keep the joint stable. Weak muscles tire easily and respond more slowly. Eventually, this places more stress on other supporting joint structures and begins the breakdown of the overall joint structure. It also limits the supporting structures' abilities to protect the joint from possible harm from sudden movement. Together, these factors may increase the stress on the joints and may cause small tears in the cartilage that contribute to its wear.

Studies show that weakness in the thigh muscles is one of the earliest symptoms reported by people who have osteoarthritis in the knee. Weakness also plays a role in determining how severe and disabling osteoarthritis in the knee will be.