Obesity, heavy sports activity and brisk exercise involving the knee joints cause more wear and tear in the cartilages in the ends of bones involved in joint formation. Thinning cartilages exposes the bones and there occurs pain in the joints.
Exercises without weight bearing on the joints like swimming relax the ligaments and muscles around the joints that ease pain. Now it has been seen that light walking is better for osteoarthritic joints than vigorous walking or sports activities.
Another cause, overweight has to be addressed to offload the knee joints from the added weight.