How does exercise help prevent osteoarthritis?

Unfortunately, nothing totally prevents osteoarthritis, but resistance exercise definitely helps reduce your risk of developing it, and any exercise in an aligned joint helps prevent progression of osteoarthritis. Strong muscles make strong, lubricated, cushioned joints, which are a lot less likely to get osteoarthritis. When your muscles are strong, they support your joints and hold them in the right position. That cuts down on the wear and tear that leads to creaky, stiff joints. And there’s a bonus, too: Strong muscles also help you keep your balance and avoid falls.

Exercise is a great way to prevent osteoarthritis (OA). Regular exercise keeps your joints flexible, builds strength in the muscles and bones that support your joints, and improves your overall strength and balance. Not only do all those benefits help prevent OA, they also help prevent joint injuries that can lead to OA down the line. Plus, exercise helps you keep your weight down, which also helps prevent OA.

Exercise is invaluable in helping prevent osteoarthritis. When your muscles are strong, they reduce extra stress on the joints by holding them in the correct position, which helps prevent osteoarthritis. Studies show, for example, that having strong thigh muscles helps prevent knee arthritis.  Strong muscles also help you keep your balance and avoid falls that could injure a joint, which would then be more likely to develop osteoarthritis later on.  

http://www.niams.nih.gov/Health_Info/Osteoarthritis/default.asp#pic_4

http://www.hopkins-arthritis.org/patient-corner/disease-management/exercise.html