Until recently, giving you guidance would be mere guesswork. Now we can say that your safest bet is to avoid any activities that cause a lot of impact on the knee, such as heavy jumping, lunging, and fast starts and stops. Research also shows that jogging and downhill walking put too much stress on the joint. Cycling and level walking are safer choices because the forces that happen during these activities are more evenly spread over the surface of the joint. Exercising in a pool is a good idea, too, because the water’s buoyancy allows you to move and exercise more easily, and there is less pressure on the joint.