Two joints commonly affected by arthritis, the knee and the shoulder, can benefit from isometric and isotonic exercises. Isometric, or squeezing, exercises involve tightening a muscle for several seconds, without moving any other body parts, to condition muscle fiber. Isotonic exercise, which promotes muscle contraction, involves pushing against a moveable resistance. Both types of exercise can strengthen the support structure around the knee to protect it. They can also strengthen the rotator cuff muscles that help stabilize the shoulder. Here are four exercises recommended by Cleveland Clinic physical therapist and athletic trainer Jeff Ciolek. If you have a particularly painful joint, stick to the isometric exercises, which have the advantage of allowing you to strengthen your muscles without moving a sore joint.