Strengthening exercises
You should work with your physical therapist to learn the best exercises and strengthening programs for your needs. Studies suggest that strengthening the leg muscles, especially the quadriceps femoris muscles (muscles are at the sides and front of the thighs) through exercise can help support and protect the knee joint. Following are some easy ways to strengthen these muscles;
Straighten and raise the leg while sitting down or lying.
Place one foot up on a step or a table/stool. Step down, and then the other repeat the step-ups with the alternate foot.
Sit on a chair for a moment, and then stand. Sit and stand repeatedly for a minute. Doing this in a slow, controlled way can help strengthen the working muscles. For better results, avoid using the hands to support you.