This exercise is used to help activate and start the strengthening of the Quadriceps and help the VMO (Vastus Medialis Obliquus) increase in tone. The VMO is a very important muscle as it helps the knee cap to track centred and smoothly in the groove that it lies in. The VMO muscle can become weak after knee pain or surgery and it is important to rehab it properly to decrease pain and regain function in the knee. Because this is an isometric exercise (the knee joint does not move during the muscle action) it is appropriate to do early on during the rehab phase. Do not start exercising post-operatively until instructed by your physio or surgeon.