Sit on a chair and place another chair in front of you. Your butt should be in contact to the backrest of the chair. Extend your right knee and place the heel on the chair in front of you.
Using your quadriceps try to move your knee down while you flex the ankle. Maintain the tension during the required time and then repeat with the other leg.TIPS: While your are doing the exercise, move only the legs, make sure you don't move any other part of your body.