Use the plie, a classic ballet posture, to work the muscles of the thighs.  Place your hands on your hips and stand with your heels together and your toes pointing outwards.  Breathe in and rise up onto your toes.  Breathe out and lower yourself into a squatting position, making sure that your back is straight. Do not go any lower than is comfortable and stop if you feel any strain in your knees.  Breathe in again and, pressing on the balls of your feet, raise yourself as slowly as you can to the standing position.  Breathe out and rest.  Repeat three times.