Stand up straight with a fitness ball behind your back and against the wall, your feet about shoulder-width apart. Slide down the wall until your knees reach a 90-degree angle, being careful to keep your heels flat on the floor. If you can't bend your knees to a 90-degree angle, simply go as low as you can — then return to the starting position. You might want to have someone stand next to you to prevent you from losing your balance. Gradually work up to 10 repetitions
