HOW: Sit down with your feet directly below your knees. Drive the balls of your feet into the ground and raise your heels off the ground. Your knees should come up in the position while the balls of your feet remain in contact with the floor. If you would like, you can increase the difficulty of the exercise by pushing on your knees with your upper body or by putting weights on your lap.
FEEL: You should feel your calf muscles working to lift your heels off the ground.
COMPENSATION: When you lift your heels off the ground, ensure that you do not lose contact with your big toe against the ground. Continue to push hard through your big toe to lift your heels.