Sit on a leg extension machine and place one leg under the pad with your foot pointed forward. Place the resting leg on top of the pad. The pad should rest on your shin just above your foot and you will need to adjust it to suit. Grip the hand bars (if fitted) firmly. This is the start position. Using only your quadricep, fully extend your leg, exhaling as you do so. Hold for a count of one. Return to the start position in a smooth movement as you inhale. Repeat.