Take a seated position on the Leg Curl/Leg Extension machine. Keeping your back flat and your head erect, take hold of the sides of the machine. Tuck your legs under the weight bar with the pads just above your ankles on your shins. Take a 3/4 breath. While pressing your body down into the machine seat with your arms, extend your legs upward until your knees lock, contracting your thigh muscles. Your legs should be parallel to the floor. Hold this position momentarily, and lower your legs.