Lie facedown on a leg curl machine, position your Achilles tendons below the padded lever, and place your knees just off the edge of the bench. Grasp the bench or the handles for stability. Make sure your knees are slightly bent to protect them from overextension. Keeping your hips down on the bench, use your hamstrings to flex your knees and raise your feet toward your glutes. Squeeze the hamstrings at the top, then lower the lever arm to the starting position.