Kneel on the pad with your ankles locked under the rollers behind you and your hips resting against the front support, torso upright to start. Keeping your hips extended and your body in a straight line from knees to shoulders, lower yourself forward by letting your knees bend, controlling the descent with your hamstrings rather than dropping. Pull yourself back up using your hamstrings and glutes to bend your knees back in, not by rocking your hips or throwing your upper body. It's a small range of motion for most people at first; going lower asks a lot more of your hamstrings than a leg curl ever will.