Lie face down on a leg-curl machine and lock your heels under the foot pad. Make sure your legs are fully extended and the foot pads are resting on the back of your ankles.
If the machine is equipped with handles, grip them. If not, grip the front of the pad you are lying on.
Remaining flat on the bench, with no arching of your spine, curl your legs up in a smooth arcing motion by bending your knees until your hamstrings are fully contracted. Hold for a count of one.
Slowly lower your legs to the starting position in a smooth arcing motion.
WARNING: Don’t use so much weight for this exercise that you need to swing or jerk the weight up. Doing so can cause injury to your lower back and / or hamstrings. Start with a lower weight until your strength increases.