How to perform a seated leg extension with an animated image showing the move. Click on the picture to see the full sized animation.

1. Adjust a leg extension machine so that your back is flat on the pad and your hips are positioned so that your knee is lined up with the axis of the machine.
2. Adjust the ankle pad so that the pad is nestled comfortably between your foot and your shin.
3. Extend your legs until your feet are directly in front of you.
4. Pause before you lock your knees. Do not lock your knees.
5. Lower your legs until you are sitting comfortably again.

This is a good exercise to do as a superset with prone leg curls, which is often a part of the same machine but on the opposite side.