Glute-Ham Raise
The exact setup of this exercise depends on whether you have a specialised glute-ham raise (GHR) machine or you are improvising with an immovable object (such as a barbell or the lat pulldown machine) that allows you to hook your heels underneath to hold you in place. The following represents how to use the GHR machine however you should intuitively be able to relate the directions to the improvised version.
Position yourself face down on the GHR machine with your knees on the soft pad and feet wedged under the ankle rolls. Your buttocks point out, your back is flat and parallel to the ground and the hamstrings are not yet forced to contract. Depending on the machine type AND your overall hamstring strength, the hands may be either behind the head or holding the hamstrings in support. This is the starting position.
Commence the movement by contracting the hamstrings and slowly lowering the body down by opening up the angle at your knee. With your heels locked down, you should feel the tension through the hamstring as you lower to the floor.
As you approach the floor, most people will need to brace themselves into a push-up position before then propelling themselves off the ground to give enough momentum to get back to the starting position. Those with very strong hamstrings may be able to reverse the movement without needing to use the hands to push off the floor.