Person lies prone on the ground (stomach touching ground). Hands clasped behind head or back. Legs together and straight. Then the person has to lift head, upper body and straight leg raise simultaneously.
That is a back extension exercise for your lower back. You can also do it with your arms stretched out parellel to the floor above your head, this is called the superman. Also very good for your lower back.
I would have called it a reverse sit-up, but I have seen leg raises called reverse sit-ups also. have a look at this page, they call it a back extension www.doctorortho.com/exercises/back.html
my old gym used to have a machine for that. You'd lay your pelvis on the rest and stick your ankle between two roller cushions (above and below) which allows you to raise and lower your back through the legs. Its exactly the same as you discribed but with slightly greater range of movement. We called it "back-ups" though i suspect it's not the official term... but at least you know there are people who call it backups.
I heard a gym instructor called this name, too. I tried this exercise once, probably did something wrong, and felt very painful the 2nd day (or, just lack of exercise).
may i ask what it's purpose is? you mentioned it's good for the lower back..does it strengthen it like situps strengthen the abs?
sounds tough... it sounds like an exercise where you'd have to be careful..like many mentioned above, sounds painful..perhaps if you dont' do it correctly?
