I have never had regular access to reverse hyper machines but the few times I have used them I feel a very unusual pain towards the end of the range of motion. It is stretching sensation but not a muscular sensation, it feels almost as if the nerves are being stretched.
Has anyone else experience this? Is there some flaw in my technique?
Raining Blood - I think I've had the same experience. It doesn't particularly hurt but I try to stay away from the stretchy nerve feeling because I already have a bad l4/l5 disc and I reckon the pressure isn't good for it.
I still use the reverse hyper but drop the weight, limit ROM, and adjust my hips on the pad.
I'd say to focus on gaining extra flexibility at the hamstrings, glutes and where the hips meet the lower back (without flexing the lower back) using the downward facing dog and triangle yoga poses (in particular the triangle pose.) Lack of flexibility will make your lower back to arch at the bottom of the movement. It can also help if someone puts his hand on your lower back and apply pressure on it (this prevents flexing of the lower back and sacrum.)
Also (and this sounds counter-intuitive) make sure to always stretch your hip flexors (the iliopsas)