lower abs help needed.

[qazxc]

I have recently started exercising. I am a fatty (17st ish). I want to strengthen my core and can do crunches, obliques and back extensions.
I can't for the life of me do any exercises with legs in the air as they hurt my back. Is there any lower abs exercises that don't have legs in the air?

Have you tried rolling up a towel and putting it under the small of your back?

Also, rather than lifting your legs from the floor up which is a killer, try bringing your knees up and letting them go floppy (as though going for a smear) - then bringing your knees together and try extending from "halfway up" to beyond the vertical. It seems to be the lower portion of this leg-raise which causes lower-back issues.

The plank is your friend here

Plank/ mountain climbers. Hanging leg raises are really good but you need to be quite strong and have a good grip.

check out some pilates exercises on youtube:)