forced push down leg raises work great for lower abs heres how to do it
ly on the floor and have someone stand over you while you hold on to their legs (thier feet should be underneath your shoulders so if you look up you see their stuff) then raise your legs toward them and have him/her throw down your legs as you try to resist( you should go left side, straight, right side) and keep your legs toward him/her
its a pretty advanced movement and should be started out with not too much force but trust me movement this great
good luck