I cant do the butt kicks with that many risers. I try with 3 risers. Butt..last time I did them, I screwed up my back. I guess my core just isn't strong enough to take me over that many times and I ended up straining my back.
I think I'll just do some jumping jacks, high knees or whatever just to keep my heart rate up. I've had to take off almost 2 weeks from exercising because of it so better safe, than sorry! I'd be interested in other's modifications..