running bleachers with a medicine ball...

[RSP]

Ok so someone on here suggested running up bleachers and walking down carrying a 20lb medicine ball. Well I decided to run up and down with a 15lb medicine ball and let me tell you it was KILLER on my abs.
Has anyone done this? I presume that holding the medicine ball made the abs stabilize the core so my upper body wouldn't twist side to side b/c of the momentum the medicine ball caused? Am I correct? I know it was brutal. I did 2 sets of 10 and I didn't want to breathe b/c my abs hurt so bad.
Anyone tried these with similar results?

[BigJimCalhoun]

We used to have to hop up and down them on one foot.

[RSP]

I actually used to hop up (never down) about 5 times on 1 foot then both feet and also did "sky lunges" from one step to another. Its never been as hard as it was running with that medicine ball. My legs were a little tired but my abs were dying.

[swabe]

I never did it with a medicine ball but our coach had us run towers carrying a plate back in the day...i cant really remember if my abs where on fire from doing it but i remember it was def hell and exhausting