ab workout ... doing triceps?

yesterday I added bent-over cable tricep extensions to my routine, and I'll be damned if my abs weren't killing me by the time I was done ... did I do something wrong, or are my abs (which aren't getting as much attention as they used to) just weak?

thanks for any suggestions ...

You're not doing anything wrong. When doing that exercise your abs are working to stabalize you and keep you from flinging backwards, so if you're not used to it you'll feel the affects.

Yeah my abs get hit hard during squats.