I felt the process of paddling was using my core muscles. In fact, it feels like nearly all the effort is focused on your core muscles, and not much on limbs. And in some way, your body doesn't seem to twist all that much, you stay fairly square over your feet automatically, the board does the twisting. My core muscles hardly unclenched while I was on it.

It was surprising in that I thought I would have trouble making direction but it's almost automatic. Easier than paddling a canoe solo, makes me think, as you don't need as much(or any) of a hook at the end of your stroke to maintain a straight line.