Per novice:
ANd the only force on the paddle is the rotation of your torso? You
dont use your arm muscles?

I'm no expert, but in Bob Twogood's class that I took a few years ago
"Straight-Arm Paddling" was introduced as an exercise - so I'd say "No, the arms
are not completely straight all the time." But I'd also say that there's
very little arm effort involved and virtually all the power comes from rotating
the torso against the push of the leg.
--
PeteCresswell