whether one measures it in feet-pounds (hand-pounds?) or urgghs, one is doing measurable work as per physics and the goal (generally speaking) is to fail. i feel it's worth repeating, the goal is to fail. for the muscles to surrender, unable to follow instructions. and after each failure you rebuild so that the next time you can fail better. try again. fail again. fail better. days go by.
it's fulfilling because there's only one right way to fail -- you're assured to be failing correctly. which almost isn't failing. because in the rest of your life, your failing is flailing and far more often than not, you sense that you're not rebuilding, not preparing yourself to fail better. which almost isn't failing. whatever it is.