“How much wrist should I use?”
That above is a pretty common question in fly casting instruction. In my view it depends on your preferences. We tend to consider the wrist as the only joint providing the required rod butt rotation, but all joints act as a hinge so we actually rotate the rod with shoulder, elbow and wrist in varying degrees.
Our torso can translate back and forth, and even rotate around a vertical or horizontal axis. I think that the contribution of our trunk doesn’t get the credit it deserves as it can play an important role in fly casting. In fact, you can cast beautiful loops without using your arm joints at all.
This is a 12 m cast by means of just torso rotation. I am holding the rod with its butt firmly pressed against my belly and not using my shoulder/elbow/wrist at all. As you can see torso’s contribution is not negligible.