I based this exercise on jhern and that unnamed illustrator's posts. It helps you get the feeling for using your arm as a whip as opposed to it being the sole contributor to hand speed.
First I turn myself at the torso like I'm about to throw. (Think reachback without moving your arm yet.) My shoulder blades are near perpendicular to my hip I completely relax my throwing arm and start swinging it back and forth like a pendulum along the same line as my hips. (Jhern mentioned to think of your upper arm as being made of rope.) I swing my arm all the way back and forth in a half circle. When I'm ready I wait for my arm to swing up to the throwing position parallel to the ground. Once it reaches its apex I start swinging my torso. First from the hips and then the belly. My limp arm just naturally follows along for the ride. I can tell just from the "whoosh" my arm makes that it's flinging much faster than my normal throw.
First I turn myself at the torso like I'm about to throw. (Think reachback without moving your arm yet.) My shoulder blades are near perpendicular to my hip I completely relax my throwing arm and start swinging it back and forth like a pendulum along the same line as my hips. (Jhern mentioned to think of your upper arm as being made of rope.) I swing my arm all the way back and forth in a half circle. When I'm ready I wait for my arm to swing up to the throwing position parallel to the ground. Once it reaches its apex I start swinging my torso. First from the hips and then the belly. My limp arm just naturally follows along for the ride. I can tell just from the "whoosh" my arm makes that it's flinging much faster than my normal throw.