The Shoulders do all the work on the backswing. Then the body's core (unwinding) bring the arms down and around to the finish. The arms never help or move independently. They don't actively move away from the body (reach or stretch out) . Maybe through inertia they "elongate" (if the golfer didn't setup the arms correctly with elbows close together), but the point is that you don't use the arms to reach out or pull back in. There may be a slight pinching between the elbows "holding" or slight tension in the wrists to "maintain" the setup shape to the top and back down through impact. You want to feel the Shoulders do the work on the backswing, then just unwind and feel the body's rotation bring the arms back down and around. There is a "harmony" in this move... again like throwing a ball... the body unwinds to move the arms/club through in one continuous move
all the way to the finish. It is kind of like the body is swinging the arms, but if the arms/hands try to help, the body will stop and it ruins the move. Hope this helps.
Move Less ... Get Good! DUPLESSISGOLF