The kinetic chain tells us that having more efficient mechanics will likely increase bat speed. So, training for bat speed IS training for efficient swing mechanics. Most of us have heard of "sequencing" and that a good swing involves moving your body parts sequentially, from the ground up. Using the larger segments of the body efficiently will slingshot the bat into rotation/swing plane, instead of pushing it into rotation with the hands. This is called the kinetic chain principle. The most efficient way to move an end point is to accelerate and decelerate body segments.