We are talking about something I constantly refer to: The Secret. I learned it many moons ago, when I went to the original Yankee Stadium every chance I had and spent a lot of time watching the Yankees' Big Three pitching rotation. I saw what they were doing and how they were doing it; they all drove off the lower half of the body, using the legs, the hips and the torso in one continuous (and, it seemed to me, seamless) motion, thus creating a nonstop flow of energy all the way up through the shoulder and arm to the fingertips---and taking a lot of pressure off said shoulder and arm so they could throw harder and faster with less effort, even Ed Lopat who was not a fireballer. I made a note of what I saw and started working on this on my own, and as I practiced this essential element of good mechanics I found that I was doing exactly what those three pitchers were doing. Even though I was not a rip-roarin' fireballer I too was throwing harder---and a little faster---with less effort. How not to get a sore arm---or a sore elbow---or a sore shoulder---or a sore anything else.
The whole idea is to get the whole body involved in the process of pitching a baseball and not throwing with just the arm and the shoulder. There are some drills available that one can use in mastering THE SECRET, such as the "Hershiser" drill that aims at getting the hips fully involved. And to think that Vic Raschi, Allie Reynolds and Ed Lopat knew about it way back when! 8)