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The loading phase takes us from the stance position to the launching position and it consists of five noticeable movements: 1) the backward movement of the shoulders and arms, 2) the backward rotation of the spine, 3) the beginning of the timing step, 4) the cocking of the hips, and 5) the cocking of the wrists. In this section we will define the movements and muscles of the first noticeable movement, The Backward Movement of the Shoulders and Arms.
The first noticeable movement that takes place during the loading phase is the backward movement of the shoulders and arms toward the catcher. This action helps to load or stretch different muscles in each shoulder that will be released or contracted later during the swing. In Figures 2-1a through 2-1c, we see both shoulders and arms moving in the same direction, back and away from the pitcher, however, each shoulder uses a different set of muscles to get there.
Now, before we identify the muscles involved with these movements, I want to clarify something for you here. This movement seen in Figures 2-1a through 2-1c, with the arms and shoulders moving back toward the catcher, is often referred to as rotation of the arms or rotation of the shoulders however, this actual terminology is not anatomically correct.
And the reason why I want to bring this up to you here is because if you go to a personal trainer or strength coach who may not be familiar with the baseball swing, and you ask them to show you some exercises to help you strengthen the rotational movement of your arms or shoulders, what they are going to think that you are asking them to do is to show you exercises to help you throw a ball harder and faster (see Figure 2-2a below), and not swing the bat harder and faster, (see Figure 2-2b below).
And that’s because anatomically, Figures 2-3a and 2-3b below demonstrate external shoulder rotation, or external arm rotation, and Figures 2-4a and 2-4b demonstrate internal shoulder rotation or internal arm rotation.
Now compare Figure 2-3b and Figure 2-4b with Figure 2-5 below, which does not involve any rotation of the arms at the shoulder joint, and you should be able to see the difference.
And so this is the reason why I have chosen to identify this first step in the loading phase as the backward movement of the shoulders and arms because as you are going to see here in a minute, neither shoulder or arm is actually rotating and in fact, each shoulder and arm is being moved by a completely different set of muscles.
Okay, so with this is mind, let’s first take a look at the players left arm and shoulder. As he prepares to load his body, by going from the stance position to the launching position, the left arm and shoulder is moved backward and away from the pitcher and the correct name for this movement is adduction of the shoulder or adduction of the arm. See Figure 2-6.
This movement is caused primarily by the action of the Pectoralis Major and is also assisted by the Coracobrachialis, Latissimus Dorsi, and Teres Major muscles, all on the left side of the body. See Figure 2-7.
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