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Now, the left shoulder ends up slightly shrugged in this position (See Figure 2-6 on previous page) which is a function of the Upper Fibers of the Trapezius. The left scapula, or shoulder blade, is also protracted, or moved anterior toward the front of the body, in this position. This motion is caused by the left Serratus Anterior. See Figure 2-8 for both of these muscles.
Now, the contraction of these muscles stretches, or loads, the muscles on the back of this same leading left shoulder, namely the Posterior Deltoid, Rhomboids and Middle Fibers of the Trapezius and because the left arm is so severely adducted across the player’s body, two of the rotator cuff muscles are also undergoing a stretch and those are the Teres Minor and Infraspinatus. See Figure 2-9.
All of these muscles are now fully loaded or stretched and ready to swing forward in this position and can be seen in more anatomical detail in Figure 2-10.
Now let’s take a look at the back arm, or right arm. The movement of the back arm away from the pitcher and laterally raised away from the player’s body is known as shoulder abduction. See Figure 2-11.
This action is caused by the Supraspinatus and Middle Deltoid muscles. The right scapula may also be slightly shrugged or elevated in this position depending on the player’s style and if so, this motion caused by the Upper Fibers of the Trapezius. See Figure 2-12.
Now the contraction of these muscles stretches or loads the antagonistic, or opposing, muscles on the same side of the body namely the Latissimus Dorsi, Teres Major, Serratus Anterior and Pectoralis Major. These muscles are now fully loaded and stretched, ready to help swing the bat from this position and can be seen more clearly in Figure 2-13.
In the next section we will talk about the second noticeable movement during the loading phase which is, the backward rotation of the spine, and identify the muscles involved with it.
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