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Now let’s focus on the arms, beginning with the player’s left arm. We learned in the launching phase that the left arm pulls on the bat handle and this pulling action continues on after contact all the way through to the end of the swing as seen in Figures 5-8a through 5-8c.
The muscles responsible for this movement are the Posterior Deltoid, Rhomboids and Middle Fibers of the Trapezius muscles and by virtue of the positioning of the left arm during the swing, two of the rotator cuff muscles were also involved, those being the Infraspinatus and Teres Minor. These muscles were first seen in Figure 4-32 back on page 52 and shown again for you in Figure 5-9.
Now, regarding the player’s right arm, we also learned back in the launching phase that it pushes on the bat-handle and this pushing action continues on after contact all the way through to the end of the swing as seen in Figures 5-10a through 5-10c.
The muscles responsible for this movement after contact are the Pectoralis Major, Serratus Anterior, Coracobrachialis and Anterior Deltoid muscles. These muscles were first seen in Figure 4-42 back on page 56 and shown again for you in Figure 5-11.
Finally, the wrists and forearms do a rollover after contact where the right forearm, which is initially in a supinated position at contact seen in Figure 5-12a ends up in a pronated position at the end of the swing seen Figure 5-12b.
The left forearm, which is in a pronated position at contact seen in Figure 5-12a, ends up in a supinated position at the end of the swing seen in Figure 5-12b.
These alternating forearm positions enable the player to swing the bat unimpeded through contact so that there is no loss of speed or power.
The muscles in the right forearm that pronate the forearm are the Pronator Teres and Pronator Quadratus. These muscles were first seen in Figure 2-45 , page 26 and are shown for you again in Figure 5-13.
The muscles that that supinate the left forearm are the Biceps Brachii and Supinator. These were first seen in Figure 4-39, and are shown for you again in Figure 5-14.
This completes all of the muscles involved in the swing from the loading phase to the launching phase and in to the follow through. As you can see, a significant amount of your skeletal muscles are involved. With proper understanding of the role each muscles plays, your training will become more efficient and your batting average should improve.
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