There are six phases to the softball windup. When describing the phases of the windup, you should imagine the hands of a clock. The pitcher's throwing arm makes a complete circle, with the starting and ending points both at approximately 6 o'clock. Check the image below:
Here, you can see Phase 1 (the windup), Phase 2 (6 o'clock to 3 o'clock), Phase 3 (3 o'clock to 12 o'clock), Phase 4 (12 o'clock to 9 o'clock), Phase 5 (9 o'clock to 6 o'clock), and Phase 6 (ball release/follow-through).
Time to go a little more in-depth:
Phase 1:
The windup is the preparatory movement of the motion. This is where the pitcher generates their momentum. Not all windups are the same, with a wide range of variation from pitcher-to-pitcher. The main goal of this phase is to transfer your momentum efficiently to Phase 2. A pause or interruption can put the pitcher at risk of injury as they (after pausing) may try to generate momentum from somewhere other than their lower body/trunk.
Phase 2:
This is where muscle activation begins to elevate more quickly. Here, the pitcher's body weight is on the ipsilateral leg while striding out, thereby activating the gluteal muscles in order to stabilize the pelvis (more on that in post #2). The contralateral leg undergoes knee extension, as well as hip flexion. In the upper body, the supraspinatus activates to help stabilize the humeral head. The deltoids are also working here, helping to elevate the throwing arm.
Phase 3:
The supraspinatus activity drops off during this phase, but there is an increase in teres minor, infraspinatus, and posterior deltoid activation. Here, the pitcher should be striding directly toward home plate. Studies have shown that pitchers with a greater stride length tend to throw with a higher velocity. (Note: it is important that the pitcher's support foot remains in contact with the ground, because if that foot "leaps" off the ground, the pitch is considered illegal)
Phase 4:
Here, the pectoralis major and subscapularis engage in an effort to protect the anterior capsule. As the stride leg begins to take on a greater portion of the body weight, the pitcher's gluteus medius must work to keep the pelvis elevated on the opposite side to efficiently transfer energy from one foot to the other. We also see the greatest activation of the biceps here, helping to accelerate the arm.
Phase 5:
During this Phase, the pectoralis major and subscapularis are still active, while we see the activity of the serratus anterior spike. The pectoralis and subscapularis act together to internally rotate and adduct the humerus while the serratus anterior helps to stabilize the scapula.
Phase 6:
This is the follow-through phase. The pitcher's glutes, triceps, and teres minor are most active here. Hip rotation is also important here, ending in a more perpendicular orientation to home plate.
Conclusion:
Long story short, the bulk of the energy generated during the softball windup is created in the lower extremities. Because the pitcher spends the majority of the time in a single-leg-stance, the gluteals are working hard throughout the movement. They are working to stabilize the pelvis which, in turn, helps to transfer momentum from the lower half of the body to the upper half.
This wraps up post 1 of 2. In the next post, we'll dig into injury prevention and how focusing on the hips and pelvis during your workouts can reduce injury risk in the pitcher's upper extremities. Thanks for reading!
Sources:
1: http://hhpr.uark.edu/biomechanics/KINS/ATT_oliver_pt1.pdf
2: http://www.dynamicchiropractic.com/mpacms/dc/article.php?id=38688
3: http://lowerextremityreview.com/cover_story/powering-the-windmill-lower-body-mechanics-of-softball-pitching
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