Mechanics of Rotation Part 2: The Throw

In the previous post we talked about some of the foundations of human movement. To sum that up, movement is the combination of expansion and compression, and our guts and air pressure in the thorax have a significant impact on movement. Compensations occur based on these factors that can determine movement capabilities.

With this understanding as our foundation of understanding human movement and rotation, let’s take a deep dive into some particular movements in sports that involve rotation.

The throw has typically been broken down into the following phases: wind up, stride, cocking (early and late), arm acceleration, and arm deceleration. There are certain positions that the thrower needs to get into in each phase to have an efficient throwing motion.

Wind Up: This phase is marked by picking up the front foot and shifting the bodyweight to the back leg. This requires the ability to expand the posterior hip on the back leg. This gives space to load the back hip.

Stride: This phase consists of the back leg beginning to push and the lead leg stepping forward and making contact with the ground. This requires a couple of things to happen. The back hip has to begin moving from the expanded state from the wind up through compression to push the body weight forward to the lead leg. The lead leg in this phase also goes through a transition. It will start in expansion and begin compressing when the foot hits the ground.

Early Cocking: In this phase, the throwing side chest has to expand to allow the arm to lay back.

Late Cocking: This phase leads into arm acceleration because the previously expanded chest wall begins to compress to bring the arm forward. Also, the lead leg is continuing to compress and push into the ground to get lead hip pullback. We also need a front side ab wall to remain compressed in order to maintain the proper arm slot on the throwing side. A weak front side ab wall that cannot stay compressed as force from the ground moves up the kinetic chain will cause the athlete to side bend towards the back side. This leaves him in a poor position for efficient rotation.

Arm Acceleration: This phase involves a continued compression of the throwing side chest wall. This allows the shoulder to internally rotate. As the throwing side chest wall compresses, the opposite side chest wall must begin expanding to allow a turn towards the lead side.

Arm Deceleration: The most important part of this phase is an expansion of the upper, posterior ribcage on the throwing side. This expansion helps to slow the arm down through follow through. The opposite side chest wall is also expanded in this phase. This expansion is important to continue turning toward the front side over the lead leg. An inability to rotate the torso toward the front side has been shown to correlate highly with throwing shoulder injury.

Training for throwing: Now that we know the joint position and expansion/compression requirements for throwing effectively, let’s talk a little bit about training to throw. Training for shoulder care is much more than just mindlessly using a band for internal and external rotation. The athlete has to be able to get in and out of all the positions mentioned before. This is part of why the assessment process is so crucial to effective training. Understanding how the athlete moves and what positions he lacks sets the stage for a training program that will transfer to throwing harder and staying healthy. There are two common problem areas that we see with many throwers. The first is poor posterior expansion of the back hip. This does not allow the thrower to load the back hip effectively. This can lead to other compensations to continue throwing hard such as too much knee bend on the pushing leg or excessive trunk rotation to make up for the lack of hip loading. Correcting this should use exercises that put the pelvis into a position that allows expansion in that area. This could look like a split squat with a cable reach on the same side arm of the leg that is forward. The second is a lack of posterior expansion of the upper rib cage on the throwing side. This means that the thrower will have a tough time decelerating the arm after the throw. This puts a lot of stress on the smaller rotator cuff muscles to slow the arm down. Training this can be done with any reaching type activities. This can be trained at the top of a push up or with a cable press and reach.

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