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Think of your body’s muscles and connective tissues as a series of elastic bands, and when stretched, they pull back with greater force and increased power.
The largest one is in your mid-section between your pelvis and trunk and becomes stretched when the hips and trunk rotate in opposite directions. For example, if you look down on a pitcher or hitter from above, you would see the generation of elastic energy by the large mid-section stretch that occurs when the hips open and the trunk stays closed.
We call this hip-shoulder separation or just “separation.”
For pitching, max separation occurs at foot contact, where the pelvis rotates toward the plate while the trunk rotates away. This movement creates a stretch between the lead hip and the throwing arm, and any athlete who cannot differentiate this rotation is at a disadvantage.
However, the magnitude of the stretch between the pelvis and trunk is not the only tell-tale aspect in performance. The time of the mid-section stretch and the speed of the stretch are also essential factors.
Research has shown that altered lower body and rotational features for the trunk and pelvis decrease throwing arm velocity by limiting elastic energy generation and transfer through the trunk. These limitations also challenge the dynamic stabilizers of the shoulder and elbow and may lead to injury (ref).
In this ACIQ, we talk about the finer points of the stretch-shortening cycle between the pelvis and the trunk. We’ll look at points of singulation (when the pelvis and trunk are stacked on each other) and the degree of stretch that can be achieved between them.
We can evaluate stretch-shortening biomechanics to qualify our training and determine if the athlete is experiencing fatigue, tissue restrictions, or separation changes that may result in arm pain. Specifically, we share information on the relationship between separation and shoulder internal rotation torque and valgus torque which are involved in elbow and shoulder injuries.
An important take-home is the need to evaluate throwing arm strength to ensure that if a pitcher’s separation mechanics change, there are no weak links downstream. By improving arm strength and remediating deficits, the athlete is protected from other physical compensations that may drive up throwing arm loads.
Additionally, in our podcast, we dive into some real-world examples for training the kinematic sequence and separation. We’ll also discuss examples of how technology can assist pitching coaches, strength coaches, and clinicians in improving health and performance.