Aguinaldo AL, Chambers H. Correlation of Throwing Mechanics With Valgus Overload in Adult Baseball Pitchers. American Journal of Sports Medicine, 2009, 37: 2043-2048.
The purpose of this study was to correlate the valgus stress experienced at the elbow with biomechanical characteristics of the individual throwing mechanics of 69 pitchers. The subjects played either professional or college baseball with a mean age of 20 years. They threw off of an elevated mound to a strike zone at the regulation distance from home plate. The fastest pitch that hit the strike zone with mechanics judged to be normal for that individual was selected for analysis.
Part of the statistical analysis focused on two of these biomechanical characteristics: trunk rotation and trunk lean. For trunk rotation, the subjects were divided into two groups based on whether the trunk rotation towards the target started before or after the striding led touched the ground. The findings, consistent with other studies, showed that early trunk rotation leads to increased elbow stress. The elbow stress in the pitchers that initiated rotation early had valgus torque over 40% greater than the pitchers that started rotation after foot contact.
The primary focus of this blog will be the study results related to the trunk lean. The group was divided into those pitchers that had a lateral trunk position that was flexed away from the arm and those whose trunk was laterally flexed towards the throwing arm (contralateral versus ipsilateral). This differentiation of trunk position created “overhand” and “sidearm” groups. Fourteen of the 69 pitchers had a sidearm delivery (laterally flexed towards throwing arm). This group was discovered to have 43% more elbow valgus torque than the “overhand” group. This finding raises the following questions: Is this their natural throwing motion, and they have to deal with the increased torques? Should these pitchers be encouraged to alter their mechanics? Is there a restriction in the thoracic spine that might be altering their mechanics?
At Gray Institute®, the thoracic spine is considered one of the “big rocks” of function. The thoracic spine has a substantial amount of motion in all three planes. In addition, the thoracic spine must have the ability to provide these motion resources in any combination that the function dictates. During the windup phase of throwing, almost all pitchers will rotate and laterally flex to the throwing side with some flexion as well. As the body is maximally load and then begins to throw the ball after foot contact, the thoracic vertebrae will rotate towards the target, but the motion at the joints in the spine becomes complex. The lateral flexion of the spine towards the throwing side changes to away from the throwing side as seen in the “overhand” thrower group in this study. In the sagittal plane, the thoracic spine will go from a flexed to an extended and back to flexed position throughout the throw.
Knowledge of the changing lateral position of the trunk, combined with rotation and extension, then challenges movement professionals who train and rehabilitate pitchers. Could a loss of lateral flexion away from the throwing side cause a pitcher to subtly shift from and “overhand” towards “sidearm”? Could this then result in injury from the increased elbow torque? Does the movement specialist have a strategy for restoring contralateral flexion of the spine during the complex mechanics of throwing?
The 10 Observational Essentials of Certification in Applied Functional Science® (CAFS) provide multiple strategies for practitioners to start with the movement success that a pitcher demonstrates in order to restore the combination of motions required of the thoracic spine. Using asymmetrical driving motions of the arms, or prepositioning the trunk are two powerful opportunities to convert what the patient / client can do into the combination that they are having difficulty creating.