Failures of the ulnar collateral ligament (UCL) and damage to the osseous articulation of the elbow are common and severe elbow injuries that occur in baseball pitchers as a result of the excessive elbow valgus moment imposed by the baseball pitching motion. Despite high injury risk to elbow musculoskeletal structures during pitching, research characterizing muscle contributions to protecting this joint during the pitching task is extremely limited. One reason for this limitation is that common experimental methods in cadavers and living subjects are not sufficient to understand muscle function in this high-performance, high-velocity, multiarticular task. Consequently, biomechanical modeling and simulation are required to better understand contributions from individual muscles and associated injury implications. The goals of this project were to develop a framework for simulating the baseball pitching motion and to use this framework to characterize potential muscle contributions to protecting the elbow joint during this complex task.

To achieve these goals, an upper-extremity and a whole-body musculoskeletal model were developed for use in a quasi-static sensitivity analysis and a forward dynamic analysis, respectively. Additionally, because an important medial elbow muscle (flexor digitorum superficialis) inserts in the hand, a method was defined and evaluated for recording hand motion with an instrumented glove. The quasi-static simulation indicated that adopting a flexed elbow posture at a critical juncture in the pitching motion substantially decreased the ability of the medial elbow muscles to generate protective varus moments. Therefore, a more extended elbow posture may mitigate elbow injury risk. In a forward dynamics simulation of a single subject’s pitching motion, activation and contraction dynamics limited the ability of the medial elbow muscles to actively counter the rapid increase in the elbow valgus moment imposed by the pitch. In simulation, it was demonstrated that the intrinsic stiffness properties of muscles that allow them to instantaneously respond to perturbations may be an essential mechanism for protecting baseball pitchers from UCL injury. Overall, the simulation framework developed in this project represents an essential advancement to the field of pitching biomechanics that, for the first time, allows researchers and clinicians to evaluate potential contributions of the elbow muscles.