Intra-Athlete Variability in Pitching Biomechanics at the Shoulder Joint

Introduction: Human variability is defined as the possible values for any measurable inconsistent characteristics in human beings. New studies are showing that elite athletes are not able to perform skills without variability in their movements. Many coaching techniques stress repetitious training which can lead to overuse injuries. The discovery of variability in athletes form may help to change training techniques to exercises that will help promote variability in athletes form and prevent overuse injuries. Purpose: The purpose of this study is to evaluate the variability in the shoulder biomechanics of DII college baseball pitchers during their pitching motion. Subjects: Five NCAA division II baseball pitchers (mean age: 19.4 ± 1.5 yrs; mean mass: 83.4 ± 3.3 kg) from a university in the northeast part of the United States participated in the study. Each pitcher performed between 12 and 15 pitches with their motion recorded using an 8-camera 3D system (Vicon). Three dimensional angles at the shoulder, elbow, and wrist were calculated and comparisons were made between maximal external rotation of the shoulder, maximal elbow flexion and maximal wrist flexion of each trial for each individual athlete. The average joint angles and standard deviations across the trials were then calculated. Results: The average values for maximal external shoulder rotation were greater than for both elbow flexion and wrist flexion for all subjects. The variability in the joint angles ranged from small (1.09 degrees) to large (4.87 degrees), with no joint demonstrating greater variability than any other across the five subjects. Similarly, each subject demonstrated their largest variation at a different joint. Conclusion: The existence of variability in the motion of these trained pitchers implies that consistency is not achieved in terms of the upper-body kinematics. Furthermore, each subject appeared to demonstrate an individual movement pattern despite the goal of the skill being consistent. This suggests that coaches should avoid relying on a single 'optimal model' when skill acquisition is required in multi-joint, ballistic movements.