Eric Berkson, Ryan Aylward, James Zachazewski, Joseph Paradiso, Thomas J. Gill

Abstract

Previous biomechanical studies have attempted to quantify the mechanics of throwing and to measure the forces sustained in the upper extremity during high-velocity pitching. Biomechanical testing of pitchers in its current state, however, is subject to inaccuracy and cumbersome to perform. Testing requires controlled laboratory conditions where “high-speed” cameras are set in fixed positions around the subject, and the motion of the arm is tracked with navigational markers affixed to the pitcher. Variables such as acceleration and velocity are derived from a series of calculations based on positional data. We hypothesized that direct measurements of acceleration and velocity could improve kinematic analysis of baseball pitching. To assess this hypothesis, a controlled validation study of a novel Inertial Measurement Unit (IMU) array was performed. Each IMU consists of three-dimensional accelerometers and gyroscopes, permitting direct measurements of acceleration and angular velocity. Simultaneous testing of a single professional baseball pitcher was undertaken utilizing both “high-speed” camera-based motion tracking and our newly developed IMU array. Results indicated an acceleration phase during the pitching cycle lasting 0.022 seconds. During this phase, traditional motion tracking cameras recorded four data points. Thirty data points were recorded by each IMU. The IMUs recorded 60.4g’s of acceleration at the shoulder and 83.0g’s of acceleration at the wrist. Acceleration over 100g’s was documented at the hand. While no statistical comparison between systems was possible in this early proof-of-concept study, the IMU array successfully recorded appropriate rises in acceleration and velocity when compared to the camera-based motion-analysis system and offers the first direct measurement of acceleration in a professional pitcher. As such, the IMU array promises to provide more accurate kinematic measurements than alternative methods. The technique also allows measurements outside of controlled laboratory conditions and therefore could provide positive practical and clinical applications ranging from improved player training to injury prevention and rehabilitation.