Relationship Between Arm Path, Ball Velocity, and Elbow Varus Torque in Professional Baseball Pitchers
Brittany Dowling; Alexander Hodakowski; Bjorn A. Olmanson; Matthew R. Cohn; Patrick J. Pauley; Nikhil N. Verma; Gregory P. Nicholson; Grant E. Garrigues
Descriptive laboratory study · Volume 11, Issue 12, December 2023
Background
The question this study asked
Most pitching instructors coach a shorter arm path, meaning less total distance traveled by the arm across the pitch. The theory behind it is that a shorter path sequences the body segments better, moves energy through the kinetic chain more efficiently, and produces more velocity while keeping torque on the elbow down. The authors set out to test that, going in with the hypothesis that shorter arm paths would come with higher ball velocity and lower elbow varus torque.
Methods
How the study was conducted
One hundred and eighty-two professional pitchers each threw between eight and twelve fastballs while being recorded by three-dimensional motion capture at 480 Hz. Arm path was measured as the total distance traveled by a marker on the hand across the pitch, and was broken into an early phase, a late phase, and a total. A linear regression model examined how arm path, elbow varus torque, and ball velocity related across different pitchers, and a linear mixed-effects model with random intercepts examined the same relationships within individual pitchers.
Results
What the measurements showed
Comparing pitcher against pitcher, total arm path showed only a weak correlation with higher elbow varus torque. Ball velocity, by contrast, correlated strongly with early, late, and total arm path. Within individual pitchers the relationship was stronger still, with elbow varus torque strongly and positively correlated to both early and total arm path. Individual pitchers varied considerably in their own arm paths across pitches, by roughly 30 cm in the early phase and 21 cm in the late phase. Quantified, every 30 cm of additional early arm path came with a 1.29 N rise in elbow varus torque and a gain of 0.354 m/s, or about 0.79 mph, in ball velocity.
Conclusion
What it means
Within an individual pitcher, a shorter arm path came with less elbow varus torque but also less velocity. The two move together, so shortening the arm path reduces load on the medial elbow at a cost to the pitch. Working out which mechanics reduce elbow torque for a given pitcher may help coaches and trainers correct the patterns that matter, and a clearer understanding of what shortening the arm path does to the throwing arm may help reduce injury risk.
