The Effect of Throwing Intensity on Overhand Throwing Mechanics

Abstract

Overhead throwing is a dynamic and demanding movement that places great amounts of stress on the throwing arm. Current consensus attributes most throwing-related injuries to repeated microtrauma of the musculoskeletal structures surrounding the shoulder and elbow. After sustaining an injury to the shoulder or elbow, overhead athletes complete an interval throwing program as part of the rehabilitation process. Interval throwing programs gradually increase throwing intensity over several weeks by manipulating throwing volume and distance to produce successively more throws at successively longer distances. Recently, there has been an increased call for objective methods of quantifying how and when to progress through the interval throwing program, including monitoring throwing intensity with a calibrated radar gun. Although objective methods of throwing intensity quantification are beneficial to the rehabilitation process, how the demands placed on the throwing arm change throughout the intensity range typically seen in throwing rehabilitation programs is not well understood. Therefore, the purpose of this research was to model changes in throwing arm joint loads as pitchers progressed from low to high intensity throwing.

Thirty-two skilled throwing athletes were recruited to participate ($21 \pm 2$ yrs; $1.86 \pm 0.08$ m; $89.0 \pm 10.2$ kg). Once participants completed their typical non-throwing warm up, 50 reflective markers were placed at relevant anatomical locations and participants had their throwing mechanics recorded during their throwing warm up using a passive optical motion capture system. The primary findings of this project were two fold: first, the intra-participant relationship between throwing arm joint loading and throwing speed appears to be nonlinear in form. Specifically, the form of this relationship is quadratic linear concave up indicating that, as throwing arm joint loading increases, corresponding increases in throwing speed become successively smaller and smaller. Second, as body mass and height increase, the slope estimating the relationship between throwing arm joint loading and throwing speed decreases. In addition to providing novel insight into the intra and inter-participant relationships between throwing arm joint loading and throwing speed, these findings also serve as an initial exploration of, and proof-of-concept for, the use of multilevel modeling strategies in sports biomechanics research.