Intro to Biomechanics Using PitchAI: Introduction

Introduction to

Biomechanics Using PitchAI

Mike Sonne, PhD / Colin McKinnon, PhD / Elora Brenneman Wilson, PhD


When ball tracking started to rise to prominence 10 years ago, everyone knew spin rate and axis were important things to consider when evaluating pitcher performance. With PitchAI, human motion (biomechanics) data are now becoming available to every player and coach for the first time. Much like when the Rapsodo first came out – everyone knows these data are important – but what do they mean? This is meant to walk you through your first ever biomechanics assessment using PitchAI, and give you the information you need to make it part of your daily routine.

But first, definitions…

Biomechanics is defined as “the study of the mechanical laws relating to the movement or structure of living organisms”. In our case – we’re talking about humans. Humans that throw things as hard as they can. When we study biomechanics, we’re primarily looking at two things:

Kinetics and Kinematics

Kinetics describe the forces that are acting on, within, or produced by the body. These are typically described with metrics like pounds, kilograms, Newtons, Newton-metres, grams, etc.

Kinematics describe the angles associated with human motion, and are typically described in degrees, degrees per second, or distances travelled.

So, how does this impact pitching?

When we are looking at the pitching delivery, we typically want to see the pitcher move faster, while minimizing the forces produced. That can be tough! f you are moving faster, you typically require more force to do so (exposing the body to greater forces!) The idea that an athlete can move faster, while reducing their forces, is often referred to as efficiency (and in PitchAI, that is exactly how we define efficiency).

How does everything work together?

While this is meant to be a biomechanics primer, I want you to keep one thing in mind – for every single aspect of biomechanics, researchers and scientists dive into the minutia of how forces are produced and tolerated by the body. Getting into the weeds, you’ll learn about concepts like joint stiffness and stability, and how those things can be impacted by constraints and environmental challenges. For those of you with a biomechanics background, this is simply the beginning. For the rest of you – let’s start small (super small) and build from there.

Years and years of biomechanics research by people like Glen Fleisig, Gretchen Oliver, Kyle Boddy, Tom House, Ryan Crotin, and Ben Hansen, have identified key items of focus when understanding the generation of velocity in pitching. When you’re first getting started, it’s more than fine to focus on one of these metrics. That being said, as your skills grow, you’ll begin to understand things like:

  • A greater external rotation of the shoulder is typically associated with greater arm speed. 
  • A longer stride can impact the ability to separate the hips and shoulders. 
  • Greater stride lengths can increase how effortful a pitch becomes.

Don’t get lost in the amount of detail – let’s start small and build outwards. One of the best ways to interpret biomechanics data is to look at examples and compare them – for example, someone who throws hard compared against someone with lesser velocity. A young athlete against a more veteran one. Someone throwing off of flat ground vs a mound. All of these use cases are great ways to use PitchAI – but also great foundations for understanding mechanics

My first biomechanics report - diving into PitchAI

So, you have filmed a pitch and the results are back. Let’s dive into our first PitchAI biomechanics report and break down some of the data. The metrics in PitchAI can be broken down into a beginner, intermediate, and advanced knowledge base.