Sift - OpenBiomechanics Project: Analysis of Baseball Hitters at Different Levels of Competition

Abstract

The OpenBiomechanics project is an initiative started by Driveline Baseball Research & Development, and provides the general public a marker-based motion capture data set of 100 pitchers and 98 hitters at different levels of competition [1].

The authors provide raw data without any reports or analysis, allowing the general public to use it as they see fit. While numerous articles provide in depth looks into the biomechanics of the baseball swing [2-4], there is a noticeable scarcity in articles that delve into biomechanical disparities between various levels of competition, such as contrasting differences between college and high school baseball players.

This tutorial is designed to demonstrate the use of Sift to analyze the variance in pelvic angular velocity in internal/external rotation between high Blast bat speeds [5] among college and high school baseball players.

Downloads and Relevant Links

Start by downloading the following two zip files.

1. OpenBiomechanics Project: Driveline Baseball data
2. C-Motion Specific Files

Please note, these downloads contain a large amount of data. Building CMZs is a slow process, so if you want to speed it up to follow along with building CMZ portion of this tutorial cut the number of datasets under openbiomechanics-main down to 3-5 subjects.

If you want to skip the Build CMZ step of this tutorial and focus on the metadata applications, you can:

• download this pre-built CMZ workspace.
• download the C-Motion Specific Files.

For more technical information about loading metadata, see: Metadata Documentation

Data

The OpenBiomechanics data set provides cleaned c3d files with 3D kinematic data for 47 body markers, 22 lower limb and pelvic markers, and 25 head, upper limb, and trunk markers; there are also 10 markers placed along the bat. Important metadata that is being considered are highest_playing_level, the level of competition that the subject is currently competing at, and blast_bat_speed_mph_x, the bat speed at contact as measured by Blast Motion sensor in miles per hour. For this tutorial, only the baseball_hitter data set will be analyzed.

Some important contents of the workspace are briefly described below:

• additional_resources: Folder includes additional resources which may be of interest for further exploration, folders you will find include:
  • books_articles: Explore scholarly articles pertaining to the field of sports biomechanics, all available as pdfs.
  • tutorials: Two tutorials for basic exploration of c3d files using ezc3d package in Python, as well as utilizing ISBS workshop.
• baseball_hitting & baseball_pitching: contains Data, Code, and Imgs folder along with a README.md file. For this tutorial the Data folder is important, but it is worth looking through the other folders.
  • Data: c3d is the only folder of interest for this tutorial, it contains all of the folders for each subject with all of their corresponding .c3d files.

Notes:

• If you have downloaded the prebuilt CMZ workspace you will only find baseball_hitting.

Tables below show the Tags, Signals, and Refinements that will be used in this tutorial. These will be seen in later steps.

Table 1: Tag Definitions

Tags	Definition
R	Right side hitters

Table 2: Signal Definitions

Signals	Definition
PELVIS_ANGULAR_VELOCITY	Rate of change of angular position of the pelvis over time

Table 3: Refinements Definitions

Refinements	Definition
HIGHSCHOOL	Filters c3d file, retaining data entries where “highest_playing_level” value is equal to “high_school”
College	Filters c3d file, retaining data entries where “highest_playing_level” value is equal to “college”
lowBatSpeed	Filters c3d file, retaining data entries where the 'blast_bat_speed' value falls within a specified “low” range (depending on subjects playing level)
highBatSpeed	Filters c3d file, retaining data entries where the 'blast_bat_speed' value falls within a specified “high” range (depending on subjects playing level)