MARC THOMAS DUEMMLER. Investigation of Shoulder Rotational Properties as Related to Injury History for Collegiate Baseball Pitchers.(Under the direction of DR. NIGEL ZHENG) Baseball is one of the most common sports played in the United States. It can be played starting as a child in the Little Leagues and pursued well into adulthood by the top players in Major League Baseball. Pitching in baseball produces tremendous stress on the shoulder joint, which commonly leads to injury. Additionally, this repetitive stress over time has shown to alter the shoulder rotational properties of the throwing arm. The purpose of this study was to analyze the shoulder rotational properties of collegiate baseball pitchers and determine if they can be used to identify a history of upper extremity injuries. Shoulder rotational properties analyzed in this study that are common in the literature were glenohumeral internal rotation deficit (GIRD), total rotational motion (TRM) deficit, and a combination of those two deficits known as pathological GIRD. Additionally, a new variable was introduced (that analyzed the throwing arm exclusively) and is known as the external rotation to internal rotation ratio, or E/I ratio. The methods of this study involved collecting an injury questionnaire as well as collecting shoulder rotational properties with a custom sensor during a physical from Division I and Division II baseball pitchers. The results of this study showed that neither GIRD, TRM deficit, not pathological GIRD had any statistically significant association with injury history. Therefore, these properties show potential in being used as return-to-play metrics following injury. However, the novel variable, E/I ratio, did have a statistically significant association with injury history. This statistical association showed that pitchers with a high E/I ratio were less likely to have a past injury. Future work will analyze how these variables can be used to identify potential risk of future injury as opposed to identifying past injuries.