A player's range-of-motion (ROM) patterns are widely considered by many researchers and medical professionals to be one of the gold-standards in assessing throwing-related injury risk. This correlation has been shown multiple times throughout the years in both prospective and retrospective research studies regardless of age. Listed below are the primary ROM risk factors outlined within the research, along with their associated risks. Keep in mind that these are statistically significant measures that have been proven to determine injury risk.
Dominant Total Arc Motion Deficit (DTAMD): 2.5x Injury Risk
Glenohumeral Internal Rotation Deficit + Dominant Total Arc Motion Deficit (GIRD + DTAMD): 3.5x Risk
Glenohumeral External Rotation Deficit (GERD): 2.3x Injury Risk
Dominant Shoulder Flexion Deficit (DSFD): 2.8x Injury Risk
Without going into a full review on the specifics of each of these patterns, DTAMD is fairly straight forward and it just so happens to be one of the stronger predictors of injury. In essence, DTAMD occurs when the throwing arm becomes limited relative to the non-throwing arm by more than 5º. Under normal circumstances, the throwing arm should have at least the same amount of total motion as the non-throwing arm. GIRD implies that the throwing arm has less internal rotation than the non-throwing arm. Although people vary on the exact amount, it is generally accepted that GIRD implies a deficit of 20º or more. GERD occurs when the external rotation difference between the throwing arm and the non-throwing arm is less than 5º. Typically, the throwing arm should have at least 5º or more of external rotation than the non-throwing arm due to specific adaptations that occur while throwing through the "growth years." Lastly, DSFD occurs when the throwing arm is limited in shoulder flexion by more than 5º relative to the non-throwing arm.
Although the mechanisms behind these deviations are contentious, it is safe to say that they are fundamentally due to the fact that the body isn't effectively and efficiently supporting the forces that are being placed upon it.
To make things easier when relating to DTAMD, we use negative and positive numbers to explain the relationship between each arm. Simply, a negative number implies that the throwing arm is limited in degrees relative to the non-throwing arm for that specific test. On the contrary, a positive number means that the throwing arm has more degrees in comparison to the non-throwing arm relative to a specific test. Based on the actual value of each number, it can then be determined if an individual falls into a risk category.