The Risk Factors:
It’s understandable why these numbers are kept in the dark from most people. They’re boring and complicated! However, it’s almost scary how many of our youth and professional athletes actually fall within at least 1 of these categories, if not multiple. Below is a quick, general outline of what each risk factor actually entails.
What is TAM (Total Arc Motion)?
TAM is currently the gold-standard for assessing and predicting shoulder health in the overhead athlete. Ideally, the throwing shoulder should have at least the same amount of total motion, if not a little more, in comparison to the non-throwing shoulder. However, excess stress, trauma, and overuse (i.e. Throwing a baseball) will create dysfunction within the shoulder musculature, thus making the joint unstable. As a result, the throwing shoulder limits motion in order to protect the joint. Continuing to throw while exhibiting limitations in excess of 5 degrees put your health and performance at a significant risk.
What is GERD (Glenohumeral External Rotation Deficit)?
GERD is an range-of-motion limitation that occurs within the throwing shoulder that can lead to excess stress on the shoulder and elbow when throwing a baseball. Based on the forces that act on the shoulder throughout a throwers career, certain adaptations occur at the bone that yield greater external rotation (i.e. layback). These adaptations have been reported as high as 29 degrees in elite level throwers, however, they begin very early in a player’s developmental years. In light of this, any player that has been throwing a baseball for any significant period of time will exhibit this trait to some degree. Even still, both youth and adolescent athletes portray this characteristic frequently for reasons that most likely stem from shoulder instability. As the athlete progresses with age and playing experience, this trait will continue to become more pronounced. With these concepts in mind, no athlete with moderate playing experience should have less external rotation in their throwing arm in comparison to the non-throwing shoulder. Additionally, more mature athletes with extremely significant playing experience (i.e. several years) should exhibit greater than 5 degrees of external rotation in their throwing arm when comparing it to the opposite shoulder.
What is GIRD (Glenohumeral Internal Rotation Deficit)?
GIRD is evident in baseball athletes of all ages with any amount of moderate playing experience. This adaptation, which occurs on the throwing shoulder of an overhead athlete, is predominantly due to the forces that are exerted onto bone throughout a player’s developmental years. These changes that occur are not only advantageous from a health standpoint, but they allow for increased throwing velocity as well. However, if this deviation exceeds 20 degrees in magnitude and is combined with a TAM limitation of greater than 5 degrees, then the athlete is shown to be at a significant risk for injury and decreased velocity.
In simple terms, think of these range-of-motion (ROM) measures as your check engine light. Most people aren’t even are of the warning signs, much less have a way to actually fix the problem. These values have been shown to worsen throughout the course of a season and career, so it’s important to stay ahead of the problem. Poor mechanics and overuse play huge roles in this process as well, all of which you can become properly informed upon here at ITS.
Why do these ROM deviations occur?
Stress, overuse, and trauma will all have a negative impact on a muscle’s ability to contract (shorten) efficiently. This is important to understand because unlike various other joints in the body, the shoulder heavily relies on the musculature to provide stability and create the axis’ of rotation that will ultimately allow for efficient movement. In light of this, deficiencies within the muscular system will result in instability and limited movement. Relate it to walking on ice. Your body tightens up on an unstable surface as a protective mechanism in order to prevent you from falling. The further away you get
from your center-of-mass, the more vulnerable you are to falling and getting hurt. The same thing happens within your body, in this case, the shoulder. When the brain and spinal cord sense that the joint lacks stability ((i.e. failure of a muscle(s) to provide that stability)), the body will tighten up and ‘stay closer to home’ in order to prevent vulnerability. Why would your brain consciously allow you to assume a motion that is unstable or that you have no control in? It wouldn’t…hence the tightening and limitations.
Thus, once you gain an understanding of the source behind these limitations, they actually serve to help you and provide very important information regarding how well your shoulder is functioning. Would you drive you car to California and back at 100 mph if your check engine light was on? I didn’t think so. This is a fitting analogy considering throwing a baseball is the single-most violent act in all of sports. Do it over and over again throughout the course of a season or career…You guessed it.
In summary, these range-of-motion limitations within your throwing shoulder act as your check engine light and ITS can serve as your personal shoulder mechanic to make sure you are primed and ready to go each time you decide to throw.