Are asymmetries in the FMS acceptable in one-sided dominant sports?
Here is a question I received in Coaches Club
"I have a question about 3/2 asymmetries on the FMS. I understand that 3/1s and 2/1s are never accepted or acceptable. 3/2s are acceptable on shoulder mobility and pitchers because of the adaptations in the shoulder from throwing." I assume it refers to the humeral torsion that occurs, a bony adaptation there. "Are 3/2 symmetries ever accepted or expected in one-sided dominant sports on other patterns such as rotary stability or any unilateral pattern? And a few athletes that come to mind could be possible as one-footed dominant soccer players, football kickers, and baseball players."
Understanding FMS Asymmetry and Injury Risk in Unilateral Athletes
We frequently encounter athletes whose sports demand high performance predominantly from one side of the body – think baseball pitchers, tennis players, golfers. A common question arises when using the Functional Movement Screen (FMS) with these individuals: How much asymmetry is acceptable? Is the difference we see between their left and right sides simply a normal adaptation to their sport, or is it a red flag signaling increased injury risk? In this article I want to try to cut through the confusion and provided clarity on how to interpret FMS asymmetry in unilateral athletes and, more importantly, what factors truly demand our immediate attention.
What Do We Mean by FMS Asymmetry in Unilateral Athletes?
First, let's be clear on terms. In the context of the FMS, asymmetry simply refers to a difference in the score achieved between the left and right sides on a given test pattern. For instance, a baseball pitcher might score a 2 on the Shoulder Mobility test with their right arm and a 3 with their left. This becomes particularly relevant in unilateral athletes because their sports inherently create asymmetrical loading patterns. Does this consistent one-sided stress naturally lead to asymmetrical FMS scores and is this asymmetry ok since their sport is asymmetrical? While some research often flags a difference of more than one point as potentially significant, the picture is more nuanced, especially when considering the specific demands placed on these athletes. In baseball pitchers, this 2/3 asymmetry is not only common, it would be considered normal in this population. If a baseball pitcher has 3/3 Shoulder Mobility, I actually want to be SURE that there motor control (Y Balance Test Upper Quarter) and strength (isolated rotator cuff strength, grip strength, hangs, FCS Carry Test, etc.) is optimal in this cases. Having that much mobility without the required stability is a recipe for disaster.
Is FMS Asymmetry "Normal" or Just "Acceptable" in Some Cases?
The concept of "normal" versus "acceptable" is useful here. Is perfect symmetry on the FMS truly "normal" for an elite tennis player or pitcher who has spent years developing specific, dominant-side adaptations? Perhaps not. The reality of high-level unilateral sport might mean some degree of asymmetry is an acceptable adaptation, allowing for elite performance without necessarily predisposing the athlete to injury – provided fundamental movement competency is maintained. The crucial distinction lies not just in if asymmetry exists, but also in the proficiency of movement indicated by the scores themselves.
Prioritizing Pain and Dysfunction: The Critical FMS Scores for Injury Risk
This brings us to the core message: Focusing solely on asymmetry can cause us to miss the forest for the trees. The most critical information the FMS provides regarding immediate injury risk lies in the presence of pain or significant movement dysfunction, regardless of symmetry.
- Score of 0 (Pain): Pain during any FMS test is never acceptable. It's a major red flag indicating an underlying issue that requires immediate attention and likely referral for further evaluation and treatment. Addressing pain overrides any discussion of symmetry or asymmetry.
- Score of 1 (Dysfunction): A score of 1 signifies the athlete cannot perform the fundamental movement pattern correctly, even with compensations. This indicates a lack of basic movement competency. Addressing these "1s" should be the next priority before worrying about whether an athlete scores a 2 on one side and a 3 on the other. Improving these fundamental weaknesses is key to building a robust foundation and mitigating risk.
What About Asymmetry Between Functional Scores (2s vs. 3s)?
So, what if an athlete shows asymmetry, but it's between functional scores – say, a 2 on one side and a 3 on the other, with no 0s or 1s present anywhere on their screen? This is where asymmetry is most likely to be acceptable, particularly in a unilateral athlete. An asymmetry between a 2 and a 3 doesn't carry the same immediate implications as the presence of pain or a score of 1. It might represent a sport-specific adaptation or an area for future optimization, but it's not the primary fire to put out or may not be something we address at all (think baseball pitcher example).
A Practical Approach for Clinicians: Address Dysfunction Before Chasing Symmetry
When working with unilateral sport athletes, this leads to a clear, practical hierarchy for interpreting and acting on FMS results:
- Address Pain (Score 0): Identify and refer out or manage any pain revealed during the screen. This is non-negotiable.
- Improve Fundamental Competency (Address Score 1): Target corrective exercises towards any movement patterns scoring a 1. Build the foundation first.
- Consider Asymmetry (Especially 2 vs. 3): Once pain and significant dysfunction are resolved (no 0s or 1s), then you can evaluate asymmetries between scores of 2 and 3. Decide if addressing this FMS asymmetry is relevant for the athlete's goals, injury history, or performance needs.
Chasing perfect symmetry before ensuring fundamental competency is often counterproductive. Focus on cleaning up the 0s and 1s first – that’s where the biggest impact on reducing injury risk lies.
Interpreting the FMS in unilateral athletes requires nuance. While FMS asymmetry is common, it's not automatically benign or detrimental. The key is context and prioritizing the most significant findings. Don't let the simple presence of asymmetry distract from the critical imperatives: eliminating pain and correcting significant movement dysfunction (scores of 0 and 1). By focusing on establishing fundamental movement competency first, we can build more resilient athletes and make more informed decisions about when, and if, chasing perfect symmetry is truly necessary.
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