Asymmetries are common in the human body and can lead to a wild goose chase in musculoskeletal assessment. But how do we know which asymmetries are important and will lead to injury? Well, let’s look at some common misconceptions as well as the research.
Common Misconceptions About Asymmetries
1. If someone performs well at their sport with an asymmetry, the asymmetry doesn’t matter.
Who ever said that asymmetry IS related to performance? Asymmetry is related to injury risk, not necessarily performance. While I am concerned about performance, I am more concerned about keeping them in the sport and participating without being encumbered by injury.
2. Asymmetries are only important if they cause pain.
I am mostly concerned with asymmetries that cause movement inefficiency or are related to injury risk. To me, asymmetrical fundamental movement patterns will lead to injury or inefficiency (i.e. energy expenditure that is unnecessary for performance of the activity).
3. There is no research that indicates asymmetry increases risk of injury
Those who have an anterior reach distance asymmetry on the Y Balance Test (Star Excursion Balance Test) are at increased risk of injury in high school basketball and multiple collegiate sports (Plisky 2006, Lehr 2013)
Those who have an asymmetry on the Functional Movement Screen (Kiesel 2013 in press) are at increased risk of injury in professional football
Strength and flexibility asymmetries:
- Athletes experienced more lower extremity injuries if they had knee flexor and hip extensor strength asymmetries (Knapick 1991, Nadler 2001)
- Eccentric hamstring strength asymmetries were at greater risk of sustaining a hamstring muscle strain. (Fousekis 2011)
- Hamstring/quad ratio asymmetry (Soderman 2001)
- Ankle strength asymmetry (Baumhauer 1995)
Asymmetrical landing patterns predict second ACL tear in previously reconstructed athletes (Paterno 2010)
Bottom Line: I really don’t put much stock into isolated bony asymmetries (e.g. torsions, misalignments, etc.), but I do feel that modifiable movement asymmetries that are related to risk of future injury are extremely important. Further, the literature is replete with studies that indicate asymmetries exist after pathology (Gribble 2013, Hewett 2013). Since previous injury is the most robust risk factor for future injury, we owe it to our athletes to normalize these modifiable risk factors.
What do you think?