Does Asymmetry Enhance Injury Risk?

…below are a few studies saying it does. 

Whether left-to-right asymmetry enhances injury risk is a topic of hot debate in the rehab and performance fields.  Some asymmetry is natural, but how much?  At what point does asymmetry become unnatural?  At what point, if any, does it present an injury risk? 

In rotational sports, we’re often interested whether asymmetries can be beneficial.  Perhaps asymmetries make gifted athletes proficient moving in one direction and are necessary for high performance in specialized activities (swinging a golf club, throwing a baseball, freestyle swimming when breathing to one side only, etc).

Should we treat asymmetries as analogous to hemiparesis, a condition for which it is believed the “good” limb can overpower the “bad” limb if the movement disparity is extreme?  Perhaps the common practice of training more on the weak side to correct an asymmetry is the sports performance analog to Constraint Based Movement Therapies.    

I certainly don’t have definitive answers to those questions, but here are a few prospective studies showing a connection between asymmetry and injury.

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1)  Nadler SF, Malanga GA, Feinberg JH, Prybicien M, Stitik TP, DePrince M.  Relationship between hip muscle imbalance and occurrence of low back pain in collegiate athletes: a prospective study.  Am J Phys Med Rehabil. 2001 Aug;80(8):572-7.

 ***“for female athletes, the percentage difference between the right and left hip extensors was predictive of whether treatment for LBP (low back pain) was required over the ensuing year (P = 0.05)”

2)  Söderman K, Alfredson H, Pietilä T, Werner S.  Risk factors for leg injuries in female soccer players: a prospective investigation during one out-door season.  Knee Surg Sports Traumatol Arthrosc. 2001 Sep;9(5):313-21.

***“All five players who suffered an anterior cruciate ligament injury during the study period had a lower hamstring-to-quadriceps ratio during concentric action on the injured side than on their noninjured side.”

3)  Baumhauer JF, Alosa DM, Renström AF, Trevino S, Beynnon B.  A prospective study of ankle injury risk factors. Am J Sports Med. 1995 Sep-Oct;23(5):564-70.

***“plantar flexion strength and the ratio of dorsiflexion to plantar flexion strength was significantly different for the injured ankle compared with the contralateral uninjured ankle.”

4)  Rauh MJ, Koepsell TD, Rivara FP, Rice SG, Margherita AJ.  Quadriceps angle and risk of injury among high school cross-country runners. J Orthop Sports Phys Ther. 2007 Dec;37(12):725-33. Epub 2007 Aug 29.

***“Runners with >4 degrees absolute right-left Q-angle difference were at 1.8 times greater risk (RR, 1.8; 95% CI: 1.4, 2.5) compared to runners with a smaller difference.”

5)  Ekstrand J, Gillquist J.  The avoidability of soccer injuries.  Int J Sports Med. 1983 May;4(2):124-8.

***“Players sustaining knee sprains not due to collision had reduced muscle strength in the injured leg.”

6)  Knapik JJ, Bauman CL, Jones BH, Harris JM, Vaughan L.  Preseason strength and flexibility imbalances associated with athletic injuries in female collegiate athletes.  Am J Sports Med. 1991 Jan-Feb;19(1):76-81.

*** “Athletes experienced more lower extremity injuries if they had: 1) a right knee flexor 15% stronger than the left knee flexor at 180 deg/sec; 2) a right hip extensor 15% more flexible than the left hip extensor; 3) a knee flexor/knee extensor ratio of less than 0.75 at 180 deg/sec. There was a trend for higher injury rates to be associated with knee flexor or hip extensor imbalances of 15% or more on either side of the body.”

7)  Plisky PJ, Rauh MJ, Kaminski TW, Underwood FB. Star Excursion Balance Test as a predictor of lower extremity injury in high school basketball players.  J Orthop Sports Phys Ther. 2006 Dec;36(12):911-9.

***“Logistic regression models indicated that players with an anterior right/left reach distance difference greater than 4 cm were 2.5 times more likely to sustain a lower extremity injury (P<.05)”