Is Left to Right Asymmetry a Factor in Running Injuries?

Runners certainly suffer their fair share of injuries.  Diagnosing and treating running injuries is one thing, but most runners would like to know why they’re injured.  One question that often surfaces goes something like this: “Why did this just happen to one leg and not the other?  After all, I take the same number of steps with my right as I do with my left.”   A simple question without a simple answer.running asymmetry

It is logical reasoning though.  There must be some side to side difference in order for one side to be injured and the other side spared.  These side to side differences could broadly be split into a few categories:

Left to right asymmetry in:

  1. Anatomy
  2. Mobility and/or joint angles during running (aka kinematics)
  3. Forces generated while running (aka kinetics)

1) Left to right asymmetry in anatomy:

This category would include one leg being shorter than the other, a flatter foot on one side, a larger Q angle, etc. We know that minor variations in anatomy have very little to do with running injuries.  For example, the leg length discrepancy argument has been investigated over and over again and has nothing to to with running injuries, unless the difference is greater than 2cm which is extremely large and also quite rare to happen naturally (acquired leg length differences due to a hip replacement or leg fracture is a different story).

2) Left to right asymmetry in mobility and/or joint angles during running

Measurement of mobility, limb positioning and joint angles is referred to as “kinematics”.  This may include knee flexion angle, hip internal rotation angle, etc.  Side to side asymmetry in kinematics has been shown to not be associated with running injuries (1,2).

3)  Left to right variability in forces generated while running

Measurement of forces generated in movement is called “kinetics”.  This may include loading rate, impact peak, joint moments etc.  Side to side asymmetry in kinetics has been shown to not be associated with running injuries (1,2,3,4,5).  In fact, LESS asymmetry is usually found in those who are already injured or those who eventually get injured

My thoughts:  We must keep in mind that injuries occur because the load you are applying to the body is exceeding the ability of the body to adapt to those loads.  In other words, we don’t give enough time for the tissues to adapt to the load we apply to them.  These can be broadly categorized as training errors. Usually, injury has occurred because something has changed in your training; whether it’s adding mileage too quickly, adding speed work too quickly, too many miles in a new pair of shoes, a change in terrain, diet, stress, hormones, etc.  Basically, you’ve changed something too quickly.

Along with training errors, we know there are issues with running technique that are associated with certain running injuries such as cadence, loading rate and rearfoot and forefoot striking.  While these can be associated with running injuries,  there isn’t any greater left to right asymmetry in those runners than in non-injured runners.  In fact, the asymmetry is usually LESS in the injured runners.

So why then does the injury happen only on one side?  The answer to that is beyond our capability for the time being.  Obviously there has to be some movement or anatomical variability in order for one side to become painful.  Unfortunately, there are so many confounding factors, it is virtually impossible to reveal an easy answer, such as “one leg is too short.”  There is likely a constellation of factors that contribute to injury.  These left to right asymmetries may theoretically be detectable, but for now, the research tools that are available for measuring these have been unable to provide any answers


10 Comments so far:

  1. Brian Hazard says:

    The slant of the road can be a factor, especially with peroneal tendinitis.

    • Kevin Maggs says:

      Sure, any asymmetric load could cause an asymmetric injury. However, we still have to realize that if we give the body enough time, and as long as the load isn’t excessive, the body should adapt. For example, we know that since track runners are usually going around an oval track in a counterclockwise fashion, their tissues gradually adapt and they develop asymmetrical changes in strength of the ankle invertors and evertors.
      Depending on the length of time given to adapt, and the magnitude of the slant of the road, a runner could gradually adapt, or as you said, the runner may get injured. Great point Brian. Thanks!

      • Brian Hazard says:

        Interesting! That makes sense.

        Personally, I’ve had pain in the cuboid bone of my right foot for maybe a year now! It doesn’t seem to get worse or better overall, but it hurts more after workouts and long runs. I guess that doesn’t qualify as tissue that will adapt! t try to avoid running too long/hard on a road that slants upwards toward it.

        I’ve also had a couple bouts with peroneal tendinosis, so I’m very conscious of the slant of the road. Even if it’s not the root cause of my issue, running on the “right” side can aid recovery.

  2. Keith Bartley says:

    Thorough and using “common sense”! Your thoughts never disappoint and always keep us rational. Thanks

  3. Great post Kevin
    I would also add the hypothesis that recovery may be slightly different from one side to the other (vascular flow, neural input, etc.). Even if loading is symmetrical, recovery may be asymmetrical 🙂
    JF Esculier

    • Kevin Maggs says:

      Yes, great point JF. Asymmetric recovery is certainly a possibility as is asymmetric interpretation of pain through descending pain inhibition. I guess the broader point of the thought of the blog post was pain and injury are complex, multifactorial issues. Runners are typically looking for anatomical, kinematic or kinetic answers but most often, we simply can’t give a definitive answer, even in a complex 3D gait lab setting. Given the left to right asymmetries that are of greater magnitude in healthy runners, the answers are not easy. The Running Clinic’s main tenet of allowing time for tissue adaptation/ mechanical stress quantification is the best approach. Or, as Greg would say, “calm shit down, then build shit up”

  4. Dan says:

    Great post Kevin! With proper training and right preparation, I don’t think left to right asymmetry could be a factor in running injuries. I truly appreciate your effort in explaining this one. I think everyone should have an idea about this so that they won’t conclude that runners are only for those individuals with normal running capabilities.

  5. Mike Huizenga says:

    I recently worked through a bout of IT Band and then runners knee in my right leg that I believe was bought on by a leg strength difference. I’ve been a long time basketball player (high school, college and then 2 hour pickup games at the YMCA) for the last 40 years. I am right handed and my left leg became stronger than my right from repeated layups and jumps that use my right hand. In January of this year I decided to return to serious running after a 20 year absence. I followed a gradual increase in weekly mileage from 10mpw to 30mpw over the course of 3 months; however at around 30mpw I developed ITB pain in my right leg. After a period of rest I tried to assess the root cause of this problem and while my gait is not perfectly symmetrical, it’s not bad; however, when I try to perform single leg squats or Bulgarian squats to assess each leg’s strength, I discovered a noticeable difference. My right leg was measurably weaker (3-4 fewer reps at the same load) and breaks in form (the knee would dive inward crossing through my body’s sagittal plane midpoint). I also notice a difference in balance as well. When I get up on one leg on a 360 degree wobble board I’m able to balance rather well on my left leg; however, my right leg could not maintain balance at all.

    I’m working through my leg strength and balance stability imbalance to the best of my ability. I have been able to return to running without knee pain and now run 35mpw.

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