Thought experiment on symmetry: Does symmetry always matter?

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the short answer is probably not. the long answer is maybe...

This study looked at gait variability asymmetry in small cohort of experienced distance runnners. They measured different variables at 1500, 3000, 5000, 7500 and 9500 m of a 10000 meter run (about 6.2 miles) on a treadmill. Generally speaking, variability was low and athletes were symmetrical for 5 of seven variables measured and assymetry, when present, was in flight time and impact forces Most aththletes were asymetrical for at least one variable as well.

Their conclusion basically said that being asymmetrical in a few variables is not abnormal and not indicative of asymmetrical gait and since many practitioners analyze symmetry (and variability) caution should be exercised when determining the need for intervention.

So what do we think this means?

most likely:

  • these folks were symmetrical with low variability. In other words, when asymmetry was present, it was small

  • some asymmetry, in some parameters, is probably normal...but,it is usually small if it doesn’t matter. Keep in mind these were expreienced, uninjured folks. th results could have been different with a bigger cohort and less experienced runners and thus...

  • The study does not talk about inexperienced runners. Symmetry and/or asymmetry may not be normal for inexperienced runners

  • Results may have been vastly different if the run had been longer. The study did show that variability increased the further along on the run the athlete was.

  • The study was performed on a treadmill, which may not exemplify or highlight asymmetry, as it creates artificial constraints which we have discussed in by us here, here, and here:

  • We think asymmetry matters, particularly when it comes to hard deformities like torsions and versions, which change the biomechanics of that individual extremity and can be a diagnostic tool for future problems

  • perhaps asymmetry is significant in his population of runners on a subclinical basis

Hanley B, Tucker CB. Gait variability and symmetry remain consistent during high-intensity 10,000 m treadmill running. J Biomech. 2018 Oct 5;79:129-134. doi: 10.1016/j.jbiomech.2018.08.008. Epub 2018 Aug 16.