The importance of joint moments in running injury risk and running economy

Back from a holiday and was planning on getting in back into the routine of posting and was planning on writing something totally different today and then the study below turned up. It was not a study on runners and was not on running (it was on walking), so my title for this post is a bit misleading, but I think the study is informing. The study was about joint moments and their differences between the left and right side. A “joint moment” can be roughly interpreted as the “force needed to try to move a joint”. If more force is needed to move a joint, then this is potentially an injury risk factor and the muscles have to work harder to produce motion which is an economy issue. In the context of running, if joint moments are lower, then there is a theoretically lower injury risk factor and a more economical action of running (ie run faster with less injury risk), Here is the study just published:

Evidence for joint moment asymmetry in healthy populations during gait
Rebecca L. Lambach, Jessica L. Asay, Steve T. Jamison, Xueliang Pan, Laura C. Schmitt, Katerina Blazek, Robert A. Siston, Thomas P. Andriacchi, Ajit M.W. Chaudhari
Gait & Posture; Articles in Press
The purpose of this study was to determine the presence and prevalence of asymmetry in lower extremity joint moments within and across healthy populations during overground walking. Bilateral gait data from several studies performed at two institutions were pooled from 182 healthy, pain-free subjects. Four distinct populations were identified based on age, activity level and body mass index. Mean peak external joint moments were calculated from three to six trials of level overground walking at self-selected speed for each subject. Right and left limb moments were reclassified as “greater” or “lesser” moment for each subject to prevent obscuring absolute asymmetry due to averaging over positive and negative asymmetries across subjects. A clinically relevant asymmetry measure was calculated from the peak joint moments with an initial chosen cutoff value of 10%. Confidence intervals for the proportion of subjects with greater than 10% asymmetry between limbs were estimated based on the binomial distribution. We found a high amount of asymmetry between the limbs in healthy populations. More than half of our overall population exceeded 10% asymmetry in peak hip and knee flexion and adduction moments. Group medians exceeded 10% asymmetry for all variables in all populations. This may have important implications on gait evaluations, particularly clinical evaluations or research studies where asymmetry is used as an outcome. Additional research is necessary to determine acceptable levels of joint moment asymmetry during gait and to determine whether asymmetrical joint moments influence the development of symptomatic pathology or success of lower extremity rehabilitation.

Again, this was not a study on runners or running and has nothing to do with evidence for anything I said above in the opening paragraph. The study simply showed that there is an asymmetry in joint moments between the left and right side of people when walking. There is no reason to believe that the same asymmetry does not exist in runners and could be a potential risk factor for unilateral injury.

I have long been on about loads in tissues as a key risk for overuse injury (see: The Key to Preventing Overuse Injury in Runners is Load Management) and have discussed the simple clinical measurement of a couple of foot specific leads (ie supination resistance and windlass forces) and the potential implications of them, including the often observed asymmetry between the left and right sides in them. The reason for the variation is most likely variations in joint moments, which is invariably due to variations in the lever arms that tendons have to joint axes of motion. See Why ‘one size does not fit all’ when it comes to running in which I also wrote of relevance to this topic:

I recall reading a while back a study in the cerebral palsy literature and I apologize profusely for not providing the reference, as I just can’t find it again! In the study they used MRI to look at the distance between muscle insertions into the pelvis and the center of the hip joint. There was a massive variation in the lever arms between the subjects which had implications for the surgical management of gait problems in cerebral palsy. There is no reason to doubt that the same variation exists in runners and that is going to have implications for running form and how easy or harder it is going to be or not be to change the proximal control of gait.

While the above study did focus on asymmetry in joint moments, it also does point to the variability between individuals in joint moments. Lets extrapolate from that the implications that this might have for running:

  1. If the joint moments are higher, then the loads on the tissues  that  move that joint  are increased. That is a potential risk factor for injury.
  2. If the joint moments are higher, then the muscles need to work harder to move the joint. This increases the effort needed to run (ie running economy)
  3. If there are differences between the left and right side, then the left and right side will respond differently to running shoe or foot orthotic design features on each side.
  4. The variability between individuals in joint moments may explain why some get hurt with a particular running technique and not with another.
  5. It may also explain why some individuals can transition or adapt easily to changes in the running technique and others cannot do it easily; this also could be a factor in the success or failure of gait retraining.

Don’t you just love a good thought experiment?

As always, I go where the evidence takes me until convinced otherwise…..

Lambach, R., Asay, J., Jamison, S., Pan, X., Schmitt, L., Blazek, K., Siston, R., Andriacchi, T., & Chaudhari, A. (2014). Evidence for joint moment asymmetry in healthy populations during gait Gait & Posture DOI: 10.1016/j.gaitpost.2014.06.010

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