What happens during the swing phase that is related to impact loads?

The biomechanics of peak impact loads and loading rates continue to be researched on the assumption that they are related to an increased risk for injury. I keep harping on about the evidence for that is hardly compelling and there is plenty of evidence that it is not a risk factor for injury and some evidence that says that it is. I would have thought that more energy needs to be expended in the field or on prospective epidemiological studies on if it really is a risk factor or not and if it is, just how important is it. Only if it is definitively established as a risk, then expending energy in the lab investigating ways to decrease it can be better justified. This lab based study on swing phase factors associated with impact variables appeared a few weeks ago:

Variables during swing associated with decreased impact peak and loading rate in running
Anne Schmitz, Michael B. Pohl, Kaitlin Woods, Brian Noehren
Journal of Biomechanics; Available online 22 October 2013
When the foot impacts the ground in running, large forces and loading rates can arise that may contribute to the development of overuse injuries. Investigating which biomechanical factors contribute to these impact loads and loading rates in running could assist clinicians in developing strategies to reduce these loads. Therefore, the goals of our work were to determine variables that predict the magnitude of the impact peak and loading rate during running, as well as to investigate how modulation of knee and hip muscle activity affects these variables. Instrumented gait analysis was conducted on forty-eight healthy subjects running at 3.3 m/s on a treadmill. The top four predictors of loading rate and impact peak were determined using a stepwise multiple linear regression model. Forward dynamics was performed using a whole body musculoskeletal model to determine how increased muscle activity of the knee flexors, extensors, hip flexors, and hip extensors during swing altered the predictors of loading rate and impact peak. A smaller impact peak was associated with a larger downward acceleration of the foot, a higher positioned foot, and a decreased downward velocity of the shank at mid-swing while a lower loading rate was associated with a higher positioned thigh at mid-swing. Our results suggest that an alternative to forefoot striking may be increased hip flexor activity during swing to alter these mid-swing kinematics and ultimately decrease the leg’s velocity at landing. The decreased velocity would decrease the downward momentum of the leg and hence require a smaller force at impact.

The only finding of this study that jumped out at me was the implications of their findings, namely:

Our results suggest that an alternative to forefoot striking may be increased hip flexor activity during swing to alter these mid-swing kinematics and ultimately decrease the leg’s velocity at landing.

That is, of course, only if you believe that impacts are even a problem and need to be reduced.

As always, I go where the evidence takes me until convinced otherwise, and this study confirms the premise that no one size does not fit all and if you want to reduce impacts, there are other ways to do it.

Anne Schmitz, Michael B. Pohl, Kaitlin Woods, Brian Noehren (2013). Variables during swing associated with decreased impact peak and loading rate in running Journal of Biomechanics DOI: 10.1016/j.jbiomech.2013.10.026

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About Craig Payne

University lecturer, runner, cynic, researcher, skeptic, forum admin, woo basher, clinician, rabble-rouser, blogger, dad. Follow me on Twitter, Facebook and Google+

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One Response to What happens during the swing phase that is related to impact loads?

  1. Anne Schmitz November 22, 2013 at 2:22 pm #

    Hi Craig,

    First off, thanks for mentioning our article. Second, I find your comment “That is, of course, only if you believe that impacts are even a problem and need to be reduced.” inline with what we say in the Discussion of the paper. Bones need a certain level of loading to remain healthy. Completely removing bone loading may not be the best while too much loading is bad too. You kind of allude to this in your introduction on whether running loads are bad, but what we really don’t know is that sweet spot.

    Thanks,

    Anne

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