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The Physics of ChiRunning, Summary

There are many that suggest “gravity is a vertical force”, which is true, and that “it only acts downward”, which is also true. But then they say “gravity can’t help you move forward”. This I contend is not true. Without a full physics analysis considering all the forces present it is not possible to determine the net force on the object or whether acceleration or deceleration will result. Plus you can feel this effect is about 30 seconds …

The other physics misconception is that running at a constant pace means you have a constant velocity. But if you look at the gait cycle there are times when velocity is decreasing and times when velocity is increasing.

  • Velocity decreases due to resistance. Either air resistance or the runner’s position/motion resistance.
  • Velocity increases due to propulsion. Either by pushing/pulling or by subtly falling.

One way to increase running efficiency is to decrease resistance which allows you to also decrease propulsion effort to maintain momentum (or velocity). In a phrase, resist less so you can work less. Or in ChiRunning this means resist less and you can lean less. You can read more about momentum here (The Physics of ChiRunning, Momentum).

You can represent this velocity variation from step to step through a velocity graph like the one shown below. The graph is not meant to be exact, the velocity curve may not be as smooth as shown depending on the runner. There may be flat areas and more pronounced areas of deceleration and/or acceleration, etc. This is a concept graph only showing a variation. The perceived “pace” is the center line as the average.

If you consider two runners with the same cadence, then the following two graphs together *might* suggest the green runner is more efficient than the red runner:

  • The runner with less deceleration and less acceleration step to step is probably working less to maintain the same pace.
  • But there are many variables to make that conclusive.

And if you consider two runners with different cadences, then these two graphs together *might* again suggest the green runner is more efficient than the dotted line red runner with slower cadence:

  • In general the runner with the slower cadence has a longer stride forward and is on their feet longer. Both of these traits tend to create more resistance.
  • The slower cadence results in less steps per minute but more work in each step.
  • But again there are many variables to make this conclusive as well.

Overall, my experience has been that if I focus more on resisting less (through all the options listed here: The Physics of ChiRunning, Momentum), I don’t have to work as much re-creating momentum with each step. Meaning I think “How can I flatten and smooth out my step to step velocity curve?” as a run … so I am maintaining my forward momentum with the least amount of effort.

It seems this “allowing” or resisting less must come first since you can reduce resistance without needing more propulsion but it is less likely you will be able to increase propulsion without further increasing resistance.

[See the Physics Resource Page for more information.]

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David Stretanski is a holistic health, fitness and wellness coach – and Certified ChiRunning®/ChiWalking® Instructor.  For more information on David, please see his About MeContact page or his website at http://www.eChiFitness.com.

ChiRunning® and ChiWalking® are registered trademarks of ChiLiving, Inc.

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Posted on Sunday, Aug. 12th 2012 3:51 PM | by echifitness | in All, ChiRunning, Gravity | No Comments »

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