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Question on running down hill.

topic posted Tue, September 25, 2007 - 11:59 AM by  Curry
I go out running with some friends who do not want to run on the street because it is too hard.
These same people do not mind trail running down steep hills.
I think that running down hill should have more impact that just a hard surface.
Question:
Is there some easy way to figure out how much more impact you would get for different slopes?
Or a slope of 30 degrees? That would be a steep down hill trail.
posted by:
Curry
offline Curry
SF Bay Area
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  • PaulaC
    PaulaC
    offline 61

    Re: Question on running down hill.

    Tue, September 25, 2007 - 6:46 PM
    Impact can be measured, but you must also consider the hardness of the surface before considering ground reaction force. Also, the only way I have been able to measure GRF is using video, as one also must consider the angle of joints involved that also absorb the impact. The way you run down hill and others will differ not only by technique, but morphology.
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    • Curry
      Curry
      offline 17

      Re: Question on running down hill.

      Tue, September 25, 2007 - 8:10 PM
      Thanks for responding though it is not much help.
      Maybe I could try running flat and stepping on a scale, then have someone read the weight.
      Next I could place the scale on a slope of say 5 degrees and get a new running weight.
      Next I could place the scale on a slope of say 10 degrees etc.
      This would give me some data to consider.
      I could see what slope would double the flat weight.
      I'm liking this idea.
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      • PaulaC
        PaulaC
        offline 61

        Ground Reaction Force

        Tue, September 25, 2007 - 9:30 PM
        The scale will only read the ground reaction force in one 'plane' and would only work if 'plodding' on flat ground. This force changes as the angles change, as does your physical mechanics to compensate.

        Note here that a force plate measures force in x, y, and z planes.
        www.bsu.edu/web/ykwon/pe.../grf_lab.html

        Sorry if it is not much help. The downside to biomechanics is that the variables are more 'soft' as bodies have greater variability than non-biological things such as a rod of iron, granite boulder, or 'frictionless surface'. This means that in order to be more accurate, you can't simplify the formula.
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        • Curry
          Curry
          offline 17

          Re: Ground Reaction Force

          Tue, September 25, 2007 - 10:44 PM
          Thanks for the link. It looks like a great start.
          The GRF can be 2 to 3 times your body weight.
          That is more than I thought.

          Well the running on the scale idea did not work.
          My scale did not like being jumped on like that.
          The dial just spun out of control. It is a simple bath scale.
          I'm sure it was never ment to be jumped on.
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          • PaulaC
            PaulaC
            offline 61

            Re: Ground Reaction Force

            Tue, September 25, 2007 - 10:54 PM
            Indeed. The GRF I had studied was more than twice the body wieght, but it was on the shoulder during a shoulder roll, done by a novice, whereas the expert doing the same action was able to reduce impact considerably. Technique is also important, and don't forget the reaction of the different surfaces.
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            • Curry
              Curry
              offline 17

              Re: Ground Reaction Force

              Wed, September 26, 2007 - 4:49 PM
              I went running on the bay trail this morning. It has a packed sand path next to a paved path.
              Some observations about impact:

              When jogging with a lot of up and down motion and a short stride:
              There was a small but noticeable difference between running on the dirt vs running on the paved surface.
              I went back and forth many times.

              When running with a longer stride and a lot less up and down motion:
              There was a lot less impact than from the jogging (with a lot of up and down) and there was very little difference in impact between the dirt and paved surface.
              I tryed this change in stride and surface many times.

              The bay trail is flat so no slope to try.
              I'll try up in tilden another day.

              Of course I know from running that down hill has more impact than a hard surface.
              What I need is a way to prove it to non-believers.
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