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I Energy transfer during uphill vs downhill running

  1. Jan 11, 2017 #1
    Hello Physics Gurus,

    Please critique the following logic...

    When a runner hikes/runs to the top of a mountain, the chemical potential energy inside the muscles transferred into the potential energy of the runner's body mass at the higher elevation (Pe = mass*gravity*height = mgh). Energy is also transferred into the heat of the muscles, the breakage of chemical bonds in the muscle, and friction losses on the ground.

    When a runner now runs DOWN the hill. The potential energy of the body being at a high altitude is lost. With each step, the runner is transferring the potential energy into the heating and tearing of their muscles. Some energy is also lost to friction effects from the shoe on the ground and air resistance. The effect of this potential loss is significantly more damage to the muscle, because the potential energy has to be absorbed by the body.

    Conclusion: running uphill depletes the energy stores in your muscles more than running downhill. Running downhill does more muscular-skeletal damage because the potential drain is absorbed by tearing and heating muscles.

    Is this reasoning correct? Am I missing something? Is my conclusion that the potential is absorbed by damaging the muscles correct?

    Thank you!
     
  2. jcsd
  3. Jan 11, 2017 #2

    russ_watters

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    Staff: Mentor

    Welcome to PF!

    I'm not sure I would describe it the same way, but for the most part I agree that running downhill is potentially more damaging due to the greater impact on your bones vs the greater workload on your muscles for running uphill.
     
  4. Jan 11, 2017 #3
    I agree that the runner must dissipate the energy when running downhill. I disagree that the act of dissipating that energy is necessarily more damaging. For the most part the energy goes into stretching muscles which converts the energy into metabolic heat. The muscles are good at this and need not be damaged so long as they are not mechanically overloaded. Our thermal regulation is good at shedding the excess heat and the body needn't be damaged unless thermally overloaded. The heating of the muscles is considerably less than while putting out work to go up the hill because our muscles are just that inefficient. The forces, impacts, and movements moving down the hill are comparable to those going up the hill. The loads on the muscles, bones, and tendons are similar unless you get out of control and start making unusual movements. While some joint or other may be more stressed under one case or the other due to configuration or technique, I see no reason that running downhill should be intrinsically more damaging than running up hill. More dangerous, sure. Bigger consequences if you screw up, yes. But more damaging just from the normal action? I doubt it.
     
  5. Jan 11, 2017 #4

    berkeman

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    I disagree. How much trail running have you done? What reading have you done about this? Can you post links to your reading? There are certainly differences in the physiology of running uphill and downhill, but IMO your post is not correct in your conclusions/assumptions. :smile:
     
  6. Jan 12, 2017 #5

    A.T.

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    Yes, but the muscles adapt to it. Look up "eccentric muscle contraction" and "eccentric training".
     
  7. Jan 12, 2017 #6
    Running down hill takes more brain power and I think you would use energy from muscles that would not be employed going up.

    My old coach made us sprint down steep hills to improve our reflexes, agility and motor skills.
     
  8. Jan 12, 2017 #7
  9. Jan 12, 2017 #8
    All,

    Thanks for the replies. I should clarify that when I said I believe downhill running to be more "damaging," I did not mean injury or permanent damage. I just meant general muscle tearing that occurs during exercise.

    Berkeman, yes, I have done a lot of trail running and still do. There is a noticeable difference in delayed onset muscle soreness (256bits mentioned it) after I come down a steep trail fast, vs a hard uphill push. That is what led me to think about why that was the case. To A.T.'s comment, it makes sense that eccentric muscle exercises lead to more soreness - because eccentric muscle soreness seems to be the case when we "absorb" potentials.

    What's even more interesting to me is that the energy that can't be converted to heat leads to chemical bonds separating in the muscles (maybe).
     
  10. Nov 13, 2017 #9
    Hello, I try to relate Physics and Trail Running with my secondary students in Spain. I've got the same question but just thinking about Mecanical Energy.

    For example, when a runner climbs a mountain the energy spent to overcome the gravity pull is PE = mgh, but when you go down the hill you also spend energy ... but less than when you climb ... even going downhill is more muscular damaging, you don't get as tired as you feel when going uphill (well, or maybe your body gets tired in a different way).

    So taking in account that when you run downhill you need to brake not to fall over, I estimate the PE you spend as the work you do to cancel the X-weight, so then PEdownhill = mg (sin alpha) h.
    I know it's just and estimation for secondary education to be able to calculate the total PE both uphill and downhill.

    About Kinetical Energy, it can be calculated taking only in account the distance as a flat surface. Then, the total spent energy TE=PE+KE.

    What do you think about it?
     
  11. Nov 13, 2017 #10
    So far, so good. I don't know enough about eccentric muscle action to correct your conclusions. I suggest posting your question at www.runningahead.com/forums. There's some people there that can shed further light on this subject.

    I do know that the quadricep muscles used in downhill running are the same muscles that keep your legs from collapsing at footstrike when running on level ground. Note to myself: Do more downhill running before my next marathon.
     
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