Physics and running

[elissaann]

This morning, as I ran in Central Park, I was thinking about the force of landing on each leg. How does it change with the following variables: speed, height of the step, length of the stride, which part of my foot lands, whether I use my toes, etc?

Comments

[wcg]

There are only two things that come into play here: The speed of impact and the size of the contact area. Speed of impact is the vertical component of your foot's velocity, so the higher your step, the larger that vertical component is going to be. The total contact area depends on how much of your foot touches the ground.

But wait! There's more! (As the Ginsu knife commercial puts it...)

Your arches are nifty little naturally spring-loaded things. So while it puts more force against your arch to not run flat-footed, you do yourself a favor by loading all that energy into your arch so it can put it back into motion as it flexes again.

[flarenut]

The area of impact doesn't really matter for the legs, because it's all averaged out by the time it gets through the ankle. What does count is how long it takes from the time you touch the gound to the time your feet and legs stop moving vertically (which depends in turn on the kind of surface you're running on, your stride style, blah blah blah). Also how much tension you have in your muscles and how much your knees flex to absorb the shock. And that's just the vertical stuff. If you're accelerating or decelerating, or just running at other than the natural pendulum pace of your legs/feet/body, there will be horizontal forces as well. (Mostly in the forward or backward direction -- if there are side forces when you're running straight, that generally means you're doing something bad for you.) There's a whole huge field of kinesiology for running and other sports, and professional venues have things like tracks whose resilience is tuned for the particular speeds expected of the athletes who run on them...

[elissaann]

Sounds complicated! Is muscle tension good or bad? My knees are definitely flexed. How do I determine "natural pendulum pace"? Do you have any good links for me, that might be written in language I can understand?

[elissaann]

So if I'm staying low to the ground and letting my feet work naturally, I'm minimizing the force of landing?