Geoffrey Mutai in Slow Motion

Check out this video of Geoffrey Mutai running in slow motion. This was taken at mile 21 of his recent record breaking effort at the New York City Marathon:

Look at that. Just like buttah.

This reminds me of some interesting physics of running that I learned recently.

According to basic Newtonian physics, an object moving at a constant velocity and direction will stay at a constant velocity unless another force acts on it.

Marathon runners move at a constant horizontal velocity for many miles at a time, and therefore during this time the net horizontal forces acting on them must be zero. In the case of a very efficient runner who is not over striding and braking on each step, the horizontal forces pushing them away from their direction of movement are likely to be very small, mostly limited to the forces of air friction. Therefore, the amount of forward horizontal force required to overcome this friction and maintain constant speed is very small.

What this means is that almost all the forces applied to the ground by an efficient runner are vertical. All Geoffrey is doing in this video as he glides over the ground is just pushing directly into the ground to keep himself airborne.

He is not pulling or pushing himself forward, he is just staying afloat, cruising on the constant velocity and inertia he attained in the first ten to fifteen meters of the race. In essence, he is like a ball bouncing over the ground in arced parabolas. Watch the vid again with this in mind and see if you can appreciate the bouncing quality of Mutai's running.

I should mention that these ideas are based on an influential study done by Peter Weyand a few years ago, which found that vertical ground reaction forces are the limiting factor in top speed running.

I couldn't help but think of these principles of physics last time I went for a run. It was strange and counterintuitive to think that I didn't need to push or pull myself forward with each stride, and that instead all I needed to do was push straight into the ground and just kind of bounce along the road. I'm not sure a witness would have noticed a difference in my stride when I held this idea in my head, but it made a real difference to me.

And distracted me momentarily from the fact that on many levels, I really hate running. (But I'm learning to like it.)