Gravity: The dilemma of the “slow runner.”

Some of us just want to run slowly. We don’t really want to get fast—we just don’t care.

That’s okay. We’re all entitled to our own ways of running. But while we do that, we should recognize that there are some ways of running that observe the realities of the world (and some that don’t). Someone I met once said:

All models are wrong, and some are useful.

That goes for any and all of our ideas, including our body’s idea of what is the best way to run. No idea will ever be able to exactly model the world. But some are more useful than others—and the useful ones are useful because they account for such realities with a certain success.

We must stand in observation of the reality that, when we run, the most important force we will interact with is The Force of Gravity. The quality of our interactions with gravity will determine whether we become injured or not (among other things, like speed).

In systems thinking terms, we move and live within a particular physical system. Inside of that system, there are certain constant and variable forces which the body must be capable of interacting with. If it isn’t (yet) capable of interacting with those forces, and we push it to do so, we will compromise its integrity.

In that system, if we push off the ground, we will accelerate back to it at a rate of 9.78m/s² (32ft/s²). Which means two very important things: first, that the longer we are suspended in the air, the more we will accelerate. Second, in order to maintain bodily integrity, our muscles (but also our bones and connective tissue) must be strong enough to resist the stresses incurred by interacting with that magic number.

What this amounts to in athletic terms is that body must have (1) very strong muscles, capable of responding explosively in sustained activity, and (2), the ability to maintain the center of mass (the torso) relatively stable throughout the run. In other words, it must have the ability to make the torso rise and fall as little as possible. 

How does the body achieve this mechanically?

By moving the legs faster, i.e. increasing the stride rate (to somewhere around 180 steps per minute). If we can make our feet strike the ground 20 milliseconds (.02 seconds) faster than before, that would be .02 seconds less that we’d be accelerating towards the ground. Stronger and more powerful muscles (to move our legs faster) mean that we’re accelerating less towards the ground. But here’s the kicker:

It also means that they are more capable of withstanding the stress placed on them by gravity.

But wait: there’s more!

As Owen Anderson writes in Running Science, if we could make a 20 millisecond (ms) improvement between footfalls, that would constitute a time improvement of 756 seconds across the duration of a marathon—in other words, an improvement of 12 minutes and 36 seconds! As Anderson himself writes:

[That is] an almost infinitesimal change and therefore one that most runners can easily make.

In the interest of beating this point into the ground (pun intended), that’s 12 minutes and 36 seconds we’re not accelerating towards the ground. And remember the thing about acceleration: the first 20 milliseconds and the last 20 are not created equal.

If we’re running at 150 steps per minute, we might be in the air for 60% of the gait cycle. Doing the calculations for you, we’re accelerating towards the ground for 116 ms.

At the end of the first 20 ms of acceleration, we’d be going at a speed of .09 m/s second (.29 f/s).

At the end of the 116 ms of acceleration, we’d be going at .056 m/s, or 1.64 f/s.

But if we make a 20 ms improvement from 116 (in other words, 96), our maximum falling speed would be of 0.47 m/s, or 1.54 f/s.

Let’s reiterate: A 20 ms improvement from 116 ms means that the runner is going a tenth of a foot per second slower upon hitting the ground, and it’s only that way because of muscles that are stronger.

If take the time and energy to make our bodies more capable of interacting with gravity, we will inevitably end up being the faster version of ourselves.

Let’s internalize this, because it really does constitute the minimum passing grade of the “entry exam” for a runner:

Being strong enough to interact with gravity is the minimum power requirement for a human runner.

Although elite runners have muscles that are much more powerful than necessary to deal with the requisite 9.8 m/s², that number is where the laws of physics and the Earth’s mass have set the bar for human runners. That is our system. Those are its requirements. Let’s stand in observation of that fact.

There are two good ways that I know of, that can get us to meet those requirements. The first is by jumping rope as I’ve described, and the second one is an exercise in this video by Dr. Mark Cucuzella (at 6:09).

(By all means, look at the entire video—it’s very engaging and informative).

Now, go talk to gravity until you’ve gotten to know it like an old friend.

UPDATE: You can find a couple of good discussions on stride rate and running speed here and here.

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