More and more of the newer science seems to fly in the face of conventional wisdom.

This trend brings into question everything that we know—and more importantly, everything that we think we know.

Sitting in the armchair, this isn’t a problem. If we theorize about the differences between barefoot and shod running, and never actually go out for a run, never actually pushing the system to observe its behaviors, theory seems like a great idea. It seems like all we need to do.

But we don’t do theory for its own sake. The point of theory is for it to help us in practice. So we go out and run, and if our mental model—our suppositions, assumptions, beliefs, and beliefs about our knowledge—is different from how the world actually works, the discrepancies between that mental model and the real world will begin to show up as pain on our knees.

One of the reasons I love running is because out on the road, mental models accelerate towards the ground at 32.2 ft/s2. The collision between our mental model and the ground is as close to truth as we lay athletes are ever going to get.

Writing this was brought on when I read a post by The Gait Guys, talking about achilles tendonitis, and possible solutions to it. Conventional wisdom would suggest that the way to reduce achilles tendonitis is by shortening the achilles tendon, a.k.a. raising the heel on the shoe.

Why? Simple. If you raise the heel of a shoe, you loosen the achilles, so it’s not carrying the weight of the body anymore. By all counts, that should do the trick.

(It doesn’t).

But that’s the problem. This solution was thought up in the armchair, and never tested in practice. Theoretically, it should work. But that’s because a theory is a mental model: a self-contained little idea of the world. Given the rules of that model, raising the heel is an excellent solution. Now, all that has to happen is for that model to coincide with the realities of the body.

In academic circles, those kinds of suppositions are known as “pipe dreams.”

The body isn’t just a series of simple machines put together. It is a complex entity, built from stacks and stacks of systems, each doing a different job. And the job of one of those systems is to regulate impact force by using touch receptors.

Because that subsystem—the central nervous system—is also at play, the behaviors of the body/system will be “unpredictable.” But it’s only unpredictable because the theoretical model doesn’t account for that subsystem.

When we account for this system, its actual behavior seems a lot more reasonable: in order to maintain tension on the achilles, the body raises the foot as the leg approaches the ground. However, this means that the leg can accelerate for a longer period of time, making the initial contact forces that much more powerful.

We need to understand the systems we’re playing with.

We need to go out and test them, and get a feel for their behavior. The phrase “push the envelope” comes from test pilots: every one of those pilots climbed into the cockpit fully aware of the mathematical model that predicted the flight capabilities of the airplane—also called the “flight envelope.” Pushing the envelope literally means taking the plane into unpredicted territory—literally pushing the aircraft beyond what the mathematical predictions say that it can take.

Dangerous? Yes. Necessary? Absolutely. The reason flying such a safe mode of transportation these days is because a few brave and knowledgeable people understood that there is a big discrepancy between the armchair and the road—between the predictive model and the actual system.

Let’s take these lessons and put them into our running. Let’s push our own running envelopes to see what sorts of behaviors our body exhibits—and then modify our training and adapt accordingly.