You don't just run with your legs

I've been watching with interest the running gait research and theories with great interest. But I also watch it with a bit of amused chagrin.

Researchers like to simplify things in order to more easily analyze them. I get that. Engineers use things called "free body diagrams" to lump large structures into a single unit in order to simplify calculations.

Much of the research and theorizing of running gait likes to treat the upper body as a "free body diagram" and isolate the running movement to those parts of us from the hips down. Further, the motion of the legs is simplified to acting like springs, neglecting the complex coordination of muscles and skeleton.

I've gotten into discussions with some of these people with regards to the landing of the foot under the body's center of gravity. They mostly vehemently declare that it is PHYSICALLY IMPOSSIBLE for the foot to make initial landing directly under the center of gravity unless it is undergoing acceleration. I maintain that it is not only possible, but also preferable, for the initial landing of the foot to be directly under the body's CG.

It comes down to resolution of moments, and realizing that the body CANNOT be simplified to acting only in the legs. The body is constantly rotating about the body's center of gravity, the hips coming forward and backward relative to the CG, the arms swinging, the shoulders rotating, the feet providing forward force as well as vertical force (and not in direct proportion to each other)... Rotations in three axes that allow what, on paper and over simplified, seems impossible.

Yes, if you ignore all these rotations and moments, and look at the body as a static mass at the hips (and also ignore the rotation of the hips about a vertical axis near the spine), then I agree -- the only way to keep the mass moving in a constant velocity is to balance the stance phase of the gait in both directions, forward and backward, about a vertical line through the CG. But this isn't reality. Simplifying the human body so makes any conclusions drawn as far from reality as the assumption that everything above the hips is static.

Of course all of this is really just mental gymnastics on something that is so natural that it's comical to ponder it for too long. That some people are getting PAID to study this in so much (horrific) detail is mind-boggling. It's interesting, but...

It's so much better, and more fun, to just run.