I love the television shows where physicists, doctors, self-defense experts and computer visualization artists all get together to look at what goes on inside the human body when it gets used as a punching bag.

Like the show Fight Science:

Of course, things go wrong when everyone involved assumes that the human body behaves like a punching bag, as if it’s suspended from the ceiling by a chain or anchored to the ground by a weighted base.

The human body, being an auto-balancing structure, actually behaves much more like a bag of seawater balanced precariously on two hinged sticks. It moves when struck, whether from the body’s innate withdrawal reflex or from being unbalanced. The only thing anchoring it is its own inertia, and that’s easily overcome — sometimes surprisingly so — when struck.

Unless the person is bracing himself against the blow, leaning into it with one of their legs wedged against the ground behind them, you’re going to have a hard time transferring all the kinetic energy of the strike into the distortion of tissue. As they begin to move, the volume change in the tissue is reduced, allowing it to spring back into shape.

Think about a water balloon. It’s hard to make it pop by slapping at it sideways so it can roll away. But if you smash it against the ground, it distorts until it bursts.

This is why we emphasize using as much of your mass as possible for each strike during self-defense, and trying to stick it as far through the target as you can. You need to squish the water balloon of his spleen against his inertia and punch it all the way through to make it pop, instead of squishing it a little bit and then having it spring back into shape as he moves off your fist.

As for the video, the pubic symphysis is a great target — busting the ring of the pelvis makes it very difficult to stand up and run around. It’s a crippler. But I have my doubts about getting it done on a standing man by bouncing your hand off of it. A downed man, sure, stomp on it as hard as you can, with the pelvis braced against the ground and you can snap it.

The video seems to bear this out since the dummy used in the latter half is anchored to the ground by a weighted base, not balanced on two hinged sticks like a real person would be. Also, wet bone is more elastic than dry bone. And organisms reflexively withdraw from negative stimuli. So any strike to break the pubic bone would need to overcome both of these problems with penetrating distance. Much easier to ensure it snaps by stomping on it once the man is downed by other injuries during self-defense.

This stuff is expensive to put together — paying all the experts, writers, production staff, getting it on TV — so it amazes me every time that the more obvious details of the human machine are overlooked. Data collected from punching bags and anchored dummies are only applicable to injuring the downed man, not a standing one.