I’d be remiss if I didn’t point out a delightful little post on karate breaking — the bare-knuckled smashing of hard objects — by former Sci Am editor in chief John Rennie (aka my former boss). Rennie, a 17-year karate practitioner, is striking back against an io9 post that propagates a misunderstanding of breaking physics.
From io9 (emphasis Rennie’s):
It’s also important to strike quickly at the surface of the block. Most blows are part connective smack and part push. This delivers the most damage when fighting flesh, but helps protect concrete or wood. Concrete and wood have a good mix of rigidity and elasticity. The materials will bend, and even flex back like a rubber band would, but the limits of their malleability are much lower. Bending and snapping back can do more damage to them than it can to things that flex easier. By making the blow fast and pulling back, the striker hits the block hardest and allows the material to do the maximum amount of bending. A follow-through push will keep the material from snapping back, and snapping itself.
Follow through is actually all important, Rennie says:
When you break a board, or concrete, or a Louisville slugger or anything else routinely used these days in demonstrations of tameshiwari (breaking), you have to follow through on the strike. Indeed, advice commonly given to students learning to break is that they should aim at an imaginary target several inches beyond the actual object, for two reasons. First, doing so helps to make sure that the actual strike occurs closer to the movement’s point of peak biomechanical efficiency. Second, it helps to override our natural tendency (partly psychological, partly reflexive) to slow down ballistic movements such as punches and kicks before they reach full extension, which helps to protect the connective tissues around our joints.
Similarly, it’s my understanding as a fan of mixed martial arts and other schools of whoop-ass that when punching someone, kneeing them, etc., you want to aim a little behind where your strike will hit, presumably to take advantage of the biomechanical efficiency mentioned above. Rennie links to a technical discussion of breaking [pdf] that corroborates me on that:
One well-known piece of advice that karate instructors give their students is to focus their punches into their target. Thus if you were striking another person in the chest you would aim to terminate the punch about a fists length inside of your opponent.
Kids, go practice this at home and report back in comments.