Picture this: A man stands on a platform above a stack of seven massive slabs of ice, each one weighing nearly 300 pounds (136 kilograms). Putting his hands behind his head, he suddenly bends his upper body down to the top slab and touches it with his forehead. He repeats this process several times until, on the last bend, he follows through and hammers his skull into the slab. Incredibly, all seven blocks of ice break in half and fall to the ground.
This really happened. Strongman J.D. Anderson, aka the Iceman, smashed 2,000 pounds (907 kilograms) of ice to pieces with his head on "The Tonight Show with Jay Leno." That's extreme, and not recommended (see How Chronic Traumatic Encephalopathy Works), but it demonstrates how phenomenally powerful the body can become given training and focus.
Breaking boards with your bare hand is a simpler feat than the one described above, and less potentially injurious (although your hand is a precious thing, too, and should be treated accordingly — more on that later). Typically, beginners start with a single board, roughly 1 foot (30 centimeters) wide. The material is usually pine, which is a softwood that breaks much more easily than a resilient hardwood like oak. The board should also be free of knots.
There are a wide range of techniques students can use, such as "hammer fist" (bringing your clenched fist down), "palm heel" (striking with the heel of your palm) and "knife hand" (the good old karate chop). Someone can hold the board, or it can be placed on supports. It should be held or supported on the sides, rather than the ends, allowing the practitioner to break the wood along its grain. Going against the grain, as the expression suggests, is much more difficult.
Regardless of what technique a practitioner uses to break a board, instructors usually emphasize preparedness through practice. Hitting a padded surface repeatedly helps increase accuracy, speed and strength while also toughening up the striking area of the hand or foot.
Mental preparation is as important as physical in this case. Hitting anything accurately requires focus. Practitioners work on their focus through breathing techniques, such as breathing out sharply or even shouting as they strike.
And when breaking a board, it's important to hit it as close to the center as possible. One of the key mental limitations that must be overcome is the body's natural instinct to slow down when approaching hard surfaces in order to avoid injury. Paradoxically, if your hand or foot slows down before hitting the board, the wood won't break, and if it doesn't break, the force of your blow will rebound into your hand and injure it. For this reason, instructors get their students to focus on hitting, not the board's surface, but a point a few inches beyond it. Imagining this point helps prevent the instinctive slow-down and ensures follow-through, which in turn helps transfer the full force of the blow to the board, breaking the wood instead of your hand or foot [source: American Martial Arts Academy].
That's all very well, but technique doesn't really explain how it's actually possible to smash apart hard objects with your soft, pliable extremities.