Sport Science: How Karate Experts Break Boards

Sport Science: How Karate Experts Break Boards

Dick Moss, Editor, PE

We've all seen impressive demonstrations in which karate experts break boards with their bare hands. But how do they do it?

In fact, it's not an ancient mystical secret—it's really just basic physics.

Timing is absolutely vital in performing this feat. A human hand moving at top speed at the point of impact can generate almost six times the force needed to break a board, and almost a third more force than required to break a concrete block.

But here's where training comes in. Karate experts ensure the correct timing by aiming their hand at a point below the surface of the board—this produces the maximum force as the hand contacts with the board.

Tension & Compression in Karate
If you look closely at these demonstrations, you'll see that the boards are supported at both ends. This is critical, because this setup allows the board to bend.

The bending squeezes the upper portion of the board (the part contacted by the hand) closer together (compression), while pulling the wood fibers in the lower portion of the board apart (tension).

This pulling action causes a crack to form beneath the board, which spreads upward, causing the board to break.

Why Don't They Hurt Their Hand?
And why don't experts hurt their hand? Experts use the “knife hand,” or “hammer fist” position which places the meaty, outside portion of their hand between the board and their bones. This absorbs some of the impact and transmits the rest up the arm. Again, training is important to ensure contact with this part of the hand.

Should You Give it a Try?
    As you can see, there's no mystical secret to breaking a board with your bare hands—we can all generate many times the force required. However, don't go out and try it without training. Karate experts spend years learning to apply force with the correct timing and using the optimal part of the hand.

1. Carol Gold & Hugh Westrup, How Sport Works: An Ontario Science Centre book, Kids Can Press, 1988.
2. Frank Vizard (Editor), Robert Lipsyte (Foreward), Why a Curveball Curves: The Incredible Science of Sports  (Popular Mechanics),  Hearst Publishers, 2009.

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