Quoted for win. The only thing I can think to add is that speed breaks really do test your speed, and water breaks are just plain evil. Alot of it has to do the physics of the break. Doing one board (for the average person) isn't a problem. Push on it and the thing will break. Two boards with spacers is basically the same thing. Two boards without spacers becomes a different animal all together. At the second board without spacers you're basically testing how precise you are, because if you don't hit in the exact right spot, you're not going to break the board. The third board is testing your timing. If you're not extended at the right time, you're not going through even if you're hitting the right spot. At four boards you're basically testing everything you have. Are you hitting where you're aiming? Is your timing right? Are you moving fast enough? Is your attack moving in perpendicular to the target? Is your technique correct? After the fourth board you aren't generally going to be demonstrating anything new, except for how dumb you are (it starts to get fairly risky in the long term after four). People break glass, ice, roofing tiles, cement blocks, coconuts, baseball bats, and numerous other things, but all basically test the same thing as a regular break, or are just the person doing them trying to show off (like the guy breaking glass Ps1 mentioned). Can you test the same thing on a heavy bag? No, not really. Bag work develops the needed skills for breaking boards, sure, but it does not test them. With a bag you can lie to yourself and say you hit more accurately then you really did. You can hit and push instead of actually hitting. And you generally can only measure your progress on a heavy bag by how long you can go on it before your knuckles start to hurt. Which might be the same amount of time as when you started if you continuously hit harder.