Mmm, guess I didn't explain my point clearly...
About that two examples: no, those are actually something an untrained person couldn't do (and I'll explain why below). Those bricks I was talking about are damn tough, but I know what Gculk is talking about: I use to chuckle watching martial arts shows, 'cause most of the time those exercise are obvious fakes (well, when you have trained in the "same field", you can spot a sawed wooden plank or a brittle brick quite easily).
Fact is, half of the success in an exercise of that kind is
believing you can do it.
To smash a brick with a fist, you don't' have to strike the brick, you have to strike like you are trying to hit something
below it. Your fist don't have to hit the brick, it has to pass through the brick.
That's where a "normal" (untrained) person would fail; mostly because they would hesitate.
Now that's where concentration can really help you (especially the first times you try), removing your doubts and fears.
In fact, what you really need to do that is just being trained enough to punch something without hurting yourself, and with a decent strength. Nothing uber-human. I mean, when I did that the first time I trained for 2 years: it's a short time, since a decent "mastery" level is attained in about 5 years.
This is especially evident in that exercise I wrote about, breaking a stick pointed at your throat. Truth to be told, I'm not quite capable to explain how it works: it's a combination of breathing, combined with the tension of the muscles... anyway, what would make most people fail this kind of exercise if simply fear: feeling something pressing against the throat it's obviously something that would scare to death most people. If I can do that it's just because I believe (know) I can do it; and because I know what I'm doing (that is, I know that there is no real risk).
Now, what about the superior force that good martial artists seems capable of exerting with their blows or thecniques, even if they haven't a massive build?
Traditional explanation is the focusing of Chi, of course.
More practically, in my opinion it's just they way a trained martial artist strikes, grapples, etc. An untrained person would, for example, punch using just the strength of his arm; most martial arts train you to position yourself and strike using many other muscles to coadiuvate that strikes: the legs, pelvis and abdominals muscles all play a part in delivering a powerful punch.
Of course, this is even more evident in more elaborate thecniques, like grappling and throwing: a martial artist can put an untrained opponent off balance without much of a thought.
So, to resume: I think concentration gives an edge, simply because it removes "disctractions": you are no longer hindered by fears, doubts, hesitation. With your mind totally focused on the goal of combat (take out your opponent, as fast as you can), you are determined and "unrestrained": you strike without hesitation with full force.
No doubt, the effect looks impressive. But it's something just about everyone could do, with proper training. And no doubt, the more you train, the more impressive the "tricks" you can do become. But that's just a show of the mastery you have reached over your mind and body, not the effect of some obscure mojo.
(this is not to say I don't appreciate Chinese philosophy, btw)
Edit: were my old English teacher to read this post...
