how a karate player can break a pile of tiles with a single blow of his hand

A martial artist learns to deliver higher force than average people. But that much is not sufficient to break a pile of concrete. What he does actually is he strikes the piles in a very short time in a very small area. Since, impulse, I = F × t and this implies F = I//t. ‘t’ becoming very short the force becomes very large. And as the area is small a tremendous is pressure is generated by his hand on the brick which exceeds the breaking stress and finally it breaks.