body mass in the punch power equation

I have recently read a couple of studies on the power of boxing one thing i fpound very interesting. many boxers were studied from flyweight to superheavy the punch speed was roughly 10m/s for all of them but its the weight that confused me. The scientists had some kind of machine to tell them how much weight was behind the fist at it ranged from less than 2kg for a flyweight to 8kg for a superheavy. even 8 kg is only the weight of a large mans forearm! so its official boxers do not punch with all their weight! i suppose it was quite obvious really as a 100kg(a heavy weight) moving at 10m/s would certainly crush the skull.