Originally Posted by atberry
Yet a bigger muscle is a stronger muscle, and a stronger muscle is a faster muscle
That's a very big simplification. I'm not against weight training, when used properly. However, while a bigger muscle may
generate more force, the acceleration of the fist is some function of the force divided by the body mass that you must move during the range of motion. This force/mass issue also affects the deceleration required, when a punch misses, to return the fist to a defensive position. It is not clear at what point exactly that increased muscle mass is detrimental. At lower weights it's obviously a much lower threshold, at HW it's not so easy to determine.
I think there is enough empirical evidence to be fairly certain that there must be a physical limit to any increased speed resulting from appropriate weight training.
More importantly, the applicability of that speed to boxing is crucial, if you adversely affect your stamina, flexibility etc by gaining weight then you start to greatly increase the risk of it having a detrimental affect on your overall performance. I would never recommend that someone like Khan purposefully bulk up in misguided belief that it would improve his speed. He'd just end up in a higher weight class, and would get obliterated.