First and foremost, amazingly nobody has referred to the #1 factor in punching power and that would be Mother Nature. Secondly, heavy benching is going to bulk muscles and shorten/ tighten their fibers, and needless to say both processes will slow down a punch out of the gate. Consider Mackie Shilstone had Spinks work with hand weights via shadowboxing, not bench like the second coming of Bill Kazmaier. Finally, nobody herein is referring to the most critical upper body factor for punching power and speed, and that would be the rotator cuff. Heavy benching causes anterior rotation and thus suppresses the complementary mechanism of the posterior situated rotator cuff. Most anyone can perceive the parallel between throwing a punch and a baseball. Do you see pitchers focusing on rotator cuff strengthening, stretching and stabilizing or instead cranking benches like an Ed Coan wannabe? Carlos Zarate had a 95.5% KO record (yeah, lotta Mexican cab drivers but ditto for JCC el padre) and he fought as a beanpole 5'8 bantam. Any pics of Bob Foster benching? For strength building for boxing the tried and true since time immemorial has been the functional, explosive, sustained whole body synch acts of ax and sledge work, and, in the case of Cleveland Williams on the mend, he swore his salvation was baling hay. Truly, baling hay makes tons of sense for everything about conditioning but think of the exact relationship to punching per whole body action and explosive rotation from legs>trunk>back>shoulder+arm. And, of course there's the sustained cardio of ax-sledge-hay baling v. a bench set. Marciano and Frazier's movement and on into their power punch reflected haybaling entirely. I'll close with the words of a pretty decent puncher: "My real advice would be this: chop wood, lift hay bales; go back to old-school, natural methods of training. My trainer, Archie Moore, he told me to go away and chop trees for two weeks before a fight – and I did and it made all the difference in the world; all the difference to my life. I’d say doing things like that increases your punching power by at least 25 percent – forget lifting weights, that just makes you muscle-bound and takes away your speed. Weights are no good for you, that’s what I say. Go back to nature when you train, that’s what I did." - Earnie Shavers