My original point was on muscle mass affecting speed; I never said it was the ideal boxer's physique.
Also, your point is academic: A marathon is consistent running/fast jogging over 2.5 hours and a boxing match is quick bursts of staccato action throughout a round, as well as minute's rest between them. Of course stamina is required, but it is combined with speed and explosive power. This is why many more boxers these days don't do long jogs, preferring to weight train, do short, sharp sprints and spar.
I don't really understand how you can imply a fighter's speed can diminish if he gains lean mass (within reason). Is Pacquiao really any slower at 140 than he was at 122?
Bookmarks