Brian Cronin has an article posted on the LA Times site discussing the question of whether Jack Dempsey "loaded" his gloves during his title fight against Jess Willard on July 4, 1919. Apparently this has been a lingering controversy in boxing ever since the fight itself, inspired by the fact that Dempsey didn't just defeat Willard, but absolutely pummeled him senseless, knocking him down seven times in the first round alone.
There are two theories of how Dempsey might have loaded his gloves. The first is that Dempsey coated his hands with plaster of paris, so that he was essentially hitting Willard with cement blocks. But as Boxing Illustrated discovered when they tested this theory, plaster of paris would have cracked the first time Dempsey hit Willard, causing huge damage to Dempsey's own hands with each successive hit. However, Dempsey's hands seemed fine after the fight. It's also hard to believe that neither Willard nor his managers would have noticed the plaster of paris when they inspected Dempsey's hands before the fight.
The second theory is that Dempsey had an iron spike hidden in his gloves. But this should have caused far more damage to Willard than was actually the case.
So Cronin concludes there's no evidence Dempsey loaded his gloves. The guy was just a really powerful fighter. (Incidentally, Cronin has an entire site devoted to analyzing sports urban legends.)