Trainers for Manny Pacquiao and Juan Manuel Marquez say hard work and fitness, not performance-enhancing drugs, have allowed their fights to add muscle and power as they move up in weight classes.
Doping has been an issue for both fighters in Saturday's welterweight fight between Filipino icon Pacquiao, with world titles in a record eight weight classes, and Mexico's Marquez, who seeks a world crown in his fourth division.
Unbeaten US star Floyd Mayweather failed to make a deal for a megafight with Pacquiao in part because he wanted more extensive blood tests than usual, issuing taunts that prompted "PacMan" to file a slander lawsuit.
Marquez's bulking up for the fight came under greater scrutiny after Twitter notes from Victor Conte, the central figure in the BALCO steroid scandal, revealed that Marquez's strength and conditioning coach is Angel Heredia.
Heredia admitted providing performance-enhancing substances to Trevor Graham, the former coach of disgraced dope cheats Marion Jones and Tim Montgomery as well as other former US athletics stars.
"There are different ways to get a fighter very strong. We've done it the right way," Ignacio Beristain, Marquez's trainer, said through a translator. "I don't see why somebody should doubt we have done it the right way."
Marquez denies his bigger bulk has come through banned substances and has said he will take random blood or urine tests to prove he is not a dope cheat.
"I have done a clean preparation for this fight like always," Marquez said through a translator. "I will take any test any time. That's why anti-doping exams exist.
"It's a shame all the work I've done has been trashed."
Beristain said Thursday that his man received no help from banned substances, but was aided by nutrition and technique guidance from Heredia.
"I'm grateful for what he did with my fighter. I got a great guy who is strong," Beristain said.
"Juan would never do anything wrong. If he came to Juan with something, I know he wouldn't take it. I know Juan well enough to know that.
"Mexican fighters don't take that stuff. They know better. We teach them what that stuff can do to their bodies."
Freddie Roach, Pacquiao's trainer, said his camp had enough of such taunts from Mayweather to ever think of tossing such charges at Marquez.
"I'm so tired of that bulls---," Roach said. "You get a fighter in shape and make him work hard and (some people think) there must be something fishy about that. I don't want to do that to them."
As for someone with doping links like Heredia working with Marquez, Roach was unmoved.
"He was a rat," Roach said. "But I don't care about that."
Pacquiao, 53-3 with two drawn and 38 knockouts, will defend his World Boxing Organization welterweight crown against Marquez, 53-5 with one drawn and 39 knockouts.
"I've got two clean fighters," promoter Bob Arum said.