The image of Juan Manuel Marquez here and on the RingTV.com homepage, called “The Scientist,” was painted by Tyler Streeter, an emerging artist who greatly admires the sport of boxing. He began drawing and painting fighters at the age of 10 after watching Marvelous Marvin Hagler fight Sugar Ray Leonard. The chemistry between Tyler Streeter and the “Sweet Science” is evident in his paintings. Reflecting the beautifully sharpened minds and courageous hearts of these modern day warriors, Streeter brings to life the mental anguish and physical stamina unique to boxing. Streeter lives in Las Vegas. You can view his works at www.tylerstreeter.com.

LAS VEGAS — Juan Manuel Marquez is roughly a 3-to-1 betting favorite to retain his world lightweight title against Juan Diaz on Saturday.

Although Marquez (50-5-1, 37 knockouts) is 10 years older than his 26-year-old challenger, who the future hall of famer knocked out the in ninth round of last year’s Fight of the Year, the prevailing wisdom is that the Mexico City veteran has more left than Diaz.

However, fans can only assume Marquez is going to be as sharp as he was in the first Diaz fight, which took place last February, given his age and the fact that he fought at a career-high 142 pounds for his welterweight bout with Floyd Mayweather Jr. last September.

Who knows what effect if any packing on seven pounds to his 5-foot-7 frame just one year after his first lightweight bout and then dropping back down to 135 pounds will have on Marquez, a former featherweight and junior lightweight titleholder?

Strength and conditioning coaches who also specialize in nutrition say Marquez could be playing with fire if he didn’t put on and take off the weight properly.

“It’s a risky proposition,” said Darryl Hudson, a veteran conditioning coach who has worked with some of the top fighters. “There’s a history of older fighters going up in weight and losing a lot speed, strength, power and stamina when they’ve attempted to come back down to what used to be a more natural weight for them. The tail-end of Sugar Ray Leonard’s career comes to mind.”

Leonard, who forged his legend at welterweight, campaigned at middleweight, super middleweight and light heavyweight (weighing between 160 and 165 pounds) after his successful comeback victory over Marvin Hagler in 1987. In 1991, he decided to drop down to 154 pounds to fight junior middleweight titleholder Terry Norris. The hall of famer had nothing in the way of speed or reflexes against the young tiger and absorbed a humiliating beating over 12 rounds.

“Getting older is hard for anyone because the body slows down in so many ways, but it’s especially hard for an athlete,” said Hudson. “When the metabolism slows down, it’s harder on the body to take weight off, especially if that weight wasn’t put on correctly. If a fighter just loses weight, it’s dangerous. If he loses muscle weight — that’s Roy Jones.”

The former four-division titleholder's return to light heavyweight from his heavyweight foray has become the modern cautionary tale for boxers putting on and taking off considerable amounts of weight.

Jones put on 18 pounds for his challenge of then-heavyweight beltholder John Ruiz in March of 2003. He enlisted the aid of fitness guru Mackie Shilstone to put the pounds on and the result was a bigger, stronger version of Jones with the same speed he exhibited at light heavyweight. Ruiz didn’t stand a chance.

However, Jones also might've needed expert assistance in returning to the 175-pound, which he did later that year. The result was a monumental struggle against Antonio Tarver, in which the pound-for-pound king looked like a shell of himself winning a majority decision. He was knocked out in the second round of their rematch.

“You can throw your body off when you lose a lot of muscle,” said Hudson. “I know a lot of fans won’t see any comparisons between Jones and Marquez because Jones lost 18 pounds and Marquez is only dropping seven or eight but that’s a lot of weight for a smaller guy. And they have to keep in mind that smaller fighters expend more energy in a fight than light heavyweights and heavyweights.

“Losing a lot of weight is dangerous with the type of guy Marquez is fighting. Diaz is going to press the action and set a very fast pace. So for Marquez’s sake, I hope he put on and took off that weight intelligently. I hope he didn’t try to do everything himself like a lot of old-school Mexican fighters do.”

Alex Ariza, the fitness mastermind behind Manny Pacquiao’s successful rise in weight in recent years, said the method by which Marquez put on the weight is the $1 million (his guaranteed purse for the Diaz fight) question.

“I only know what I’ve seen on 24/7,” said Ariza. “But if he really put on the weight by throwing big rocks and drinking 29 raw quail eggs every morning, that’s not a good sign. That’s archaic. That’s irresponsible. So I hope that was just for the TV cameras. Eating raw eggs in that quantity poses a lot of health problems and tossing around rocks is not a functional exercise.”

Marquez’s trainer Nacho Beristain said his fighter worked with a specialist to put on the weight for the Mayweather fight.

“That was a job, in camp, that I developed with a physical conditioning coach that I’ve worked with in the past,” Beristain told the media on a recent conference call. The traditionalist trainer also said he enlisted the assistance for Marquez against his better judgment.

“I didn’t like certain things (about it),” Beristain said. “It was part of that camp, part of the fightÔǪ I wasn’t 100 percent on board with it but it was necessary for that fight.”

Beristain had concerns about Marquez’s weight training because of his fighter’s tendency to push himself too hard.

“With Juan, what could be his defect is that he loves what he does, he loves to work hard,” he said. “But at times he can exaggerate the work. He’s a very fine fighter and he doesn’t need to overtrain or over-exaggerate to perform up in the ring. And I think in that fight, for instance an example, instead of working on the weights a couple of weeks he might have done it for four weeks and done a little bit too much of.”

The welterweight version of Marquez appeared slow and sluggish against Mayweather, who won a painfully one-sided unanimous decision.

However, if he overdid it a little bit in putting on the weight, Marquez assured the media on the same conference call that he took the pounds off the right way.

“We’ve done it very carefully, very healthy, very well,” Marquez said of reducing back to the lightweight limit. “We have had the help of a nutritionist. I did, obviously, gain a few pounds to go up in weight. But we’re working, as always, very hard, working with the weight and working in the gym, and we’ll be there for a very good fight, a strong fight, and at weight come July 31.”

Former heavyweight titleholder Chris Byrd, who has experience in dropping too much weight for a fight, believes Marquez.

Byrd, a small heavyweight who usually weighed between 210 and 215 pounds for his fights, dropped down to the light heavyweight division to fight fringe contender Shaun George in May of 2008. Byrd got down to the 175-pound limit weeks before the ESPN2-televised fight and appeared to be fit. However, he found that he was unable to mount an offense or protect himself against George, who stopped him in the ninth round.

Byrd doesn’t foresee that fate for Marquez.

“I think Marquez will be alright,” Byrd said. “He didn’t stay at welterweight for a long time and then come down to lightweight. His body didn’t get used to being at welterweight. He went up in weight as a one-time thing, for a big fight. It was almost like an experiment to see how he would do at junior welterweight and welterweight because I think Marquez wanted to follow Pacquaio to those heavier weights.

“The opportunity with Floyd came along and he took it, but he learned that he couldn’t carry that much weight and be himself. He didn’t have his usual speed and reflexes versus Floyd, and for a counter-puncher like Marquez, speed and reflexes are everything.”

Byrd doesn’t think Marquez’s speed, reflexes or stamina will be compromised by losing the weight he put on for the Mayweather fight.

“He didn’t pack on pure muscle,” he said. “Marquez was solid, but he didn’t look like a body builder in there with Floyd. He wasn’t big and bulky. There was even some natural body fat around his midsection. That tells me that the 148 pounds he weighed on fight night was mostly water weight. A fighter doesn’t hurt himself losing water, he hurts himself losing muscle.

“Roy Jones debilitated himself because he put on so much muscle for Ruiz and then took it all off. When he weighed in at 192, 193 pounds and fought at 199 it didn’t look like water weight. It looked like pure muscle and it was everywhere. His back was bigger, his chest was bigger, his shoulders, thighs and arms were bigger. He even put muscle on his neck. He still had a small frame for a heavyweight but he looked beefier than Ruiz when they stood next to each other. Roy kept that weight on for months after the fight. When he took the muscle off for that first fight with Antonio Tarver, he ruined his career because he was never the same after that.”

Byrd believes chances are good that Marquez will be able to return to his 135-pound form because lightweight is a “comfortable” division for the former featherweight.

“I think he made 135 pounds fairly easy before he went up in weight,” Byrd said. “If he tried to go below 135 pounds for some reason, then maybe there would be some cause for concern. That’s what happened to me. I tried to go too low in weight and I made the mistake of dropping down to fighting weight five weeks before the fight.

“Oscar De La Hoya did the same thing when he fought Pacquaio. I think he was thinking the same thing I was: ‘I have to get my weight down low before the fight so people don’t think I’m trying to pick on a little guy.’ Big mistake. Fighters are used to making lighter-than-natural weights from when they are little kids. We think we can do it when we are in our mid-30s and that’s not always the case.”

Fans may get a clue as to whether Marquez’s drop back to lightweight was successful at Friday’s weigh-in.

“You can often tell when a fighter has messed up with his weight when he steps on that scale,” Hudson said. “I always pay attention to their faces. If their lips are dry and chapped and their cheeks are sucked in around their jaws and ears, that’s a tell tale sign. If there are dark circles around their eyes, you know they are in trouble. I call it the raccoon look.”

Jones and De La Hoya had that look before their fights with Tarver and Pacquiao. Byrd did not have it before the George fight.

Fans might have to wait until Marquez steps into the ring with Diaz to find out whether he was smart about his welterweight foray.