What path will Canelo follow as he makes 15-pound leap to light heavyweight?

Bob Fitzsimmons was a geeky-looking guy. His receding hairline had been in full retreat since puberty and his freckled torso looked too big for his spindly Babe Ruth legs. John L. Sullivan called him a "fighting machine on stilts."

Wonder if Canelo Alvarez, who challenges Sergey Kovalev for the WBO light heavyweight title on Saturday, has heard of Fitzsimmons. If he has, maybe he knows the Cornishman out of Australia was boxing's first triple champion, winning three world titles in three different weight classes -- middleweight (1891), heavyweight (1897) and light heavyweight (1903).

Fitzsimmons was the original division hopper, an opportunist taking refuge at any weight that would have him. Back then, when fighters wrapped flags around their waists and fought with five-ounce gloves, the weights for various divisions were, to say the least, fluid.

Fitzsimmons knew how to use the scales. He was 170 pounds when he outpointed George Gardner for the light heavyweight title and only three pounds less than that when he stopped 184-pound Jim Corbett for the heavyweight title.

The Kovalev-Alvarez match is just the latest installment of boxing's version of changing lanes, pioneered more than a century ago by a cunning fighter nicknamed "Ruby Robert."

Most boxers, except heavyweights, will tell you the toughest part of boxing is making weight. Drying out is often torturous and dangerous. Cutting too much weight for too long nearly always leads to trouble. Moving up isn't a panacea, but it beats seriously damaging your body.

Boxers move up in weight for two reasons: They can no longer make weight in the division in which they are competing, or there is more money to be made elsewhere. The two are not necessarily mutually exclusive.

More than anything else, it's a search for a new beginning.

It would be wrong to get the impression that moving from middleweight to light heavyweight is a fail-proof remedy for ambitious, aging or out-of-shape 160-pounders. Like most everything in boxing, it comes down to ability and circumstances. Overall, it's close to a 50-50 deal. There have been six middleweight champs who successfully moved up to become light heavyweight titleholders, and five who failed. Even some of the most celebrated middleweights fell short.

Former welterweight and middleweight champion Mickey Walker was the perfect fighter for the Roaring Twenties, an era exemplified by F. Scott Fitzgerald's novel "The Great Gatsby." It was a time of prosperity and cultural change, when inhibitions faded and the phrase "anything goes" was popularized. The Harlem Renaissance was in full flower and Art Deco architecture gave rise to the Chrysler Building in Manhattan. In 1920, the 18th Amendment made intoxicating liquors illegal, which led to bootleg booze and speakeasies.

Walker was a hard-punching, hard-drinking, devil-may-care Irish-American. He loved the bright lights and nightlife of Broadway, where he drank with everybody from Al Capone to the Prince of Wales.

Walker liked to brag, "Sober or stiff, I belted the guts out of the best of them," which was true a lot of the time, but not always. In three cracks at the light heavyweight title, he came up short against Mike McTigue (1925), Tommy Loughran (1929) and "Slapsie" Maxie Rosenbloom (1933).

Neither braggadocio, booze nor bravery helped Walker against them. All three were shifty defensive specialists, and he lacked the conditioning to catch up and overwhelm them.

Nearly every longtime boxing fan knows about middleweight champ Sugar Ray Robinson's failed attempt to take the light heavyweight title from Joey Maxim on June 25, 1952, at Yankee Stadium. How Robinson melted in the 104-degree temperature under the ring lights and how referee Ruby Goldstein fainted and had to be replaced by Ray Miller in the 10th round.

But did you know that the night before the fight Robinson dreamed that he -- not his opponent -- would die? And it almost came true. Ahead on all three scorecards, he succumbed to heat exhaustion and couldn't continue after 13 rounds.

"People don't know how near dying Dad was," Ray Robinson Jr. wrote in "Pound For Pound," the biography he co-authored with Herb Boyd. "His body was covered in blisters. He could not retain anything in his stomach for two days, and he was delirious and not well for six months after the fight."

Robinson's near-fatal sortie into the light heavyweight division was purely for money. He fought on for years afterward as a middleweight.

Then there's James Toney, the incredible expanding boxer. He's in a category of his own. Toney began his professional career weighing 160 pounds in October 1988 and ended up weighing 248¾ pounds for his most recent bout, a sixth-round knockout of Mike Sheppard in May 2017.

"I ran two times a day to make weight and I lived on water and lettuce fight week," Toney said. "I was at my best at super middleweight, but it was still tough to make 168 pounds. I'm a big fellow."

Toney, one of the most skillful boxers of his era, won major titles at middleweight, super middleweight and cruiserweight, plus minor titles at light heavyweight and heavyweight. He spoke from time to time about having an eating disorder, without which he would certainly have accomplished even more.

The cliché that boxers are the last to know when they're slipping is a fallacy. They might try to hide it, but they're usually the first to know. For some boxers, moving to a higher weight class can significantly prolong their careers.

"After the two Jermain Taylor fights I knew I couldn't fight at middleweight and be as strong as I was," said Bernard Hopkins of the back-to-back decision losses to Taylor that cost him the middleweight championship. "During a decade at middleweight, I found my niche, but the niche became past due. It was time to go.

"Richard Schaefer [then CEO of Golden Boy Promotions] said, 'We can get you a title fight at super middleweight,' but I wanted to go up two divisions. I needed an opponent that would get me pumped. I couldn't go in there with just anybody. I wanted Antonio Tarver. If I'm going to go out, I'm going out fighting a world champion. I wanted to chase history."

Hopkins knew he needed extra help transforming his body ahead of the Tarver fight, and turned to fitness guru to the stars, Mackie Shilstone. Mackie's clients range from Serena Williams to Peyton Manning, but also included boxers such as Michael Spinks, Roy Jones Jr., Riddick Bowe and Hopkins.

"When I went down to Tulane University to work with Mackie, I told him I wanted to be bigger, but big and fast, a middleweight in a light heavyweight's body," says Hopkins, who was pleased with the end result. "My movement and speed hadn't been compromised. My mechanics were middleweight mechanics, which gave me an advantage."

Modern training techniques are tools, not magic wands. In the end it's all about the fighter.

Hopkins' upset victory over Tarver in June 2006 by unanimous decision for a vacant belt was the start of a lucrative string of light heavyweight fights that stretched all the way to December 2016. Using the same guile he displayed in the ring, Hopkins oversaw a decade-long slow fade that added millions to his earnings. It's doubtful he would have been anywhere as successful had he stayed a middleweight.

Dick Tiger is another remarkable case. He was a late bloomer who became a TV favorite in the United States before he became middleweight champion, due to his aggressive, no-nonsense approach.