Ten years from now, Israel Vazquez will slowly pull himself out of a chair, wince, and think of Rafael Marquez.
In 15 years, Marquez will roll over in bed, feel a pain, and remember Vazquez.
They won't be the same men. They'll carry with them for the rest of their lives the reminders of their epic battles: A sore this, a painful that.
They won't be the same men on Saturday, when they meet for a fourth time in their epic series at the Staples Center in Los Angeles, as they were the night in 2007 when they first stood across the ring from each other.
Then, they were young fighters eager to please, anxious to pummel someone as much for glory and honor as for the ability to secure their futures. Now, they're grizzled, wizened veterans, keenly aware of the toll the sport exacts on some of its greatest warriors.
They're no less proud and no less competitive, though, and so Saturday's Showtime-televised bout likely won't be significantly different from the first three.
They'll punish each other and push each other to their limits and beyond.
The human body isn't made to endure the kind of punishment Marquez and Vazquez inflicted upon each other in those three fights, which were contested in a two-year span.
Earl Campbell was, for a few years, one of the three or four greatest running backs who ever lived.
At 23 years old, he literally ran over the top of Isiah Robertson while playing for the Houston Oilers against the Los Angeles Rams.
At 33 years old, Campbell couldn't walk a city block without enduring pain in one part or another of his body.
Vazquez-Marquez I was one of the great fights of 2007, ended prematurely when Vazquez badly broke his nose and couldn't breathe. Their rematch three months later became the 2007 Yahoo! Sports Fight of the Year. Vazquez gained revenge by stopping Marquez.
Seven months later, they put on perhaps the best match of the three, standing in front of each other for 12 heated rounds.
When they finished that night, each man took a deep breath. They had to feel the way Muhammad Ali felt on Oct. 1, 1975, when Joe Frazier couldn't make the bell for the 15th round of their third bout.
It was one of the most brutal wars in heavyweight history, fought in the searing heat of Manila. Ali was about to quit when he learned that Frazier had beaten him to it.
"It was like death," Ali said after the fight. "Closest thing to dying that I know of."
Ali had taunted Frazier mercilessly before that bout. When the fight ended, though, Ali had learned to respect Frazier.
Frazier wanted to win so badly that nothing stopped him from pressing forward, not the cleanest, hardest punches Ali landed in his legendary career.
"Man, I hit him with punches that would bring down the walls of a city," Ali marveled after the fight. "Lordy, he's great. Joe Frazier is one hell of a man. If God ever calls me to a holy war, I want Joe Frazier fighting beside me."
It's safe to assume that Vazquez would want Marquez on his side, and vice versa.
Theirs is one of the five greatest trilogies of the last 50 years along with Ali-Frazier, Evander Holyfield-Riddick Bowe, Marco Antonio Barrera-Erik Morales and Arturo Gatti-Micky Ward.
In each instance, there was something about one man that brought out the best in the other.
The fourth fight between Vazquez and Marquez won't be contested at the skill level that marked the first three.
The wars they fought left something of each in those rings.
It doesn't matter, though, because it won't change the fact that they'll put on another compelling show on Saturday.
Marquez might have been a slightly better boxer. Vazquez was probably slightly stronger. Marquez might have been better defensively; Vazquez was likely a better finisher.
Before they met the third time, Vazquez said, "When we get together, we produce boxing magic."
They haven't been heard from much since that third fight. Vazquez had a detached retina and has fought only once in 26 months.
Marquez, took, has had just one fight in those 26, a year ago on Sunday, in what was little more than a tune-up.
They understood the toll the series had taken on their bodies. Rest was the only possible answer.
They've grown old together and probably will become fast friends. Years from now, they're show up on the banquet circuit or the autograph circuit together, smiling for the cameras and acknowledging their fans.
Because of those three fights, and because of Saturday's impending battle, they're inextricably linked in the sport's history.
Just like you can't say Ali without Frazier, you won't be able to say Vazquez without Marquez.
They're not the greatest fighters ever, but they've put on one of the greatest series ever.
It's one that has had to be seen to be believed – and Saturday fight fans get perhaps the final chance.