The knock against running backs is that they burn out quickly. The physical punishment of playing season after season makes it difficult to sustain a career, never mind elite performance, for very long.

Enter Le’Veon Bell.

After five seasons in the league, Bell took a one-year hiatus. Sure, it was for contract reasons. But the unintended consequence is that Bell now believes he’s in better physical condition than at any other point in his professional career. It’s as if he hit the reset button on his body.

So, if Bell comes back and becomes his Pro Bowl self again with the Jets this season, could other running backs try to copy his playbook? Bell’s layoff wasn’t designed around physical revitalization. But if it works, could this whole thing turn into a grand experiment on how to extend an NFL running back’s career?

“It might be," Pro Football Hall of Famer Terrell Davis said. “It might be like the midway point, taking a year off just to get rejuvenated. It takes a toll on you.”

Davis knows firsthand just how grueling 300 or 400 touches per year can be. His career with the Broncos lasted just seven seasons – and he played just 17 games in the final three years, due to injuries.

“I mean, I wish I’d had a year off,” Davis said.

For generations, running backs have been used up and spit out. Players, even great ones, have started out strong, only to fall off and eventually peter out. If you charted the average career, it would probably look like the back half of a bell curve – a brief uptick, then a climax, followed by a steepening decline.

But no elite talent has ever willing walked away from the game for a full year while healthy. So we don’t have a true grasp of what Bell’s absence could mean for his career trajectory. Will it be the same as everyone else’s, minus a year of lost statistics and salary in the middle? Or did he just stumble into a way to put off that inevitable descent?

“Whatever that franchise tag was, (Bell’s) not going to get that money back” fellow Hall of Famer LaDainian Tomlinson said. "But will it preserve him a little bit, maybe he can play an extra two years? That’s a good point. I think it’s possible.”

All three Hall of Famers we talked to – Davis, Tomlinson and Barry Sanders – believe there could be something to the idea of hitting the reset button mid-career, with an eye toward tacking some extra years onto the back end.

But they all also know that the logistics of taking a year off aren’t easy.

For starters, teams want their talent on the field – not sitting at home or training solo.

“I don’t know if any team’s going to be like, ‘Yeah, we’re going to give you one year off to rest up,'” Davis said. “That isn’t happening.”

The obvious workaround, then, is for a running back to take his gap year once he hits free agency. But it’s isn’t quite that simple, either; if you skip a year in your prime, you have to make even more money later in your career to justify the losses.

“You’re not just sitting out just because,” Sanders said. “You’re sitting out demanding a larger contract. But I think it’s kind of a new math that some of these players may have to consider and it may work for some. But at the same time, obviously there’s always great players coming into the league and there’s certainly a risk involved in doing that.”

In other words: Sit out and you could get forgotten, then replaced. But that obviously didn’t happen to Bell. He was elite enough to still command attention when he returned. Surely, there are others who fit that bill, too. But how many can safely pull it off and command a large enough late-career salary to make it worth the risk?

“I think what’s interesting is a guy like Melvin Gordon,” Tomlinson said. "Can he do that? I don’t know. I don’t know if he can do that, I don’t know if he can afford to sit out a year and come back and say, ‘Oh, I deserve this amount of money.' Le’Veon was a unique situation. Maybe top three (running backs can do it). Top five, I don’t know. It’s tough.”

So, simply put, gap years aren’t about to become standard practice for running backs across the league. The pool of candidates who could try to copy Bell’s blueprint is very, very small.

But that doesn’t mean some of the lessons from Bell’s extended rest won’t be utilized in other ways.

“If it does work out, somebody is going to try to figure out a way to use that and to be able to get those legs back, to be able to save the body from all the punishment,” Davis said. “I just don’t know what scenario that somebody else is going to use.”

One idea Davis floated? Teams allowing running backs to sit out a handful of games, instead of a full season. Effectively just a smaller-scale version of what Bell did, to minimize some of the risks.

Some other potential leg-savers? Skipping training camp altogether. Blowing off full weeks of practice. There’s plenty of ways to build in extra rest, if teams are willing to get creative and believe it will lead to more production from their running backs.

But first, it’s up to Bell to prove that added rest actually works. And this experiment will go beyond 2019, too – we’ll all be watching until the day he retires, searching for signs that this hiatus did or didn’t help.

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Sure, Bell’s goal was simply to lock up more guaranteed money. There was no grander sport-changing plan in mind. But he may have fallen into one along the way. Now, he’s created a de facto experiment that the NFL world will watch unfold each and every Sunday.

Matt Stypulkoski may be reached at mstypulkoski@njadvancemedia.com. Follow him on Twitter @M_Stypulkoski. Find NJ.com Jets on Facebook.