It seems a record is broken every year at the NFL Scouting Combine.

Players are bench-pressing more weight. They are running faster. They jump higher. No mark of physical achievement is static.

Except one.

The four-second 40-yard dash.

It is the man-lands-on-Mars challenge in football, one that may not be achieved for decades.

Even as players edge closer to it, you need only ask them if they think it's possible to understand the barrier the mark represents.

"I don't think so," said retired running back Chris Johnson, who ran a 4.24 40 in 2008.

Two-time Super Bowl champion Torrey Smith, a wide receiver who ran a 4.43 40 at the 2011 combine, was even more definitive about whether he thought someone, anyone, could break the four-second threshold:

"No."

At the combine, nothing dazzles and captures attention like the 40. It does more than open scouts' eyes; a fast time can transform a player's draft prospects.

A fast 40 doesn't just produce waves. It changes lives.

Johnson's 4.24 dramatically improved an already solid draft stock, prompting the Tennessee Titans to select him 24th overall in '08. After running for more than 1,200 yards as a rookie, he became one of just six players to produce a 2,000-yard rushing season (Adrian Peterson later made it seven).

Johnson's 40 record stood for almost a decade until receiver John Ross broke it with a 4.22 in 2017. The Cincinnati Bengals picked him ninth overall.

Ross, however, serves as an example that while the 40 has become a bigger part of talent evaluation, it is not an indicator of certain success. After Ross, who said he struggled with his physical health as a rookie after undergoing shoulder surgery before the draft, didn't record a single catch his first year, he had 21 receptions for 210 yards and seven touchdowns last season. This week, NFL Network's Ian Rapoport reported the Bengals are attempting to trade him.

Both the Johnson and Ross stories are set to play out again this weekend at the NFL Scouting Combine, when some player will undoubtedly run a blistering 40 time and see his draft stock rise as fast as his legs move.

But running a 4.0 40? That is a different matter.

Or is it?

If there were a player who had one foot in the international track world and possessed world-class speed and was also a first-class football player, he'd have a chance. And if that player trained extensively to run the 40 at the combine, maybe, just maybe...

"It would be really tough, but it's not impossible," said sprinter Christian Coleman, one of the fastest men in the world. "The thing is, no sprinters have really worked on the 40. No one has tried to beat a 4.0 40. But I feel like if I worked on it, I could do it."

Coleman ran a 9.79 100-meter sprint in Brussels last year, tied for the third-best time ever for an American. He believes any sprinter who has run a 9.8 or faster in the 100 meters would have a chance of running a 4.0 or faster.

That isn't just idle, boastful talk. Once, Coleman—his legs still recovering from running in the nationals—ran the 40 as almost a dare and had it filmed. He ran a staggering 4.12, which would have been the fastest combine run ever. He also didn't train for it.

"That was two years ago," Coleman said, "and since then I've gotten faster. That's why I say someone could do it, and I might be able to."

Don't believe him? Usain Bolt ran a 4.22 40 during Super Bowl week this year, at 32 years old and retired from sprinting, while wearing sweat pants and sneakers.

Like almost all athletic feats, 40 times seemingly have become more impressive each year. From 1988 to 1998, as Sports Illustrated's Ivan Maisel noted, just 18 players ran a sub-4.4 40. In the 2018 combine alone, there were 12. When Deion Sanders ran a 4.27 before the 1989 draft, it was seen as the stuff of legend. While the tale has lived on, the mark did not, as it has been bested numerous times since.

It's not just that players are getting faster. They are getting faster at a rapid pace and doing so because they train relentlessly for it.

Coleman ran a 4.12 and said: "I wasn't even really trying. "It's not a crazy thought that in a few years someone finally does it.

"It would just have to be someone either blessed with world-class speed or a really good track guy who also plays football. I've been around a lot of football guys, and while those guys are fast, there's a big difference between football speed and track speed. The fast track guys are just on a different level when it comes to speed.

"But if you got someone who was a true hybrid from both of those worlds, then watch out."

Dallas Cowboys Hall of Fame receiver Bob Hayes was one of those. Considered one of the fastest humans ever, Hayes is the only player to win an Olympic gold medal (two golds, in fact) and a Super Bowl ring. There's no record of Hayes' 40 time, but according to the late Ralph Wiley, he supposedly once ran a 5.28 60 (handheld timer) on a cinder track.

Hayes would have been a candidate to break a 4.0 40, but he was a rarity, and to this day, there's never been anyone like him in the NFL.

Even someone as fast on a football field as Sanders didn't possess what would be considered elite speed in the track world. Had Sanders been raised competing in meets against the fastest on the planet while also playing football, then the 4.0 40 barrier would have had a chance to fall.

But guys like Sanders, Hayes and Johnson do not currently exist in large enough numbers to threaten the 4.0-second barrier.

But one day, Coleman figures, they will. Maybe, with his help, they will. Recently, Coleman worked with Georgia running back Elijah Holyfield, son of the boxing champion Evander, in his preparation for the combine.

Holyfield won't break the mythical 4.0 barrier, but it's possible, just possible, one day we'll watch someone do it.

Mike Freeman covers the NFL for Bleacher Report. Follow him on Twitter, @mikefreemanNFL.

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