One of these years, Adrian Peterson isn't going to be an awesome Fantasy running back.

But are you going to bet against him?!

Since 2008, I've done work to provide guidelines on when a running back will start to break down. It all began when I scoffed at the idea that turning 30 was when everything went downhill.

The parameters that seemed consistent in the majority of rushers were eight full seasons of work and/or 2,400 total touches. Those benchmarks were for healthy running backs -- the ones with major injuries were expected to break down sooner.

A few years ago I tweaked the research to create a unique number, called a TEN (Total Evaluation Number), to identify a breaking point. This number was the cumulative amount of every regular and postseason carry a running back took plus one-third of the total amount of receptions.

If a player's TEN is 2,100 or larger, watch out. If a player has multiple red flags including injury, watch out. Those are more meaningful indicators than the actual age of the player.

Here's the evidence you need that age is nothing but a number.

Career carries Career rec. TEN Major injury Week 1 age
Reggie Bush 1,320 498 1,486 31
Jamaal Charles 1,420 284 1,514 29
Justin Forsett 781 198 847 30
Matt Forte 2,077 500 2,243
Arian Foster 1,559 272 1,649 29
Frank Gore 2,842 394 2,973
Rashad Jennings 749 156 801 31
Chris Johnson 2,104 303 2,205
Ryan Mathews 1,048 168 1,104 28
LeSean McCoy 1,702 341 1,833 28
Darren McFadden 1,277 251 1,360 29
DeMarco Murray 1,171 218 1,243 28
Adrian Peterson 2,497 244 2,578
Darren Sproles 637 517 809 33
James Starks 676 121 716 30
Jonathan Stewart 1,373 155 1,424 29
DeAngelo Williams 1,665 221 1,738 33
Danny Woodhead 543 279 636 31

Weighing the RB risk

So while Fantasy owners can probably get behind steering clear of Matt Forte, Frank Gore and Chris Johnson based on the research, it's Adrian Peterson who continues to stand out as the exception.

Adrian Peterson
DET • RB • 28
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Risk factor: High For the second year in a row, Fantasy owners shouldn't overlook the amount of work Peterson has had. We're talking nearly 2,500 carries over eight seasons, so he's clearly flying in the danger zone.

Reward factor: High It's easy to overlook his TEN when you know what he has delivered year after year -- double-digit touchdowns and at least 1,100 total yards (with 1,700 total yards last year). He landed 10-plus Fantasy points in 11 of 16 games in 2015, a completely reasonable projection for him to match. The Vikings offense is centered around him and will be until he cracks.

Worth taking: Round 1 Yep, the same spot as always. Why not? He's going to get close to 20 touches per game, pick up goal-line work and do all the things we wish other running backs would do. Picking up Jerick McKinnon with a selection in Round 10 to back him up is a really good idea.

Matt Forte
NYJ • RB • 22
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Risk factor: High Trust the data. Forte has done the heavy lifting for eight straight years and has a thick TEN of 2,243. We've seen him crack a little. He missed three games to injury last season and has seen his average take a dip to 4.0 yards per rush over his last two seasons. The Bears willingly let him walk and the Jets signed two running backs the day after they picked him up. A large workload nor a 16-game season is guaranteed.

Reward factor: Medium And this is why Forte's not worth a top-30 pick anymore. What's the expectation? Another 1,500-yard, eight-score season? Will he even have the chance to do that splitting reps?

Worth taking: Round 5 If we're putting him in the 1,000-yard range, then 50th overall is the better time to draft him. I might not even count on a sizable bump in PPR leagues since Bilal Powell could eat into Forte's passing downs. Plus Khiry Robinson might take some goal-line reps away. Let someone else draft Forte.

Frank Gore
NYJ • RB • 21
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Risk factor: High To be fair, Gore's been risky for years. Last season was the first time we saw his stats turn ugly, but it wasn't necessarily all his fault. The Colts have since beefed up their O-line and Andrew Luck is healthy again to help keep defenses honest, but it doesn't change the fact Gore has more career carries than anyone else currently in the league.

Reward factor: Medium The Colts haven't fielded a 1,000-yard rusher since 2007, five years before Luck came into the league. Gore's going to be the guy to do it?! He came close in '15, falling 33 yards shy. But he did it in the most painful way possible, averaging 3.7 yards per rush and 73.4 yards per game. Moreover, he had just five games with 10-plus Fantasy points last season, down from six in 2014.

Worth taking: Round 7 Why invest anything in Gore? If you land six strong starters before adding Gore, you're doing it right ... unless you just pass up Gore altogether.

LeSean McCoy
TB • RB • 25
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Risk factor: Medium If we're watching McCoy's TEN number, this will be his last productive NFL season. He's at 1,833, close to that 2,100 benchmark that signals breaking down. McCoy has never been a major injury risk, but he's come up with smaller issues that could build toward something more severe. His 2015 season ended with a torn MCL, and that came after he strained his hamstring. Tack on the Bills' young depth at running back and we could see McCoy's touches start to slide.

Reward factor: High It's probably unlikely we'll see McCoy lead the league in rushing as he did in 2013, but putting together a 1,300-total-yard, 10-touchdown campaign can't be ruled out. The Bills' scheme is designed to lean on the running back, plus quarterback Tyrod Taylor will help open lanes for McCoy with his own threat of taking off with the football. When he's on the field, he has a shot at great numbers.

Worth taking: Round 2 We're talking late Round 2, basically at the point where you see him on the board, realize his potential and take him after the top-of-the-top rushers are gone.

Jamaal Charles
RB •

Risk factor: Medium Coming back from one torn ACL is impressive. Coming back from two would be legendary. Charles' TEN of 1,514 shouldn't worry anyone, but the knee injuries will stop you in your tracks. Andy Reid might slow Charles' roll and give the Chiefs' backup running backs some work from game to game to keep his star back fresh. Charles has averaged 16.9 touches in his past 20 games with Reid. Could that number shrivel?

Reward factor: High Look, you know what he's capable of. There's really only one thing Charles has to do, and that's produce. If he makes plays like we know he can, Reid will forget about the other running backs and give the motherload to Charles. Those past 20 games? We're talking 93.3 total yards per game with 19 total touchdowns.

Worth taking: 12th overall Given the safety offered by other receivers and the overwhelming potential of a handful of other running backs, you shouldn't have to pick up Charles until 12th overall at the earliest. Technically, that's a first-round pick but one that comes with the top pick in Round 2 in 12-team formats. Backing up Charles with Charcandrick West is advised.

The numbers say you should stay away from Matt Forte. USATSI