This is the story you don't want to read about Adrian Peterson. The one that's been years and years in the making ... maybe since he was a superstar running back at Oklahoma.

You see, Peterson is getting old. Old in terms of the NFL and in terms of how much work he can take on without slowing down or getting hurt. Not old in terms of real-life old. He's still very much young in that regard.

For several years, we've tracked how many carries and catches a running back gets and have found a correlation between when the touches pass a certain threshold and when a player begins to suffer injury. It has nothing to do with the exact age of a player -- saying a guy is 30 years old and therefore worthless is irresponsible. But ... many players from the past entered the NFL at age 21 or 22, put up eight solid seasons of work and totaled well over 2,000 carries before falling off the proverbial cliff. Their numbers went down the drain and their careers followed soon thereafter.

That threshold used to be 2,400 carries, but two years ago we changed the formula because backs were running a little less and catching a little more. So we made up a "Total Evaluation Number" based on the number of carries and catches a back had. Simply put, we totaled a player's receptions, divided by three and added it to the player's carries totals (including playoffs but not the preseason) to come up with the number. The new number to watch out for? 2,100 -- and Peterson passed it last season.

Now this is the same monster who came back from a torn ACL in less than nine months and steamrolled the NFL for 2,097 yards. He also has scored at least 10 touchdowns every year of his seven seasons. It's clear he's a rare breed. But even if we judge Peterson by our old criteria for running backs, which doesn't take receptions into consideration whatsoever, he's due for one more big year. And then ... man, I don't even want to type it. I can put that off for another year.

Here are the running backs carrying risk for becoming a physical liability to his NFL team and your Fantasy team.

Running back Career carries Career rec. Total evaluation # Major injury Week 1 age
Frank Gore 2,327 349 2,443 31
Fred Jackson 1,688 256 1,773 33
Steven Jackson 2,571 443 2,718   31
Maurice Jones-Drew 1,818 342 1,932 29
Adrian Peterson 2,126 210 2196 29
Darren Sproles 497 522 671 31
DeAngelo Williams 1,387 174 1,445   31

What happened last year?

A year ago we tested the theory against two tried-and-true Fantasy stallions in Steven Jackson and Frank Gore. Gore had just crossed the 2,100 barrier during the Super Bowl and Jackson had long blown past it. Gore had seen his carries decline for three straight years previously but got a bump up to 17.3 carries per game during the regular season and did very well with them. Jackson wasn't as fortunate, getting hurt in Week 2 and missing a big chunk of the season before coming back. He struggled to maintain a good rushing average but was able to still be a factor at the goal line. Long story short: Gore did well, Jackson didn't.

While one might suggest that every back is different and shouldn't be judged on a system created by an over-zealous Fantasy writer, one could also say Jackson had it coming while Gore might have gotten by because he barely topped the Total Evaluation Number heading into 2013 and the Niners did a very good job maintaining him. We'd be shocked if either guy had big seasons this year now that Gore has crossed over fully into red-flag territory with more than 2,300 career carries and Jackson now has a staggering evaluation number of 2,718.

Risky runners

Fred Jackson and Maurice Jones-Drew also are getting close to the 2,100 mark for adjusted touches and are considered risky running backs. Jackson's NFL carries don't make up all of his work -- he used to play indoor football and after much research we got a hold of just how many touches he had. Even with them and at the ripe old age of 33, he still has enough left in the tank for one or two more seasons, especially if the Bills can lighten his load and limit him to passing downs/two-minute drill/goal-line work. Don't expect another big year from him but he could provide decent depth and work as an insurance policy for C.J. Spiller.

Jones-Drew isn't much better off even if he's the best back on the Raiders. After messing up his foot in 2012 Jones-Drew struggled in 2013 to get even 1,100 total yards with five scores. It wasn't that long ago he led the NFL in rushing! With 1,818 career carries and an evaluation number of 1,932, Jones-Drew is a candidate to keep struggling to stay healthy this season. He's less than 200 carries from hitting the red-flag mark, and he'll only get there faster if he's involved in the Raiders passing game. That doesn't even take into account the team he's on or the fact that he'll split carries with Darren McFadden (while he's healthy). No one should aim to have MJD on their Fantasy team this season unless it's as a flex or a backup.

There's one more name on the list -- DeAngelo Williams. He's 31 but has been used rather sparingly throughout his career (at least compared to other backs). Williams isn't scary in terms of breaking down because he hasn't been overused -- he's scary to use for Fantasy because you just don't know how much work he'll get from week to week. Williams is a backup Fantasy rusher who could keep going until he's 33 or 34 thanks to his lack of work when he was younger.

What to watch out for

This year we should see one popular running back get to our warning level for a break down with another three get close. It's something to keep in mind if you're in long-term formats or just thinking about the future of well-known running backs.

Running back Career carries Career rec. Total evaluation # Major injury Week 1 age
Ahmad Bradshaw 1,073 159 1,126 28
Reggie Bush 1,228 451 1,378 29
Matt Forte 1,593 354 1,711   28
Arian Foster 1,236 216 1,308 27
BenJarvus Green-Ellis 1,074 59 1,093   29
Rashad Jennings 387 97 419 29
Chris Johnson 1,753 273 1,844   28
Marshawn Lynch 1,877 207 1,946   28
Ray Rice 1,618 406 1,753   27
Pierre Thomas 818 301 918   29

Marshawn Lynch is the one who is going to be ripe for a breakdown in 2015 -- if it doesn't happen in 2014 first. Lynch is not only coming off of a Super Bowl run, typically the precursor to a back slowing down, but he also took on more than 400 touches last season if you include the playoffs. He also has 1,002 carries over the last three seasons. These are all dangerous numbers -- eventually backs who take on this much work start to crack. The hunch here is that Lynch doesn't quite hold up to expectations. Christine Michael has been rumored all offseason to be the guy who will get a bump in work even if Lynch stays healthy this season.

Matt Forte, Chris Johnson and Ray Rice are the ones to keep an eye on, but their respective workloads don't make them high-risk players for the injury report. At least not yet. While Johnson and Rice have other issues around them that keep them from being appealing Fantasy choices, Forte is in a perfect situation where he won't share the ball too much and should contend for 10 or more touchdowns. You might think he's been overworked but he has just 740 carries and 170 catches over the last three seasons. By comparison, Johnson (817 carries, 135 catches) and Rice (887 carries, 208 catches) have had more.