Philadelphia, PA (Sports Network) -
There is mounting evidence that overworking a running back causes problems the following year.
Most avid fantasy owners know about the "Rule of 370." According to a 2007 study by Football Outsiders, the drop in rushing yards is significant for a back who carries the ball 370 times or more - 35 percent, while the drop in yards-per-carry is eight percent.
Fortunately, there were no backs that ran the ball that often in 2012-13.
But in the same study they showed evidence that running backs with 300-369 carries also encountered a drop in production - a 15 percent drop in yardage and two percent fall in yards-per-carry.
In 2011-12 there were two backs with at least 300 rushing attempts - Maurice Jones-Drew and Michael Turner. Both were busts last season.
Jones-Drew rushed 343 times for 1,606 yards two seasons ago, but could only get on the field for six games last season due to a lingering foot injury. He's still not back after surgery.
Turner's final season in Atlanta proved to be a bust for fantasy owners as his totals dropped from 1,340 yards and six touchdowns in 2011-12 to just 803 yards and two touchdowns last season. His yards per rushing attempt fell from 4.5 to 3.6.
Going back another year there were seven backs which fit these parameters and three showed significant drops in production, two suffered small drops and two improved slightly.
Heading into opening day this season there are five running backs with 315 or more attempts last season. Which means there are five backs that you should be concerned about: Arian Foster (351 carries), Adrian Peterson (348), Alfred Morris (335), Doug Martin (319) and Marshawn Lynch (315).
Foster already has been dealing with health concerns - both a calf injury and a sore back. He hasn't practiced since the end of May and fantasy owners are beginning to think it's going to affect his season. Not a big movement, but his overall rating has dropped from 2.4 in April, to 2.6 in July and 3.0 in early August.
Peterson is coming off a phenomenal season (2,097 yards rushing, 12 TDs), made even more impressive by the fact that he had major reconstructive knee surgery just nine months earlier. And while we think of him as "Superman," able to leap tall buildings and linebackers in a single bound, his 388 total touches in 2012-13 could take a toll on his production. In addition the loss of the team's second-best offensive threat, Percy Harvin, could lead to "All-Day" facing a lot of eight-man fronts.
Morris, a rookie, rushed an amazing 335 times last season and totaled 1,613 yards and 13 touchdowns. What's most curious about his totals is that noted tinkerer, Mike Shanahan, didn't play games with his backfield and stuck with the rookie over 16 games. But the former Florida Atlantic running back never rushed more than 263 times in college and his three-year average as the team's starter was 241 rushing attempts, meaning his workload increased by 39 percent with Washington.
Morris wasn't the only rookie to post amazing rushing statistics. In Tampa Bay, Martin was displaying his ability both as a runner and a receiver, posting 1,454 yards and 11 TDs on the ground and adding 49 receptions for 472 yards and another score through the air. That's 368 touches for those not counting - also a huge increase over his days at Boise State.
Lynch is an extremely physical runner, who has rushed 600 times over the past two seasons. That's a lot of collisions. His numbers may drop simply because Seattle has developed two young running backs (Robert Turbin, Christine Michael) who can help with the workload.
All five running backs are excellent fantasy options this season, but beware of the pitfalls of overwork and be sure to handcuff the appropriate back for insurance.