by Aaron Schatz

Back in the comments of my introductory post, Jason_in_nashvegas asked:

What are the odds Chris Johnson gets the season rushing record this year?

Those odds are very, very long. There simply is no precedent for any running back, even the all-time greats, having a two straight years similar to the season Johnson had in 2009. The five running backs before Johnson who rushed for 2,000 yards in a season all averaged at least 5.3 yards per carry—and each one saw his rushing average fall by at least one full yard per carry the following year.

Only one running back in history ran for more than 1,750 yards in two straight seasons: Eric Dickerson in 1983 and 1984. In fact, there are only three backs who had more than two 1,750-yard seasons, period: Dickerson, Barry Sanders, and O.J. Simpson.

I do want to clarify the issue of Johnson's workload, however. In a response comment to the original Chris Johnson question, Juba2 wrote:

CJ saw 400+ touches. He might start showing signs of wear and tear this year and revert to the mean.

Football Outsiders has done a lot of work on the issue of running back workloads; it is one of the things we are most famous for. Our famous "Curse of 370" theory suggests that "a running back who carries the ball over 370 times in a season will tend to break down or lose effectiveness the following year, unless his name is Eric Dickerson." Yes, it is meant to be somewhat pithy, and no, 370 is not some magic line where everyone who goes past it tears their ACLs. However, we've also done research on receptions and there's no indication at all that the concept of high workload includes "touches" rather than "carries." In fact, receptions are generally a positive indicator for a running backs future rushing performance, not a negative one. You'll find all of these issues discussed in this article on our website.

As for "reverting to the mean," that's something that tends to happen to every player and team in every sport, and it is not particularly related to wear and tear. The more extremely good or bad a player is one season, the less likely the player is to repeat that performance the next season. That goes for Jay Cutler's 2010 interception total as much as it goes for Chris Johnson's 2010 rushing yardage total.