Over at Footballguys.com, I try to unravel the relationship between workload and age. Eight years ago, Doug wrote three articles on the topic; sadly, I’m not sure we’ve come very far since then. So I decided to at least begin the process of measuring how much of an impact “mileage” really has on running backs.

Conventional wisdom suggests that, all else being equal, running backs with “low mileage” are more likely to age gracefully than running backs who have accumulated a significant number of carries.

This, unfortunately, is a very complicated issue to test. For example, new Giants running back Rashad Jennings is 29 years old, but he has just 387 career carries.  This makes Jennings a “young” 29, but is that better than being an “old” 28? The best way to test this question is to analyze running backs of similar quality as Jennings — but who had a lot of carries by the time they were 28 years old — and see how the rest of their careers unfolded.  The problem is that the list of running backs with a lot of carries through their age 28 season bear no resemblance to Jennings. The players with the most carries through age 28 are Emmitt Smith, Edgerrin James, Jerome Bettis, Barry Sanders, LaDainian Tomlinson, Curtis Martin, and Walter Payton, which basically serves as a who’s who of running backs who are not comparable to Rashad Jennings.

Generally speaking, the best running backs get the most carries: did you know that Jim Brown is the only player to lead the NFL in carries more than 4 times? He did it six times in his nine-year career. Along the same line of thinking, the running backs with the most carries are generally among the best running backs.  Running backs who haven’t had a lot of carries through age 28 generally either aren’t very good or have suffered multiple injuries, which makes it tough to find players who feel like true comparables to a player like Jennings.

One could argue that running back workload and running back quality are so inextricably tied that it’s impossible to accurately measure whether age or workload is more important.  But today, I want to take a step back from examining the specifics of a player like Jennings and look at the big picture.  There are some examples that appear to support the “running back mileage” theory.  Shaun Alexander had a significant number of carries through age 28, and was excellent at age 28; the fact that he then declined so significantly, so quickly, could be a sign that workload really mattered. After all, few players suffer such sharp declines when turning 29. But that’s just one data point.  What if we can bring in many more?

You can read the full article here.