A recent study reported that National Football League (NFL) running backs with more than 300 carries in a season are not more likely to miss time with an injury the following season than those with considerably fewer carries. For fantasy football players, this is great news. But for sports medicine experts, it’s a reminder that injury risk rarely can be boiled down to a single parameter.
Conventional wisdom in football holds that any running back older than 30 years is a risky proposition, due to the extremely physical nature of the position, and many NFL teams are reluctant to sign older running backs to large contracts even if they have been consistently productive.
That’s why the recent study findings, published in February by the Orthopaedic Journal of Sports Medicine, are somewhat surprising. One might assume the running backs with the most carries per season are those most likely to take a beating over time and, eventually, those most likely to spend some time on the disabled list. But in fact, the study found running backs with 300 carries or more missed fewer games due to injury the following season than running backs who carried the ball between 150 and 250 times (despite similar mean ages for both groups).
But coaches and clinicians who work with football players know the number of carries in a season is not necessarily reflective of a running back’s workload. A running back is often involved in far more plays than just the ones in which he is given the ball. And, even if a running back doesn’t end up with the ball, his blocking assignment for that play could easily be just as physical and the injury risk just as high. It would be interesting to see whether a running back’s injury risk is associated with total snap count, rather than just number of carries.
That said, an even more important determinant of injury risk involves not just the previous season’s workload but how that previous season’s workload compares to the athlete’s current workload. As Australian sports scientist Tim Gabbett, PhD, discussed in a keynote presentation in Monaco at the recent IOC World Conference on Prevention of Illness and Injury in Sport, a growing body of research suggests the ratio of acute-to-chronic workload is strongly associated with injury risk in certain athletes. Workload spikes—going from limited activity to high activity within a short period of time—are of particular concern.
And another recent study from the UK found that three workload-related factors were associated with injury risk in rugby players: a high number of matches in the previous year, a low number of matches in the previous year, and a low-moderate number of matches in previous year followed by intense play in the recent past.
It’s possible that maintaining a high workload over time really is protective against injury in NFL running backs. But until that theory has been effectively tested, running backs like LeGarrette Blount (who had 299 carries for the New England Patriots last season) might not want to get too comfortable.