A new study that investigates the relationship between foot strike and running speed adds to our understanding of how the two are linked. But it doesn’t make life any easier for anyone. Indeed, the study authors posit a fourth kind of runner foot strike that hasn’t been previously noted.
Before, there were three footstrikes: rearfoot, midfoot and forefoot, with the later two often getting lumped together. Now, say well-known U.S. running biomechanics expert Ned Frederick and his coauthors from Ghent University in Belgium, there’s a fourth: the “atypical rearfoot striker.”
Frederick and colleagues noticed this when they asked 55 experienced Belgian road runners (average training distance: about 40km/week) to run across a force plate at four different speeds, ranging from 5:14/km to 2:42/km. All runners wore identical shoes, and all managed to hit all paces, including 2:42/km, for the brief period that was required.
The researchers looked first at the relationship between running speed and foot strike. At 5:14/km, 82% of the runners landed on the rearfoot and 18% on the midfoot. At 2:42/km, 46% landed on the rearfoot, 32% on the midfoot, and 22% on the forefoot.
Similar results from other studies, including those with elite runners, have led some to suggest that switching from a rearfoot to a midfoot landing could help you run faster. However, there’s always the chicken-and-egg problem: Which comes first?
Frederick and friends believe that speed comes first. “Our results suggest that the greater percent of midfoot striking in elite runners might just be a consequence of their running speeds,” they note.
The researchers also looked closely at the loading rate of the rearfoot runners, and found that they split into two groups. Typical rearfoot runners use the body’s heel-pads and the running shoe’s cushioned midsole to transition gradually forward, and produce moderate loading rates. “Atypical” rearfoot runners also land on the heel, but then transition quickly to the forefeet. This produces high loading rates, which may be associated with increased injury risk. (Check out this Runblogger.com post for a more detailed description of differences between typical and atypical heel strikers.)
The authors note that their results add to “the complex task of a shoe design.” First the shoe has to work smoothly when you’re running slow, and when you’re running fast, because you probably change footstrike along the way. Second, most runners are heel strikers, but that doesn’t mean they all run the same way. There appear to be two different styles of heel striking.