Photo by informatique/Flickr
Does the way you run determine how fast you are, or whether you get injured? Since 2009, and the publication of Chris McDougall's book Born to Run, that's been one of the most popular questions in distance running. Form is paramount in most sports—imagine a tennis player who ignored serving technique, or even a cross country skier who never learned V2—but for distance runners it's less clear whether it matters. And it just got even more unclear.
McDougal's book helped touch off a revolution in running-shoe design, almost singlehandedly creating a market for (so-called) minimalist shoes. Because shoe design appears to influence some fundamental aspects of technique, the conversation about what are "good" shoes quite often turns into a conversation about what is "good" form.
Today, when people talk about bad form, they often mean an exaggerated heel strike, where a runner lands heel-first with his leg extended in front of his center of mass as in the picture at the top of this page. There's some evidence that this kind of landing is injurious, and it is probably inefficient in races shorter than the marathon. (The marathon may be a different story, though.)
Heel-first landings also require longer, slower stride lengths, and when runners move to mid-foot or forefoot landing patterns, it's common to see stride length drop and cadence, or stride rate, increase. That observation has been coupled with an observation that physiologist Jack Daniels made in the 1980s that elite runners almost all take roughly 180 steps per minute.
When I reported a story about form for Runner's World earlier this year, that 180 figure came up repeatedly. I heard about it from scientists, coaches, journalists, and physical therapists. Anecdotally, in the past two years, a number of elite runners have also played with their cadence in an effort to hit 180 strides per minute. As I was working on the story, I did too.
But as journalist, physicist, and former elite runner Alex Hutchinson notes, the 180-strides-per-minute benchmark isn't all it's cracked up to be. There are serious problems with Daniels's obervations (among them, a small sample size and no analysis of stride length plotted against speed), and other research has contradicted some of its conclusions. More likely, Hutchinson writes, runners play with both stride length and stride frequency when they run, and 180 makes sense at some speeds and not at others. Blogger and Nike coach Steve Magness has made similar observations.
Why is this important? In reporting of the form story, the 180-strides-per-minute rule came up as one of the few objective measures of good form. Nobody said it was the most important measure—if good form exists, it probably has more to do with dorsiflexion angles and knee position at ground contact—but for runners to change form, it helps to know what to aim for. And it's much easier to count strides than it is to measure dorsiflexion angles, never mind figure out what dorsiflexion means.