Posted by Dave on July 12, 2011 | 9 Comments
The plan for this site has always been to supplement discussion of peer-reviewed science with other reasoned discussions based on anecdotes and experience. When I’m discussing the peer-reviewed research, I always include the Research Blogging icon you see at the top of this post. When I’m discussing books or other non-peer-reviewed sources, I don’t. That doesn’t mean the conclusions are wrong, just that they haven’t been systematically tested. But since some commenters expressed doubt about the conclusions of my post last week on cadence (based on the advice of legendary running coach Jack Daniels), I thought I’d see what I could find in the scientific literature on the subject.
So, is there scientific research to support the conclusion from the post that “you might be able to reduce your risk of injury associated with landing shock by increasing your cadence”—that is, the number of steps you take per minute?
I found a 2004 review article on the subject by Alan Hreljac. Hreljac examined all the work he could find on impact injuries to see if he could identify the most important risk factors. The key insight is this: Three separate studies found that runners on treadmills who landed hardest were more susceptible to injuries than those who generated less force when they land. A runner can incur up to five times her body weight in force each time her foot hits the ground. But runners vary in many different ways, and those whose running form limits this vertical force are significantly less likely to get injured.
How can you limit this force? A more recent study suggests that one way this can be achieved is by reducing stride length while maintaining the same speed. The only way to reduce stride length at a constant speed is to increase cadence, which is exactly what Daniels suggests. The researchers analyzed the stride of runners who decreased stride length—and increased their cadence—by ten percent and found a significantly decreased chance of injury. This isn’t a true empirical test, but the model the researchers used did find that likelihood of injury is reduced with a shorter stride. The other studies Hreljac mentions in his review support this model: They find fewer real-world injuries in runners with less vertical impact in each stride.
Is there a better way to decrease your risk of running injuries? Absolutely: Run less. But since this site is “Science-Based Running” and not “Science-Based Sitting Around,” that’s not exactly an option we take very seriously, is it?
Actually, it is: One key to effective training is to minimize the types of training that may lead to injury, and in future posts I’ll be discussing some ways to do that.