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New study shows increasing stride rate reduces impact forces absorbed at the knee and hip.
The speed of running is a function of stride rate and stride length. If you’re running at a certain pace and you want to run a little faster, you can attain that extra speed either by taking longer strides or by taking faster strides, or by doing a little bit of both. These adjustments are made entirely unconsciously, of course. All you think about is going faster, and your body decides whether you go faster by increasing your stride length or stride rate.
In fact, stride length varies much more than stride rate does as the speed of running changes. As you move from a very slow jog to a full sprint, your stride rate will increase a little, but your stride length will increase a lot more. The reason is that this way of attaining any given speed is more mechanically efficient than the alternative. Each runner has a certain stride rate range that is most efficient for him or her, so all runners automatically stay within that range as they adjust their running speed.
The most efficient stride rate for any given runner depends on his or her body structure, primarily. For example, short-legged runners are typically more efficient at a higher stride rate than longer-legged runners. The most gifted runners tend to have high natural stride rates. Because of this, some running experts encourage runners with lower stride rates to force themselves to increase their stride rate to match that of the elites, but research has shown that the desired increase in efficiency does not occur. In fact, runners always become less efficient when they run at any stride rate other than the one that is natural for them.
However, stride rate appears to be artificially influenced by footwear. Most runners exhibit a lower stride rate at any given speed in shoes than barefoot. In other words, shoes cause many runners to take “unnaturally” long strides—that is, to overstride. Overstriding is associated with greater impact forces and higher injury risk. So in some cases it may be best for a runner to sacrifice efficiency by forcing himself or herself to take shorter, faster strides in order to reduce impact forces and injury risk. (The other option would be to always run barefoot, but this is not practical for most runners and it may increase the risk for some injuries.)
Researchers at the University of Wisconsin recently studied the effects of manipulating stride rate on the level of impact forces absorbed at the knee and hip joints—two common sites of injury in runners. Forty-five runners were recruited to participate in the study. All ran on treadmills at their natural stride rate and at stride rates 5 and 10 percent greater and 5 and 10 percent lower than natural, all at a fixed, moderate speed.
The researchers found that increasing stride rate by 5 percent reduced impact forces absorbed at the knee, while increasing stride rate by 10 percent reduced impact forces absorbed at the knee and hip. Impact forces increased substantially when stride rate was reduced by 10 percent.
These results fall far short of demonstrating that increasing stride rate reduces injury risk generally, but they do provide solid evidence that it might.
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