Read running shoe reviews, and you’ll soon come across the statement that you hit the ground with three to five times your bodyweight with every step. Conventional wisdom says these impact forces are a major contributor to injury. After all, three to five times your bodyweight! How can that not hurt you?
Are Average Runners Getting Faster? It Depends a new study: Because your bones, muscles, and other tissues are built to absorb those vertical forces. What might be more significant, the study says, are the horizontal forces that occur when your foot hits the ground. The study measured what’s known as “peak braking force”—the maximum amount of horizontal force opposite to the direction of travel. This research, just published in the Scandinavian Journal of Medicine & Science in Sports, found that runners with the highest peak braking force were almost eight times as likely to get injured than runners with the lowest peak braking force.
Fortunately, it’s easy to lower your peak braking force and, theoretically, lower your injury risk.
Adidas Unveils Boston Marathon Jacket
One interesting thing about this new study: The finding about peak braking force wasn’t the main result the researchers expected at the outset.
Using as subjects relatively new women runners, researchers tested several variables as the women ran on a treadmill at a self-selected “moderately hard” pace, then after that testing the women did a 15-week half marathon training program overseen by the lead researcher, Chris Napier, a University of British Columbia physiotherapist with a 2:33 marathon PR.
[Looking for a complete program to reduce injuries and run stronger? Check out RUN 360]
Sixty-five women completed the training program. Napier and his colleagues tracked their injury rate, defined as being running-related, related to overuse—as opposed to, say, twisting an ankle—affecting the legs or lower back, and leading to missing three training days within two weeks.
Napier’s primary hypothesis was that average vertical loading rate, or how hard your foot hits the ground with every step you take on a run, would show the greatest correlation with injury rate. But it didn’t. In fact, average vertical loading rate, as well as other measurements of vertical force, had no relation to injury rate.
Only peak braking force did. And that relationship was significant. When the runners were divided into three groups of lowest, medium, and highest peak braking force, those in the highest group had eight times the injury rate compared to those in the lowest, and even five times the injury rate of those in the middle group.
Why might this be the case? “Bone withstands vertical (compressive) forces better than it does horizontal (shear) forces,” Napier wrote in an email to Runner’s World. “Most joints and soft-tissue structures in the lower extremities are built to withstand these same vertical forces, so perhaps they fare worse against the shear forces from increased braking.”
Shoes & Gear?
You might think that hard heel strikers are good candidates for having a high peak braking force. But in Napier’s study, that wasn’t the case. He found no difference in injury rate among types of foot strike (e.g., heel striking versus midfoot striking). Unfortunately, without visiting a lab, you can’t really tell if you have a high peak braking force. “Since the braking force is about one-tenth of the vertical force, or one-quarter to one-third of bodyweight, it is much more difficult to ‘feel’ this force when you are running,” Napier said.
But that doesn’t mean peak braking force isn’t worth addressing, or that there’s nothing you can do about it.
In a follow-up study that has yet to be published, Napier gave runners real-time information on their braking forces. The only cue the researchers gave the runners was to aim to lower their braking forces. All of the runners were able to reduce those forces from high to low.
Devices That Measure Running Dynamics
We may earn commission from links on this page, but we only recommend products we back
How? Most of the runners said they tried to shorten their stride and increase their turnover. The runners also said they tried to “land softly.” Later analysis found that the runners increased their cadence and shortened their stride by about 7 percent without altering their foot strike.
So, Napier recommends, if you’re frequently injured, consider increasing your cadence 5 to 10 percent and focus on landing softly. What have you got to lose?
Scott is a veteran running, fitness, and health journalist who has held senior editorial positions at Runner’s World and Running Times. Much of his writing translates sport science research and elite best practices into practical guidance for everyday athletes. He is the author or coauthor of several running books, including USATF to Elect New President Amid Budget Deficit, Advanced Marathoning, and Sara Hall Smashes American Masters Marathon Record. Pro Runners Ask: Is My Agent Worth the Fee Slate, The Atlantic, the Washington Post, and other members of the sedentary media. His lifetime running odometer is past 110,000 miles, but he’s as much in love as ever.
