Do Running Shoes Make Us Run the Risk of Injury?
Three Key Joints Feel The Pressure
"It was surprising that the percent increase was so high with running shoes," says Kerrigan, an expert in biomechanics, human movement and gait who has a medical degree from Harvard University. "We really didn't see those dramatic increases in walking."
Overall, the study finds that while today's running shoes do a good job of protecting the foot, wearing them dramatically increases pressure in three lower-extremity joints -- the hip, knee and ankle -- when compared to running barefoot. For example, researchers note that wearing running shoes while running leads to an average 54% increase in what's called hip internal rotation torque, pressure that may increase the risk of osteoarthritis in the hip joint.
To put things in perspective, walking in high heels -- long considered a joint-busting exercise -- increases knee joint torques (a pressure measurement) by no more than 26%, while the effect of running shoes on knee joint torques while running leads to up to a 38% increase, the researchers say.
With all the runner's out there -- the U.S. Bureau of Labor Statistics says more than 7% of the U.S. population regularly runs for exercise -- the increased potential for osteoarthritis is a big concern. There's no cure for the degenerative joint disease, the most common form of arthritis, which costs about $186 billion a year in the U.S. to treat.
First Athletic Shoe In 1972
So why is it that with the first athletic shoe invented in 1972, designers nearly four decades later still haven't figured out how to make a shoe that can spare us from all these joint problems? Despite increasingly expensive shoes, there's been little change over the years in the rate of injury of runners.
Kerrigan argues that despite recent advances in gait analysis, the increased understanding of biomechanics hasn't yet been incorporated into shoe construction. While the cushion in the heel and the medial arch may keep the foot comfy in existing designs, they disrupt how the foot helps mitigate forces.
When running barefoot, people typically come down on the heel but quickly roll over to the inside of their foot. "Running shoes typically inhibit your ability to do that," says Kerrigan, who ran track in high school and college and continues to run today. "Ideally, what you want to do is enhance those abilities."
Running barefoot, however, isn't the answer, she says, unless you can run on grass with spongy topsoil underneath. "When you're running on hard surfaces, you just don't have that springy interface," says Kerrigan, a former professor and chair of the department of physical medicine and rehabilitation at the University of Virginia. "Unfortunately, our feet haven't evolved to accommodate hard surfaces."
Current Shoe Design Found Lacking
As chairman of the Charlottesville, Virginia-based "optimal" shoe-design firm JKM Technologies, it's no shock that Kerrigan's research finds faults with current running shoes. But it actually builds on loads of previous research suggesting there is something lacking in current running-shoe design.
"A lot of foot and knee injuries currently plaguing us are caused by people running with shoes that actually make our feet weak, cause us to over-pronate and give us knee problems," Daniel Lieberman, a professor of biological anthropology, told the U.K. newspaper the Daily Mail earlier this year. "Until 1972, when the modern athletic shoe was invented, people ran in very thin-soled shoes, had strong feet and had a much lower incidence of knee injuries."
In Kerrigan's study, researchers looked at 68 healthy young adult runners (31 men and 37 women) who each run at least 15 miles a week. An integrated measurement system that included a specialized treadmill, computers, cameras and reflective markers placed on the runners' "anatomical landmarks" calculated joint torques as they ran.
But as Kerrigan points out, there are limitations to this method: Researchers can estimate the net difference between the forces on either side of a joint, but not the actual joint-contact forces, the study says. "The only way would be to put a force transducer into a live joint," says Kerrigan. "We haven't been able to find any volunteers for that."
Brooks Explores All Innovations
The shoe used in the research was the Brooks Adrenaline shoe made by Bothell, Washington-based shoe and apparel maker Brooks Sports, a subsidiary of Berkshire Hathaway (BRK.A). The shoe was not singled out for any reason, except for its "neutral classification and design characteristics typical of most running footwear."
Informed of the study by DailyFinance, Brooks says in a statement that it takes running biomechanics and injury prevention very seriously. "We value the results of this study and are in active research and development on many unique, performance running footwear solutions at Brooks," says the statement. "This includes styles that enhance the natural motion of the foot and body while offering protection from weather conditions, road debris and individual biomechanical variances. We continue to explore all innovations that deliver real, relevant solutions to today's runner."
One person who might be eager to talk to Brooks is Kerrigan herself. The mom of three daughters, who are also runners, is working on a shoe design that she says better responds to the natural movement of walking and running. Called the CDC Suspension System, it has a flexible carbon fiber cantilever unit that keeps the inside of the sole open -- imagine the sole like a "U" turned on its side.
"This one has been able to show that it provides true compliance and compresses and releases at the precise time that true forces reach their peak," Kerrigan says. "The heel cushions in existing shoes don't really provide true compliance."
Kerrigan isn't the only one looking to reinvent the running shoe. Concord, Mass.-based Vibram has come out with a shoe it likens to running barefoot, the "FiveFingers" model that resembles a glove for the foot.
Walking Shoe In The Works
As for Kerrigan, she's looking to license her technology to other shoe companies, a move she says that could lead to a new shoe in about a year. But so far, nobody's bitten, so she may develop it on her own, which could take three years, she says.
JKM Technologies is planning to release a women's walking shoe in the fall under the name OESH. "Hopefully we can get that made and get some feedback," she says. No doubt, the shoe industry will be listening.