Building a Shoe Right Out of the Gait
Gait research highlights the need for a new shoe design and, more important, a revised standard for footwear.
Another athletic shoe is entering the market. Instead of the typical manufacturer-based development team, however, this shoe comes from one woman’s years of research at prestigious universities.
This shoe was created to change the way people think about gait.
D. Casey Kerrigan, MD, MS, professor and chair of the department of physical medicine and rehabilitation at the University of Virginia (UVA), set out to study gait and found that current shoe designs do not offer proper support when walking or running.
A good deal of evidence supports this discovery. According to Kerrigan, at least 80% of adults who begin exercising have to stop or slow down a mere 6 to 8 weeks into the exercise program because of musculoskeletal injury, despite the cardiovascular improvements they experienced. So far, there has been no comprehensive answer to why.
Kerrigan’s initial desire to study gait stems from her years at Harvard Medical School. She recalls spending months learning about the heart, which requires a great deal of invasive technology to understand.
“We have no idea why things are occurring during walking and running because nobody has spent the time or the effort to understand the science behind [them],” she told O&P Business News.
She took it upon herself to make this commitment, starting with the movement of walking. By understanding the body’s response to the energy it takes to walk, she could figure out how to reduce the demands of that energy. Her research team redefined some key principles about how the body moves and preserves energy.
“We came up with something that was counter to what had been believed for many, many years,” she said.
Kerrigan and her team deconstructed the act of walking, examining the muscles, tendons, joint forces and reaction forces involved, to understand both macroscopically and microscopically what happens during walking and running. Theoretically, this provided a conceptual foundation for the team; tying in the data with biomechanics and clinical information, however, brought a greater understanding of actual issues. In this way, Kerrigan was able to determine those elements’ correlation to injury.
For example, the team demonstrated that, if footwear is altered to affect the knee joint torque, that could have ill effects elsewhere in the body. What may reduce knee joint torque on the knee, Kerrigan said, could increase the chance for plantar fasciitis. When making any adjustments to the foot, she must consider the effects on the entire body.
The team discovered that maximum hip extension is a determinant to maintaining the ability to walk later in life. They also found that people who lack that hip extension are more likely to fall. In addition, the limit in hip extension is associated with postural compensations that can result in back pain.
Kerrigan’s team recently received a grant from the National Institutes of Health (NIH) to study a specific hip flexor stretch and, in particular, its effect on gait biomechanics. This multimillion-dollar study marks the first time the NIH has funded research to study the whole-body effect of one specific component of exercise, Kerrigan said.
“We prescribe exercise and we think … you’ll get better, but it’s not necessarily true,” Kerrigan said. “A lot of research needs to be done to identify what specific part of exercise is causing the improvement.”
Designing the shoe
JKM Technologies, a privately held company co-owned by Kerrigan and her husband Bob Kusyk, has patented the CDC Suspension System based on Kerrigan’s extensive studies. The Suspension System is an athletic shoe that offers support to the wearer specifically during mid-stance.
Kerrigan’s research has shown that the current practice of supporting the foot at heel strike actually is counterproductive. Stunting the impact at heel strike does the most damage because the body needs that impact to properly realign itself after the stride. In fact, it is in mid-stance, when all the body’s weight is balanced on one foot, that the body experiences the most damage.
The CDC Suspension System technology, in contrast, accepts the change of body weight through heel strike and then suspends the foot precisely at mid-stance.
“The CDC Suspension System is a way to more properly align the body,” Kusyk said. “Because it is so efficient, it is thereby a more healthy means of gait.”
The shoe’s design allows a view into the sole from the medial side, into the center of the large heel cantilever and four smaller forefoot cantilevers. This cantilever design bounces back during the propulsion phase of the gait cycle.
In addition, Kerrigan determined that most overuse injuries occur because the runner’s body naturally attempts to achieve a balance in the coronal plane, which would result in better alignment. The CDC Suspension System, Kerrigan said, respects that plane and provides compliance relative to the plane, relieving the stresses and strains at the right place and time in the gait cycle.
Although each person’s body and center of balance are different, everyone is built the same way and is predisposed to similar conditions when walking and running. An athletic shoe, therefore, must support the body in such a way that it corrects any number of these conditions, such as plantar fasciitis and shin splints.
Putting women first
When developing the CDC Suspension System, Kerrigan noted that women seem to be more prone than men to different types of musculoskeletal injuries, from knee osteoarthritis to fibromyalgia. Moreover, the initial inspiration for her research was the correlation between women’s shoes and knee osteoarthritis.
The CDC Suspension System, she said, offers improved support for those ailments.
Because she assumes that this thinking may be too optimistic, Kerrigan also plans to develop a low-profile version of the technology that would fit inside other shoe designs.
The model Kerrigan envisions would fit well inside a more formal shoe with a sensible heel.
Although users could use a low-profile version in their own dress shoes, a shoe with a drastic heel would defeat the purpose of the insert.
Her research has shown that a heel height of even 1 1/2 inches increases knee torque; she believes anything lower than a one-half-inch heel height is acceptable.
Marketing the technology
This fall, JKM will begin a targeted launch at specialty running stores throughout the country, with a broader distribution planned for 2009. Kusyk and Craig Heisner, who works as adviser for JKM Technologies, would like pedorthists and others educated in shoe development to serve as liaisons for the market the company hopes to reach.
“They … gear people toward buying this particular shoe versus that particular shoe,” Kerrigan said. “We [want to] target the people that we can communicate with and see if they like it.”
The difference in the CDC Suspension System’s marketing, Kusyk says, lies in Kerrigan’s extensive credentials. During the time that Kerrigan was at Harvard, she worked with one of the most advanced laboratories in the United States to observe gait and locomotion.
In 2002, she began working at UVA’s gait laboratory, which has the only force-plate instrumented treadmill in the world that can capture and measure ground reaction force in all three planes during walking or running, according to UVA’s Web site.
“Our … level of expertise is not what you find at even the biggest of the running shoe companies. They are all clamoring for the legitimacy that a true researcher gives them, but they don’t have it in-house,” Kusyk said. “We are a little different in that regard, and frankly I like that.”
With years of experience on the marketing teams for both Brooks Sports Inc. and New Balance, Heisner fosters the relationship between JKM and Brooks Sports. Brooks partly sponsors Kerrigan’s research at UVA and in turn, Kerrigan’s team acts as Brooks’ research facility, evaluating the companies’ various shoe designs and making recommendations.
Kerrigan also continues her research at UVA through its running laboratory. At the SPEED Clinic, the research team evaluates runners and suggests ways for people to improve their running performance and prevent injuries. The USA Track and Field team recently partnered with the SPEED Clinic to assess its top athletes. By evaluating the top runners in the United States, Kerrigan’s team then can generalize that information for all runners, and determine proper form and procedure.
Trying to get people to change their running and walking form is not a simple task, Kerrigan said, because of the physical changes they have to make and because of the acceptance of the need to change.
“You can argue about all this stuff but in the end, you do learn a lot,” Kerrigan said. “[When] studying all of these elite athletes, down to people who have severe [physical ailments], you come back to the fact that we have the same challenges. This is the global picture of what we need to do to improve performance and reduce injury.”
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Stephanie Z. Pavlou is a staff writer for O&P Business News.