Insoles Reduce Impact for Runners
Stress fractures, shin splints, plantar fasciitis – runners go to great lengths to avoid these obstacles that prevent them from pounding out their weekly miles. They search for the right shoe, the right stride and the right training routine.
In a study recently published in the Journal of the American Podiatric Medical Association, two UW Health researchers examined an affordable and easy method that may reduce impact force injuries common to distance running.
Katy O'Leary, a physical therapist at the UW Health Rehabilitation and Athletic Performance Clinic who specializes in athletic injuries, joined Bryan Heiderscheit, PhD, an associate professor in the University of Wisconsin School of Medicine and Public Health and director of UW Health Sports Medicine's Runners Clinic, to examine the beneficial aspects of shock-absorbing insoles placed in running shoes.
While the results of the study stop short of guaranteeing a reduction in injury for runners, O'Leary and Heiderscheit did find that insoles significantly reduce impact forces associated with running.
Podiatrychannel.com, a health information Web site maintained by board-certified podiatry physicians, lauds running as great exercise but cautions about the toll it takes on the body.
Jogging, the Web site states, "generates forces equivalent to at least three times the body's weight (with each step). It is important to do everything possible to protect the feet, ankles, knees, hips and lower back vertebrae."
To find if cushioned insoles provide such protection, O'Leary and Heiderscheit recruited 16 recreational runners from the Madison area. All were between 20 and 36 years old and screened to eliminate anyone with a recent history of lower-extremity injury.
"They had to run an average of 20 miles per week and couldn't have any neurological or musculoskeletal impairments that wouldn't allow them to run comfortably," O'Leary says about the selection process.
The subjects were given identical shoes and asked to perform 10 15-meter trials during which they ran at their own pace across a force plate, which measures a runner's ground reaction force (the force projected back up through the body while running). To ensure the runners used their normal stride, they were not told to hit the force plate with their right foot, the foot from which O'Leary and Heiderscheit derived the data.
Accelerometers were attached to the subjects' ankles to measure the amount of tibial acceleration that occurred while they ran. O'Leary and Heiderscheit were also careful to monitor the consistency of the subjects' knee angles when their feet hit the force plate, because widely varying angles could have skewed the results.
Five of the trials were conducted with only shoes. For the remaining five, subjects used insoles, manufactured by the Ohio-based company Sorbothane. O'Leary and Heiderscheit both stressed that Sorbothane was not involved in any phase of the study, other than the insole donation.
"They were blind to everything until we sent them the final results paper," Heiderscheit said.
"We found a couple of good things," O'Leary says. "When the runners had the insoles in, there was a significant reduction in the ground reaction force at the initial contact point."
On average, the ground reaction force was nearly 7 percent less with the insoles. It may seem like a paltry number, but remember that's 7 percent less force per step.
"When you think of a 7 percent reduction for, say, a 10-mile run, that's a lot," Heiderscheit says.
Tibial acceleration also decreased, by 15.8 percent. Both factors are considered potential culprits for impact force injuries.
O'Leary and Heiderscheit emphasize the study results do not definitively prove that cushioned insoles reduce running injuries. That's a much larger task and would require a more elaborate setup.
"We couldn't come out and say it's going to reduce injuries but it certainly has the potential to," Heiderscheit says. "The piece we're missing is following these people over time. We'd have to account for their training differences."
Still, both are encouraged sufficiently to broach the subject with their patients.
"In my practice I'm willing to say, 'Try it out,' " O'Leary says. "If it's uncomfortable, you're probably not going to run normally. But if you have a pair of insoles that you're comfortable with and you feel good about it, there's a chance it might help reduce your risk. It's something I'm willing to put out there."
And Heiderscheit believes the benefit of insoles is more likely to be reaped by casual runners rather than hard-core trainers who have their sights set on future marathons or Ironman competitions.
"If you're putting in 10 to 12 miles per week, your body's adaptation to those types of impacts will be much slower and you won't have the same level of tissue strength as somebody who's putting in 50 miles per week," he says.
Plus, the insoles could save money, because they protect not only the runner from impact force but insulate shoes from trauma, as well. With insoles at about $15 to $20 per pair, they're a relative bargain compared with shoes that often cost $100 or more.
"Shoes are expensive but insoles are cheap," Heiderscheit says. "They can get you maybe an extra 200 miles out of your shoe."
Date Published: 02/12/2008