March 2015

Retraining gains: In-field cadence cues reduce impacts

In the moment: Sports medicine

3ITMsports-iStock14637030By P.K. Daniel

In-field gait retraining, which cues a modest increase in step rate, can help address biomechanical risk factors associated with tibial stress fracture in runners, according to research from East Carolina University in Greenville, NC.

Richard W. Willy, PhD, PT, OCS, an assistant professor in the Physical Therapy Department at East Carolina University and colleagues assessed the effects of step-rate retraining in 30 runners with high impact forces.

“If they didn’t have high loading, we didn’t necessarily want to change their running mechanics,” Willy said.

The study group included 30 runners with a range of experience and skill levels, including a couple of elite runners, but all were injury-free. They were randomized to retraining (age, 21.1 ± 1.9 years; average distance, 22.1 ±10.8 km/wk) or control groups (age, 21 ± 1.3 years; average distance, 23.2 ± 8.7 km/wk).

All participants wore a commercial running computer system featuring a wrist watch (feedback monitor) and foot pod (a wireless accelerometer that collects and sends speed, distance, and step-rate data) positioned on the runner’s right shoe. The system cued the runners in the retraining group to increase their preferred step rate by 7.5% during eight unsupervised training sessions. After a lab testing session, the runners wore the system for an additional 30 days unsupervised, during which time researchers continued to collect step-rate data but the runners’ watch displays no longer provided step-rate feedback. Runners in the control group also wore the watches and foot pods for the entire study period but were not given any step-rate feedback.

“We wanted to test out the real-world application of this technique. They weren’t coming into a clinic or to a laboratory to do the study,” Willy said. “The participants weren’t asked to change their normal running routine, only their step rate.”

The majority of runners in the retraining group achieved the prescribed step rate during in-field runs and retained those changes through 30 days. The in-field gait retraining was also associated with reduced impact forces, peak hip adduction, and eccentric knee joint work compared with baseline; impact forces were also significantly lower than in the control group. The findings were epublished in February by the Scandinavian Journal of Medicine & Science in Sports.

“It was certainly effective in increasing their step rate,” Willy said. “We saw some really nice reductions in impact forces, as well as knee joint loads.”

Stacey Meardon, PhD, PT, ATC, CSCS, assistant professor in the Physical Therapy Department at East Carolina University, has also studied the effects of gait modification on tibial stress during running. In a lab-based study, published in the August 2014 issue of the Journal of Biomechanics, Meardon and colleagues found that tibia stresses were influenced by step width.

“We found that tibia stresses were influenced by step width, which to me means when you run narrower, your tibia undergoes greater stress than when you run wider,” Meardon said. “Part of the driving factor for me doing my study was to evaluate whether a change in technique can actually influence the loading environment of the bone. And basically what I found was that, yes, we can change the way we run, and we can alter the load that the bone experiences.”

When performing gait modification in a clinical setting, it’s important to match the retraining program to the runner’s specific mechanics, Willy said.

“If you have a runner whom you suspect has much more of a sagittal plane contribution to their excess of loading on the tibia, then maybe the step-rate modification is the way to go,” he said. “But if you feel like it’s more of a frontal plane issue—they’re crossing over a lot—then the step width [modification] is the way to go.”

There would be no added benefit to changing both variables, Willy said.

“You basically need to pick your poison and stick with that,” he said.

Sources:

Willy RW, Buchenic L, Rogacki K, et al. In-field gait retraining and mobile monitoring to address running biomechanics associated with tibial stress fracture. Scand J Med Sci Sports 2015 Feb 4. [Epub ahead of print]

Meardon SA, Derrick TR. Effect of step width manipulation on tibial stress during running. J Biomech 2014;47(11): 2738-2744.

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