July 2013

Brace relations: Complex effects are not only mechanical

In the moment: Ankle

Photo courtesy of DeRoyal

Photo courtesy of DeRoyal

By Jordana Bieze Foster

Research presented in late June at the annual National Athletic Trainers Association (NATA) meeting in Las Vegas added to the body of evidence suggesting that the effects of ankle bracing are not solely mechanical, and that even the mechanical effects may be more complicated than they seem.

In 15 adults with chronic ankle instability (CAI), investigators from the University of Virginia in Charlottesville found that muscle activation patterns, particularly for the peroneus longus muscle, were closer to what would be expected in uninjured individuals when the CAI patients wore a lace-up ankle brace than when they wore no brace.

The researchers used surface electromyography to assess muscle activation in the study participants as they walked on a treadmill at 3 mph. The CAI patients had an average history of 4.5 ankle sprains, but had not experienced a sprain in the past 15 months.

Precontact muscle amplitude for the peroneus longus was significantly lower with the brace than without. Brace wear was associated with significantly delayed activation of the peroneus longus, gluteus medius, rectus femoris, and anterior tibialis. And the peroneus longus and rectus femoris muscles were activated for a significantly smaller percentage of the gait cycle with the brace than without.

Greg Barlow, MEd, ATC, a former graduate assistant athletic trainer at the University of Virginia who is now an athletic training resident at the University of Wisconsin in Madison, theorized that patients with CAI may be overly reliant on peroneus longus activation to properly position the foot prior to heel strike, and wearing a brace decreases that reliance.

“With application of the brace, the activation pattern shifts more toward that of healthy people,” said Barlow, who presented his group’s findings at the NATA meeting. “Decreasing activation of the peroneus longus over a period of time may actually improve its ability to respond to a perturbation.”

Two other studies presented at NATA came to different conclusions about ankle bracing’s effect on balance. In 21 physically active healthy volunteers, researchers from the University of Minnesota-Duluth found no significant effects of a lace-up ankle brace or ankle taping on mediolateral or anterior-posterior dynamic stability, as measured using a computerized balance platform. Meanwhile, researchers from the University of North Carolina at Chapel Hill found that mediolateral balance, assessed using time to boundary measures, was significantly better with a lace-up brace than with no brace in 19 individuals with a history of ankle sprain and 19 matched controls.

In a fourth study, investigators from the University of South Alabama in Mobile assessed the effect of three different braces on inversion-eversion rotation under low (0-2 Nm) and high (2-4 Nm) load conditions; higher loads were experienced as the ankle approached the limits of its range of motion (ROM). All three braces significantly restricted ROM, but the effects were most pronounced under the low-load condition.

“These results are somewhat counterintuitive. I would have thought the greatest effect of the brace would be at the extremes of range of motion, but there seems to be a different effect,” said John E. Kovaleski, PhD, ATC, a professor of exercise science at the University of South Alabama, who presented the findings at the NATA meeting.

Kovaleski hypothesized that, because the ankle joint itself becomes stiffer near the extremes of ROM, the relative contribution of the brace in that high-load zone is smaller than in the middle range.

Sources:

Barlow G, Donovan L, Hart JM, Hertel J. Effect of lace-up ankle braces on electromyography measures during walking in subjects with chronic ankle instability. Presented at the National Athletic Trainers’ Association 64th Annual Meeting and Clinical Symposia, Las Vegas, June 2013.

Gear WS, Bookhout JL, Solyntjes AL. Effect of prophylactic ankle support on actual and perceived dynamic balance. Presented at the National Athletic Trainers’ Association 64th Annual Meeting and Clinical Symposia, Las Vegas, June 2013.

Goodrich ME, Oyama S, Goto S. Ankle bracing enhances mediolateral postural stability in those with and without a history of ankle sprains. Presented at the National Athletic Trainers’ Association 64th Annual Meeting and Clinical Symposia, Las Vegas, June 2013.

Kovaleski JE, Gurchiek LR, Heitman RJ. The effects of load range and brace support in ankle complex stability. Presented at the National Athletic Trainers’ Association 64th Annual Meeting and Clinical Symposia, Las Vegas, June 2013.

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