Athletes, coaches, and trainers have long known that ankle sprains—the most common athletic injury—seem more likely as games wear on and players become tired. Only recently, however, have researchers begun to quantify how fatigue affects biomechanics and what those changes may imply for injury risk and prevention.
In a 2007 paper published in the Journal of Sports Rehabilitation, for example, University of Delaware researchers tested subjects on inversion/eversion or plantar flexion/dorsiflexion movements. Fatigue was associated with declines in median frequency, force production, and peak activation in primary and secondary muscles involved in each motion, potentially increasing ankle sprain risk.
This April, an article in the American Journal of Sports Medicine reported that a fatigue protocol made it harder for subjects to recognize passive and active repositioning of their ankles. And at the International Foot and Ankle Biomechanics (i-FAB) conference in September, Iowa State researchers reported that fatigue was associated with increased peroneus brevis activity during landing preparation, particularly when subjects wore an ankle brace.
But how does such research translate into injury prevention? For Patrick McKeon, PhD, ATC, an assistant professor in athletic training at the University of Kentucky, one approach is balance training.
“Fatigue changes something within the system, and muscle control is altered,” McKeon said. “We want to tune the system’s ability to cope with changes, and that’s where balance training comes in.”
Balance exercises include one-legged standing under varying conditions and the “star excursion” balance test (SEBT). In 2008, McKeon and another researcher reported in the Journal of Athletic Training that such exercises lowered risk of recurrent ankle sprain.
They may not be enough in fatigued conditions, however. Jonathan Chang, MD, a clinical assistant professor of orthopedics at the University of Southern California, said, “You can do all the balance training in the world, but if you are too fatigued, you can’t protect your ankle.”
McKeon acknowledges that the task is challenging.
“During a sprain, the ankle moves at about 400 degrees per second, and it’s almost impossible for the peroneals to generate a meaningful contraction to stop that,” he said. “So what are the other muscles of the body doing prior to the foot touching the ground? We should be working the abdominal core and the hip core. We should get patients fatigued, then put them through the exercises and balance training. We also need to pay more attention to the intrinsic muscles of the foot.”
Jay Hertel, PhD, ATC, McKeon’s coauthor on the 2008 paper, and director of the graduate programs in athletic training and sports medicine at the University of Virginia, is particularly interested in the intrinsic muscles that lie on the plantar surface of each foot. Those that help support the medial longitudinal arch—the abductor hallucis, flexor hallucis brevis, and the medial branches of the lumbricals and interossei—are thought to be the most important, Hertel said.
“Even though the extrinsic muscles are the prime movers of the ankle, we’ve found that there appear to be deficits in intrinsic function in people with lower extremity injuries,” he said. “In a research abstract presented at the 2009 [National Athletic Trainers Association] annual meeting, we demonstrated that subjects with chronic ankle instability performed worse on the intrinsic foot muscle test compared with healthy controls.”
Hertel believes that patients should strengthen the intrinsics the same way that those with lower-back injuries work their abdominal core.
“We want to look at how to activate the muscles that stabilize the joints in the foot, then move on to the extrinsics,” he said.
Hertel’s approach is similar to a Pilates exercise called “foot doming.”
“You have the foot flat on the ground, and you try to heighten the medial longitudinal arch,” he said. “As you do that, you’re trying to pull the first metatarsal head back toward the heel while keeping the foot flat.”
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