February 2010

In the Moment: Sports Medicine

By Jordana Bieze Foster

Walk this way: Heels first

Rearfoot strike pattern uses less energy

Forefoot strike patterns, particularly those of the barefoot variety, have generated a lot of buzz in running circles lately. But a University of Utah study suggests that rearfoot strike patterns have advantages as well.

When walking, a heel-first gait pattern is significantly more economical than a less plantigrade foot posture, according to research e-published on February 12 by the Journal of Experimental Biology. The same study found that foot strike pattern made no significant difference in energy consumption during running, however.

This economy of walking is unique to humans, other great apes, and bears; most other species adopt a digitigrade foot strike pattern during both walking and running.

“We [humans] are remarkably economical walkers,” said David Carrier, PhD, a professor of biology at the university and lead author of the study. “We are not efficient runners. In fact, we consume more energy to run than the typical mammal our size. But we are exceptionally economical walkers.”

Carrier and colleagues analyzed 27 volunteers as they walked or ran for five minutes on a treadmill. Walking trials were performed a self-selected speed and included three different foot strike patterns: plantigrade, low-digitigrade (heel slightly elevated), and high-digitigrade (heel elevated as much as possible). Running trials were conducted at speeds between 7.1 km/h and 13.7 km/h and included plantigrade and low-digitigrade strike patterns only (high-digitigrade running was excluded to avoid injury risk).

They found that the oxygen consumption required to walk one kilometer (cost of transport, or COT) was 53% higher for the low-digitigrade condition than the plantigrade condition, and 83% higher for the high-digitigrade condition. COT did not differ significantly between foot strike conditions during running, which was consistent with previous findings.

Digitigrade walking was not associated with postural impairment, but was associated with increased external mechanical work by the limbs, reduced exchange of kinetic and potential energy, increased ground reaction force moment at the ankle, and increased activation of the multifidus, biceps femoris, rectus femoris, and lateral gastrocnemius muscles.

“One of the things that may explain such economy is the unusual structure of our foot,” Carrier said. “The whole foot contacts the ground when we walk. We have a big heel. Our big toe is as long as our other toes and is much more robust. Our big toe is also parallel to and right next to the second toe. These features are distinct among apes, and provide the mechanical basis for economical walking. No other primate or mammal could fit into human shoes.”

Fellow evolutionary biologist Daniel Lieberman, PhD, agrees—but suggests that fitting into human shoes isn’t helping humans run. Lieberman and colleagues at Harvard University made headlines in January with their Nature study identifying differences in foot strike patterns and other kinematic and kinetic variables during running between athletes who had grown up wearing shoes and those who had not.

The Nature study compared 30 adult runners who ran at least 20 miles per week, under barefoot and shod conditions. The 14 Kenyan subjects, who did not wear shoes until a mean age of 12, used a forefoot strike pattern 91% of the time while barefoot and 54% of the time while shod. By comparison, eight Americans who had worn shoes since infancy used a rearfoot strike pattern 83% of the time while barefoot and 100% of the time while shod. Similar differences were seen between Kenyan teens who had worn shoes since the age of 5 and those who had never worn shoes, suggesting no effect of race.

Habitually barefoot runners with FFS patterns had significantly lower peak impact force than RFS runners under either shoe condition. Rate of impact loading in the habitually barefoot forefoot strikers was similar to that of shod rearfoot strikers but significantly lower than barefoot rearfoot strikers.

Shoe-surface combination with lowest risk of ACL injury pairs cleats with grass

Cleats and natural grass represent the shoe-surface combination least likely to cause anterior cruciate ligament injury, according to a cadaver study from the Hospital for Special Surgery in New York.

The cleat-grass combination was associated with significantly lower levels of strain at the anteromedial bundle of the ACL than three other shoe-surface combinations that involved artificial turf surfaces. The findings were published in the January issue of the Journal of Biomechanical Engineering.

Investigators created an injury model in which a cadaveric knee was positioned upright in 30º of flexion (where most ACL injuries occur), standing on a turf sample atop a force plate that could be rotated to simulate a cutting maneuver. They then applied a 500 N axial load (representing body weight) and a 1.5 Nm internal rotation moment, both of which were found to have a linear relation ship with ACL strain.

In eight cadaver specimens, average maximum strain was 3.90 for AstroTurf plus turf shoes, 3.19 for modern playing turf plus turf shoes, 3.14 for modern playing turf plus cleats, and 2.16 for natural grass plus cleats.

Gender affects response to eccentric training for Achilles tendinopathy

Eccentric training more effectively relieves symptoms of Achilles tendinopathy in men than in women, according to research from Hannover Medical School in Germany.

Twelve weeks of eccentric training was associated with significantly greater improvements in pain and function in 38 male patients with mid-portion Achilles tendinopathy than in 25 female patients. The findings were e-published on December 9 by Knee Surgery, Sports Traumatology, Arthroscopy.

Morning resting pain decreased by 44% in male patients compared to 27% in female patients, a statistically significant improvement for the men only. Victorian Institute of Sports Assessment-Achilles (VISA-A) test scores improved by 27% in men and 20% in women. For the Foot Ankle Outcome Score assessment measure, male patients demonstrated improvement in the categories of symptoms, pain, all-day-life, and sport; female patients improved only in the sport category.

Interestingly, the female patients had a greater microcirculatory response to the intervention than their male counterparts. In a 2008 study of eccentric training and Achilles tendinopathy, published in Disability & Rehabilitation, the same group found that reduced venous filling pressure accompanied pain relief following training.

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