Spring In Your Step Helps Avert Disastrous Stumbles, Scientists Say

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Spring In Your Step Helps Avert Disastrous Stumbles, Scientists Say

http://www.medicalnewstoday.com/medicalnews.php?newsid=53863

From graceful ballerinas to clumsy-looking birds, everyone

occasionally loses their footing. New Harvard University research

suggests that it could literally be the spring, or damper, in your

step that helps you bounce back from a stumble.

The work, published this week in the journal Proceedings of the

National Academy of Sciences, sheds new light on how legged animals

maintain a remarkable degree of stability on uneven terrain,

highlighting the dynamic elastic and dampening roles of ankles,

feet, and other distal extremities in helping us recover after

stumbling. It could also help engineers develop better prosthetics

and robots robust enough to navigate terrain that would leave

today's automatons spinning their wheels.

" Limbs perform wonderfully on uneven terrain, " says author A.

Biewener, the P. Lyman Professor of Biology in Harvard's

Faculty of Arts and Sciences. " Legged animals routinely negotiate

rough, unpredictable terrain with agility and stability that

outmatches any human-built machine. Yet, we know surprisingly little

about how animals accomplish this. "

Together with colleague A. Daley of Harvard's Department of

Organismic and Evolutionary Biology, Biewener conducted experiments

wherein helmeted guinea fowl (Numida meleagris) stepped unexpectedly

into a concealed hole while running. Even though the hole's 8.5-

centimeter depth equaled some 40 percent of the length of the birds'

legs, the fowl remained stable and managed to maintain forward

velocity, albeit most often by speeding up.

By monitoring the real-time forces exerted by the limb on the

ground, as well as the angles and locations of key joints at the

hip, knee, and ankle, Biewener and Daley determined that the

stumbling birds' movements were consistent with a mass-spring model

that treats the body as a mass balanced atop legs serving as

springs. This springiness of the leg was concentrated at its distal

end, near the ankle and foot, with only moderate effects seen at the

knee and little change occurring at the hip.

" Ordinary walking is a patterned movement of repeating, predictable

motions, " Biewener says. " Our work suggests that even falling into a

hole while running does not significantly disturb the regularity of

hip motion. By contrast, the distal ankle and

tarsometatarsophalangeal joints act as dampers, absorbing energy

when the limb contacts the ground at an unexpected steep angle and

shorter limb length, or as springs, returning energy when the limb

contacts the ground at an unexpected shallow angle and more full

extension. "

These dynamic processes occur with astonishing speed: In the case of

the guinea fowl, the leg modulates itself within 26 milliseconds as

it falls into an unexpected void. The lower limbs' spring action

helps the birds retain energy and momentum, stabilize their center

of mass, and continue forward motion through the hole.

Biewener says this work could help create better prosthetic legs and

more stable robots. Most current legged robots engage the

proximal " hip " joint to generate limb work but do not incorporate

dampening or modulated spring-actuation functions into more distal

joints, making the machines more likely to tumble over in an

irregular landscape.

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Daley and Biewener's work was funded by the Medical

Institute and the National Institutes of Health.