Getting A Leg Up

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Getting A Leg Up

http://www.medicalnewstoday.com/medicalnews.php?newsid=65158

Scientists have known for years that the energy cost of walking and

running is related primarily to the work done by muscles to lift and

move the limbs.

But how much energy does it actually take to get around? Does having

longer legs really make a difference?

Herman Pontzer, Ph.D., assistant professor of physical anthropology

in Arts & Sciences, has developed a mathematical model for

calculating energy costs for two and four-legged animals. His

research was published in a recent issue of The Journal of

Experimental Biology.

" All things being equal, leg length is one of the major determinants

of cost, " says Pontzer, " If two animals are identical except for leg

length, the animal with longer legs is more efficient. "

The fossil record shows that two million years ago, there was a big

increase in leg length in early humans. Pontzer suggests that one

reason for this increase could have been the energy saved by having

longer legs. " If you greatly increase the distance that you travel

each day, then you'd expect evolution to act on walking efficiency, "

he says.

" That way, the energy you save on travel can be spent instead on

survival and reproduction. " Pontzer's LiMB model is an equation that

predicts walking and running. Importantly, the model predicts that

the rate of force generation - and therefore the rate of energy use -

is related to limb length. Longer legs mean less force production

and lower energy cost.

To test his equation, Pontzer put people, goats and dogs on a

treadmill in his lab, and measured how much oxygen each used during

walking and running at various speeds. He found that the LiMB model

explained more of a variation in locomotor cost than other

predictors, including contact time and body mass, showing that it

worked for animals with four legs as well as two.