sexta-feira, fevereiro 26, 2010

The Bigger the Animal, the Stiffer the 'Shoes': Carnivores' Feet 'Tuned' to Their Body Size

ScienceDaily (Feb. 25, 2010) — If a Tiger's feet were built the same way as a mongoose's feet, they'd have to be about the size of a hippo's feet to support the big cat's weight. But they're not.

A big dog's weight is borne by the big pad behind the toes. The bigger the animal, the stiffer the pad. (Credit: HTO, Wikimedia Commons)

For decades, researchers have been looking at how different-sized legs and feet are put together across the four-legged animal kingdom, but until now they overlooked the "shoes," those soft pads on the bottom of the foot that bear the brunt of the animal's walking and running.

New research from scientists in Taiwan and at Duke University has found that the mechanical properties of the pads vary in predictable fashion as animals get larger. In short, bigger critters need stiffer shoes.

Kai-Jung Chi, an assistant professor of physics at National Chung Hsing University in Taiwan ran a series of carefully calibrated "compressive tests" on the footpads of carnivores that have that extra toe halfway up the foreleg, including dogs, wolves, domestic cats, leopards and hyenas. She was measuring the relative stiffness of the pads across species -- how much they deformed under a given amount of compression.

"People hadn't looked at pads," said co-author V. Louise Roth, an associate professor of biology and evolutionary anthropology who was Chi's thesis adviser at Duke. "They've been looking at the bones and muscles, but not that soft tissue."

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Read more here/Leia mais aqui: Science Daily

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Scaling and mechanics of carnivoran footpads reveal the principles of footpad design

Kai-Jung Chi1,2,* and V. Louise Roth1

-Author Affiliations

1Biology Department, Duke University, Durham, NC 27708-0338, USA

2Department of Physics and Institute of Biophysics, National Chung Hsing University, Taichung 40227, Taiwan, Republic of China

*Author for correspondence (kjchi@phys.nchu.edu.tw).

Abstract

In most mammals, footpads are what first strike ground with each stride. Their mechanical properties therefore inevitably affect functioning of the legs; yet interspecific studies of the scaling of locomotor mechanics have all but neglected the feet and their soft tissues. Here we determine how contact area and stiffness of footpads in digitigrade carnivorans scale with body mass in order to show how footpads’ mechanical properties and size covary to maintain their functional integrity. As body mass increases across several orders of magnitude, we find the following: (i) foot contact area does not keep pace with increasing body mass; therefore pressure increases, placing footpad tissue of larger animals potentially at greater risk of damage; (ii) but stiffness of the pads also increases, so the tissues of larger animals must experience less strain; and (iii) total energy stored in hindpads increases slightly more than that in the forepads, allowing additional elastic energy to be returned for greater propulsive efficiency. Moreover, pad stiffness appears to be tuned across the size range to maintain loading regimes in the limbs that are favourable for long-bone remodelling. Thus, the structural properties of footpads, unlike other biological support-structures, scale interspecifically through changes in both geometry and material properties, rather than geometric proportions alone, and do so with consequences for both maintenance and operation of other components of the locomotor system.

allometry biomechanics digitigrade mammals feet footpad function locomotion

Footnotes

Received December 18, 2009.
Accepted February 1, 2010.
© 2010 The Royal Society

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