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."
Whether running, walking or standing still, the bulk of the animal's weight is borne on that pillowy clover-shaped pad behind the four toes, the metapodial-phalangeal pad, or m-p pad for short. It's made from pockets of fatty tissue hemmed in by baffles of collagen. Chi carefully dissected these pads whole from the feet of deceased animals (none of which were euthanized for this study), so that they could be put in the strain meter by themselves without any surrounding structures.
Laid out on a graph, Chi's analysis of 47 carnivore species shows that the area of their m-p pads doesn't increase at the same rate as the body sizes. But the stiffness of pads does increase with size, and that's what keeps the larger animal's feet from being unwieldy.
The mass of the animal increases cubically with its greater size, but the feet don't scale up the same way. "A mouse and an elephant are made with the same ingredients," Roth said. "So how do you do that?"
Earlier research had found that the stresses on the long bones of the limbs stay fairly consistent over the range of sizes, in part because of changes in posture that distribute the stresses of walking differently, Roth said. But that clearly wasn't enough by itself.
The researchers also found that larger animals have a pronounced difference in stiffness between the pads on the forelimbs and the pads on the hind limbs. Bigger animals have relatively softer pads on their rear feet, whereas in smaller animals the front and rear are about the same stiffness.
Chi thinks the softer pads on the rear of the bigger animals may help them recover some energy from each step, and provide a bit more boost to their propulsion. (Think of the way a large predator folds up its forelimbs and launches itself with its hind legs.)
"It is as if the foot pads' stiffness is tuned to enhance how the animal moves and how strength is maintained in its bones," Roth said.
The research appears today in the Journal of the Royal Society, Interface. It was supported by the National Science Foundation.
Chi has new work under way that looks at the construction of the human heel in the same ways.
Karl Leif Bates | EurekAlert!
Water forms 'spine of hydration' around DNA, group finds
26.05.2017 | Cornell University
How herpesviruses win the footrace against the immune system
26.05.2017 | Helmholtz-Zentrum für Infektionsforschung
Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.
Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
26.05.2017 | Life Sciences
26.05.2017 | Life Sciences
26.05.2017 | Physics and Astronomy