WEDNESDAY, Dec. 7, 2005 (HealthDay News) -- Science is going to the dogs again, with a new study explaining why four legs are better than two when it comes to speed.
According to two British researchers, dogs can maintain stability and support their weight with their front legs as they propel themselves forward off their hind legs.
This gives the animal a distinct advantage over their human companions, whose two lower limbs must do both jobs at once.
The result: Even top-notch Olympic athletes must slow down when turning corners at maximum speeds of 25 miles per hour, but dogs -- particularly those bred to run fast, such as greyhounds -- can round curves at speeds of 40 miles per hour without decelerating.
"For you and I, we sort of protect the loads our legs experience, because if it gets too high our legs collapse. But with dogs, their legs are much better able to bear loads because the weight support is separate from propulsion," explained study co-author Alan M. Wilson, of the Structure and Motion Lab at The Royal Veterinary College in Hatfield, England.
The findings, published in the Dec. 8 issue of Nature, were released Wednesday alongside studies that showed an in-depth picture of the dog genome.
For their study, Wilson and colleague James R. Usherwood looked at the results of 200-meter races at the 2004 Olympics and World Indoor Championship. They then watched videotapes of greyhounds running high-speed, pre-competition races while chasing a mechanical hare at maximum speed.
The pace and timing of foot-to-ground contact were assessed for 17 greyhounds running in groups of one dog to three dogs per race. Notes were made of canine movement behavior as they entered a final stretch in the straightaway, and then again while cornering.
Another 23 greyhounds were observed commencing the second straightaway, following the same bend.
The researchers found that the greyhounds moved their limbs much as a racing cyclist would ride his bike -- maintaining a steady pace while rounding curves. This caused them to bear a 65 percent increase in pressure on their limbs as result.
Foot-to-ground timing remained practically unchanged despite this added pressure, they noted. That's in contrast to humans, who typically compensate for this type of increased load by slowing down and by increasing foot-to-ground contact.
The researchers said they believed dogs are able keep up such speeds because of their ability to leverage their hips and backs while moving -- a spring-like mechanism used by four-legged animals to compensate for increases in load while sprinting.
"There are limits to what the human system can stand," said Wilson. "So humans have a self-preservation mechanism which guides them to slow down -- something dogs don't have."
The findings are the first of their kind, and dramatically increase scientists' understanding of motor function, he added.
"In terms of injury, you're starting to understand how the legs are designed and what they're designed for," he said. "This will help us understand how animals compensate for injury, as in the case of a lame dog, or a lame horse or a lame cow. And the principles are the same for humans."
"Robotics is also a field that can benefit from this work," he added. "This information could be incorporated into the designing of a prosthetic limb or in the designing of a leg-based chair instead of a wheel-chair -- to get over a curb, for example. Legs are much better than wheels, but when you try to make a legged robot it's actually very difficult to do economically and efficiently. This is something animals are very good at. They've been at it for a few million more years."
Ronna Dornsife, the research grants administrator for the American Kennel Club Canine Health Foundation, expressed enthusiasm for the findings.
"This study is very interesting and applicable for health concerns for both canine and humans," she said. "It relates to things we know that are unique about dogs and can help in the application of sports medicine for both dogs and humans."
Dornsife also noted that the AKC Foundation was a partial sponsor of one of the dog genome studies -- published in the December issue of Genome Research -- which compared the genome sequences of two types of dogs: the standard poodle and a boxer.
In this study, researchers from the Institute for Genomic Research (TIGR) analyzed pieces of DNA in both breeds and found evidence of key genetic differences between the two.
Further genetic comparisons to nine additional dogs, four wolves, and one coyote highlighted the significant genetic variation present between canine types.
The researchers believe the finding could help track diseases specific to certain breeds, and might even aid in the understanding of human illness.
In addition, in a second study in Nature, researchers from 15 institutions describe a high-resolution draft of the boxer genome.
More information
For more on dogs, check out the The American Kennel Club Canine Health Foundation.
