A Simon Fraser University (SFU), Burnaby, British Columbia, Canada, study on how kangaroos use their tails as a “fifth” leg is providing insight into the diversity of biological movement, and specific insight into why we walk the way we do.
The study was published July 1, in the Royal Society journal Biology Letters. Max Donelan, PhD, of SFU’s Locomotion Laboratory, the study leader and an SFU associate professor in the Department of Biomedical Physiology and Kinesiology, found kangaroos, commonly viewed as hoppers, move with a “pentapedal” gait, planting their tails on the ground in combination with their front and hind legs. “We measured the forces the tail exerts on the ground and calculated the mechanical power it generates, and found that the tail is responsible for more propulsive force than the front and hind legs combined,” said Donelan. “It also generates almost exclusively positive mechanical power, performing as much mechanical work as a human leg when walking at the same speed. Their muscular tail is used to propel and power their motion-just like a leg.”
Measurements were carried out at the University of New South Wales, Sydney, Australia, in 2001, but the researchers were only just recently able to analyze them properly, thanks to innovations by Donelan’s collaborator, Shawn O’Connor, PhD, a postdoctoral fellow in the Department of Biomedical Physiology and Kinesiology.
“One of the central findings of our human walking research is that it is very important to time the push-off of your back leg to make walking less effortful,” said Donelan. “People recovering from strokes or spinal cord injury can’t do this as well because their legs are partially immobilized, making walking more effortful.
“Based on our original human research, fellow scientists and engineers have built prosthetics and exoskeletons that help improve ability and make walking easier,” Donelan said. “And now we know that it is important enough that kangaroos have harnessed a limb originally evolved for swinging from trees to serve this role as [a] functional fifth leg.”
Unusual gaits by unusual animals, such as pentapedal walking by kangaroos, provide insight into the breadth of solutions available to the same biomechanical problem, noted Donelan, who has also studied the movement of shrews, cats, crocodiles, giraffes, and elephants.
Editor’s note: This story was adapted from materials provided by Simon Fraser University.