Reaching high speed with tiny steps and the powerful "fifth" leg - kangaroo part 2

kangaroo part 2

“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,” explains Donelan, an associate professor in the Department of Biomedical Physiology and Kinesiology (BPK).

“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 in Sydney Australia back in 2001, but the researchers were only just recently able to analyze them properly, thanks to innovations by Donelan’s collaborator, Dr. Shawn O’Connor.

“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,” says Donelan, founder and scientific advisor to Bionic Power. The university spin-off company develops energy harvesting technology for those who depend on portable power. “People recovering from strokes or spinal cord injury can’t do this as well because their legs are partially immobilized, making walking more effortful.”

Kangaroos, meanwhile, have very short front legs that can’t be used to push off. “The timing and position of the tail, on the other hand, is perfect,” he says. “So, we wondered if they are able to use their tail just like a leg to push off and power their walking.”

What’s remarkable about this, suggests Donelan, is that the tail is anatomically quite different, being made up of more than 20 vertebrae taking on the roles of our feet, calves and thigh bones. “Animals have discovered many uses for their tails,” he says, “but as far as we know, this is the first use of one as a leg.”