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Seeing the Bounce in Kangaroos

Infrared motion cameras show how kangaroos get up to hopping speed without breaking their bones.

When it comes to jumping, kangaroos are oddballs. They don't adjust their posture to be more upright, a technique most animals use to reduce muscular demands. Instead, roos keep their forward hunch, a baffling position since physics would suggest they'd suffer muscular or skeletal damage while accelerating that way. To find out why this is not the case, researchers went to Alma Park Zoo in Brisbane, Australia, and set up an experiment to capture kangaroo motion with infrared cameras.

Why infrared? The alternative, and still common, method of studying animal mechanics is to take high-speed video and painstakingly analyze it, frame-by-frame. Infrared motion-capture instead uses small reflective balls secured on the outside of an animal's body - for the roos, on specific points of the joints and limbs - which the cameras track when the kangaroo is illuminated with infrared light. This way, with cameras arranged in a semicircle around the test "lane" where the roos hop, researchers could get the data they wanted right away. Not only that, but the setup allowed them to see where the marker balls were in 3D.

This technology has notably been used in film to translate the movement of actors into animated characters (like Gollum in Lord of the Rings) as well as in sports to analyze motions like golf swings. However, because the sun produces a lot of ambient infrared radiation, using infrared cameras outdoors has been troublesome until the new system from Vicon which could adapt for this extra "brightness."

While being filmed in motion, the kangaroos also jumped onto ground plates that measured the forces exerted downward. The data, collected by researchers from the Royal Veterinary College in London, the University of Idaho, the University of Queensland and the University of Western Australia, still remains to be analyzed, but will hopefully solve some mysteries about the kangaroo's bounce and be useful to biomechanical scientists and veterinarians alike.

Check out this video from New Scientist TV/Vicon of the research in Brisbane:

Credit: Martin Ruegner/Getty Image