Stories from Physics for 11-14 14-16
Researchers have found that the way in which large kangaroos move has an interesting feature — the metabolic cost of the marsupials’ movement is independent of speed, making their hopping gait highly efficient. Typically, metabolic costs are proportional to speed, but kangaroo-hopping has an energetic advantage over other animals, particularly at high speeds. During hopping, energy is stored in collagen in the hind legs but the reasons underlying the efficiency of the motion are not well understood. Researchers have modelled kangaroo muscles as having a maximum stress of 300 kPa and have estimated that a typical 50 kg kangaroo can store nearly 360 J of strain energy, by contrast with the 55 J stored by similarly sized mammals.