How Do Kangaroos Hop So Efficiently?

A kangaroo's large hind legs have long, elastic Achilles tendons. When it lands, these tendons stretch and store elastic energy, which is then released to power the next hop, much like a pogo stick. As a result, red kangaroos use little extra energy when they hop faster over a range of speeds, unlike running humans. Their breathing is also linked to their hopping rhythm, as the movement of internal organs helps push air in and out of the lungs. Their heavy tail acts as a counterbalance and, when moving slowly, as a fifth limb.