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Why does hopping become more energy efficient for red kangaroos at higher speeds?
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kangaroo
A group of red kangaroos (Macropus rufus) using their powerful hind legs and feet to hop.
For the red kangaroo, bipedal hopping becomes increasingly energy-efficient at higher speeds due to the storage and release of elastic strain energy within their tendons and muscles.1
While kangaroos expend more energy than similarly sized quadrupeds at low speeds, they become more efficient as they accelerate. This efficiency is further supported by the movement of their heavy tail, which swings downward as the legs move backward to counteract the natural pitching motion of the head and upper body, serving as an additional energy-saving mechanism.1