Kinematics of a kangaroo hopping; numbers are time in msec from takeoff.

Recordings of the forces exerted on the ground by a hopping kangaroo recorded using a force platform; the kangaroo exerts a forward then backward horizontal force on the ground and a vertical force.

Schematic of the arrangement of the limb bones, muscles (gastrocnemius and plantaris), and Achilles tendon for a hopping kangaroo when landing and jumping. When landing, the impact force and weight of the kangaroo is absorbed by active stretching of the muscle and elastic stretch of the Achilles tendon. When jumping, the weight is accelerated by a recoil force due to active muscle contraction and elastic recoil of the Achilles tendon.

(Drawn from Maybridge 1957: modified from Alexander 1977.)