Movie 2

Four sequences at Î = 10 show how gait changes with increasing speed at a large Murphy number. At low speeds, a two-beat gait is optimal. At higher speeds, a gait emerges with DF < 0:5 (a run by the classic Hildebrand definition) but with alternating phases of walking-like vaulting between four-and hind limbs. Around Uʹ = 0:9, a hybrid gait emerges, with a vaulting phase in hindlimbs and bouncing phase in forelimbs. At still higher speeds, a four-beat run emerges. The ground-reaction forces associated with these cases are shown in Fig 2E-H. Animations are adjusted so that one stride cycle takes 4 seconds. Leg contact is displayed when ground reaction force exceeds 0:01mg. The center of mass (COM) is marked with an “x”, while squares mark a radius of gyration from the COM