Gait cycle

The gait cycle is the complete sequence of leg motions from one foot's contact with the ground to its next contact — stance phase (foot on ground) and swing phase (foot in air). The fundamental unit of bipedal locomotion analysis. Cycle frequency, duty factor (stance fraction), and step length together specify any gait — from walking to running.

Earlier-generation humanoid walking (the Honda Asimo lineage) used zero-moment-point (ZMP) gait planning: pre-computed footstep trajectories the controller tracked. Modern platforms — Atlas, Digit, Apollo, Figure 03 — use model-predictive whole-body control that optimizes the gait in real-time over a short horizon. The shift unlocked robust uneven-terrain walking, dynamic recovery from disturbances, and the running gaits Boston Dynamics has demonstrated since the mid-2020s.