Simulation of gait and gait initiation associated with body oscillating behavior in the gravity environment on the Moon, Mars and Phobos

A double-inverted pendulum model of body oscillations in the frontal plane during stepping [Breniere and Ribreau (1998) Biol Cybern 79. 337-345] propo sed an equivalent model for studying the body oscillating behavior induced by step frequency in the form of: (1) a kinetic body parameter, the natural body frequency (NBF), which contains gravity and which is invariable for h umans, (2) a parametric function of frequency, whose parameter is the NBF, which explicates the amplitude ratio of center of mass to center of foot pr essure oscillation, and (3) a function of frequency which simulates the equ ivalent torque necessary for the control of the head-arms-trunk segment osc illations. Here, this equivalent model is used to simulate the duration of gait initiation, i.e., the duration necessary to initiate and execute the f irst step of gait in subgravity, as well as to calculate the step frequenci es that would impose the same minimum and maximum amplitudes of the oscilla ting responses of the body center of mass, whatever the gravity value. In p articular, this simulation is tested under the subgravity conditions of the Moon, Mars, and Phobos, where gravity is 1/6, 3/8, and 1/1600 times that o n the Earth, respectively. More generally, the simulation allows us to esta blish and discuss the conditions for gait adaptability that result from the biomechanical constraints particular to each gravity system.