Ground reaction forces for various standing tasks considering generic terrain

Many of the tasks presented to people in everyday life include standing on terrain that is not level or coplanar. Uneven terrain can affect the way in which people distribute their weight between their feet. This paper proposes a method for predicting human standing posture and the associated ground reaction forces (GRFs) taking into account a generic orientation of the ground support plane. Postures are predicted using multi-objective optimization (MOO) techniques and a 55 DOF digital human model. The human performance measures used in the cost function include musculoskeletal discomfort, delta potential energy, and visual displacement. The GRF are determined by a linear distribution model derived from the zero moment point (ZMP) and the Lagrangian recursive dynamic formulation. Postural stability based on the location of the ZMP will be discussed. Three postural cases are considered: standing on flat ground, standing with one foot on a stair, and standing with arbitrary support plane angles. Three different simulations are carried out for each case representing different tasks. Predicted GRFs have realistic values and follow the general trends expected for each of the postural cases.