Evaluating the influence of induced passive torques in the simulation of time-varying human poses

In the computerized generation of human poses, it is important to take into account not only the active component of the torque, but also the ligaments and connective tissues which produce a passive torque at the limits of the joint range of motion. We present a fatigue model in which both active and passive torque components are essential parameters integrated in an inverse kinematics animation framework. We then use fatigue evolution to optimize the generated posture. We introduce an hysteresis activation pattern for each joint in order to set, whenever necessary, a fatigue reduction scheme through an active torque reduction constraint. The fatigue reduction scheme analyzes the fatigue level of each individual muscular group; when it is above a given threshold, a statically optimal joint variation is enforced to locally reduce the active torque while still achieving a desired task (e.g. reaching a point in 3D space). For that purpose we integrate the influence of passive/resistive torque in an active torque reduction scheme, allowing either the generation of reactive poses (i.e. an active strategy) or, on the contrary, the adoption of more relaxed ones (i.e. a passive strategy). (C) 2008 Elsevier Ltd. All rights reserved.