From bone to plausible bipedal locomotion using inverse kinematics.

The purpose of this study is to validate a method based on anatomical data and biomechanical locomotor hypotheses that could be applied in palaeontology to simulate locomotion in fossil hominids. The main problem is to ensure that purely mathematical simulation, based on anatomical descriptions, is enough to test hypotheses on human motion control. A 3D geometric model of the lower limb was therefore processed from anatomical descriptions. From this 3D model, we developed a method to retrieve natural lower-limb motion depending on chosen constraints. We assumed that the role of lower-limb motion is to make the feet move from one footprint to the next by following a trajectory that resembles that of living humans (primary task). This method based on inverse kinematics also allows biomechanical laws of bipedal locomotion to be taken into account (secondary tasks). The laws tested in this study relate to preserving joint limits, minimizing energy and minimizing the distance to a rest posture proposed by anthropologists and viewed as input to our system. A weighted sum of the resulting derivable cost functions enabled us to select a specific solution in the null space of the primary task. In order to validate this approach, we compared simulated and captured motion from ten subjects for whom anthropometrical data were recorded. We concluded that this "anatomically based bipedalism simulation" seems promising as a means of investigating natural locomotion behaviour and might also be used to retrieve natural locomotion in fossil hominids where only little knowledge is available.