INTERNAL WORK ESTIMATION IN 3-DIMENSIONAL GAIT ANALYSIS

Many studies concerning the internal work of human motion have used tw o-dimensional kinematic models to estimate kinetic energy of the segme nts. The generalised cc-ordinate concept has been applied here to a si multaneous and bilateral gait analysis. A three-dimensional kinematic model based on quaternions has been developed. To estimate the kinetic energy of a multi-body system, only two constants and two variables a re needed: the segment body mass, the inertia tensor, the position and the orientation of the local cc-ordinate system with respect to the i nertial co-ordinate system. The variation of the kinetic energy is use d in the calculation of the internal work for an able-bodied subject d uring the gait cycle. Both the internal work and the instantaneous ene rgy correlation coefficient enable the determination of a conservative phase delimited by the beginning of the single support phase until th e flat-foot phase, and a non-conservative phase corresponding to the p eriod from heel-off to contralateral heel-strike including the double support phase.