Joint powers have been used to evaluate mechanical energy flows for individual joints. If added for all major joints of the body during gait, the sum represents a mechanical energy cost for movement, an important parameter for the estimation of mechanical efficiency. Traditionally, joint models have allowed only rotations at joints and did not account for translations such as sliding, compression, and distraction.Our immediate objective is to complement full six degree-of- freedom (DOF) joint models for the lower extremity, i.e., allow for three rotational and three translational movements (DOFs) We believe this detailed model will provide more robust calculations for joint powers, improving reliability and accuracy in total mechanical power estimates. An engineering methodology called """""""" inverse dynamica"""""""" provides us with resultant forces and moments at major anatomical joints during walking. These """"""""joint reactions"""""""" perform mechanical work, and consequently have power associated with them. Traditional models assumed that translational powers canceled each other across a joint. Our new methods no longer force this relationship, but account for joint powers associated with three translational DOFs. Lower extremity data are calculated over full stride cycles for multiple walking trails. Ensemble averages and coefficients of variability are determined for each DOF. Preliminary ankle results for inter-subject data (n=25) have shown that X-axis rotational powers (associated with ankle dorsi/plantarflexion) predominant, with peaks (normalized by body mass) approaching 4.5 W/kg. Peaks for the remaining five DOFs were below 10% of the predominant DOF. When all six DOFs were added to provide total power at the ankle complex, the combined effect of the smaller power terms was to attenuate the peak in dorsi/plantarflexion related powers. Similar relative magnitudes were found for intra-subject calculations (n=5). Joint powers at the knee and possibly the hip are likely to be studied to complete the major joints of the lower extremity. A separate but related project may be undertaken to better understand the source of the measured joint translations.
