An engineering methodology called """"""""inverse dynamics"""""""" provides the resultant forces & moments at major anatomical joints during walking. These """"""""joint reactions"""""""" perform mechanical work, & consequently have power associated with them. Joint powers have been used to evaluate mechanical energy flows for individual joints. If added for all major joints of the body, the sum represents a mechanical energy cost for movement, which is an important parameter for estimation of mechanical efficiency. Traditionally, joint models have allowed only rotations at joints, without accounting for translations such as sliding & compression/distraction. Our immediate objective is to implement full six degree-of-freedom (DOF) joint models for the lower extremity, allowing for three rotational & three translational movements (DOFs). Traditional models assumed that translational powers canceled each other across a joint; our new methods include joint powers associated with the three translational DOFs. We believe this detailed model will provide more robust calculations for joint powers, improving reliability & accuracy in total mechanical power estimates. Lower extremity data are collected over full stride cycles for multiple walking trials. Ensemble averages & coefficients of variability are determined for each DOF. Results at the ankle joint for an intra-subject analysis (n=5) showed that X-axis rotational power (associated with ankle dorsi/plantarflexion) predominates, with a peak value of 360 W. The next largest peak in joint power was for the vertical translational DOF, and was less than 10% of the predominant peak. Positive work during push-off was significantly less (ps0.05) for the 6 DOF model (27.9 J) than for either 1 or 3 DOF models (30.3 & 29.9 J, respectively). Negative work during early stance was also significantly less for the 6 DOF model (-10.3 J) than for either 1 or 3 DOF models )-13.1 & -12.6 J, respectively). Inter-subject analyses (n=50) were conducted on joint power data, with similar results. Joint powers at the knee are currently being studied.
