The problem of the study was to determine the joint power and work at the ankle and knee relative to three-dimensional (3D), anatomically meaningful axes during the stance phase of barefoot walking over level, uphill (8.3%), and downhill (8.3%) grades. Also, intermediate calculations provided values for joint angles, instantaneous angular velocities, and net reaction moments. The study was needed to provide an initial data base for these parameters during activities in addition to simple, level walking, against which patients with gait pathologies could be compared before and after treatment.

The calculation of kinetic parameters of gait required the combination of information from three basic areas:​ body segment parameters, 3D kinematics for segments of the lower extremity, and ground reaction forces. Body segment parameters were estimated from cadaveric multiple regression studies, and from geometric modeling. Kinematic parameters were calculated using screw axis theory with global position data obtained through dnematographical analysis. Ground reaction forces were measured using a piezoelectric force plate. The data were combined in custom FORTRAN software on a laboratory-based microcomputer for nine adult male subjects.

Results for primary axes (ankle dorsiflexion/plantarflexion;​ knee flexion/extension) showed the ankle to be critical in propulsion, with the knee's function being primarily shock absorption and control. The peak extensor moment, peak power generation, and positive work performed at the ankle increased with grade. Results at the knee were more variable. Here, trends were not consistent across grades, but shock absorption at heel-strike appeared to be more important than control at mid-stance for grade walking, while the reverse was true for level walking. Results for secondary axes were similar. Data indicated that gait parameters calculated for all three anatomical axes have biomechanical relevance. Although magnitudes for parameters along secondary axes are relatively small, it seems unwise to disregard them as unimportant. This is especially true in a clinical setting where 3D analyses can shed light on disease processes and treatment outcomes.