We studied the coordination of body segments during treadmill walking. Specifically, we used the uncontrolled manifold hypothesis framework to quantify the segmental angular momenta (SAM) synergies that stabilize (i.e., reduce the across trials variability) the whole body angular momentum (WBAM). Seven male subjects were asked to walk over a treadmill at their comfortable walking speed. A 17-segment model, fitted to the subject's anthropometry, was used to reconstruct their kinematics and to compute the SAM and WBAM in three dimensions. A principal component analysis was used to represent the 17 SAM by the magnitudes of the first five principal components. An index of synergy (DeltaV) was used to quantify the co-variations of these principal components with respect to their effect on the WBAM. Positive values of DeltaV were observed in the sagittal plane during the swing phase. They reflected the synergies among the SAM that stabilized (i.e., made reproducible from stride to stride) the WBAM. Negative values of DeltaV were observed in both frontal and sagittal plane during the double support phase. They were interpreted as "anti-synergies", i.e., a particular organization of the SAM used to adjust the WBAM. Based on these results, we demonstrated that the WBAM is a variable whose value is regulated by the CNS during walking activities, and that the nature of the WBAM control changed between swing phase and double support phase. These results can be linked with humanoid gait controls presently employed in robotics.
Three computer models of varying complexity were developed in order to investigate the kinematics, kinetics, muscle operating ranges, and energetics of rock climbing. First, inverse dynamic models were used to investigate the joint angles and torques used in climbing and to quantify the total mechanical work required for typical rock climbing. Climbing experience was found to have a significant effect on the kinematics used in climbing; however, there were no significant differences in mechanical work. Second, a musculoskeletal model of the whole body was developed, this model combined with the kinematic data was used to analyze the operating ranges of the upper and lower limb muscles during climbing. In general, the experienced climbers employed kinematic motions that corresponded to muscle fibers used for climbing operating much closer to their optimum length than the kinematics of inexperienced climbers. Third, a forward dynamic model was developed to predict the metabolic goal of climbing. The results of this model suggest that an experienced climbing style minimizes the fatigue of muscles while an inexperienced climbing style minimizes the total joint torques generated.
We examined how the application of a forward horizontal force applied at the waist alters the metabolic cost, kinematics, and external work of gait. Horizontal assist forces of 4%, 8% and 12% of a subject’s body weight were applied via our testing apparatus while subjects walked at comfortable walking speed on a level treadmill. Kinematic and metabolic parameters were measured using motion capture and ergospirometry respectively on a group of 10 healthy male subjects. Changes in kinematic and metabolic parameters were quantified and found similar to walking downhill at varying grades. A horizontal assist force of 8% resulted in the greatest reduction of metabolic cost. Changes in recovery factor, external work, and center of mass (COM) movement did not correlate with changes in metabolic rate and therefore were not driving the observed reductions in cost. The assist force may have performed external work by providing propulsion as well as raising the COM as it pivots over the stance leg. Assist forces may decrease metabolic cost by reducing the concentric work required for propulsion while increasing the eccentric work of braking. These findings on the effects of assist forces suggest novel mobility aids for individuals with gait disorders and training strategies for athletes.
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