Journal of biomechanics
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Journal of biomechanics · Jan 2013
Spring-like gait mechanics observed during walking in both young and older adults.
A spring loaded inverted pendulum model successfully demonstrated the oscillatory behavior of the center of mass (CoM) and corresponding ground reaction forces (GRFs) of young healthy subjects. This study questioned whether spring-like leg walking dynamics are consistently observed in the walking of older adults that exhibit different gait characteristics, such as slower gait speed, from the young. Eight young and eight older adult subjects participated in overground walking experiments performed at four different gait speeds, ranging from their self-selected speed to a maximum walking speed. ⋯ We observed that the GRFs data from both age groups were reasonably well fitted by spring-like leg dynamics throughout the broad range of gait speeds. The leg stiffness and damping constant consistently increased as a function of the walking speed in both age groups, but slightly greater variations of the model parameters were observed for the older adults' trials. The results imply that human walking dynamics and the variation with respect to age can be well captured by spring-like leg dynamics.
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Journal of biomechanics · Nov 2012
A non-invasive technique for estimating carpal tunnel pressure by measuring shear wave speed in tendon: a feasibility study.
Although a close relationship between carpal tunnel pressure and median nerve dysfunction has been found, the current methods for pressure measurements are invasive, using a catheter in the carpal canal to monitor the pressure. A noninvasive method for quantifying carpal tunnel pressure would be useful as an alternative to the catheter method. ⋯ This indicates that the tendon could serve as a strain gauge to evaluate the tunnel pressure by detecting the changes of wave propagation speed. However, further validations in human cadavers and clinical subjects are necessary.
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Journal of biomechanics · Nov 2012
Gait strategy changes with acceleration to accommodate the biomechanical constraint on push-off propulsion.
To maintain steady and level walking, push-off propulsion during the double support phase compensates for the energy loss through heel strike collisions in an energetically optimal manner. However, a large portion of daily gait activities also contains transient gait responses, such as acceleration or deceleration, during which the observed dominance of the push-off work or the energy optimality may not hold. In this study, we examined whether the push-off propulsion during the double support phase served as a major energy source for gait acceleration, and we also studied the energetic optimality of accelerated gait using a simple bipedal walking model. ⋯ We measured the ground reaction force (GRF) of three consecutive steps and the corresponding leg configuration using force platforms and an optical marker system, respectively, and we compared the mechanical work performed by the GRF during each single and double support phase. In contrast to the model prediction of an increase in the push-off propulsion that is proportional to the acceleration and minimizes the mechanical energy cost, the push-off propulsion was slightly increased, and a significant increase in the mechanical work during the single support phase was observed. The results suggest that gait acceleration occurs while accommodating a feasible push-off propulsion constraint.
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Journal of biomechanics · Sep 2012
Can micro-imaging based analysis methods quantify structural integrity of rat vertebrae with and without metastatic involvement?
This study compares the ability of μCT image-based registration, 2D structural rigidity analyses and multimodal continuum-level finite element (FE) modeling in evaluating the mechanical stability of healthy, osteolytic, and mixed osteolytic/osteoblastic metastatically involved rat vertebrae. μMR and μCT images (loaded and unloaded) were acquired of lumbar spinal motion segments from 15rnu/rnu rats (five per group). Strains were calculated based on image registration of the loaded and unloaded μCT images and via analysis of FE models created from the μCT and μMR data. Predicted yield load was also calculated through 2D structural rigidity analysis of the axial unloaded μCT slices. ⋯ Qualitatively, strain patterns in the vertebral bodies generated using image registration and FEA were well matched, yet quantitatively a significant correlation was found only between mean strains in the healthy group (r=0.934). Large structural differences in metastatic vertebrae and the complexity of motion segment loading may have led to varied modes of failure. Improvements in load characterization, material properties assignments and resolution are necessary to yield a more generalized ability for image-based registration, structural rigidity and FE methods to accurately represent stability in healthy and pathologic scenarios.
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Journal of biomechanics · Aug 2012
Muscle and prosthesis contributions to amputee walking mechanics: a modeling study.
Unilateral, below-knee amputees have altered gait mechanics, which can significantly affect their mobility. Below-knee amputees lose the functional use of the ankle muscles, which are critical during walking to provide body support, forward propulsion, leg-swing initiation and mediolateral balance. Thus, either muscles must compensate or the prosthesis must provide the functional tasks normally provided by the ankle muscles. ⋯ As a result, lower overall energy was delivered to the residual leg. The prosthesis also acted to accelerate the body laterally in the absence of the ankle muscles. These results provide further insight into muscle and prosthesis function in below-knee amputee walking and can help guide rehabilitation methods and device designs to improve amputee mobility.