Evidence suggests that the nervous system controls motor tasks using a low-dimensional modular organization of muscle activation. However, it is not clear if such an organization applies to coordination of human walking, nor how nervous system injury may alter the organization of motor modules and their biomechanical outputs. We first tested the hypothesis that muscle activation patterns during walking are produced through the variable activation of a small set of motor modules. In 20 healthy control subjects, EMG signals from eight leg muscles were measured across a range of walking speeds. Four motor modules identified through nonnegative matrix factorization were sufficient to account for variability of muscle activation from step to step and across speeds. Next, consistent with the clinical notion of abnormal limb flexion-extension synergies post-stroke, we tested the hypothesis that subjects with post-stroke hemiparesis would have altered motor modules, leading to impaired walking performance. In post-stroke subjects ( n = 55), a less complex coordination pattern was shown. Fewer modules were needed to account for muscle activation during walking at preferred speed compared with controls. Fewer modules resulted from merging of the modules observed in healthy controls, suggesting reduced independence of neural control signals. The number of modules was correlated to preferred walking speed, speed modulation, step length asymmetry, and propulsive asymmetry. Our results suggest a common modular organization of muscle coordination underlying walking in both healthy and post-stroke subjects. Identification of motor modules may lead to new insight into impaired locomotor coordination and the underlying neural systems.
KAUTZ, S.A., and R.R. NEPTUNE. Biomechanical determinants of pedaling energetics: Internal and external work are not independent. Exerc. Sport Sci. Rev., Vol. 30, No. 4, pp. 159–165, 2002. Simulation analyses of pedaling demonstrate how individual muscle forces act to accelerate and decelerate the leg segments and the crank to perform external work. The work done by the muscles to accelerate the leg segments ultimately drives the pedals because when the legs decelerate, their mechanical energy is used to overcome the external load.
Abstract Balance perturbations are often used to gain insight into reactive control strategies used to prevent falls. We developed a perturbation platform system (PPS) that can induce perturbations in both vertical and angled directions. The PPS was evaluated using human subject testing to verify its function and performance. The final system consisted of two box platforms that can individually perform vertical and angled surface perturbations. Following a perturbation, the system can automatically reset for the next iteration under the weight of the standing participant. The PPS achieves a peak downward acceleration of 4.4 m/s2 during drop events that simulate sudden surface changes. The experimental testing revealed that the perturbation induced a peak limb loading of 280 ± 38% of body weight (BW) during vertical drops and that participants' center of mass displacements were consistent with previous balance studies evaluating vertical perturbations. The system can be used in a laboratory or clinical setting to better understand balance response and control mechanisms and assist in rehabilitation training to improve balance control and help mitigate the incidence of falls.
Selective laser sintering (SLS) is a powerful manufacturing technology that does not require part-specific tooling or significant human intervention and provides the ability to easily generate parts with complex geometric designs. The present work focuses on developing a manufacturing framework using this technology to produce subject-specific transtibial amputee prosthetic sockets made of Duraform PA, which is a nylon-based material. The framework includes establishing an overall socket design (using the patellar-tendon bearing approach), performing a structural analysis using the finite element method (FEM) to ensure structural reliability during patient use, and validating the results by comparing the model output with experimental data. The validation included quantifying the failure conditions for the socket through a series of bending moment and compression tests. In the case study performed, the FEM results were within 3% of the experimental failure loads for the socket and were considered satisfactory
A very attractive advantage of manufacturing prosthetic sockets using solid freeform fabrication is the freedom to introduce design solutions that would be difficult to implement using traditional manufacturing techniques. Such is the case with compliant features embedded in amputee prosthetic sockets to relieve contact pressure at the residual limb-socket interface. The purpose of this study was to present a framework for designing compliant features to be incorporated into transtibial sockets and manufacturing prototypes using selective laser sintering (SLS) and Duraform™ material. The design process included identifying optimal compliant features using topology optimization algorithms and integrating these features within the geometry of the socket model. Using this process, a compliant feature consisting of spiral beams and a supporting external structure was identified. To assess its effectiveness in reducing residual limb-socket interface pressure, a case study was conducted using SLS manufactured prototypes to quantify the difference in interface pressure while a patient walked at his self-selected pace with one noncompliant and two different compliant sockets. The pressure measurements were performed using thin pressure transducers located at the distal tibia and fibula head. The measurements revealed that the socket with the greatest compliance reduced the average and peak pressure by 22% and 45% at the anterior side distal tibia, respectively, and 19% and 23% at the lateral side of the fibula head, respectively. These results indicate that the integration of compliant features within the socket structure is an effective way to reduce potentially harmful contact pressure and increase patient comfort.
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