Journal of biomechanics
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Journal of biomechanics · Jan 2007
Mechanical energetic contributions from individual muscles and elastic prosthetic feet during symmetric unilateral transtibial amputee walking: a theoretical study.
Energy storage and return (ESAR) foot-ankle prostheses have been developed in an effort to improve gait performance in lower-limb amputees. However, little is known about their effectiveness in providing the body segment mechanical energetics normally provided by the ankle muscles. The objective of this theoretical study was to use muscle-actuated forward dynamics simulations of unilateral transtibial amputee and non-amputee walking to identify the contributions of ESAR prostheses to trunk support, forward propulsion and leg swing initiation and how individual muscles must compensate in order to produce a normal, symmetric gait pattern. ⋯ To compensate, the residual leg gluteus maximus and rectus femoris delivered increased energy to the trunk for forward propulsion in early stance and late stance into pre-swing, respectively, while the residual iliopsoas delivered increased energy to the leg in pre- and early swing to help initiate swing. In the intact leg, the soleus, gluteus maximus and rectus femoris delivered increased energy to the trunk for forward propulsion in the first half of stance, while the iliopsoas increased the leg energy it delivered in pre- and early swing. Thus, the energy stored and released by the ESAR prosthesis combined with these muscle compensations was able to produce a normal, symmetric gait pattern, although various neuromuscular and musculoskeletal constraints may make such a pattern non-optimal.
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Journal of biomechanics · Jan 2007
Clinical TrialBiomechanics of the double rocker sole shoe: gait kinematics and kinetics.
The use of footwear with contoured soles is common in treatment and care of patients with diabetes; these rocker sole shoes are designed to alleviate loading in key areas on the plantar surface of the foot, reducing pressure in key areas and alleviating pain, and potential soft tissue damage. While investigations of pressure changes have been conducted, no quantitative study to date has addressed the three-dimensional (3D) kinematic and kinetic changes that result from using these shoes. ⋯ These results demonstrate the maintenance of gait function with minimal kinematic changes when using the rocker sole shoe. Investigations of multisegmental foot motion may reveal additional information about the contour effects; analysis of contour variations may also be warranted to investigate the possibility of controlling motion based on rocker sole parameters.
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Journal of biomechanics · Jan 2007
Computational and experimental models of the human torso for non-penetrating ballistic impact.
Both computational finite element and experimental models of the human torso have been developed for ballistic impact testing. The human torso finite element model (HTFEM), including the thoracic skeletal structure and organs, was created in the finite element code LS-DYNA. The skeletal structure was assumed to be linear-elastic while all internal organs were modeled as viscoelastic. ⋯ A comparison of the HSTM and HTFEM response showed similar pressure profiles and less than 35% peak pressure difference for organs near the ballistic impact point. Furthermore, the peak sternum accelerations of the HSTM and HTFEM varied by less than 10% for impacts over the sternum. These models provide comparative tools for determining the thoracic response to ballistic impact and could be used to evaluate soft body armor design and efficacy, determine thoracic injury mechanisms and assist with injury prevention.
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Journal of biomechanics · Jan 2007
Lumbosacral orthoses reduce trunk muscle activity in a postural control task.
Biomechanical modeling estimated that trunk muscle activity during various tasks could be reduced by 1-14% without the loss of spine stability when a lumbosacral orthosis (LSO) is worn [Cholewicki, J., 2004. The effects of lumbosacral orthoses on spine stability: what changes in EMG can be expected? Journal of Orthopedic Research 22, 1150-1155]. The present study experimentally tested these theoretical predictions in an unstable sitting task. ⋯ No significant differences were present in the abdominal muscle activity. These results agree with earlier spine modeling simulations, which predicted the greatest reduction in muscle activity due to LSO to occur in TES and LES. It was hypothesized that such a reduction in muscle co-contraction could benefit patients with low back pain, who exhibit elevated muscular activity during postural tasks such as walking, standing and sitting.
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Finite element (FE) models are used to identify head injury mechanisms and design new and improved injury prevention schemes. Although brain-skull boundary conditions strongly influence the model mechanical responses, limited experimental data are available to develop an informed representation. We hypothesize that the spinal cord tension and gravity contribute to the pons displacement in vivo. ⋯ By comparing images before and after the motion, we found that while the rotation of the pons is negligible relative to the skull, the pons displaces significantly at the foramen magnum, on the order of approximately 2 mm. When the spinal cord tension and gravity act in concert, the pons moves caudally; when opposed, superiorly, such that the influence of gravity on the pons is six times that of the spinal cord tension. Based on these findings, we recommend that the brainstem-skull interface be treated as a sliding (with or without friction) boundary condition in FE models of the human head.