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- J Biomech 43(2):IFC (2010)
- Numerical simulations of the blood flow through vertebral arteries
Jozwik K Obidowski D - J Biomech 43(2):177-185 (2010)
Vertebral arteries are two arteries whose structure and location in human body result in development of special flow conditions. For some of the arteries, one can observe a significant difference between flow rates in the left and the right arteries during ultrasonography diagnosis. Usually the reason of such a difference was connected with pathology of the artery in which a smaller flow rate was detected. Simulations of the flow through the selected type of the vertebral artery geometry for twenty five cases of artery diameters have been carried out. The main aim of the presented experiment was to visualize the flow in the region of vertebral arteries junction in the origin of the basilar artery. It is extremely difficult to examine this part of human circulation system, thus numerical experiments may be helpful in understanding the phenomena occurring when two relatively large arteries join together to form one vessel. The obtained results have shown that an individu! al configuration and diameters of particular arteries can exert an influence on the flow in them and affect a significant difference between flow rates for vertebral arteries. It has been assumed in the investigations that modelled arteries were absolutely normal, without any pathology. In the numerical experiment, the non-Newtonian model of blood was employed. - Modeling muscle activity to study the effects of footwear on the impact forces and vibrations of the human body during running
Zadpoor AA Nikooyan AA - J Biomech 43(2):186-193 (2010)
A previously developed mass-spring-damper model of the human body is improved in this paper, taking muscle activity into account. In the improved model, a nonlinear controller mimics the functionality of the Central Nervous System (CNS) in tuning the mechanical properties of the soft-tissue package. Two physiological hypotheses are used to determine the control strategies that are used by the controller. The first hypothesis (constant-force hypothesis) postulates that the CNS uses muscle tuning to keep the ground reaction force (GRF) constant regardless of shoe hardness, wherever possible. It is shown that the constant-force hypothesis can explain the existing contradiction about the effects of shoe hardness on the GRF during running. This contradiction is emerged from the different trends observed in the experiments on actual runners, and experiments in which the leg was fixed and exposed to impact. While the GRF is found to be dependent on shoe hardness in the former! set of experiments, no such dependency was observed in the latter. According to the second hypothesis, the CNS keeps the level of the vibrations of the human body constant using muscle tuning. The results of the study show that this second control strategy improves the model such that it can correctly simulate the effects of shoe hardness on the vibrations of the human body during running. - A generic analytical foot rollover model for predicting translational ankle kinematics in gait simulation studies
Ren L Howard D Ren L Nester C Tian L - J Biomech 43(2):194-202 (2010)
The objective of this paper is to develop an analytical framework to representing the ankle–foot kinematics by modelling the foot as a rollover rocker, which cannot only be used as a generic tool for general gait simulation but also allows for case-specific modelling if required. Previously, the rollover models used in gait simulation have often been based on specific functions that have usually been of a simple form. In contrast, the analytical model described here is in a general form that the effective foot rollover shape can be represented by any polar function ρ=ρ(φ). Furthermore, a normalized generic foot rollover model has been established based on a normative foot rollover shape dataset of 12 normal healthy subjects. To evaluate model accuracy, the predicted ankle motions and the centre of pressure (CoP) were compared with measurement data for both subject-specific and general cases. The results demonstrated that the ankle joint motions in both vertical an! d horizontal directions (relative RMSE 10%) and CoP (relative RMSE 15% for most of the subjects) are accurately predicted over most of the stance phase (from 10% to 90% of stance). However, we found that the foot cannot be very accurately represented by a rollover model just after heel strike (HS) and just before toe off (TO), probably due to shear deformation of foot plantar tissues (ankle motion can occur without any foot rotation). The proposed foot rollover model can be used in both inverse and forward dynamics gait simulation studies and may also find applications in rehabilitation engineering. - Invariant ankle moment patterns when walking with and without a robotic ankle exoskeleton
Kao PC Lewis CL Ferris DP - J Biomech 43(2):203-209 (2010)
To guide development of robotic lower limb exoskeletons, it is necessary to understand how humans adapt to powered assistance. The purposes of this study were to quantify joint moments while healthy subjects adapted to a robotic ankle exoskeleton and to determine if the period of motor adaptation is dependent on the magnitude of robotic assistance. The pneumatically powered ankle exoskeleton provided plantar flexor torque controlled by the wearer's soleus electromyography (EMG). Eleven naïve individuals completed two 30-min sessions walking on a split-belt instrumented treadmill at 1.25 m/s while wearing the ankle exoskeleton. After two sessions of practice, subjects reduced their soleus EMG activation by 36% and walked with total ankle moment patterns similar to their unassisted gait (r2=0.98±0.02, THSD, p>0.05). They had substantially different ankle kinematic patterns compared to their unassisted gait (r2=0.79±0.12, THSD, p<0.05). Not all of the subjects reached ! a steady-state gait pattern within the two sessions, in contrast to a previous study using a weaker robotic ankle exoskeleton (Gordon and Ferris, 2007). Our results strongly suggest that humans aim for similar joint moment patterns when walking with robotic assistance rather than similar kinematic patterns. In addition, greater robotic assistance provided during initial use results in a longer adaptation process than lesser robotic assistance. - A numerical model of cellular blebbing: A volume-conserving, fluid–structure interaction model of the entire cell
Young J Mitran S - J Biomech 43(2):210-220 (2010)
In animal cells, blebs are smooth, quasi-hemispherical protrusions of the plasma membrane that form when a section of the membrane detaches from the underlying actin cytoskeleton and is inflated by flowing cytosol. The mechanics behind this common cellular activity are not yet clear. As a first step in the development of a full computational framework, we present a numerical model of overall cell behavior based upon the interaction between a background Newtonian-fluid cytosol and elastic structures modeling the membrane and filaments. The detailed micromechanics of the cytoskeletal network are the subject of future work. Here, the myosin-driven contraction of the actin network is modeled through stressed elastic filaments. Quantitative models of cytoskeletal micromechanics and biochemistry require accurate estimates of local stress and flow conditions. The main contribution of this paper is the development of a computationally efficient fluid–structure interaction mo! del based on operator splitting, to furnish this data. Cytosol volume conservation (as supported by experimental evidence) is enforced through an intermediate energy minimization step. Realistic bleb formation and retraction is observed from this model, offering an alternative formulation to positing complex continuum behavior of the cytoplasm (e.g. poroelastic model of Charras et al., 2008). - Fluid–structure interaction in aortic cross-clamping: Implications for vessel injury
Chen HY Navia JA Shafique S Kassab GS - J Biomech 43(2):221-227 (2010)
Vascular cross-clamping is applied in many cardiovascular surgeries such as coronary bypass, aorta repair and valve procedures. Experimental studies have found that clamping of various degrees caused damage to arteries. This study examines the effects of popular clamps on vessel wall. Models of the aorta and clamp were created in Computer Assisted Design and Finite Element Analysis packages. The vessel wall was considered as a non-linear anisotropic material while the fluid was simulated as Newtonian with pulsatile flow. The clamp was applied through displacement time function. Fully coupled two-way solid–fluid interaction models were developed. It was found that the clamp design significantly affected the stresses in vessel wall. The clamp with a protrusion feature increased the overall Von Mises stress by about 60% and the compressive stress by more than 200%. Interestingly, when the protrusion clamp was applied, the Von Mises stress at the lumen (endothelium) side! of artery wall was about twice that of the outer wall. This ratio was much higher than that of the plate-like clamp which was about 1.3. The flow reversal process was demonstrated during clamping. Vibrations, flow and wall shear stress oscillations were detected immediately before total vessel occlusion. The commonly used protrusion clamp increased stresses in vessel wall, especially the compressive stress. This design also significantly increased the stresses on endothelium, detrimental to vessel health. The present findings are relevant to surgical clamp design as well as the transient mechanical loading on the endothelium and potential injury. The deformation and stress analysis may provide valuable insights into the mode of tissue injury during cross-clamping. - Rib fractures under anterior–posterior dynamic loads: Experimental and finite-element study
Li Z Kindig MW Kerrigan JR Untaroiu CD Subit D Crandall JR Kent RW - J Biomech 43(2):228-234 (2010)
The purpose of this study was to investigate whether using a finite-element (FE) mesh composed entirely of hexahedral elements to model cortical and trabecular bone (all-hex model) would provide more accurate simulations than those with variable thickness shell elements for cortical bone and hexahedral elements for trabecular bone (hex–shell model) in the modeling human ribs. First, quasi-static non-injurious and dynamic injurious experiments were performed using the second, fourth, and tenth human thoracic ribs to record the structural behavior and fracture tolerance of individual ribs under anterior–posterior bending loads. Then, all-hex and hex–shell FE models for the three ribs were developed using an octree-based and multi-block hex meshing approach, respectively. Material properties of cortical bone were optimized using dynamic experimental data and the hex–shell model of the fourth rib and trabecular bone properties were taken from the literature. Overal! l, the reaction force–displacement relationship predicted by both all-hex and hex–shell models with nodes in the offset middle-cortical surfaces compared well with those measured experimentally for all the three ribs. With the exception of fracture locations, the predictions from all-hex and offset hex–shell models of the second and fourth ribs agreed better with experimental data than those from the tenth rib models in terms of reaction force at fracture (difference <15.4%), ultimate failure displacement and time (difference <7.3%), and cortical bone strains. The hex–shell models with shell nodes in outer cortical surfaces increased static reaction forces up to 16.6%, compared to offset hex–shell models. These results indicated that both all-hex and hex–shell modeling strategies were applicable for simulating rib responses and bone fractures for the loading conditions considered, but coarse hex–shell models with constant or variable shell thickness were more ! computationally efficient and therefore preferred. - In vivo patellar tracking induced by individual quadriceps components in individuals with patellofemoral pain
Lin F Wilson NA Makhsous M Press JM Koh JL Nuber GW Zhang LQ - J Biomech 43(2):235-241 (2010)
Patellofemoral pain is a common knee disorder with a multi-factorial etiology related to abnormal patellar tracking. Our hypothesis was that the pattern of three-dimensional rotation and translation of the patella induced by selective activation of individual quadriceps components would differ between subjects with patellofemoral pain and healthy subjects. Nine female subjects with patellofemoral pain and seven healthy female subjects underwent electrical stimulation to selectively activate individual quadriceps components (vastus medialis obliquus, VMO; vastus medialis lateralis, VML; vastus lateralis, VL) with the knee at 0° and 20° flexion, while three-dimensional patellar tracking was recorded. Normalized direction of rotation and direction of translation characterized the relative amplitudes of each component of patellar movement. VMO activation in patellofemoral pain caused greater medial patellar rotation (distal patellar pole rotates medially in frontal plane! ) at both knee positions (p<0.01), and both VMO and VML activation caused increased anterior patellar translation (p<0.001) in patellofemoral pain compared to healthy subjects at 20° knee flexion. VL activation caused more lateral patellar translation (p<0.001) in patellofemoral pain compared to healthy subjects. In healthy subjects the 3-D mechanical action of the VMO is actively modulated with knee flexion angle while such modulation was not observed in PFP subjects. This could be due to anatomical differences in the VMO insertion on the patella and medial quadriceps weakness. Quantitative evaluation of the influence of individual quadriceps components on patellar tracking will aid understanding of the knee extensor mechanism and provide insight into the etiology of patellofemoral pain. - Direct contribution of axial impact compressive load to anterior tibial load during simulated ski landing impact
Yeow CH Lee PV Goh JC - J Biomech 43(2):242-247 (2010)
Anterior tibial loading is a major factor involved in the anterior cruciate ligament (ACL) injury mechanism during ski impact landing. We sought to investigate the direct contribution of axial impact compressive load to anterior tibial load during simulated ski landing impact of intact knee joints without quadriceps activation. Twelve porcine knee specimens were procured. Four specimens were used as non-impact control while the remaining eight were mounted onto a material-testing system at 70° flexion and subjected to simulated landing impact, which was successively repeated with incremental actuator displacement. Four specimens from the impacted group underwent pre-impact MRI for tibial plateau angle measurements while the other four were subjected to histology and microCT for cartilage morphology and volume assessment. The tibial plateau angles ranged from 29.4 to 38.8°. There was a moderate linear relationship (Y=0.16X; R2=0.64; p<0.001) between peak axial impact ! compressive load (Y) and peak anterior tibial load (X). The anterior and posterior regions in the impacted group sustained surface cartilage fraying, superficial clefts and tidemark disruption, compared to the control group. MicroCT scans displayed visible cartilage deformation for both anterior and posterior regions in the impacted group. Due to the tibial plateau angle, increased axial impact compressive load can directly elevate anterior tibial load and hence contribute to ACL failure during simulated landing impact. Axial impact compressive load resulted in shear cartilage damage along anterior–posterior tibial plateau regions, due to its contribution to anterior tibial loading. This mechanism plays an important role in elevating ACL stress and cartilage deformation during impact landing. - A stochastic model of cell aggregation under planar flow in the dilute regime
Ganghoffer JF Kabouya N Mefti N - J Biomech 43(2):248-253 (2010)
Models of the adhesion of a population of cells in a plane flow are developed, considering the dilute regime. Cells considered as rigid punctual entities are virtually injected at regular times within a plane channel limited by two fixed planes. The pressure profile is supposed to be triangular (constant gradient), in accordance with the assumptions of a Poiseuille flow. The cell adherence to the channel wall is governed by the balance of forces, accounting for gravity, non-specific physical interactions, such as electrostatic effects (repulsive) and Van der Waals forces (attractive), specific adhesive forces representing the ligand–receptor interactions, and friction between cells and the fluid in the vicinity of the endothelium wall. The spatial distribution of the adhesion molecules along the wall is supposed to be a random event, accounted for by a stochastic spatial variability of the dipolar moments of those molecules, according to a Gaussian process. Experimen! tal trends reported for the rate of aggregation of L-selectin mediated leukocytes under shear flow are in qualitative accordance with the evolution versus time of adhering cells obtained by the present simulations. The effect of the maximal injection pressure on those kinetics is assessed. - Morphing methods to parameterize specimen-specific finite element model geometries
Sigal IA Yang H Roberts MD Downs JC - J Biomech 43(2):254-262 (2010)
Shape plays an important role in determining the biomechanical response of a structure. Specimen-specific finite element (FE) models have been developed to capture the details of the shape of biological structures and predict their biomechanics. Shape, however, can vary considerably across individuals or change due to aging or disease, and analysis of the sensitivity of specimen-specific models to these variations has proven challenging. An alternative to specimen-specific representation has been to develop generic models with simplified geometries whose shape is relatively easy to parameterize, and can therefore be readily used in sensitivity studies. Despite many successful applications, generic models are limited in that they cannot make predictions for individual specimens. We propose that it is possible to harness the detail available in specimen-specific models while leveraging the power of the parameterization techniques common in generic models. In this work we show that this can be accomplished by using morphing techniques to parameterize the geometry of specimen-specific FE models such that the model shape can be varied in a controlled and systematic way suitable for sensitivity analysis. We demonstrate three morphing techniques by using them on a model of the load-bearing tissues of the posterior pole of the eye. We show that using relatively straightforward procedures these morphing techniques can be combined, which allows the study of factor interactions. Finally, we illustrate that the techniques can be used in other systems by applying them to morph a femur. Morphing techniques provide an exciting new possibility for the analysis of the biomechanical role of shape, independently or in interaction with loading and material properties. - Exercise training changes the gating properties of large-conductance Ca2+-activated K+ channels in rat thoracic aorta smooth muscle cells
Zhao HC Wang F - J Biomech 43(2):263-267 (2010)
Large-conductance Ca2+-activated K+ (BKCa) channels play a critical role in regulating the cellular excitability in response to change in blood flow. It has been demonstrated that vascular BKCa channel currents in both humans and rats are increased after exercise training. This up-regulation of the BKCa channel activity in arterial myocytes may represent a cellular compensatory mechanism of limiting vascular reactivity to exercise training. However, the underlying mechanisms are not fully understood. In the present study, we examined the single channel activities and kinetics of the BKCa channels in rat thoracic aorta smooth muscle cells. We showed that exercise training significantly increased the open probability (Po), decreased the mean closed time and increased the mean open time, and the sensitivity to Ca2+ and voltage without altering the unitary conductance and the K+ selectivity. Our results suggest a novel mechanism by which exercise training increases the K+ ! currents by changing the BKCa channel activities and kinetics. - Do kinematic models reduce the effects of soft tissue artefacts in skin marker-based motion analysis? An in vivo study of knee kinematics
Andersen MS Benoit DL Damsgaard M Ramsey DK Rasmussen J - J Biomech 43(2):268-273 (2010)
We investigated the effects of including kinematic constraints in the analysis of knee kinematics from skin markers and compared the result to simultaneously recorded trajectories of bone pin markers during gait of six healthy subjects. The constraint equations that were considered for the knee were spherical and revolute joints, which have been frequently used in musculoskeletal modelling. In the models, the joint centres and joint axes of rotations were optimised from the skin marker trajectories over the trial. It was found that the introduction of kinematic constraints did not reduce the error associated with soft tissue artefacts. The inclusion of a revolute joint constraint showed a statistically significant increase in the mean flexion/extension joint angle error and no statistically significant change for the two other mean joint angle errors. The inclusion of a spherical joint showed a statistically significant increase in the mean flexion/extension and abduct! ion/adduction errors. In addition, when a spherical joint was included, a statistically significant increase in the sum of squared differences between measured marker trajectories and the trajectories of the pin markers in the models was seen. From this, it was concluded that both more advanced knee models as well as models of soft tissue artefacts should be developed before accurate knee kinematics can be calculated from skin markers. - Early response to tendon fatigue damage accumulation in a novel in vivo model
Fung DT Wang VM Andarawis-Puri N Basta-Pljakic J Li Y Laudier DM Sun HB Jepsen KJ Schaffler MB Flatow EL - J Biomech 43(2):274-279 (2010)
This study describes the development and application of a novel rat patellar tendon model of mechanical fatigue for investigating the early in vivo response to tendon subfailure injury. Patellar tendons of adult female Sprague-Dawley rats were fatigue loaded between 1–35 N using a custom-designed loading apparatus. Patellar tendons were subjected to Low-, Moderate- or High-level fatigue damage, defined by grip-to-grip strain measurement. Molecular response was compared with that of a laceration-repair injury. Histological analyses showed that progression of tendon fatigue involves formation of localized kinked fiber deformations at Low damage, which increased in density with presence of fiber delaminations at Moderate damage, and fiber angulation and discontinuities at High damage levels. RT-PCR analysis performed at 1- and 3-day post-fatigue showed variable changes in type I, III and V collagen mRNA expression at Low and Moderate damage levels, consistent with clini! cal findings of tendon pathology and were modest compared with those observed at High damage levels, in which expression of all collagens evaluated were increased markedly. In contrast, only type I collagen expression was elevated at the same time points post-laceration. Findings suggest that cumulative fatigue in tendon invokes a different molecular response than laceration. Further, structural repair may not be initiated until reaching end-stage fatigue life, where the repair response may unable to restore the damaged tendon to its pre-fatigue architecture. - Exposure to internal muscle tissue loads under the ischial tuberosities during sitting is elevated at abnormally high or low body mass indices
Sopher R Nixon J Gorecki C Gefen A - J Biomech 43(2):280-286 (2010)
Deep tissue injury (DTI) is a severe pressure ulcer characteristic of chairfast or bedfast individuals, such as those with impaired mobility or neurological disorders. A DTI differs from superficial pressure ulcers in that the onset of DTI occurs under intact skin, in skeletal muscle tissue overlying bony prominences, and progression of the wound continues subcutaneously until skin breakdown. Due to the nature of this silently progressing wound, it is highly important to screen potentially susceptible individuals for their risk of developing a DTI. Abnormally low and high values of the body mass index (BMI) have been proposed to be associated with pressure ulcers, but a clear mechanism is lacking. We hypothesize that during sitting, exposure to internal muscle tissue loads under the ischial tuberosities (IT) is elevated at abnormally high or low body mass indices. Our aims in this study were: (a) to develop biomechanical models of the IT region in the buttocks that rep! resent an individual who is gaining or losing weight drastically. (b) To determine changes in internal tissue load measures: principal compression strain, strain energy density (SED), principal compression stress and von Mises stress versus the BMI. (c) To determine percentage volumes of muscle tissue exposed to critical levels of the above load measures, which were defined based on our previous animal and tissue engineered model experiments: strain≥50%, stress≥2 kPa, SED≥0.5 kPa. A set of 21 finite element models, which represented the same individual, but with different BMI values within the normal range, above it and below it, was solved for the outcome measures listed above. The models had the same IT shape, size, distance between the IT, and (non-linear) mechanical properties for all soft tissues, but different thicknesses of gluteus muscles and fat tissue layers, corresponding to the BMI level. The resulted data indicated a trend of progressive increase in inter! nal tissue loading, particularly in volumetric exposure to cri! tical loading for BMI values outside the 17≤BMI≤22 kg/m2 range, supporting our hypothesis for this study. We concluded that exposure to internal muscle tissue loads under the IT during sitting is optimally reduced at the low-normal BMI range, which is important not only in the context of DTI research, but also for understanding general sitting biomechanics. - Mandibular bone remodeling induced by dental implant
Lin D Li Q Li W Duckmanton N Swain M - J Biomech 43(2):287-293 (2010)
The ability to assess the effects of an implant on bone remodeling is of particular importance to prosthesis placement planning and associated treatment assurance. Prediction of on-going bone responses will enable us to improve the performance of a restoration. Although the bone remodeling for long bones had been extensively studied, there have been relatively few reports for dental scenarios despite its increasing significance with more and more dental implant placements. This paper aimed to develop a systematic protocol to assess mandibular bone remodeling induced by dental implantation, which extends the remodeling algorithms established for the long bones into dental settings. In this study, a 3D model for a segment of a human mandible was generated from in vivo CT scan images, together with a titanium implant embedded to the mandible. The results examined the changes in bone density and stiffness as a result of bone remodeling over a period of 48 months. Resonance! frequency analysis was also performed to relate natural frequencies to bone remodeling. The density contours are qualitatively compared with clinical follow-up X-ray images, thereby providing validity for the bone remodeling algorithm presented in dental bone analysis. - Computational simulation of simultaneous cortical and trabecular bone change in human proximal femur during bone remodeling
Jang IG Kim IY - J Biomech 43(2):294-301 (2010)
In this study, we developed a numerical framework that computationally determines simultaneous and interactive structural changes of cortical and trabecular bone types during bone remodeling, and we investigated the structural correlation between the two bone types in human proximal femur. We implemented a surface remodeling technique that performs bone remodeling in the exterior layer of the cortical bone while keeping its interior area unchanged. A micro-finite element (μFE) model was constructed that represents the entire cortical bone and full trabecular architecture in human proximal femur. This study simulated and compared the bone adaptation processes of two different structures: (1) femoral bone that has normal cortical bone shape and (2) perturbed femoral bone that has an artificial bone lump in the inferomedial cortex. Using the proposed numerical method in conjunction with design space optimization, we successfully obtained numerical results that resemble a! ctual human proximal femur. The results revealed that actual cortical bone, as well as the trabecular bone, in human proximal femur has structurally optimal shapes, and it was also shown that a bone abnormality that has little contribution to bone structural integrity tends to disappear. This study also quantitatively determined the structural contribution of each bone: when the trabecular adaptation was complete, the trabecular bone supported 54% of the total load in the human proximal femur while the cortical bone carried 46%. - Optimizing the tissue anchoring performance of barbed sutures in skin and tendon tissues
Ingle NP King MW - J Biomech 43(2):302-309 (2010)
The focus of the current work was to study how the geometric design of a single barbed monofilament suture effects its biomechanical behavior. Different cut angles and cut depths of barbs were prepared and tested in vitro for their tensile and tissue anchoring properties by means of a novel suture/tissue pullout test. Experiments were also performed using bovine tendon and porcine skin tissues. The experimental results revealed that since tendon tissue has a higher modulus than skin it needs a more rigid barb to penetrate and anchor the surrounding tissue. A cut angle of 150° and a cut depth of 0.18 mm are therefore recommended. On the other hand, for the softer skin tissue, a cut angle of 170° and a cut depth of 0.18 mm provides a more flexible barb that gives superior skin tissue anchoring. These findings confirm that the future development of barbed suture technology requires a detailed understanding of the biomechanical properties of the tissue in which they are ! to be used. This will lead to the future development of a range of tissue-specific barbed sutures. - Towards a footwear design tool: Influence of shoe midsole properties and ground stiffness on the impact force during running
Ly QH Alaoui A Erlicher S Baly L - J Biomech 43(2):310-317 (2010)
Several spring–damper–mass models of the human body have been developed in order to reproduce the measured ground vertical reaction forces during human running (McMahon and Cheng, 1990; Ferris et al., 1999; Liu and Nigg, 2000). In particular, Liu and Nigg introduced at the lower level of their model, i.e. at the interface between the human body and the ground, a nonlinear element representing simultaneously the shoe midsoles and the ground flexibility. The ground reaction force is modelled as the force supported by this nonlinear element, whose parameters are identified from several sets of experimental data. This approach proved to be robust and quite accurate. However, it does not explicitly take into account the shoe and the ground properties. It turns out to be impossible to study the influence of shoe materials on the impact force, for instance for footwear design purposes. In this paper, a modification of the Liu and Nigg's model is suggested, where the origi! nal nonlinear element is replaced with a bi-layered spring–damper–mass model: the first layer represents the shoe midsole and the second layer is associated with the ground. Ground is modelled as an infinite elastic half-space. We have assumed a viscoelastic behaviour of the shoe material, so the damping of shoe material is taken into account. A methodology for the shoe-soles characterization is proposed and used together with the proposed model. A parametric study is then conducted and the influence of the shoe properties on the impact force is quantified. Moreover, it is shown that impact forces are strongly affected by the ground stiffness, which should therefore be considered as an essential parameter in the footwear design. - Passive nonlinear elastic behaviour of skeletal muscle: Experimental results and model formulation
Calvo B Ramírez A Alonso A Grasa J Soteras F Osta R Muñoz MJ - J Biomech 43(2):318-325 (2010)
The goal of this study was to characterize the passive elastic behaviour of muscle and tendon tissues of rat tibialis anterior. For that purpose, tissue samples from 3 month old female Wistar rats were mechanically tested in vitro. Moreover, an in vivo device was developed to measure the muscle–tendon unit response to increasing load. Mechanical tests, consisting of uniaxial loading along the longitudinal axis of tendon and muscle strips, revealed the nonlinear mechanical behaviour of these tissues. A material model was formulated and its parameters fit to the experimental data using the Levenberg–Marquardt optimization algorithm. The fit goodness was assessed and R2 values close to 1 and very low values were obtained. The passive behaviour of a future finite element model of a muscle–tendon unit will be validated against the in vivo passive extension tests by comparing the reaction force–extension curves. - Three-dimensional modeling of in vitro hip kinematics under micro-separation regime for ceramic on ceramic total hip prosthesis: An analysis of vibration and noise
Sariali E Stewart T Jin Z Fisher J - J Biomech 43(2):326-333 (2010)
Micro-separation corresponds to a medial–lateral hip laxity after total hip replacement (THR). This laxity has been shown to generate higher wear rates and a specific pattern of stripe wear caused by edge loading of the head on the rim of the cup. Recently some authors have implicated edge loading as a source of noise generation and in particular squeaking. The goal of this study was to model hip kinematics under the micro-separation regime in a computational simulation of total hip prosthesis including joint laxity and to analyze the vibration frequencies and the potential for noise generation. A three-dimensional computer model of the Leeds II hip simulator was developed using ADAMS® software, simulating a controlled micro-separation during the swing phase of the walking cycle and replicating the experimental conditions previously reported. There was an excellent correlation between the theoretical values and the experimental values of the medial–lateral separation during the walking cycle. Vibratory frequencies were in the audible zone but were lower in magnitude than those reported clinically in relation to squeaking. Micro-separation and rim loading may explain the generation of some sounds from noisy hips after THR. However, the computational model, and the experimental model of micro-separation were unable to replicate the higher frequency squeaking reported clinically. In contrast, other experimental studies involving normal kinematics in combination with third-body particles have replicated clinically relevant frequencies and noises. - An accurate validation of a computational model of a human lumbosacral segment
Moramarco V Pérez Del Palomar A Pappalettere C Doblaré M - J Biomech 43(2):334-342 (2010)
Clinical studies have recently documented that there is sufficient evidence to suggest that abnormal motion may be an indicator of abnormal mechanics of the spine and, therefore, may be associated with some types of low-back pain. However, designating a motion as abnormal requires knowledge of normal motions. This work hence aims to develop an accurate computational model to simulate the bio-mechanical response of the whole lumbosacral spinal unit (L1–S1) under physiological loadings and constraint conditions. In order to meet this objective, computed tomography (CT) scanning protocols, finite element (FE) analysis and accurate constitutive modelling have been integrated. Then the ranges of motion (ROM) under flexion, extension and lateral bending moment were measured and compared with experimental data, finding an excellent agreement. In particular, the ability of the model to reproduce the relative rotation between each couple of vertebrae was proved. Finally, the ! shear stresses for the most extreme load cases were reported in order to predict which are the most risky conditions and where the maximum damage would be located. The results indicate that the greater values of the stresses were located at L4–S1 levels just in the interfaces between disc and vertebrae across the posterior and posterolateral zone. This result can be clinically correlated with the existence of damage exactly where the stresses were maximal in the proposed finite element model. - Body position determines propulsive forces in accelerated running
Kugler F Janshen L - J Biomech 43(2):343-348 (2010)
Rapid accelerations during running are crucial for the performance in a lot of sports. While high propulsive forces are beneficial to forward acceleration, vertical forces have to be small to attain high stride frequencies. However, propulsive and vertical force components cannot be altered independently, because the resultant force vector affects the angular momentum of the body. Therefore we hypothesized that propulsive forces in accelerated running mainly depend on body position regardless of performance level. In our cross-sectional study 28 male and 13 female physical education students performed submaximal and maximal accelerations. Ground reaction forces and whole body kinematics were recorded. Higher accelerations were generated by lower, but more forward oriented forces. The orientation of the maximum force vector strongly correlated with the forward lean of the body at toe-off . All subjects demonstrated similar propulsive forces at equal body positions. This! indicates an external constraint of propulsive force application by the mechanical requirement of running to maintain a stable body posture. Faster subjects utilized a more posterior foot plant or a longer ground contact time. Both strategies facilitated greater forward leans of the body which finally resulted in greater propulsive forces. Consequently, maximizing forward propulsion requires optimal, not maximal force application. - Stress relaxation microscopy: Imaging local stress in cells
Moreno-Flores S Benitez R Vivanco MD Toca-Herrera JL - J Biomech 43(2):349-354 (2010)
Biomechanics is gaining relevance as complementary discipline to structural and cellular biology. The response of cells to mechanical stimuli determines cell type and function, while the spatial distribution of mechanical forces within the cells is crucial to understand cell activity. The experimental methodologies to approach cell mechanics are diverse but either they are effective in few cases or they rule out the innate cell complexity. In this regard, we have developed a simple scanning probe-based methodology that overcomes the limitations of the available methods. Stress relaxation, the decay of the force exerted by the cell surface at constant deformation, has been used to extract relaxational responses at each cellular sublocalisation and generate maps. Surprisingly, decay curves exerted by test cells are fully described by a generalized viscoelastic model that accounts for more than one simultaneously occurring relaxations. Within the range of applied forces (! 0.5–4 nN) a slow and a fast relaxation with characteristic times of 0.1 and 1 s have been detected and assigned to rearrangements of cell membrane and cytoskeleton, respectively. Relaxation time mapping of entire cells is thus promising to simultaneously detect non-uniformities in membrane and cytoskeleton and as identifying tool for cell type and disease. - A unified multiscale mechanical model for soft collagenous tissues with regular fiber arrangement
- J Biomech 43(2):355-363 (2010)
In this paper the mechanical response of soft collagenous tissues with regular fiber arrangement (RSCTs) is described by means of a nanoscale model and a two-step micro–macro homogenization technique. The non-linear collagen constitutive behavior is modeled at the nanoscale by a novel approach accounting for entropic mechanisms as well as stretching effects occurring in collagen molecules. Crimped fibers are reduced to equivalent straight ones at the microscale and the constitutive response of RSCTs at the macroscale is formulated by homogenizing a fiber reinforced material. This approach has been applied to different RSCTs (tendon, periodontal ligament and aortic media), resulting effective and accurate as proved by the excellent agreement with available experimental data. The model is based on few parameters, directly related to histological and morphological evidences and whose sensitivity has been widely investigated. Applications to simulation of some physiopath! ological mechanisms are also proposed, providing confirmation of clinical evidences and quantitative indications helpful for clinical practice. - The need for muscle co-contraction prior to a landing
Yeadon MR King MA Forrester SE Caldwell GE Pain MT - J Biomech 43(2):364-369 (2010)
In landings from a flight phase the mass centre of an athlete experiences rapid decelerations. This study investigated the extent to which co-contraction is beneficial or necessary in drop landings, using both experimental data and computer simulations. High speed video and force recordings were made of an elite martial artist performing drop landings onto a force plate from heights of 1.2, 1.5 and 1.8 m. Matching simulations of these landings were produced using a planar 8-segment torque-driven subject-specific computer simulation model. It was found that there was substantial co-activation of joint flexor and extensor torques at touchdown in all three landings. Optimisations were carried out to determine whether landings could be effected without any co-contraction at touchdown. The model was not capable of landing from higher than 1.05 m with no initial flexor or extensor activations. Due to the force–velocity properties of muscle, co-contraction with net zero joi! nt torque at touchdown leads to increased extensor torque and decreased flexor torque as joint flexion velocity increases. The same considerations apply in any activity where rapid changes in net joint torque are required, as for example in jumps from a running approach. - In vivo estimation of the glenohumeral joint centre by functional methods: Accuracy and repeatability assessment
Lempereur M Leboeuf F Brochard S Rousset J Burdin V Rémy-Néris O - J Biomech 43(2):370-374 (2010)
Several algorithms have been proposed for determining the centre of rotation of ball joints. These algorithms are used rather to locate the hip joint centre. Few studies have focused on the determination of the glenohumeral joint centre. However, no studies have assessed the accuracy and repeatability of functional methods for glenohumeral joint centre. This paper aims at evaluating the accuracy and the repeatability with which the glenohumeral joint rotation centre (GHRC) can be estimated in vivo by functional methods. The reference joint centre is the glenohumeral anatomical centre obtained by medical imaging. Five functional methods were tested: the algorithm of Gamage and Lasenby (2002), bias compensated (Halvorsen, 2003), symmetrical centre of rotation estimation (Ehrig et al., 2006), normalization method (Chang and Pollard, 2007), helical axis (Woltring et al., 1985). The glenohumeral anatomical centre (GHAC) was deduced from the fitting of the humeral head. Four subjects performed three cycles of three different movements (flexion/extension, abduction/adduction and circumduction). For each test, the location of the glenohumeral joint centre was estimated by the five methods. Analyses focused on the 3D location, on the repeatability of location and on the accuracy by computing the Euclidian distance between the estimated GHRC and the GHAC. For all the methods, the error repeatability was inferior to 8.25 mm. This study showed that there are significant differences between the five functional methods. The smallest distance between the estimated joint centre and the centre of the humeral head was obtained with the method of Gamage and Lasenby (2002). - Optimal average path of the instantaneous helical axis in planar motions with one functional degree of freedom
Page A Galvez JA de Rosario H Mata V Prat J - J Biomech 43(2):375-378 (2010)
This paper presents a model for determining the path of the instantaneous helical axis (IHA) that optimally represents human planar motions with one functional degree of freedom (fDOF). A human movement is said to have one fDOF when all degrees of freedom (DOFs) are coordinated such that all the kinematic variables can be expressed, across movement repetitions, as functions of only one independent DOF, except for a small natural intercycle variability quantified as lower than a prespecified value. The concept of fDOF allows taking into account that, due to motor coordination, human movements are executed in a repeatable manner. Our method uses the measurement of several repetitions of a given movement to obtain the optimal average IHA path. The starting point is a change of variables, from time to a joint position magnitude (generally an angle). In this way, instead of operating with the time-dependent single-valued trajectory of the successive cycles, our model permit! s the representation of any motion variable (e.g. positions and their time derivatives) as a cloud of points dependent on the joint angle. This allows the averaging to be performed over the displacements and their derivatives before determining the mean IHA path. We thus avoid the nonlinear magnification of errors and variability inherent in the IHA computation. Moreover, the IHA path can be considered as a geometric attribute of the joint and the type of motion, rather than of each single movement execution. An experiment was performed that show the accuracy and usefulness of the method. - Improvements to Hoang et al.'s method for measuring passive length–tension properties of human gastrocnemius muscle in vivo
Nordez A Fouré A Dombroski EW Mariot JP Cornu C McNair PJ - J Biomech 43(2):379-382 (2010)
While the passive mechanical properties of a musculo-articular complex can be determined using the relationship between the articular angle and the passive torque developed in resistance to motion, the properties of different structures of the musculo-articular complex cannot be easily assessed. Recently, an elegant method has been proposed to estimate the passive length–tension properties of gastrocnemius muscle–tendon unit (Hoang et al., 2005). In the present paper, two improvements of this method are proposed to decrease the number of parameters required to assess the passive length–tension relationship from 9 to 2. Furthermore, these two parameters have physical meaning as they represent a passive muscle–tendon stiffness index (α) and the muscle–tendon slack length (l0). α and l0 are relevant clinical parameters to study the chronic effects of aging, training protocols or neuromuscular pathologies on the passive mechanical properties of the muscle–ten! don unit. Eight healthy subjects performed passive loading/unloading cycles at 5°/s with knee angle at 6 knee angles to assess the torque–angle relationships and to apply the modified method. Numerical optimization was used to minimize the squared error between the experimental and the modeled relationships. The experiment was performed twice to assess the reliability of α and l0 across days. The results showed that the reliability of the two parameters was good (α: ICC=0.82, SEM=6.1 m−1, CV=6.3% and l0: ICC=0.83, SEM=0.29 cm, CV=0.9%). Using a sensitivity analysis, it was shown that the numerical solution was unique. Overall, the findings may provide increased interest in the method proposed by Hoang et al. (2005). - Balance control is altered in obese individuals
Handrigan GA Corbeil P Simoneau M Teasdale N - J Biomech 43(2):383-384 (2010)
- Spontaneous body sway and postural stability.: Reply to letter to the editor by Dr. Handrigan and colleagues "Balance control is altered in obese individual"
Blaszczyk JW - J Biomech 43(2):385-386 (2010)
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