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Reaction Forces (reaction + force)
Kinds of Reaction Forces Selected AbstractsUse of a 3D dynamometric horseshoe to assess the effects of an all-weather waxed track and a crushed sand track at high speed trot: Preliminary studyEQUINE VETERINARY JOURNAL, Issue 3 2009D. Robin Summary Reasons for performing study: Track surface quality is considered a risk factor of musculoskeletal injuries. Ground reaction force (GRF) measurement is a relevant approach to study the interaction between the hoof and the ground. Force plates are not adapted to compare different surfaces at high speed. A 3D dynamometric horseshoe (DHS), using 4 triaxial piezoelectric sensors, has been developed and validated. Objectives: To use the DHS to compare the effects of 2 track surfaces, an all-weather waxed track and a crushed sand track, on the GRF in trotter horses under training conditions. Methods: The right forelimb of 3 French Trotters was equipped with the DHS. Two tracks were tested in a straight line: a crushed sand track (S) and an all-weather waxed track (W). For each session, trials were repeated 3 times in a Latin square design. The speed of the runs was set at 10 m/s and recorded synchronously. For each trial, data acquisition was performed at 600 Hz and 10 consecutive strides were analysed. Statistical differences were tested using a general linear model procedure. Results: The amplitude of the maximal longitudinal braking force (Fx) was significantly lower on W compared to S. This event happened about 6% later in the stance phase on W. The magnitude of the GRF at impact decreased on W. The average speed and the mean stance phase duration were not statistically different on both surfaces. The stride length was about 6 cm longer on S. Conclusion and potential relevance: This study demonstrates the ability and sensitivity of the DHS to discriminate track surfaces by measuring the GRF at high speed. These preliminary results show that the loading rate, the amplitude of horizontal braking and shock at impact are attenuated on W, which suggests a reduction of stresses in the distal limb. [source] Stochastic modeling of particle motion along a sliding conveyorAICHE JOURNAL, Issue 1 2010Kevin Cronin Abstract The sliding conveyor consists of a plane surface, known as the track, along which particles are induced to move by vibrating the bed sinusoidal with respect to time. The forces on the particle include gravity, bed reaction force and friction. Because friction coefficients are inherently variable, particle motion along the bed is erratic and unpredictable. A deterministic model of particle motion (where friction is considered to be known and invariant) is selected and its output validated by experiment. Two probabilistic solution techniques are developed and applied to the deterministic model, in order to account for the randomness that is present. The two methods consider particle displacement to be represented by discrete time and continuous time random processes, respectively, and permits analytical solutions for mean and variance in displacement versus time to be found. These are compared with experimental measurements of particle motion. Ultimately this analysis can be employed to calculate residence-time distributions for such items of process equipment. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Lower extremity walking mechanics of young individuals with asymptomatic varus knee alignmentJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 11 2009Joaquin A. Barrios Abstract Varus knee alignment is associated with an increased risk for developing medial knee osteoarthritis (OA). Medial knee OA is commonly associated with altered walking mechanics in the frontal and sagittal planes, as well as altered ground reaction forces. It is unknown whether these mechanics are present in young, asymptomatic individuals with varus knees. We expected that varus-aligned individuals would generally present with frontal plane mechanics that were similar to those reported for individuals with medial knee OA. The gait mechanics of 17 asymptomatic individuals with varus knees and 17 healthy, normally aligned controls were recorded. Gait parameters associated with medial knee OA were compared between groups. The individuals with varus knees exhibited greater knee external adduction moments, knee adduction, eversion, and lateral ground reaction force than the normally aligned individuals. In addition, those with varus knees also demonstrated increased knee flexion and external knee flexor moments during midstance. These results suggest that individuals with varus knees exhibit some, but not all, of the altered mechanics seen in medial knee OA. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1414,1419, 2009 [source] A biomechanical constraint on body mass in terrestrial mammalian predatorsLETHAIA, Issue 4 2008BORIS SORKIN Observations on extant mammals suggest that large body mass is selectively advantageous for a terrestrial predator on large herbivores. Yet, throughout the Cenozoic, some lineages of terrestrial mammalian predators attained greater maximal body masses than others. In order to explain this evolutionary pattern, the following biomechanical constraint on body mass is hypothesized. The stress, set up in the humerus by the bending moment of the peak ground reaction force at maximal running speed, increased with increasing body mass within a given lineage of terrestrial mammalian predators, resulting in a decreasing safety factor for the bone, until a predator could no longer attain the maximal running speed of its smaller relatives. The selective disadvantage of reduced maximal running speed prevented further increase of body mass within the lineage. This hypothesis is tested by examining the scaling of humeral dimensions and estimating maximal body masses in several lineages of terrestrial mammalian predators. Among lineages with otherwise similar postcranial skeletons, those with the more robust humeri at a given body mass attained the greater maximal body masses. Lineages with the longer deltoid ridges/deltopectoral crests of the humeri and/or the more distally located deltoid scars (suggesting the more distal insertions of the humeral flexors) at a given body mass also attained the greater maximal body masses. These results support the existence of the proposed biomechanical constraint, although paleoecological data suggest that some lineages of terrestrial mammalian predators failed to reach the limits, imposed by this constraint, because of the small size of available prey. [source] Biomechanics of the Fractured Medial Coronoid Process and the Isolated Anconeal Process in the Canine Elbow JointANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2005J. Maierl Introduction:, Elbow dysplasia is one of the most important orthopaedic diseases of the canine elbow joint. The medial coronoid process (MCP) and the anconeal process (AP) are involved with a high incidence. Aims:, The aim of this study was to clarify whether these processes are especially loaded resulting in osteoarthrosis. Material and Methods:, Elbow joints were examined from dogs of various breeds, with a body weight over 20 kg and an age ranging from 1 to 12 years. Only joints without damage to the articular cartilage have been included in this investigation. Articular surfaces have been evaluated macroscopically, subchondral bone density (long-term loading) and split-lines (long-term tensile loading) have been determined. Results:, In the humeral fossa olecrani, there was a distinct impression on the inner side of the lateral compared to the medial epicondyle. In the ulna, the MCP was much greater than the lateral coronoid indicating that the medial process has to support the humeral condyle to a higher extent. Subchondral split lines with a transverse orientation in the fossa olecrani gave evidence of long-term transverse tensile loading in this area. Split lines on the MCP were oriented radially as if the lateral edge was bent downwards. Subchondral bone density in the fossa olecrani was higher towards the lateral epicondyle in comparison to the medial. Furthermore, there was a bone density maximum on the medial part of the humeral condyle opposite of the MCP with its very high density. Discussion:, Gait analyses showed that there is a transverse, medially oriented force of up to 4% bodyweight acting on the paw during midstance. As the carpus is stable when slightly hyperextended during midstance loading there is a long lever arm from the ground up to an assumed rotation centre in the depth of the trochlear notch. The medially directed ground reaction force slightly rotates the forearm inwards causing a bending moment about the elbow joint, which leads to an increased pressure of the AP and the MCP. This bending in addition to sagittal loading is the reason for the high susceptibility of the MCP and AP. [source] Gravity and the quantum vacuum inertia hypothesisANNALEN DER PHYSIK, Issue 8 2005A. Rueda Abstract In previous work it has been shown that the electromagnetic quantum vacuum, or electromagnetic zero-point field, makes a contribution to the inertial reaction force on an accelerated object. We show that the result for inertial mass can be extended to passive gravitational mass. As a consequence the weak equivalence principle, which equates inertial to passive gravitational mass, appears to be explainable. This in turn leads to a straightforward derivation of the classical Newtonian gravitational force. We call the inertia and gravitation connection with the vacuum fields the quantum vacuum inertia hypothesis. To date only the electromagnetic field has been considered. It remains to extend the hypothesis to the effects of the vacuum fields of the other interactions. We propose an idealized experiment involving a cavity resonator which, in principle, would test the hypothesis for the simple case in which only electromagnetic interactions are involved. This test also suggests a basis for the free parameter ,(,) which we have previously defined to parametrize the interaction between charge and the electromagnetic zero-point field contributing to the inertial mass of a particle or object. [source] Improving realism of a surgery simulator: linear anisotropic elasticity, complex interactions and force extrapolationCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3 2002Guillaume Picinbono Abstract In this article, we describe the latest developments of the minimally invasive hepatic surgery simulator prototype developed at INRIA. The goal of this simulator is to provide a realistic training test bed to perform laparoscopic procedures. Therefore, its main functionality is to simulate the action of virtual laparoscopic surgical instruments for deforming and cutting tridimensional anatomical models. Throughout this paper, we present the general features of this simulator including the implementation of several biomechanical models and the integration of two force-feedback devices in the simulation platform. More precisely, we describe three new important developments that improve the overall realism of our simulator. First, we have developed biomechanical models, based on linear elasticity and finite element theory, that include the notion of anisotropic deformation. Indeed, we have generalized the linear elastic behaviour of anatomical models to ,transversally isotropic' materials, i.e. materials having a different behaviour in a given direction. We have also added to the volumetric model an external elastic membrane representing the ,liver capsule', a rather stiff skin surrounding the liver, which creates a kind of ,surface anisotropy'. Second, we have developed new contact models between surgical instruments and soft tissue models. For instance, after detecting a contact with an instrument, we define specific boundary constraints on deformable models to represent various forms of interactions with a surgical tool, such as sliding, gripping, cutting or burning. In addition, we compute the reaction forces that should be felt by the user manipulating the force-feedback devices. The last improvement is related to the problem of haptic rendering. Currently, we are able to achieve a simulation frequency of 25,Hz (visual real time) with anatomical models of complex geometry and behaviour. But to achieve a good haptic feedback requires a frequency update of applied forces typically above 300,Hz (haptic real time). Thus, we propose a force extrapolation algorithm in order to reach haptic real time. Copyright © 2002 John Wiley & Sons, Ltd. [source] Operator-splitting method for real-time substructure testingEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2006Bin Wu Abstract It has been shown that the operator-splitting method (OSM) provides explicit and unconditionally stable solutions for quasi-static pseudo-dynamic substructure testing. However, the OSM provides only an explicit target displacement but not an explicit target velocity, so that it is essentially an implicit method for real-time substructure testing (RST) when the velocity-dependent restoring force is considered. This paper proposes a target velocity formulation based on the forward difference of the predicted displacements so as to render the OSM explicit for RST. The stability and accuracy of the resulting OSM-RST algorithm are investigated. It is shown that the OSM-RST is unconditionally stable so long as the non-linear stiffness and damping are of the softening type (i.e. the tangent stiffness and damping never exceed the initial values). The stability of the OSM-RST for structures with infinite tangent damping coefficient or stiffness is also proved, and the stability of the method for MDOF structures with a non-classical damping matrix is demonstrated by an energy criterion. The effects of actuator delay and compensation are analysed based on the bilinear approximation of the actuator step response. Experiments on damped SDOF and MDOF structures verify that the stability of the OSM-RST is preserved when the experimental substructure generates velocity-dependent reaction forces, whereas the stability of real-time substructure tests based on the central difference method is worsened by the damping of the specimen. Copyright © 2005 John Wiley & Sons, Ltd. [source] Mepivacaine local anaesthetic duration in equine palmar digital nerve blocksEQUINE VETERINARY JOURNAL, Issue 8 2004L. A. BIDWELL Summary Reasons for performing study: Perineural analgesics are used for lameness diagnosis but the duration of effect, knowledge of which would provide valuable information when performing subsequent blocks, is unknown. Objective: To evaluate the duration of a palmar digital nerve block using force plate measurements. Methods: Ten horses diagnosed with unilateral navicular syndrome were trotted at range of 3 ± 0.15 m/sec over a force plate to record ground reaction forces for 5 trials of each forelimb. Data were recorded before nerve block, and then at 15 mins, 1, 2 and 24 h post nerve block. Results: Before nerve block, peak vertical force (mean ± s.e.) was significantly higher in the contralateral forelimb (CL = 5345 ± 188 N) than in the lame forelimb (L = 4256 ± 204 N; P<0.05). At 15 mins post nerve block there was no significant difference between the 2 forelimbs (CL = 5140 ± 184 N; L = 5126 ± 129 N), and this remained the case for 1 h. By 2 h, the mean score for the lame leg had decreased (L = 4642 ± 182 N) but was still greater than preblock. By 24 h, vertical forces had returned to preblock values. Conclusions: The palmar digital nerve block was fully effective between 15 mins and 1 h. The analgesic effect began to subside between 1 and 2 h but sufficient analgesia persisted to affect gait characteristics beyond 2 h. Potential relevance: When using a palmar digital nerve block, it is important to perform lameness evaluations between 15 mins and 1 h to be sure of effective nerve blockade. [source] Joint moments in the distal forelimbs of jumping horses during landingEQUINE VETERINARY JOURNAL, Issue 4 2001L. S. MEERSHOEK Summary Tendon injuries are an important problem in athletic horses and are probably caused by excessive loading of the tendons during demanding activities. As a first step towards understanding these injuries, the tendon loading was quantified during jump landings. Kinematics and ground reaction forces were collected from the leading and trailing forelimbs of 6 experienced jumping horses. Joint moments were calculated using inverse dynamic analysis. It was found that the variation of movement and loading patterns was small, both within and between horses. The peak flexor joint moments in the coffin and fetlock joints were larger in the trailing limb (,0.62 and ,2.44 Nm/kg bwt, respectively) than in the leading limb (,0.44 and ,1.93 Nm/kg bwt, respectively) and exceeded literature values for trot by 82 and 45%. Additionally, there was an extensor coffin joint moment in the first half of the stance phase of the leading limb (peak value 0.26 ± 0.18 Nm/kg bwt). From these results, it was concluded that the loading of the flexor tendons during landing was higher in the trailing than in the leading limb and that there was an unexpected loading of the extensor tendon in the leading limb. [source] Comparison of biomechanical gait parameters of young children with haemophilia and those of age-matched peersHAEMOPHILIA, Issue 2 2009D. STEPHENSEN Summary., Quality of life for children with haemophilia has improved since the introduction of prophylaxis. The frequency of joint haemorrhages has reduced, but the consequences of reduced bleeding on the biomechanical parameters of walking are not well understood. This study explored the differences in sagittal plane biomechanics of walking between a control group (Group 1) of normal age-matched children and children with haemophilia (Group 2) with a target ankle joint. A motion capture system and two force platforms were used to collect sagittal plane kinematic, kinetic and temporal,spatial data during walking of 14 age-matched normal children and 14 children with haemophilia aged 7,13 years. Group differences in maximum and minimum flexion/extension angles and moments of the hip, knee and ankle joints, ground reaction forces and temporal,spatial gait cycle parameters were analysed using one-way anova. Significant changes (P < 0.05) in kinematic and kinetic parameters but not temporal,spatial parameters were found in children with haemophilia; greater flexion angles and external moments of force at the knee, greater ankle plantarflexion external moments and lower hip flexion external moments. These results suggest that early biomechanical changes are present in young haemophilic children with a history of a target ankle joint and imply that lower limb joint function is more impaired than current clinical evaluations indicate. Protocols and quantitative data on the biomechanical gait pattern of children with haemophilia reported in this study provide a baseline to evaluate lower limb joint function and clinical progression. [source] Analysis of single rock blocks for general failure modes under conservative and non-conservative forcesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2007F. Tonon Abstract After describing the kinematics of a generic rigid block subjected to large rotations and displacements, the Udwadia's General Principle of Mechanics is applied to the dynamics of a rigid block with frictional constraints to show that the reaction forces and moments are indeterminate. Thus, the paper presents an incremental-iterative algorithm for analysing general failure modes of rock blocks subject to generic forces, including non-conservative forces such as water forces. Consistent stiffness matrices have been developed that fully exploit the quadratic convergence of the adopted Newton,Raphson iterative scheme. The algorithm takes into account large block displacements and rotations, which together with non-conservative forces make the stiffness matrix non-symmetric. Also included in the algorithm are in situ stress and fracture dilatancy, which introduces non-symmetric rank-one modifications to the stiffness matrix. Progressive failure is captured by the algorithm, which has proven capable of detecting numerically challenging failure modes, such as rotations about only one point. Failure modes may originate from a limit point or from dynamic instability (divergence or flutter); equilibrium paths emanating from bifurcation points are followed by the algorithm. The algorithm identifies both static and dynamic failure modes. The calculation of the factor of safety comes with no overhead. Examples show the equilibrium path of a rock block that undergoes slumping failure must first pass through a bifurcation point, unless the block is laterally constrained. Rock blocks subjected to water forces (or other non-conservative forces) may undergo flutter failure before reaching a limit point. Copyright © 2007 John Wiley & Sons, Ltd. [source] Non-locking tetrahedral finite element for surgical simulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2009Grand Roman Joldes Abstract To obtain a very fast solution for finite element models used in surgical simulations, low-order elements, such as the linear tetrahedron or the linear under-integrated hexahedron, must be used. Automatic hexahedral mesh generation for complex geometries remains a challenging problem, and therefore tetrahedral or mixed meshes are often necessary. Unfortunately, the standard formulation of the linear tetrahedral element exhibits volumetric locking in case of almost incompressible materials. In this paper, we extend the average nodal pressure (ANP) tetrahedral element proposed by Bonet and Burton for a better handling of multiple material interfaces. The new formulation can handle multiple materials in a uniform way with better accuracy, while requiring only a small additional computation effort. We discuss some implementation issues and show how easy an existing Total Lagrangian Explicit Dynamics algorithm can be modified in order to support the new element formulation. The performance evaluation of the new element shows the clear improvement in reaction forces and displacements predictions compared with the ANP element in case of models consisting of multiple materials. Copyright © 2008 John Wiley & Sons, Ltd. [source] Optimization-based dynamic human walking prediction: One step formulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2009Yujiang Xiang Abstract A new methodology is introduced in this work to simulate normal walking using a spatial digital human model. The proposed methodology is based on an optimization formulation that minimizes the dynamic effort of people during walking while considering associated physical and kinematical constraints. Normal walking is formulated as a symmetric and cyclic motion. Recursive Lagrangian dynamics with analytical gradients for all the constraints and objective function are incorporated in the optimization process. Dynamic balance of the model is enforced by direct use of the equations of motion. In addition, the ground reaction forces are calculated using a new algorithm that enforces overall equilibrium of the human skeletal model. External loads on the human body, such as backpacks, are also included in the formulation. Simulation results with the present methodology show good correlation with the experimental data obtained from human subjects and the existing literature. Copyright © 2009 John Wiley & Sons, Ltd. [source] Ten-Year Longitudinal Relationship Between Physical Activity and Lumbar Bone Mass in (Young) Adults,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 2 2003Ingrid Bakker Abstract Little is known about the influence of long-term daily physical activity (PA) on lumbar bone mass after peak bone mass has been reached, that is, during [young] adulthood. The purpose of this study was to investigate the longitudinal relationship between PA and lumbar bone mineral density (LBMD) in healthy subjects over a 10-year period. The data reported here relate to 225 male and 241 female participants in the Amsterdam Growth and Health Longitudinal Study, who were measured at the mean ages of 27, 32, and/or 36. LBMD, habitual daily PA, total body weight, and calcium intake were assessed at each measurement point. The effects of two aspects of PA were analyzed: the mechanical (MECHPA; sum of all ground reaction forces) and metabolic (METPA; weighted metabolic score of intensity, frequency, and duration) components, each within a separate model. Multilevel analysis was used to investigate the relationship between PA and LBMD over the 10-year period. Gender, total body weight, and calcium intake were included in the analysis as covariates. The results indicated that MECHPA was a significant positive linear predictor of LBMD for males (r = 0.09; p < 0.001) but not for females. For the METPA, no linear longitudinal relationship with LBMD was found. The results suggest that there is a metabolic threshold at which extra PA becomes "deleterious" and METPA in its totality becomes ineffective for LBMD. It is concluded that during the (young) adult period, between 27 and 36 years of age, PA causing mechanical loading on the skeleton has a small positive influence on LBMD in males. [source] Jumping Improves Hip and Lumbar Spine Bone Mass in Prepubescent Children: A Randomized Controlled TrialJOURNAL OF BONE AND MINERAL RESEARCH, Issue 1 2001Robyn K. Fuchs Abstract Physical activity during childhood is advocated as one strategy for enhancing peak bone mass (bone mineral content [BMC]) as a means to reduce osteoporosis-related fractures. Thus, we investigated the effects of high-intensity jumping on hip and lumbar spine bone mass in children. Eighty-nine prepubescent children between the ages of 5.9 and 9.8 years were randomized into a jumping (n = 25 boys and n = 20 girls) or control group (n = 26 boys and n = 18 girls). Both groups participated in the 7-month exercise intervention during the school day three times per week. The jumping group performed 100, two-footed jumps off 61-cm boxes each session, while the control group performed nonimpact stretching exercises. BMC (g), bone area (BA; cm2), and bone mineral density (BMD; g/cm2) of the left proximal femoral neck and lumbar spine (L1-L4) were assessed by dual-energy X-ray absorptiometry (DXA; Hologic QDR/4500-A). Peak ground reaction forces were calculated across 100, two-footed jumps from a 61-cm box. In addition, anthropometric characteristics (height, weight, and body fat), physical activity, and dietary calcium intake were assessed. At baseline there were no differences between groups for anthropometric characteristics, dietary calcium intake, or bone variables. After 7 months, jumpers and controls had similar increases in height, weight, and body fat. Using repeated measures analysis of covariance (ANCOVA; covariates, initial age and bone values, and changes in height and weight) for BMC, the primary outcome variable, jumpers had significantly greater 7-month changes at the femoral neck and lumbar spine than controls (4.5% and 3.1%, respectively). In repeated measures ANCOVA of secondary outcomes (BMD and BA), BMD at the lumbar spine was significantly greater in jumpers than in controls (2.0%) and approached statistical significance at the femoral neck (1.4%; p = 0.085). For BA, jumpers had significantly greater increases at the femoral neck area than controls (2.9%) but were not different at the spine. Our data indicate that jumping at ground reaction forces of eight times body weight is a safe, effective, and simple method of improving bone mass at the hip and spine in children. This program could be easily incorporated into physical education classes. [source] Annulus cells release ATP in response to vibratory loading in vitroJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 4 2003Satoru Yamazaki Abstract Mechanical forces regulate the developmental path and phenotype of a variety of tissues and cultured cells. Vibratory loading as a mechanical stimulus occurs in connective tissues due to energy returned from ground reaction forces, as well as a mechanical input from use of motorized tools and vehicles. Structures in the spine may be particularly at risk when exposed to destructive vibratory stimuli. Cells from many tissues respond to mechanical stimuli, such as fluid flow, by increasing intracellular calcium concentration ([Ca2+]ic) and releasing adenosine 5,-triphosphate (ATP), extracellularly, as a mediator to activate signaling pathways. Therefore, we examined whether ATP is released from rabbit (rAN) and human (hAN) intervertebral disc annulus cells in response to vibratory loading. ATP release from annulus cells by vibratory stimulation as well as in control cells was quantitated using a firefly luciferin-luciferase assay. Cultured hAN and rAN cells had a basal level of extracellular ATP ([ATP]ec) in the range of 1,1.5 nM. Vibratory loading of hAN cells stimulated ATP release, reaching a net maximum [ATP] within 10 min of continuous vibration, and shortly thereafter, [ATP] declined and returned to below baseline level. [ATP] in the supernatant fluid of hAN cells was significantly reduced compared to the control level when the cells received vibration for longer than 15 min. In rAN cells, [ATP] was increased in response to vibratory loading, attaining a level significantly greater than that of the control after 30 min of continuous vibration. Results of the current study show that resting annulus cells secrete ATP and maintain a basal [ATP]ec. Annulus cells may use this nucleotide as a signaling messenger in an autocrine/paracrine fashion in response to vibratory loading. Rapid degradation of ATP to ADP may alternatively modulate cellular responses. It is hypothesized that exposure to repetitive, complex vibration regimens may activate signaling pathways that regulate matrix destruction in the disc. As in tendon cells, ATP may block subsequent responses to load and modulate the vibration response. Rabbit annulus cells were used as a readily obtainable source of cells in development of an animal model for testing effects of vibration on the disc. Human cells obtained from discarded surgical specimens were used to correlate responses of animal to human cells. © 2003 Wiley-Liss, Inc. [source] Small unilateral jaw gap variations: equilibrium changes, co-contractions and joint forcesJOURNAL OF ORAL REHABILITATION, Issue 10 2009H. J. SCHINDLER Summary, After complex prosthetic reconstructions, small differences in vertical distances between the left and right side of the jaw may occur during jaw closing, nevertheless providing bilateral tooth contacts in intercuspation by small deformations of the mandible. Their effects on the co-contraction of the masticatory muscles, the temporomandibular joint reaction forces, and the point of application of the resultant bite force vector in the maxillary occlusion plane , the so-called reduction point , have not been investigated, thus far simultaneously in one sample. The main goal of this study was to investigate variations of these measures in an experimental intercuspation simulated by one anterior and two posterior force transmission points. [source] Time series analysis of jaw muscle contraction and tissue deformation during mastication in miniature pigsJOURNAL OF ORAL REHABILITATION, Issue 1 2004Z. J. Liu summary, Masticatory muscle contraction causes both jaw movement and tissue deformation during function. Natural chewing data from 25 adult miniature pigs were studied by means of time series analysis. The data set included simultaneous recordings of electromyography (EMG) from bilateral masseter (MA), zygomaticomandibularis (ZM) and lateral pterygoid muscles, bone surface strains from the left squamosal bone (SQ), condylar neck (CD) and mandibular corpus (MD), and linear deformation of the capsule of the jaw joint measured bilaterally using differential variable reluctance transducers. Pairwise comparisons were examined by calculating the cross-correlation functions. Jaw-adductor muscle activity of MA and ZM was found to be highly cross-correlated with CD and SQ strains and weakly with MD strain. No muscle's activity was strongly linked to capsular deformation of the jaw joint, nor were bone strains and capsular deformation tightly linked. Homologous muscle pairs showed the greatest synchronization of signals, but the signals themselves were not significantly more correlated than those of non-homologous muscle pairs. These results suggested that bone strains and capsular deformation are driven by different mechanical regimes. Muscle contraction and ensuing reaction forces are probably responsible for bone strains, whereas capsular deformation is more likely a product of movement. [source] Lower extremity walking mechanics of young individuals with asymptomatic varus knee alignmentJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 11 2009Joaquin A. Barrios Abstract Varus knee alignment is associated with an increased risk for developing medial knee osteoarthritis (OA). Medial knee OA is commonly associated with altered walking mechanics in the frontal and sagittal planes, as well as altered ground reaction forces. It is unknown whether these mechanics are present in young, asymptomatic individuals with varus knees. We expected that varus-aligned individuals would generally present with frontal plane mechanics that were similar to those reported for individuals with medial knee OA. The gait mechanics of 17 asymptomatic individuals with varus knees and 17 healthy, normally aligned controls were recorded. Gait parameters associated with medial knee OA were compared between groups. The individuals with varus knees exhibited greater knee external adduction moments, knee adduction, eversion, and lateral ground reaction force than the normally aligned individuals. In addition, those with varus knees also demonstrated increased knee flexion and external knee flexor moments during midstance. These results suggest that individuals with varus knees exhibit some, but not all, of the altered mechanics seen in medial knee OA. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1414,1419, 2009 [source] Acute botulinum toxin-induced muscle weakness in the anterior cruciate ligament-deficient rabbitJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2005David Longino Abstract We established botulinum type-A toxin (BTX-A) injections as a powerful tool to cause knee extensor weakness in New Zealand White (NZW) rabbits. The purpose of this study was to determine if BTX-A induced quadriceps weakness causes muscle dysfunction beyond that caused by anterior cruciate ligament (ACL) transection in the knee of NZW rabbits. Twenty animals were randomly divided into four study groups (n = 5 each); uninjected controls, BTX-A injection alone, ACL transection alone, BTX-A injection and ACL transection combined. Isometric knee extensor torque, quadriceps muscle mass, and vertical and anterior,posterior ground reaction forces were measured four weeks post single (BTX-A and ACL), unilateral intervention. Muscle weakness, muscle atrophy and decrease in ground reaction forces were all significantly greater for the experimental compared to the untreated contralateral legs. BTX-A injection produced a greater deficit in quadriceps mass and knee extensor torque than ACL transection alone, but produced smaller deficits in the ground reaction forces. ACL transection superimposed on BTX-A injection did not change either knee extensor torque production or muscle mass. Together these results suggest that BTX-A injection causes great force and muscle mass deficits, and affects functional gait in a significant manner, but it has no measurable functional effect when superimposed on ACL transection, at least not in the acute protocol tested here. Hopefully, BTX-A injection for acutely enhancing the degree of muscle weakness in otherwise untreated animals, or in experimental models of osteoarthritis, will help in investigating the role of muscle weakness in joint degeneration. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Proposed model of botulinum toxin-induced muscle weakness in the rabbitJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2005D. Longino Abstract Osteoarthritic patients show only a weak association between radiographic signs of joint disease and joint pain and disability. Conversely, muscle weakness is one of the earliest and most common symptoms of patients with osteoarthritis (OA). However, while many experimental models of osteoarthritis include a component of muscular weakness, no model has isolated this factor satisfactorily. Therefore, the purpose of this study was to develop and validate an experimental animal model of muscle weakness for future use in the study of OA. Botulinum Type-A toxin (BTX-A) was uni-laterally injected into the quadriceps musculature of New Zealand white rabbits (3.5 unit/kg). Isometric knee extensor torque at a range of knee angles and stimulation frequencies, and quadriceps muscle mass, were quantified for control animals, and at one- and six-months post-repeated injections, in both, the experimental and the contralateral hindlimb. Ground reaction forces were measured in all animals while hopping across two force platforms. Isometric knee extension torque and quadriceps muscle mass was systematically decreased in the experimental hindlimb. Vertical ground reaction forces in the push off phase of hopping were also decreased in the experimental compared to control hindlimbs. We conclude that BTX-A injection into the rabbit musculature creates functional and absolute muscle weakness in a reproducible manner. Therefore, this model may be used to systematically study the possible effects of muscle weakness on joint degeneration, either as an isolated intervention, or in combination with other interventions (anterior cruciate ligament transection, meniscectomy) known to create knee joint degeneration. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] The initial phase of fracture healing is specifically sensitive to mechanical conditionsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2003Petra Klein Abstract Interfragmentary movements affect the quality and quantity of callus formation. The mounting plane of monolateral external fixators may give direction to those movements. Therefore, the aim of this study was to determine the influence of the fixator mounting plane on the process of fracture healing. Identically configured fixators were mounted either medially or anteromedially on the tibiae of sheep. Interfragmentary movements and ground reaction forces were evaluated in vivo during a nine week period. Histomorphological and biomechanical parameters described the bone healing processes. Changing only the mounting plane led to a modification of interfragmentary movements in the initial healing phase. The difference in interfragmentary movements between the groups was only significant during the first post-operative period. However, these initial differences in mechanical conditions influenced callus tissue formation significantly. The group with the anteromedially mounted fixator, initially showing significantly more interfragmentary movements, ended up with a significantly smaller callus diameter and a significantly higher callus stiffness as a result of advanced fracture healing. This demonstrates that the initial phase of healing is sensitive to mechanical conditions and influences the course of healing. Therefore, initial mechanical stability of an osteosynthesis should be considered an important factor in clinical fracture treatment. © 2003 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] The clinical spectrum of freezing of gait in Parkinson's disease,MOVEMENT DISORDERS, Issue S2 2008Yasuyuki Okuma MD Abstract Freezing of gait (FOG) is a common and very disabling symptom in Parkinson's disease (PD). It is usually observed in the advanced stage of the disease, although a mild form can be seen in the early stage. Although some studies have suggested that longer duration of dopaminergic treatment is associated with FOG, the disease progression alone may be responsible for the development of FOG. FOG can be experienced on turning, in narrow spaces, while reaching a destination, and in stressful situations. In PD, FOG is strongly associated with motor fluctuation. FOG is commonly observed in the "off" state and is observed less frequently in the "on" state. Dual tasking (cognitive load) aggravates FOG. Visual or auditory cues often resolve FOG. Analysis of gait revealed that the stepping rhythm suddenly jumps into high frequency (4,5 Hz) in FOG (hastening), and that floor reaction forces are disregulated. Since the hastening phenomenon was also reported in patients with lesions in the striatum and/or the frontal lobe, fronto-basal ganglia projections are considered essential for FOG. Careful observation and gait pattern analysis may lead to a successful management of individual PD patients with FOG. © 2008 Movement Disorder Society [source] Plastification and Damage in Wheel-Rail Rolling Contact , Case Study on a CrossingPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Martina Wiest A fully three-dimensional, dynamic model for a wheel running over a crossing is developed using an explicit finite element program. The full mass of the wheel and the crossing and elastic-plastic material behaviour are considered. The damage in the contact area is investigated with a very dense mesh taken from the dynamic model using a submodelling technique. With this kind of calculations the stresses and strains produced in the wheel and the crossing during the cross-over process can be determined, as well as the respective reaction forces in the bedding and the axle. Calculations for different crossing-geometries are performed. Finally a damage indicator is introduced to identify the probable location of crack initiation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Waddling and toddling: The biomechanical effects of an immature gaitAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010Libby W. Cowgill Abstract Femoral shape changes during the course of human growth, transitioning from a subcircular tube to a teardrop-shaped diaphysis with a posterior pilaster. Differences between immature and mature bipedalism and body shape may generate different loads, which, in turn, may influence femoral modeling and remodeling during the course of the human lifespan. This study uses two different approaches to evaluate the hypotheses that differences in gait between young and mature walkers result in differences in ground reaction forces (GRFs) and that the differences in loading regimes between young children and adults will be reflected in the geometric structure of the midshaft femur. The results of this analysis indicate that GRFs differ between young walkers and adults in that normalized mediolateral (ML) forces are significantly higher in younger age groups. In addition, these differences between children and adults in the relative level of ML bending force are reflected in changes in femoral geometry during growth. During the earlier stages of human development, immature femoral diaphyses are heavily reinforced in approximately ML plane. The differences in gait between mature and immature walkers, and hence the differences in femoral shape, are likely partially a product of a minimal bicondylar angle and relatively broad body in young children. Am J Phys Anthropol 143:52,61, 2010. © 2010 Wiley-Liss, Inc. [source] The interplay between speed, kinetics, and hand postures during primate terrestrial locomotionAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2010Biren A. Patel Abstract Nonprimate terrestrial mammals may use digitigrade postures to help moderate distal limb joint moments and metapodial stresses that may arise during high-speed locomotion with high-ground reaction forces (GRF). This study evaluates the relationships between speed, GRFs, and distal forelimb kinematics in order to evaluate if primates also adopt digitigrade hand postures during terrestrial locomotion for these same reasons. Three cercopithecine monkey species (Papio anubis, Macaca mulatta, Erythrocebus patas) were videotaped moving unrestrained along a horizontal runway instrumented with a force platform. Three-dimensional forelimb kinematics and GRFs were measured when the vertical force component reached its peak. Hand posture was measured as the angle between the metacarpal segment and the ground (MGA). As predicted, digitigrade hand postures (larger MGA) are associated with shorter GRF moment arms and lower wrist joint moments. Contrary to expectations, individuals used more palmigrade-like (i.e. less digitigrade) hand postures (smaller MGA) when the forelimb was subjected to higher forces (at faster speeds) resulting in potentially larger wrist joint moments. Accordingly, these primates may not use their ability to alter their hand postures to reduce rising joint moments at faster speeds. Digitigrady at slow speeds may improve the mechanical advantage of antigravity muscles crossing the wrist joint. At faster speeds, greater palmigrady is likely caused by joint collapse, but this posture may be suited to distribute higher GRFs over a larger surface area to lower stresses throughout the hand. Thus, a digitigrade hand posture is not a cursorial (i.e. high speed) adaptation in primates and differs from that of other mammals. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source] Not so fast: Speed effects on forelimb kinematics in cercopithecine monkeys and implications for digitigrade postures in primatesAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2009Biren A. Patel Abstract Terrestrial mammals are characterized by their digitigrade limb postures, which are proposed to increase effective limb length (ELL) to achieve preferred or higher locomotor speeds more efficiently. Accordingly, digitigrade postures are associated with cursorial locomotion. Unlike most medium- to large-sized terrestrial mammals, terrestrial cercopithecine monkeys lack most cursorial adaptations, but still adopt digitigrade hand postures. This study investigates when and why terrestrial cercopithecine monkeys adopt digitigrade hand postures during quadrupedal locomotion. Three cercopithecine species (Papio anubis, Macaca mulatta, Erythrocebus patas) were videotaped moving unrestrained along a horizontal runway at a range of speeds (0.4,3.4 m/s). Three-dimensional forelimb kinematic data were recorded during forelimb support. Hand posture was measured as the angle between the metacarpal segments and the ground (MGA). As predicted, a larger MGA was correlated with a longer ELL. At slower speeds, subjects used digitigrade postures (larger MGA), however, contrary to expectations, all subjects used more palmigrade hand postures (smaller MGA) at faster speeds. Digitigrade postures at slower speeds may lower cost of transport by increasing ELL and step lengths. At higher speeds, palmigrade postures may be better suited to spread out high ground reaction forces across a larger portion of the hand thereby potentially decreasing stresses in hand bones. It is concluded that a digitigrade forelimb posture in primates is not an adaptation for high speed locomotion. Accordingly, digitigrady may have evolved for different reasons in primates compared to other mammalian lineages. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source] Locomotor variation and bending regimes of capuchin limb bonesAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009Brigitte Demes Abstract Primates are very versatile in their modes of progression, yet laboratory studies typically capture only a small segment of this variation. In vivo bone strain studies in particular have been commonly constrained to linear locomotion on flat substrates, conveying the potentially biased impression of stereotypic long bone loading patterns. We here present substrate reaction forces (SRF) and limb postures for capuchin monkeys moving on a flat substrate ("terrestrial"), on an elevated pole ("arboreal"), and performing turns. The angle between the SRF vector and longitudinal axes of the forearm or leg is taken as a proxy for the bending moment experienced by these limb segments. In both frontal and sagittal planes, SRF vectors and distal limb segments are not aligned, but form discrepant angles; that is, forces act on lever arms and exert bending moments. The positions of the SRF vectors suggest bending around oblique axes of these limb segments. Overall, the leg is exposed to greater moments than the forearm. Simulated arboreal locomotion and turns introduce variation in the discrepancy angles, thus confirming that expanding the range of locomotor behaviors studied will reveal variation in long bone loading patterns that is likely characteristic of natural locomotor repertoires. "Arboreal" locomotion, even on a linear noncompliant branch, is characterized by greater variability of force directions and discrepancy angles than "terrestrial" locomotion (significant for the forearm only), partially confirming the notion that life in trees is associated with greater variation in long bone loading. Directional changes broaden the range of external bending moments even further. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] Functional analysis of the gibbon foot during terrestrial bipedal walking: Plantar pressure distributions and three-dimensional ground reaction forcesAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2005Evie Vereecke Abstract This paper gives a detailed analysis of bipedal walking in the white-handed gibbon, based on collected pressure and force data. These data were obtained from four gibbons in the Wild Animal Park, Planckendael, Belgium, by using a walkway with integrated force plate and pressure mat. This is the first study that collects and describes dynamic plantar pressure data of bipedally walking gibbons, and combines these with force plate data. The combination of these data with previously described roll-off patterns of gibbons, based on general observations, video images, force plates, and EMG data, gives us a detailed description of foot function during gibbon bipedalism. In addition, we compare the observed characteristics of hylobatid bipedalism with the main characteristics of bonobo and human bipedalism. We found that gibbons are midfoot/heel plantigrade, and lack the typical heel-strike of other hominoids. The hallux is widely abducted and touches down at the onset of the stance phase, which results in an L-shaped course of the center of pressure. The vertical force curve is trapezoid to triangular in shape, with high peak values compared to humans. The braking component is shorter than the accelerating component, and shortens further at higher walking velocities. Speed has a significant influence on the forefoot peak pressures and on most of the defined gait parameters (e.g., vertical force peak), and it alters the foot contact pattern as well. The investigation of existing form-function relationships in nonhuman primates is essential for the interpretation of fossil remains, and might help us understand the evolution of habitual bipedal walking in hominids. Am J Phys Anthropol, 2005. © 2005 Wiley-Liss, Inc. [source] | |||||||||||||||||||