Search for: bio-mechanical-models
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    An optimization-based method for prediction of lumbar spine segmental kinematics from the measurements of thorax and pelvic kinematics

    , Article International Journal for Numerical Methods in Biomedical Engineering ; July , 2015 , Volume 31, Issue 12 ; 20407939 (ISSN) Shojaei, I ; Arjmand, N ; Bazrgari, B ; Sharif University of Technology
    Wiley-Blackwell  2015
    Given measurement difficulties, earlier modeling studies have often used some constant ratios to predict lumbar segmental kinematics from measurements of total lumbar kinematics. Recent imaging studies suggested distribution of lumbar kinematics across its vertebrae changes with trunk rotation, lumbar posture, and presence of load. An optimization-based method is presented and validated in this study to predict segmental kinematics from measured total lumbar kinematics. Specifically, a kinematics-driven biomechanical model of the spine is used in a heuristic optimization procedure to obtain a set of segmental kinematics that, when prescribed to the model, were associated with the minimum... 

    Optimization of a passenger occupied seat with suspension system exposed to vertical vibrations using genetic algorithms

    , Article Journal of Vibroengineering ; Volume 15, Issue 2 , 2013 , Pages 979-991 ; 13928716 (ISSN) Afkar, A ; Javanshir, I ; Ahmadian, M. T ; Ahmadi, H ; Sharif University of Technology
    This paper presents a biomechanical model with seven degrees of freedom as a seated human exposed to vertical vibration. Experimental data is used to find the stiffness and damping parameters of the model. The data includes values of seat to head transmissibility, driving point mechanical impedance and apparent mass. The multi-objective function is used to obtain theoretical results similar to three different experimental cases. The unknown coefficients are calculated by a genetic algorithm. Improved results, in comparison with previous models, are achieved from the presented model. Next, this modified model is assembled on a quarter car and parameters of the cushion and the suspension... 

    Effects of sex, age, body height and body weight on spinal loads: Sensitivity analyses in a subject-specific trunk musculoskeletal model

    , Article Journal of Biomechanics ; Volume 49, Issue 14 , 2016 , Pages 3492-3501 ; 00219290 (ISSN) Ghezelbash, F ; Shirazi Adl, A ; Arjmand, N ; El Ouaaid, Z ; Plamondon, A ; Meakin, J. R ; Sharif University of Technology
    Elsevier Ltd 
    Subject-specific parameters influence spinal loads and the risk of back disorders but their relative effects are not well understood. The objective of this study is to investigate the effects of changes in age (35–60 years), sex (male, female), body height (BH: 150–190 cm) and body weight (BW: 50–120 kg) on spinal loads in a full-factorial simulation using a personalized (spine kinematics, geometry, musculature and passive properties) kinematics driven musculoskeletal trunk finite element model. Segmental weight distribution (magnitude and location along the trunk) was estimated by a novel technique to accurately represent obesity. Five symmetric sagittal loading conditions were considered,... 

    Artificial neural networks to predict 3D spinal posture in reaching and lifting activities; Applications in biomechanical models

    , Article Journal of Biomechanics ; Volume 49, Issue 13 , Volume 49, Issue 13 , 2016 , Pages 2946-2952 ; 00219290 (ISSN) Gholipour, A ; Arjmand, N ; Sharif University of Technology
    Elsevier Ltd 
    Spinal posture is a crucial input in biomechanical models and an essential factor in ergonomics investigations to evaluate risk of low back injury. In vivo measurement of spinal posture through the common motion capture techniques is limited to equipped laboratories and thus impractical for workplace applications. Posture prediction models are therefore considered indispensable tools. This study aims to investigate the capability of artificial neural networks (ANNs) in predicting the three-dimensional posture of the spine (S1, T12 and T1 orientations) in various activities. Two ANNs were trained and tested using measurements from spinal postures of 40 male subjects by an inertial tracking... 

    A novel stability-based EMG-assisted optimization method for the spine

    , Article Medical Engineering and Physics ; Volume 58 , 2018 , Pages 13-22 ; 13504533 (ISSN) Samadi, S ; Arjmand, N ; Sharif University of Technology
    Elsevier Ltd  2018
    Traditional electromyography-assisted optimization (TEMG) models are commonly employed to compute trunk muscle forces and spinal loads for the design of clinical/treatment and ergonomics/prevention programs. These models calculate muscle forces solely based on moment equilibrium requirements at spinal joints. Due to simplifications/assumptions in the measurement/processing of surface EMG activities and in the presumed muscle EMG-force relationship, these models fail to satisfy stability requirements. Hence, the present study aimed to develop a novel stability-based EMG-assisted optimization (SEMG) method applied to a musculoskeletal spine model in which trunk muscle forces were estimated by... 

    Biomechanical assessment of the niosh lifting equation in asymmetric load-handling activities using a detailed musculoskeletal model

    , Article Human Factors ; Volume 61, Issue 2 , 2019 , Pages 191-202 ; 00187208 (ISSN) Behjati, M ; Arjmand, N ; Sharif University of Technology
    SAGE Publications Inc  2019
    Objective: To assess adequacy of the National Institute for Occupational Safety and Health (NIOSH) Lifting Equation (NLE) in controlling lumbar spine loads below their recommended action limits during asymmetric load-handling activities using a detailed musculoskeletal model, that is, the AnyBody Modeling System. Background: The NIOSH committee employed simplistic biomechanical models for the calculation of the spine compressive loads with no estimates of the shear loads. It is therefore unknown whether the NLE would adequately control lumbar compression and shear loads below their recommended action limits during asymmetric load-handling activities. Method: Twenty-four static stoop lifting... 

    Effects of human stature and muscle strength on the standing strategies: A computational biomechanical study

    , Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 234, Issue 7 , 2020 , Pages 674-685 Ashtiani, M. N ; Azghani, M. R ; Parnianpour, M ; Khalaf, K ; Sharif University of Technology
    SAGE Publications Ltd  2020
    It has been hypothesized that the muscular efforts exerted during standing may be altered by changes in personal factors, such as the body stature and muscular strength. The goal of this work was to assess the contribution of leg muscles using a biomechanical model in different physical conditions and various initial postures. An optimized inverse dynamics model was employed to find the maximum muscular effort in 23,040 postures. The simulation results showed that mid-range knee flexion could help the healthy and strong individuals maintain balance, but those with weaker muscle strength required more knee flexion. Individuals of weak muscular constitution as well as those with tall stature... 

    Application of a kinematics-driven approach in human spine biomechanics during an isometric lift

    , Article Scientia Iranica ; Volume 15, Issue 5 , 2008 , Pages 596-612 ; 10263098 (ISSN) Arjmand, N ; Shirazi-Adl, A ; Bazrgari, B ; Parnianpour, M ; Sharif University of Technology
    Sharif University of Technology  2008
    Effective prevention and treatment management of spinal disorders can only be based on accurate estimation of muscle forces and spinal loads during various activities such as lifting. The infeasibility of experimental methods to measure muscle and spinal loads has prompted the use of biomechanical modeling techniques. A major shortcoming in many previous and current models is the consideration of equilibrium conditions only at a single cross section, rather than along the entire length of the spine, when attempting to compute muscle forces and spinal loads. The assumption of extensor global muscles with straight rather than curved paths and of the spinal segments as joints with no... 

    A novel stability and kinematics-driven trunk biomechanical model to estimate muscle and spinal forces

    , Article Medical Engineering and Physics ; Vol. 36, issue. 10 , 2014 , p. 1296-1304 Hajihosseinali, M ; Arjmand, N ; Shirazi-Adl, A ; Farahmand, F ; Ghiasi, M. S ; Sharif University of Technology
    An anatomically detailed eighteen-rotational-degrees-of-freedom model of the human spine using optimization constrained to equilibrium and stability requirements is developed and used to simulate several symmetric tasks in upright and flexed standing postures. Predictions of this stability and kinematics-driven (S. +. KD) model for trunk muscle forces and spine compressive/shear loads are compared to those of our existing kinematics-driven (KD) model where both translational and rotational degrees-of-freedom are included but redundancy is resolved using equilibrium conditions alone. Unlike the KD model, the S. +. KD model predicted abdominal co-contractions that, in agreement with... 

    Lumbopelvic rhythm during forward and backward sagittal trunk rotations: Combined in vivo measurement with inertial tracking device and biomechanical modeling

    , Article Clinical Biomechanics ; Vol. 29, issue. 1 , 2014 , pp. 7-13 ; ISSN: 02680033 Tafazzol, A ; Arjmand, N ; Shirazi-Adl, A ; Parnianpour, M ; Sharif University of Technology
    Background The ratio of total lumbar rotation over pelvic rotation (lumbopelvic rhythm) during trunk sagittal movement is essential to evaluate spinal loads and discriminate between low back pain and asymptomatic population. Methods Angular rotations of the pelvis and lumbar spine as well as their sagittal rhythm during forward flexion and backward extension in upright standing of eight asymptomatic males are measured using an inertial tracking device. The effect of variations in the lumbopelvic ratio during trunk flexion on spinal loads is quantified using a detailed musculoskeletal model. Findings The mean of peak voluntary flexion rotations of the thorax, pelvis, and lumbar was 121 (SD... 

    Estimation of spinal loads using a detailed finite element model of the L4-L5 lumbar segment derived by medical imaging kinematics; A feasibility study

    , Article World Congress on Medical Physics and Biomedical Engineering, WC 2018, 3 June 2018 through 8 June 2018 ; Volume 68, Issue 2 , 2018 , Pages 791-795 ; 16800737 (ISSN) Hashemi, M. S ; Arjmand, N ; Sharif University of Technology
    Springer Verlag  2018
    Low back pain is the most prevalent orthopedic disorder and the first main cause of poor working functionality in developed as wells as many developing countries. In Absence of noninvasive in vivo measurement approaches, biomechanical models are used to estimate mechanical loads on human joints during physical activities. To estimate joint loads via musculoskeletal models, the calculation of muscle forces are of importance. It is however difficult to estimate muscle forces as the number of muscles, i.e. unknown parameters, is far more than the existing degrees of freedom; the system is highly redundant. Therefore, in this study, instead of muscle forces estimation, their effects (i.e.,... 

    A model-based approach for estimation of changes in lumbar segmental kinematics associated with alterations in trunk muscle forces

    , Article Journal of Biomechanics ; Volume 70 , March , 2018 , Pages 82-87 ; 00219290 (ISSN) Shojaei, I ; Arjmand, N ; Meakin, J ; Bazrgari, B ; Sharif University of Technology
    Elsevier Ltd  2018
    The kinematics information from imaging, if combined with optimization-based biomechanical models, may provide a unique platform for personalized assessment of trunk muscle forces (TMFs). Such a method, however, is feasible only if differences in lumbar spine kinematics due to differences in TMFs can be captured by the current imaging techniques. A finite element model of the spine within an optimization procedure was used to estimate segmental kinematics of lumbar spine associated with five different sets of TMFs. Each set of TMFs was associated with a hypothetical trunk neuromuscular strategy that optimized one aspect of lower back biomechanics. For each set of TMFs, the segmental... 

    Prediction of the thorax/pelvis orientations and L5–S1 disc loads during various static activities using neuro-fuzzy

    , Article Journal of Mechanical Science and Technology ; Volume 34, Issue 8 , 7 August , 2020 , Pages 3481-3485 ; ISSN: 1738494X Mousavi, S. H ; Sayyaadi, H ; Arjmand, N ; Sharif University of Technology
    Korean Society of Mechanical Engineers  2020
    Spinal posture including thorax/pelvis orientations as well as loads on the intervertebral discs are crucial parameters in biomechanical models and ergonomics to evaluate the risk of low back injury. In vivo measurement of spinal posture toward estimation of spine loads requires the common motion capture techniques and laboratory instruments that are costly and time-consuming. Hence, a closed loop algorithm including an artificial neural network (ANN) and fuzzy logic is proposed here to predict the L5–S1 segment loads and thorax/pelvis orientations in various 3D reaching activities. Two parts namely a fuzzy logic strategy and an ANN from this algorithm; the former, developed based on the... 

    Interaction analysis of a pregnant female uterus and fetus in a vehicle passing a speed bump

    , Article Journal of Biomechanics ; Volume 118 , March , 2021 ; 00219290 (ISSN) Irannejad Parizi, M ; Ahmadian, M. T ; Mohammadi, H ; Sharif University of Technology
    Elsevier Ltd  2021
    Pregnant vehicle occupants experience relatively large acceleration when the vehicle passes a speed-bump. In this paper, the effect of such sudden acceleration on a pregnant uterus is investigated. A biomechanical model representing the fundamental dynamic behaviors of a pregnant uterus has been developed. The model relates to the 32nd week of gestation when the fetus is in head-down, occipito-anterior position. Considering the drag and squeeze effects of the amniotic fluid, we derive a comprehensive differential equation that represents the interaction of the uterus and fetus. Solving the governing equation, we obtain the system response to different speed-bump excitations. Using the fetal... 

    Trunk muscle fatigue and its implications in EMG-assisted biomechanical modeling

    , Article International Journal of Industrial Ergonomics ; Volume 43, Issue 5 , 2013 , Pages 425-429 ; 01698141 (ISSN) Haddad, O ; Mirka, G.A ; Sharif University of Technology
    Muscle fatigue affects the underlying EMG-force relationship on which EMG-assisted biomechanical models rely. The aim of this study was to evaluate the impact of short duration muscle fatigue on the muscle gain value. Participants performed controlled, isometric trunk extension exertions at 10, 20, and 30 degrees of trunk flexion and controlled isokinetic trunk extension exertions at 5 and 15°/sec on five separate days. Fatigue of the lumbar extensors was generated by moderate-intensity, trunk extension exertions. Participants performed controlled test contractions at defined intervals throughout the fatiguing bout and the EMG activities of trunk muscles were collected. These EMG data were... 

    The effect of parameters of equilibrium-based 3-D biomechanical models on extracted muscle synergies during isometric lumbar exertion

    , Article Journal of Biomechanics ; Volume 49, Issue 6 , 2016 , Pages 967-973 ; 00219290 (ISSN) Eskandari, A. H ; Sedaghat Nejad, E ; Rashedi, E ; Sedighi, A ; Arjmand, N ; Parnianpour, M ; Sharif University of Technology
    Elsevier Ltd 
    A hallmark of more advanced models is their higher details of trunk muscles represented by a larger number of muscles. The question is if in reality we control these muscles individually as independent agents or we control groups of them called "synergy". To address this, we employed a 3-D biomechanical model of the spine with 18 trunk muscles that satisfied equilibrium conditions at L4/5, with different cost functions. The solutions of several 2-D and 3-D tasks were arranged in a data matrix and the synergies were computed by using non-negative matrix factorization (NMF) algorithms. Variance accounted for (VAF) was used to evaluate the number of synergies that emerged by the analysis, which... 

    Revised NIOSH Lifting Equation May generate spine loads exceeding recommended limits

    , Article International Journal of Industrial Ergonomics ; Volume 47 , 2015 , Pages 1-8 ; 01698141 (ISSN) Arjmand, N ; Amini, M ; Shirazi Adl, A ; Plamondon, A ; Parnianpour, M ; Sharif University of Technology
    Elsevier  2015
    The 1991 NIOSH Lifting Equation (NLE) is widely used to assess the risk of injury to spine by providing estimates of the recommended weight limit (RWL) in hands. The present study uses the predictive equations developed based on a detailed trunk musculoskeletal biomechanical model to verify whether the RWL generates L5-S1 loads within the limits (e.g., 3400N for compression recommended by NIOSH and 1000N for shear recommended in some studies). Fifty lifting activities are simulated here to evaluate the RWL by the NLE and the L5-S1 loads by the predictive equations. In lifting activities involving moderate to large forward trunk flexion, the estimated RWL generates L5-S1 spine loads exceeding... 

    Effect of body weight on spinal loads in various activities: A personalized biomechanical modeling approach

    , Article Journal of Biomechanics ; Volume 48, Issue 2 , 2015 , Pages 276-282 ; 00219290 (ISSN) Hajihosseinali, M ; Arjmand, N ; Shirazi Adl, A ; Sharif University of Technology
    Elsevier Ltd  2015
    Epidemiological studies are divided over the causative role of body weight (BW) in low back pain. Biomechanical modeling is a valuable approach to examine the effect of changes in BW on spinal loads and risk of back pain. Changes in BW have not been properly simulated by previous models as associated alterations in model inputs on the musculature and moment arm of gravity loads have been neglected. A detailed, multi-joint, scalable model of the thoracolumbar spine is used to study the effect of BW (varying at five levels, i.e., 51, 68, 85, 102, and 119kg) on the L5-S1 spinal loads during various static symmetric activities while scaling moment arms and physiological cross-sectional areas of... 

    Comparative evaluation of six quantitative lifting tools to estimate spine loads during static activities

    , Article Applied Ergonomics ; Volume 48 , 2015 , Pages 22-32 ; 00036870 (ISSN) Rajaee, M. A ; Arjmand, N ; Shirazi Adl, A ; Plamondon, A ; Schmidt, H ; Sharif University of Technology
    Elsevier Ltd  2015
    Different lifting analysis tools are commonly used to assess spinal loads and risk of injury. Distinct musculoskeletal models with various degrees of accuracy are employed in these tools affecting thus their relative accuracy in practical applications. The present study aims to compare predictions of six tools (HCBCF, LSBM, 3DSSPP, AnyBody, simple polynomial, and regression models) for the L4-L5 and L5-S1 compression and shear loads in twenty-six static activities with and without hand load. Significantly different spinal loads but relatively similar patterns for the compression (R2>0.87) were computed. Regression models and AnyBody predicted intradiscal pressures in closer agreement with... 

    How does the central nervous system address the kinetic redundancy in the lumbar spine? Three-dimensional isometric exertions with 18 Hill-model-based muscle fascicles at the L4-L5 level

    , Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 224, Issue 3 , 2010 , Pages 487-501 ; 09544119 (ISSN) Rashedi, E ; Khalaf, K ; Nassajian, M. R ; Nasseroleslami, B ; Parnianpour, M ; Sharif University of Technology
    The human motor system is organized for execution of various motor tasks in a different and flexible manner. The kinetic redundancy in the human musculoskeletal system is a significant property by which the central nervous system achieves many complementary goals. An equilibrium-based biomechanical model of isometric three-dimensional exertions of trunk muscles has been developed. Following the definition and role of the uncontrolled manifold, the kinetic redundancy concept is explored in mathematical terms. The null space of the kinetically redundant system when a certain joint moment and/or stiffness are needed is derived and discussed. The aforementioned concepts have been illustrated,...