Navid Arjmand

Navid Arjmand
Sharif University of Technology | SHARIF · Department of Mechanical Engineering

PhD

About

84
Publications
22,857
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2,537
Citations
Citations since 2017
28 Research Items
1613 Citations
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2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300
2017201820192020202120222023050100150200250300

Publications

Publications (84)
Conference Paper
Full-text available
Introduction: Human body posture is required to be determined for the assessment of musculoskeletal risk injuries during occupational activities. The traditional motion analysis methods to measure body posture is time-consuming and limited to equipped laboratories. Therefore, posture prediction methods are presented as alternatives. When developed...
Article
Body posture measurement approaches, required in biomechanical models to assess risk of musculoskeletal injuries, are usually costly and/or impractical for use in real workplaces. Therefore, we recently developed three artificial neural networks (ANNs), based on measured posture data on several individuals, to predict whole body 3D posture (coordin...
Conference Paper
Full-text available
Musculoskeletal disorders are among the most prevalent conditions in workers performing manual material handling (MMH) activities. In this study, MMH of a dashboard was investigated in a car assembly line. Several quantitative (i.e., biomechanical models) and qualitative (e.g., NIOSH, RULA, REBA, and OWAS) assessment tools were used to evaluate the...
Conference Paper
Full-text available
Evaluation of body posture is an essential input into biomechanical models. The common motion analysis techniques to measure body posture are costly and limited to laboratories. As alternatives, posture prediction approaches such as trained artificial neural networks (ANN) based on in vivo measurements are therefore developed. Previous studies have...
Article
Measurements of spinal segment ranges of motion (RoMs), movement coordination, and three-dimensional kinematics during occupational activities have implications in occupational/clinical biomechanics. Due to the large amount of adipose tissues, obese individuals may have different RoMs, lumbopelvic coordination, and kinematics than normal-weight one...
Article
Spinal fusion surgery is usually followed by accelerated degenerative changes in the unfused segments above and below the treated segment(s), i.e., adjacent segment disease (ASD). While a number of risk factors for ASD have been suggested, its exact pathogenesis remains to be identified. Finite element (FE) models are indispensable tools to investi...
Article
Spine musculoskeletal (MS) models make simplifying assumptions on the intervertebral joint degrees-of-freedom (rotational and/or translational), representation (spherical or beam-like joints), and properties (linear or nonlinear). They also generally neglect the realistic structure of the joints with disc nuclei/annuli, facets, and ligaments. We ai...
Article
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 a...
Article
Irrespective of the lifting technique (squat or stoop), the lumbar spine posture (more kyphotic versus more lordotic) adopted during lifting activities is an important parameter affecting the active-passive spinal load distribution. The advantages in either posture while lifting remains, however, a matter of debate. To comprehensively investigate t...
Article
Workplace safety assessment, personalized treatment design and back pain prevention programs require accurate subject-specific estimation of spinal loads. Since no noninvasive method can directly estimate spinal loads, easy-to-use regression equations that are constructed based on the results of complex musculoskeletal models appear as viable alter...
Article
Background: The purpose of this study was to propose a methodology for mechanical characterization of the ligaments in subject-specific models of the patellofemoral joint (PFJ) of living individuals. Method: PFJ laxity tests were performed on a healthy volunteer using a specially designed loading apparatus under biplane fluoroscopy. A three-dime...
Article
Recent advances in medical imaging techniques have allowed pure displacement-control trunk models to estimate spinal loads with no need to calculate muscle forces. Sensitivity of these models to the errors in post-imaging evaluation of displacements (reported to be ∼0.4–0.9° and 0.2–0.3 mm in vertebral displacements) has not yet been investigated....
Article
Traditional load‐control musculoskeletal and finite element (FE) models of the spine fail to accurately predict in vivo intervertebral joint loads due mainly to the simplifications and assumptions when estimating redundant trunk muscle forces. An alternative powerful protocol that bypasses the calculation of muscle forces is to drive the detailed F...
Article
Biomechanical models of the spine either simplify intervertebral joints (using spherical joints or deformable beams) in musculoskeletal (MS) or overlook musculature in geometrically-detailed passive finite element (FE) models. These distinct active and passive models therefore fail to determine in vivo stresses and strains within and load-sharing a...
Article
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 t...
Article
Spinal diseases are prevalent and costly. Excessive mechanical loads on the spine play a crucial role in the etiology of back disorders. To estimate spinal loads one needs to calculate unknown muscle forces through either an optimization or EMG-driven approach. Both approaches involve several assumptions and simplifications regarding anatomy of mus...
Article
Full-text available
Previous studies have measured thoracic range of motion (RoM) using either skin-mounted devices or supine CT-imaging and have reported quite different RoMs. Given the inherent shortcomings of measurements of vertebrae movements from the overlying skin, the present study aims to measure normal RoM of the thoracic spine in the sagittal plane using th...
Article
Evaluation of spinal range of motions (RoMs) and movement coordination between its segments (thorax, lumbar, and pelvis) has clinical and biomechanical implications. Previous studies have not recorded three-dimensional primary/coupled motions of all spinal segments simultaneously. Moreover, magnitude/direction of the coupled motions of the thorax/p...
Conference Paper
Spinal diseases are prevalent and costly. Excessive mechanical loads on the spine play a crucial role in the etiology of back disorders. To estimate spinal loads one needs to calculate unknown muscle forces through either an optimization or EMG-driven approach. Both approaches involve several assumptions and simplifications regarding anatomy of mus...
Article
Maximum voluntary exertion (MVE) tasks quantify trunk strength and maximal muscle electromyography (EMG) activities with both clinical and biomechanical implications. The aims here are to evaluate the performance of an existing trunk musculoskeletal model, estimate maximum muscle stresses and spinal forces, and explore likely differences between ma...
Article
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...
Article
Background: Motor control exercise was claimed to improve spinal stability in patients with chronic non-specific back pain, but to investigate the effectiveness of this exercise, other outcome measures have been used rather than spinal stability itself. The aim of our study is to assess motor control exercise effects on spinal stability using a bi...
Article
Musculoskeletal models represent spinal motion segments by spherical joints/beams with linear/nonlinear properties placed at various locations. We investigated the fidelity of these simplified models (i.e., spherical joints with/without rotational springs and beams considering nonlinear/linear properties) in predicting kinematics of the ligamentous...
Article
Underlying mechanisms of obesity-related back pain remain unexplored. Thus, we aim to determine the effect of obesity and its shapes on the spinal loads and the associated risks of injury. Obesity shapes were initially constructed by principal component analysis based on datasets on 5852 obese individuals. Spinal loads, cycles to vertebral failure...
Article
A number of geometrically-detailed passive finite element (FE) models of the lumbar spine have been developed and validated under in vitro loading conditions. These models are devoid of muscles and thus cannot be directly used to simulate in vivo loading conditions acting on the lumbar joint structures or spinal implants. Gravity loads and muscle f...
Article
Ligaments assist trunk muscles in balancing external moments and providing spinal stability. In absence of the personalized material properties for ligaments, finite element (FE) models use dispersed data from the literature. This study aims to investigate the relative effects of eight different ligament property datasets on FE model responses. Eig...
Article
An essential input to the musculoskeletal (MS) trunk models that estimate muscle and spine forces is kinematics of the thorax, pelvis, and lumbar vertebrae. While thorax and pelvis kinematics are usually measured via skin motion capture devices (with inherent errors on the proper identification of the underlying bony landmarks and the relative skin...
Article
Full-text available
Development of a subject-specific computational musculoskeletal trunk model (accounting for age, sex, body weight and body height), estimation of muscle forces and internal loads as well as subsequent validation by comparison with measured intradiscal pressure in various lifting tasks are novel, important and challenging. The objective of the prese...
Article
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: 150-190cm) and body weight (BW: 50-120kg) on spinal loads in a full-factorial simulation...
Article
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 ther...
Article
A number of musculoskeletal models of the human spine have been used for predictions of lumbar and muscle forces. However, the predictive power of these models might be limited by a commonly made assumption; thoracic region is represented as a single lumped rigid body. This study hence aims to investigate the impact of such assumption on the predic...
Article
Spinal loads are recognized to play a causative role in back disorders and pain. Knowledge of lumbar spinal loads is required in proper management of various spinal disorders, effective risk prevention and assessment in the workplace, sports and rehabilitation, realistic testing of spinal implants as well as adequate loading in in vitro studies. Du...
Article
Range of motion (ROM) of the thoracic spine has implications in patient discrimination for diagnostic purposes and in biomechanical models for predictions of spinal loads. Few previous studies have reported quite different thoracic ROMs. Total (T1-T12), lower (T5-T12) and upper (T1-T5) thoracic, lumbar (T12-S1), pelvis, and entire trunk (T1) ROMs w...
Article
Background: Iatrogenic injuries to paraspinal muscles during posterior lumbar surgery cause a reduction in their contractile cross-sectional area and thus presumably their postoperative activation. This study investigates the effect of such intraoperative injuries on postoperative patterns of muscle activations and spinal loads during various acti...
Conference Paper
Full-text available
https://www.czech-in.org/cm/ESB/CM.NET.WebUI/CM.NET.WEBUI.scpr/SCPRfunctiondetail.aspx?confID=05000000-0000-0000-0000-000000000056&sesID=05000000-0000-0000-0000-000000003679&absID=07000000-0000-0000-0000-000000022469
Article
Various hybrid EMG-assisted optimization (EMGAO) approaches are commonly used to estimate muscle forces and joint loads of human musculoskeletal systems. Use of EMG data and optimization enables the EMGAO models to account for inter- and intra-individual variations in muscle recruitments while satisfying equilibrium requirements. Due to implication...
Article
A six degree-of-freedom musculoskeletal model of the lumbar spine was developed to predict the activity of trunk muscles during light, moderate and heavy lifting tasks in standing posture. The model was formulated into a multi-objective optimization problem, minimizing the sum of the cubed muscle stresses and maximizing the spinal stability index....
Article
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-b...
Article
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...
Article
Full-text available
Iatrogenic injuries to paraspinal muscles during the posterior lumbar surgery (PLS) cause a reduction in their cross-sectional areas (CSAs) and contractile densities over time post-surgery. This study aims to quantify such alterations. Pre- and postoperative CSAs (~6 months interval) of all paraspinal muscles were measured in six patients undergoin...
Article
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...
Article
Full-text available
Osteoporosis is a progressive bone disease characterized by deterioration in the quantity and quality of bone, leading to inferior mechanical properties and an increased risk of fracture. Current assessment of osteoporosis is typically based on bone densitometry tools such as Quantitative Computed Tomography (QCT) and Dual Energy X-ray absorptiomet...
Article
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 a...
Article
Full-text available
Due to the complexity of the human spinal motion segments, the intervertebral joints are often simulated in the musculoskeletal trunk models as pivots thus allowing no translational degrees of freedom (DOFs). This work aims to investigate, for the first time, the effect of such widely used assumption on trunk muscle forces, spinal loads, kinematics...
Article
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...
Article
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 bac...
Conference Paper
Full-text available
The recruitment pattern of trunk muscles is determined using a three-dimensional model of the spine with two joints and six symmetric pairs of muscles in which both equilibrium and stability requirements are satisfied. Model predictions are verified using Anybody Modeling System (AMS) and Abaqus. The model is used to test the hypothesis that antago...
Article
Two artificial neural networks (ANNs) are constructed, trained, and tested to map inputs of a complex trunk finite element (FE) model to its outputs for spinal loads and muscle forces. Five input variables (thorax flexion angle, load magnitude, its anterior and lateral positions, load handling technique, i.e., one- or two-handed static lifting) and...
Article
Full-text available
In spite of earlier experimental and modeling studies, the relative role of the intra-abdominal pressure (IAP) in spine mechanics has remained controversial. This study employs simple ana-lytical and finite element (FE) models of the spine and its surrounding structures to investigate the contribution of IAP to spinal loading and stability. The ana...
Article
Asymmetric lifting activities are associated with low back pain. A finite element biomechanical model is used to estimate spinal loads during one- and two-handed asymmetric static lifting activities. Model input variables are thorax flexion angle, load magnitude as well as load sagittal and lateral positions while response variables are L4-L5 and L...
Article
To circumvent the existing shortcoming of optimisation algorithms in trunk biomechanical models, both agonist and antagonist trunk muscle stresses to different powers are introduced in a novel objective function to evaluate the role of abdominal muscles in trunk stability and spine compression. This coupled objective function is introduced in our k...
Article
Muscle force partitioning methods and musculoskeletal system simplifications are key modeling issues that can alter outcomes, and thus change conclusions and recommendations addressed to health and safety professionals. A critical modeling concern is the use of single-joint equilibrium to estimate muscle forces and joint loads in a multi-joint syst...
Article
Response surface methodology is used to establish robust and user-friendly predictive equations that relate responses of a complex detailed trunk finite element biomechanical model to its input variables during sagittal symmetric static lifting activities. Four input variables (thorax flexion angle, lumbar/pelvis ratio, load magnitude, and load pos...
Article
Despite recent advances in modeling of the human spine, simplifying assumptions are still required to tackle complexities. Such assumptions need to be scrutinized to assess their likely impacts on predictions. A comprehensive comparison of muscle forces and spinal loads estimated by a single-joint (L5-S1) optimisation-assisted EMG-driven (EMGAO) an...
Article
A novel optimisation algorithm is developed to predict coactivity of abdominal muscles while accounting for both trunk stability via the lowest buckling load (P(cr)) and tissue loading via the axial compression (F(c)). A nonlinear multi-joint kinematics-driven model of the spine along with the response surface methodology are used to establish empi...
Article
Comparative studies between single-joint electromyography (EMG)- and optimization-driven models of the human spine in estimating trunk muscle and spinal compression forces have not been conclusive. Due to associated implications in ergonomic applications as well as prevention and treatment managements of low-back disorders, there is a need to criti...
Article
EEective 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 pre...
Article
Using an iterative kinematics-driven nonlinear finite element model, relative efficiency of individual abdominal muscles in spinal stability in upright standing posture was investigated. Effect of load height on stability and muscle activities was also computed under different coactivity levels in abdominal muscles. The internal oblique was the mos...
Article
Activities involving axial trunk rotations/moments are common and are considered as risk factors for low back disorders. Previous biomechanical models have failed to accurately estimate the trunk maximal axial torque exertion. Moreover, the trunk stability under maximal torque exertions has not been investigated. A nonlinear thoracolumbar finite el...
Article
Full-text available
Accurate estimation of muscle forces in various occupational tasks is critical for a reliable evaluation of spinal loads and subsequent assessment of risk of injury and management of back disorders. The majority of biomechanical models of multi-segmental spine estimate muscle forces and spinal loads based on the balance of net moments at a single l...
Article
Full-text available
Despite the well-recognized role of lifting in back injuries, the relative biomechanical merits of squat versus stoop lifting remain controversial. In vivo kinematics measurements and model studies are combined to estimate trunk muscle forces and internal spinal loads under dynamic squat and stoop lifts with and without load in hands. Measurements...
Article
An improved assessment of risk of spinal injury during lifting activities depends on an accurate estimation of trunk muscle forces, spinal loads and stability margin which in turn requires, amongst others, an accurate description of trunk muscle geometries. The lines of action of erector spinae muscles are often assumed to be linear despite the cur...
Article
Full-text available
The role of intra-abdominal pressure (IAP) in unloading the spine has remained controversial. In the current study, a novel kinematics-based approach along with a nonlinear finite-element model were iteratively used to calculate muscle forces, spinal loads, and stability margin under prescribed postures and loads measured in in vivo studies. Four c...
Conference Paper
Full-text available
In spite of the several experimental and modeling studies on the biomechanical characteristics of the human spine, the role and significance of the intra-abdominal pressure (IAP) in spine mechanics has remained controversial. This study represents a simple analytical and a 3-D finite element model of spine and its surrounding structures to investig...
Article
The effect of eight different cost functions on trunk muscle forces, spinal loads and stability was investigated. Kinematics-based approach combined with nonlinear finite element modeling and optimization were used to model in vivo measurements on isometric forward flexions at approximately 40 degrees and approximately 65 degrees in sagittal plane...
Article
To resolve the trunk redundancy to determine muscle forces, spinal loads, and stability margin in isometric forward flexion tasks, combined in vivo-numerical model studies was undertaken. It was hypothesized that the passive resistance of both the ligamentous spine and the trunk musculature plays a crucial role in equilibrium and stability of the s...
Article
In vivo measurements and model studies are combined to investigate the role of lumbar posture in static lifting tasks. Identification of the role of changes in the lumbar posture on muscle forces, internal loads, and system stability in static lifting tasks with and without load in hands. Despite the recognition of the causal role of lifting in spi...
Article
Full-text available
INTRODUCTION Lumbar spine, muscles around it, the effects of motor control and their connection with spinal disorders have been studied from different points of views. But there are a few studies in which muscles, IAP and their effects on spine stability have been considered. Considering experimental results and developed models show that the effec...
Article
The load in active and passive spinal components as well as the stability margin in standing postures +/- load in hands are studied using both computational model and in vivo studies. To investigate muscle activity, spinal loads, and system stability in standing postures. Study of the human trunk yields a redundant system, the satisfactory solution...
Article
Knowledge of load distribution among passive and active components of the human trunk during various occupational and sportive activities is essential to assess the risk of injury and to improve prevention, evaluation, and rehabilitation of spinal disorders. To solve the trunk redundancy toward determination of muscle forces and passive loads in fo...
Article
"Thèse présentée en vue de l'obtention du diplôme de Philosophiae Doctor (génie mécanique)" Thèse (Ph. D.)--École polytechnique, 2007.

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Projects (4)
Project
We are developing a detailed FEM model of spine which can predict forces of all tissues, either active or passive, to study load sharing between them. The model can be used for simulation of occupational tasks and spine surgeries.
Project
to examine whether obese people have really less range of motions than normal ones