Sharif Digital Repository

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,... 

The objective of this study was to quantify individual muscle function differences between level walking and backpack load carriage at the same speed by using a muscle-actuated forward dynamics simulation. As experimental investigations have revealed that backpack loads of up to 64 per cent of an individual's body mass have little effect on the sagittal plane gait kinema-tics, further biomechanical analyses are necessary to investigate the contributions of individual muscle coordination strategies to achieve a given motor task by mechanical power generation, absorption, and transference to each body segment. A biomechanical framework consisting of a musculoskeletal model actuated by 18... 

Background: Studying the kinematics of the ACL deficient (ACLD) knees, during different physiological activities and muscle contraction patterns, can improve our understanding of the joint's altered biomechanics due to ACL deficiency as well as the efficacy and safety of the rehabilitations exercises. Methods: Twenty-five male volunteers, including 11 normal and 14 unilateral ACLD subjects, participated in this study. The kinematics of the injured knees of the ACLD subjects was compared with their intact knees and the healthy group during passive flexion and isometric leg press with the knees flexed from full extension to 45° flexion, with 15° intervals. An accurate registration algorithm... 

This study investigates the effect of body acceleration on human cardiac function. Finite element analysis is conducted to simulate geometrical and mechanical properties of human heart. Heart geometrical modeling in three-dimension is performed by segmentation of cardiac MRI images. The nonlinear mechanical behavior of myocardium is modeled by Mooney-Rivlin, Polynomial, Ogden and Yeoh hyperelastic material models. Stress-strain curves of myocardial tissue are obtained from experimental compression tests on bovine heart samples. The experimental results are employed for the evaluation of material coefficients by the nonlinear least squares method. Among hyperelastic models, the Yeoh model... 

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 present study is twofold. First, it aims to update and personalize the passive and active structures in an existing musculoskeletal kinematics-driven finite element model. The scaling scheme used an existing imaging database and biomechanical principles to adjust muscle geometries/cross-sectional-areas and passive joint geometry/properties in accordance... 

Human bodies use the electrical currents to make the muscles move. Disconnection of the electrical signals between the brain and the muscles as a result of spinal cord injuries, causes paralysis below the level of injury. Functional electrical stimulation (FES) is used to stimulate the peripheral nerves of the disabled limbs. The level of these electrical signals should be selected so that the desired tasks are done successfully. Applying the appropriate controller which can result a human like behaviour and the accomplishment of the desired tasks has become a significant research area. In this paper, the multi-input multi-output (MIMO) musculoskeletal model of human arm with six muscles is... 

This study developed and validated a lumped parameter model for the FLEXI-BAR, a popular training instrument that provides vibration stimulation. The model which can be used in conjunction with musculoskeletal-modeling software for quantitative biomechanical analyses, consists of 3 rigid segments, 2 torsional springs, and 2 torsional dashpots. Two different sets of experiments were conducted to determine the model's key parameters including the stiffness of the springs and the damping ratio of the dashpots. In the first set of experiments, the free vibration of the FLEXI-BAR with an initial displacement at its end was considered, while in the second set, forced oscillations of the bar were... 

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 predictions of spinal and muscle forces. A validated thoracolumbar spine model was used with a flexible thorax (T1–T12), a completely rigid one or rigid with thoracic posture updated at each analysis step. The simulations of isometric forward flexion up to 80°, with and without a 20 kg hand load, were performed, based on the previously measured... 

3D hydrogel environment with both unique properties of nanofibrous structure and electrical character can provide a promising scaffold for skeletal muscle tissue engineering approaches. Herein, the poly acrylic acid (PAA)-based hydrogel was engineered to conductive one by aniline polymerization in the form of nanofibers. The poly aniline (PANi) nanofibers were made by the optimized chemical reactions between the surface carboxylate groups of based hydrogel and protonated aniline monomers. We found that the strong bonding which was created between PANi and camphor sulphonic acid (CSA) as a doping agent supporting the stable electrical property of composite hydrogel after incubation in cell... 

In this paper, a micromechanical model for connective soft tissues based on the available histological evidences is developed. The proposed model constituents i.e. collagen fibers and ground matrix are considered as hyperelastic materials. The matrix material is assumed to be isotropic Neo-Hookean while the collagen fibers are considered to be transversely isotropic hyperelastic. In order to take into account the effects of tissue structure in lower scales on the macroscopic behavior of tissue, a strain energy density function (SEDF) is developed for collagen fibers based on tissue hierarchical structure. Macroscopic response and properties of tissue are obtained using the numerical... 

In this study, we reported the preparation of self cross-linked oxidized alginate-gelatin hydrogels for muscle tissue engineering. The effect of oxidation degree (OD) and oxidized alginate/gelatin (OA/GEL) weight ratio were examined and the results showed that in the constant OA/GEL weight ratio, both cross-linking density and Young's modulus enhanced by increasing OD due to increment of aldehyde groups. Furthermore, the degradation rate was increased with increasing OD probably due to decrement in alginate molecular weight during oxidation reaction facilitated degradation of alginate chains. MTT cytotoxicity assays performed on Wharton's Jelly-derived umbilical cord mesenchymal stem cells... 

A combination of topographical cues and controlled release of biochemical factors is a potential platform in controlling stem cells differentiation. In this study the synergistic effect of nanotopography and sustained release of biofunctional transforming growth factor beta 1 (TGF-β1) on differentiation of human Wharton's Jelly-derived mesenchymal stem cell (hWJ-derived UC-MSCs) toward myogenic lineage was investigated. In order to achieve a sustained release of TGF-β1, this factor was encapsulated within chitosan nanoparticles. Afterwards the aligned composite mats were fabricated using poly-E-caprolacton (PCL) containing TGF-β1-loaded chitosan nanoparticles and poly-L-lactic acid (PLLA).... 

Among polymers, polyaniline (PANi) has been introduced as a good candidate for muscle regeneration due to high conductivity and also biocompatibility. Herein, for the first time, we report the use of electrospun nanofibrous membrane of PAN-PANi as efficient scaffold for muscle regeneration. The prepared PAN-PANi electrospun nanofibrous membrane was characterized by scanning electron microscopy (SEM), Attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) and tensile examination. The softer scaffolds of non-composite electrospun nanofibrous PAN govern a higher rate of cell growth in spite of lower differentiation value. On the other hand, PAN-PANi electrospun... 

The central pattern generators have been considered as a method to simplify the control of the complex rhythmic motions, e.g., walking, by the central nervous system. In this study, a control structure was designed to control the soleus and tibialis anterior muscles in a complete gait cycle. The activation patterns of the muscles were measured experimentally and used as the reference signals of a tracking problem. The hip angle and ground reaction force were also used as a feedforward. The feedback from the Golgi tendon acted as a regulator of muscle activity. The controller was applied to two gait trials. The results indicated that the designed controller was capable of tracking the... 

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. During the last few decades, researchers have used a number of techniques to estimate spinal loads by measuring in vivo changes in the intradiscal pressure, body height, or forces and moments transmitted via instrumented vertebral implants. In parallel, computational models have been employed to estimate muscle forces and spinal loads under various... 

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... 

Background: The use of functional knee braces for returning to sports or during demanding activities following anterior cruciate ligament rupture is common; yet despite being commonly prescribed, its mechanism of action remains unknown. Objectives: To examine the effect of functional knee braces on mean muscle activity when performing lunge exercises. Study design: Pre-/post-test (within-subject research design). Methods: A total of 10 male participants with unilateral isolated anterior cruciate ligament deficiency participated. Electromyographic activities of six muscles around the knee were recorded during lunge exercises, with and without wearing a custom functional knee brace. The lunge... 

Background: The use of knee-ankle-foot orthoses with drop locked knee joints produces some limitations for walking in subjects with quadriceps muscle weakness. The development of stance control orthoses can potentially improve their functionality. Objectives: The aim of this review was to compare the evidence of the effect of stance control orthoses to knee-ankle-foot orthoses with drop locked knee joints in improving kinematic variables and energy efficiency of walking by subjects with quadriceps muscle weakness caused by different pathologies. Study design: Literature review. Methods: Based on selected keywords and their composition, a search was performed in Google Scholar, PubMed,... 

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. Two intelligent optimization algorithms, i.e., the vector evaluated particle swarm optimization (VEPSO) and nondominated sorting genetic algorithm (NSGA), were employed to solve the optimization problem. The optimal solution for each task was then found in the way that the corresponding in vivo intradiscal pressure could be reproduced. Results... 

Atrogenic 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. Method: Pre- and postoperative CSAs (~6 months interval) of all paraspinal muscles were measured in six patients undergoing PLS using a 3-T magnetic resonance (MR) scanner to quantify the alterations in geometrical and tissue effective contractile (non-fatty) CSAs of these muscles at all lumbar levels. To examine the presence of any confounding effects on recorded changes within ~7-month period, measurements were also carried out on ten healthy volunteers....