Sharif Digital Repository

Study Design. A cross-sectional study to quantify trunk motor control during multidirectional isometric tracking tasks.Objective. To investigate the effect of chronic low back pain (LBP) on trunk neuromuscular performance while participants performed isometric exertions of trunk muscles to track targets in different angles with various magnitudes.Summary of Background Data. Tracking tasks especially in multidirectional activities are among the common research methods to quantify human motor control in different conditions. However, little information is available on trunk motor control during these tasks. There is no study investigating trunk accuracy during multidirectional isometric... 

Despite brilliant properties of glass ionomer cement (GIC), its weak mechanical property poses an obstacle for its use in medical applications. The present research aims to formulate hydroxyapatite/yttria-stabilized zirconia (HA/YSZ) in the composition of GIC to enhance mechanical properties and to improve fluoride release of GIC. HA/YSZ was synthesized via a sol-gel method and characterized by applying X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photo-emission spectroscopy (XPS) and simultaneous thermal analysis (STA) along with transmission electron microscopy (TEM) methods. The synthesized nanocomposite was mixed with GIC at a fixed composition of 5.... 

Purpose: According to the conventional arch model of the pelvis, stability of the sacroiliac joints may require a predominance of form and force closure mechanisms: the greater the vertical shear force at the sacroiliac joints, the greater the reliance on self-bracing by horizontally or obliquely oriented muscles (such as the internal oblique). But what happens to the arch model when a person stands on one leg? In such cases, the pelvis no longer has imposts, leaving both the arch, and the arch model theory, without support. Do lumbopelvic muscle activation patterns in one-legged stances under load suggest compatibility with a different model? This study compares lumbopelvic muscle... 

A wide range of loading conditions involving external forces with varying magnitudes, orientations and locations are encountered in daily activities. Here we computed the effect on trunk biomechanics of changes in force location (two levels) and orientation (5 values) in 4 subjects in upright standing while maintaining identical external moment of 15. Nm, 30. N. m or 45. Nm at the L5-S1. Driven by measured kinematics and gravity/external loads, the finite element models yielded substantially different trunk neuromuscular response with moderate alterations (up to 24% under 45 Nm moment) in spinal loads as the load orientation varied. Under identical moments, compression and shear forces at... 

In the adolescent idiopathic scoliosis (AIS) treatment, a brace is prescribed to the patients who have 20 to 45° curves on their spines to prevent the disorder's advancement. For the analysis of Milwaukee brace effects during time, finite element models (FEMs) of the spine (the thoracolumbar region) and the ribcage (contained 10 pairs of the ribs and the sternum) were prepared for two patients. For modeling the spine part, a new element was used in which a disc (as viscoelastic 3D beam) and a vertebra (as rigid link) were modeled as an element and the ribs and the sternum modeled by 3D elastic beams. The gravity, Milwaukee brace constraints and the forces of the brace's different regions... 

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... 

Background: Patients who have shoulder pain usually have compensatory or contributory deviation of shoulder motion during arm elevation. In the traditional scapulohumeral rhythm, the share of the acromioclavicular (AC) and the sternoclavicular (SC) joint movements and also the role of AC internal rotation angle are unknown. Objectives: The main purpose of this study was to measure and compare the segmentary scapulohumeral rhythm (SSHR) during scapular arm elevation at a steady rotational speed in athletes with and without impingement syndrome. Patients and Methods: Using a speedometer, the maximum speed of arm elevation was measured in 21 men in each of the involved and uninvolved groups.... 

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... 

Controlling topographic features at all length scales is of great importance for the interaction of cells with tissue regenerative materials. We utilized an indirect three-dimensional printing method to fabricate polymeric scaffolds with pre-defined and controlled external and internal architecture that had an interconnected structure with macro- (400-500 μm) and micro- (∼25 μm) porosity. Polycaprolactone (PCL) was used as model system to study the kinetics of tissue growth within porous scaffolds. The surface of the scaffolds was decorated with TiO2 and bioactive glass (BG) nanoparticles to the better match to nanoarchitecture of extracellular matrix (ECM). Micrometric BG particles were... 

A safe rehabilitation exercise for anterior cruciate ligament (ACL) injuries needs to be compatible with the normal knee arthrokinematics to avoid abnormal loading on the joint structures. The objective of this study was to measure the amount of the anterior tibial translation (ATT) of the ACL-deficient knees during selective open and closed kinetic chain exercises. The intact and injured knees of fourteen male subjects with unilateral ACL injury were imaged using uniplanar fluoroscopy, while the subjects performed forward lunge and unloaded/loaded open kinetic knee extension exercises. The ATTs were measured from fluoroscopic images, as the distance between the tibial and femoral reference... 

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... 

In this study, a nonlinear poroelastic model of intervertebral disc as an infrastructure was developed. Moreover, a new element was defined consisting a disc (Viscoelastic Euler Beam Element) and a vertebra (Rigid Link) as a unit element. Using the new element, three different viscoelastic finite element models were prepared for lumbar motion segment (L4/L5). Prolonged loading (short-term and long-term creep) and cyclic loading were applied to the models and the results were compared with results of in vivo tests. Simplification of the models by using the new element leads to reduction of the runtime of the models in dynamic analyses to few minutes without losing the accuracy in the results  

With the success of in vitro single-molecule force measurements obtained in recent years, the next step is to perform quantitative force measurements inside a living cell. Optical traps have proven excellent tools for manipulation, also in vivo, where they can be essentially non-invasive under correct wavelength and exposure conditions. It is a pre-requisite for in vivo quantitative force measurements that a precise and reliable force calibration of the tweezers is performed. There are well-established calibration protocols in purely viscous environments; however, as the cellular cytoplasm is viscoelastic, it would be incorrect to use a calibration procedure relying on a viscous environment.... 

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... 

The purpose of this work is to develop a computational model to describe the task of sit to stand (STS). STS is an important movement skill which is frequently performed in human daily activities, but has rarely been studied from the perspective of optimization principles. In this study, we compared the recorded trajectories of STS with the trajectories generated by several conventional optimization-based models (i.e., minimum torque, minimum torque change and kinetic energy cost models) and also with the trajectories produced by a novel multi-phase cost model (MPCM). In the MPCM, we suggested that any complex task, such as STS, is decomposable into successive motion phases, so that each... 

A new wearable assistive device (WAD) was developed to decrease required force on the lumbar spine in static holding tasks. In order to obtain moments on lumbar spine in two conditions, with and without WAD, a biomechanical static model was used for estimation of external moments on lumbar spine. The results of biomechanical models indicated that there was a reduction in the lumbar moment ranging from 20% to 43% using WAD depending on the load and flexion angle. A total of 15 male healthy subjects were tested to experimentally verify the predicted reduction of external moments on the spine by wearing WAD. Normalized electromyography (EMG) of the right and left lumbar and thoracic erector... 

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 four model outputs (L4-L5 and L5-S1 disc compression and anterior-posterior shear forces) for spinal loads and 76 model outputs (forces in individual trunk muscles) are considered. Moreover, full quadratic regression equations mapping input-outputs of the model developed here for muscle forces and previously for spine loads are used to compare the... 

An analytical approach which is popular in micromechanical studies has been extended to the solution for the interference fit problem of the femoral stem in cementless total hip arthroplasty (THA). The multiple inhomogeneity problem of THA in transverse plane, including an elliptical stem, a cortical wall, and a cancellous layer interface, was formulated using the equivalent inclusion method (EIM) to obtain the induced interference elastic fields. Results indicated a maximum interference fit of about 210 μm before bone fracture, predicted based on the Drucker-Prager criterion for a partially reamed section. The cancellous layer had a significant effect on reducing the hoop stresses in the... 

This paper presents recent developments on effects of rest and fatigue loading on properties of healthy vertebra discs. A comparison of different approaches used in literature to study the properties of intervertebral disc is presented. The major achievements in this area so far are discussed in the context of their advantages and disadvantages. The past approaches are based on bio-mechanical models which mostly used statistical techniques for the analysis and estimation of fatigue loaded Intervertebral Disc (IVD). However, those modeling techniques were not flexible enough for analysis of customized tests. In this paper, we applied System Identification (SI) based NLARX modeling technique... 

The way central nervous system manages the excess degrees of freedom to solve kinetic redundancy of musculoskeletal system remains an open question. In this study, we utilise the concept of synergy formation as a simplifying control strategy to find the muscle recruitment based on summation of identified muscle synergies to balance the biomechanical demands (biaxial external torque) during an isometric shoulder task. A numerical optimisation-based shoulder model was used to obtain muscle activation levels when a biaxial external isometric torque is imposed at the shoulder glenohumeral joint. In the numerical simulations, 12 different shoulder torque vectors in the transverse plane are...