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    Extracting Synergies in Nonlinear Dynamics and Investigating their Neural Basis

    , M.Sc. Thesis Sharif University of Technology Bayati, Hamid Reza (Author) ; Vosoughi Vahdat, Bijan (Supervisor)
    Abstract
    The existence of motor synergies in motor system as a tool for reducing degrees of freedom has been always debated. In the last two decades some experiments in vertebrates show the existence of motor primitives in spinal cord. In additional by recording electromyogram from frog some regular patterns have been shown. Recently, a motor coordination model based on stochastic optimal feedback control has extracted synergies by mathematical formulation. In addition, according to this model synergies are the optimal solution of the problem and not for simplifying it. However, this model is investigated in linear dynamics. In this thesis, first, an inverse method for extracting synergies is... 

    Multijoint coordination during sit-to-stand task in people with non-specific chronic low back pain

    , Article Biomedical Engineering - Applications, Basis and Communications ; Volume 25, Issue 1 , 2013 ; 10162372 (ISSN) Tajali, S ; Negahban, H ; Shaterzadeh, M. J ; Mehravar, M ; Salehi, R ; Narimani, R ; Parnianpour, M ; Sharif University of Technology
    2013
    Abstract
    Sit-to-stand (STS) is an important functional task affected by low back pain (LBP). It requires fundamental coordination among all segments of the body to control important performance variables such as body's center of mass (CM) and head positions. This study was conducted to determine whether LBPs could coordinate their multiple joints to achieve the task stability to the same extent as healthy controls. About 11 non-specific chronic LBP and 12 healthy control subjects performed STS task at three postural difficulty levels: rigid surface - open eyes (RO), rigid surface - closed eyes (RC) and narrow surface - closed eyes (NC). Motion variability of seven body segments, CM and head positions... 

    Comparison of the trunk-pelvis and lower extremities sagittal plane inter-segmental coordination and variability during walking in persons with and without chronic low back pain

    , Article Human Movement Science ; Volume 52 , 2017 , Pages 55-66 ; 01679457 (ISSN) Ebrahimi, S ; Kamali, F ; Razeghi, M ; Haghpanah, S. A ; Sharif University of Technology
    Elsevier B.V  2017
    Abstract
    Inter-segmental coordination can be influenced by chronic low back pain (CLBP). The sagittal plane lower extremities inter-segmental coordination pattern and variability, in conjunction with the pelvis and trunk, were assessed in subjects with and without non-specific CLBP during free-speed walking. Kinematic data were collected from 10 non-specific CLBP and 10 non-CLBP control volunteers while the subjects were walking at their preferred speed. Sagittal plane time-normalized segmental angles and velocities were used to calculate continuous relative phase for each data point. Mean absolute relative phase (MARP) and deviation phase (DP) were derived to quantify the trunk-pelvis and bilateral... 

    Coordinated activities of trunk and upper extremity muscles during walker-assisted paraplegic gait: A synergy study

    , Article Human Movement Science ; Volume 62 , 2018 , Pages 184-193 ; 01679457 (ISSN) Baniasad, M ; Farahmand, F ; Arazpour, M ; Zohoor, H ; Sharif University of Technology
    Elsevier B.V  2018
    Abstract
    Individuals with spinal cord injury (SCI) at lower thoracic levels might walk independently with the aid of mechanical orthoses and walker by using their unimpaired trunk and upper extremity muscles (TUEM). The required motor skills and the associated subtasks of the paraplegic locomotion, however, have not been well understood yet. The purpose of this study was to investigate the coordination of the TUEM activities throughout the paraplegic gait cycle using synergy analysis. For eight paraplegic individuals (30.6 ± 11.6 years; SCI level: T12), the kinematics data and the surface electromyography (EMG) signals of TUEM were recorded during 15 gait cycles. Non-negative matrix factorization... 

    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 
    Abstract
    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... 

    Modular neuromuscular control of human locomotion by central pattern generator

    , Article Journal of Biomechanics ; Volume 53 , 2017 , Pages 154-162 ; 00219290 (ISSN) Haghpanah, S. A ; Farahmand, F ; Zohoor, H ; Sharif University of Technology
    Abstract
    The central pattern generators (CPG) in the spinal cord are thought to be responsible for producing the rhythmic motor patterns during rhythmic activities. For locomotor tasks, this involves much complexity, due to a redundant system of muscle actuators with a large number of highly nonlinear muscles. This study proposes a reduced neural control strategy for the CPG, based on modular organization of the co-active muscles, i.e., muscle synergies. Four synergies were extracted from the EMG data of the major leg muscles of two subjects, during two gait trials each, using non-negative matrix factorization algorithm. A Matsuoka׳s four-neuron CPG model with mutual inhibition, was utilized to... 

    Coordination variability during walking and running in individuals with and without patellofemoral pain part 1: lower limb intersegmental coordination variability

    , Article Journal of Medical and Biological Engineering ; Volume 41, Issue 3 , 2021 , Pages 295-304 ; 16090985 (ISSN) Haghighat, F ; Rezaie, M ; Ebrahimi, S ; Shokouhyan, S. M ; Motealleh, A ; Parnianpour, M ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2021
    Abstract
    Purpose: Although it has been proposed that individuals with patellofemoral pain show less lower limb intersegmental coordination variability, the evidence to support this hypothesis is rare. The purpose of this study was, therefore, to evaluate whether individuals with patellofemoral pain exhibit less intersegmental coordination variability compared with healthy individuals during walking and running. Also, it was hypothesized that increasing task demand would exacerbate group differences regarding coordination variability measures. Methods: Three-dimensional kinematics were collected while 17 females with patellofemoral pain and 17 healthy females walked at preferred speed, and ran at...