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    A novel approach to evaluate abdominal coactivities for optimal spinal stability and compression force in lifting

    , Article Computer Methods in Biomechanics and Biomedical Engineering ; Volume 12, Issue 6 , 2009 , Pages 735-745 ; 10255842 (ISSN) Ouaaid, Z. E ; Arjmand, N ; Shirazi Adl, A ; Parnianpour, M ; Sharif University of Technology
    A novel optimisation algorithm is developed to predict coactivity of abdominal muscles while accounting for both trunk stability via the lowest buckling load (Pcr) and tissue loading via the axial compression (Fc). A nonlinear multi-joint kinematics-driven model of the spine along with the response surface methodology are used to establish empirical expressions for Pcr and Fc as functions of abdominal muscle coactivities and external load magnitude during lifting in upright standing posture. A two-component objective function involving Fc and Pcr is defined. Due to opposite demands, abdominal coactivities that simultaneously maximise Pcr and minimise Fc cannot exist. Optimal solutions are... 

    Relative efficiency of abdominal muscles in spine stability

    , Article Computer Methods in Biomechanics and Biomedical Engineering ; Volume 11, Issue 3 , 2008 , Pages 291-299 ; 10255842 (ISSN) Arjmand, N ; Shirazi Adl, A ; Parnianpour, M ; Sharif University of Technology
    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 most efficient muscle (compared with the external oblique and rectus abdominus) in providing stability while generating smaller spinal loads with lower fatigue rate of muscles. As the weight was held higher, stability deteriorated requiring additional flexor-extensor activities. The stabilising efficacy of abdominal muscles diminished at higher... 

    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...