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A Novel Stability-based EMG-assisted Model of the Lumbar Spine to Estimate Trunk Muscle Forces and Spinal Loads in Various Static Activities

Samadi, Soheil | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49987 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Arjmand, Navid
  7. Abstract:
  8. The spine like every other mechanical pillar, is exposed to buckling and loss of stability. While existing biomechanical models emphasize the pressure force on the disk as the main cause of injury, there is also a possibility of local buckling phenomenon in vertebral discs. Because of the prevalence and high cost of lower back pain, it is essential to evaluate the forces carried by disks and lumbar muscles during occupational activities more accurately. In this regard, hybrid EMG-assisted optimization (EMGAO) approaches are most common methods for estimation of spinal loads. These models, not only use EMG data to be physiologically creditable, but also satisfy equilibrium requirements at all levels by means of optimization. However, the present EMGAO approaches, in some common occupational tasks which an individual performs without difficulty, do not satisfy the condition of the stability in the spine system. So far, a handful of models based on stability has been proposed, which also provides different answers from EMG data. In this study and for the first time, a hybrid model based on stability will be proposed, that can achieve lumbar muscle forces by satisfying equilibrium and stability simultaneously in 6 levels of the lumbar spine. On the other hand, the optimization function is considered in a way that estimates muscle forces in closest state to EMG data. Moreover, in this model which contains 18 degrees of freedom and 76 main muscles, 15 typical static tasks prevalent among occupational activities are solved, and for that, the required electromyographic and anthropometric data are collected from previous studies. Initially, after assessing the activities without imposing stability condition, 7 activities were obtained unstable, and thus their answers for muscle forces were not reliable. But, after applying the stability constraint, it was observed that muscle forces remained invarient in stable activities, while increased in unstable ones. It was also reached that this increase was proportional to the degree of activity’s instability, and the Oblique muscle forces, as the antagonistic muscles, and the back global muscle forces, as agonistic muscles, has affected more than other muscles in order to stabilize the system. The correction (gain) coefficients obtained from the model vary from 0 to 52, and the mean difference of these coefficients from 1 is 1.09. Finally, the result for intradiscal pressure for L4-L5 commensurates well with Wilke experimental study
  9. Keywords:
  10. Stability ; Spine ; Optimization ; Spinal Loads ; Electromyography ; Electromyography-Assisted Optimization Model (EMGAO) ; Electromyography Data

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