Type of Document Dissertation Author Gottipati, Pranitha URN etd-12162009-111810 Title Experimental and Simulation Based Dynamic Assessment of Flexion and Extension Movements of Torso Degree PhD Department Engineering Science and Mechanics Advisory Committee
Advisor Name Title Granata, Kevin P. Committee Co-Chair Plaut, Raymond H. Committee Co-Chair De Vita, Raffaella Committee Member Grant, John Wallace Committee Member Hendricks, Scott L. Committee Member West, Robert L. Jr. Committee Member Keywords
- muscle forces
Date of Defense 2009-12-04 Availability restricted AbstractLow back disorders (LBDs) comprise one of the major health issues in the United States. Previous research used isometric studies to understand the mechanisms that cause LBDs. Occupational tasks involving dynamic trunk movements, muscle fatigue, and spinal instability are identified as major risk factors for developing low back pain. Dynamic stability and muscle forces during trunk flexion-extension movements are studied in this dissertation.
Torso muscle fatigue is known to affect the neuromuscular muscle recruitment that influences spinal stability. The first part of this dissertation investigates the effect of muscle fatigue on the stability of dynamic trunk flexion-extension movements. Participants with no self-reported low back pain history performed repetitive trunk flexion-extension exercises before and after extensor muscle fatigue. The extensor muscles were fatigued to 60% of their unfatigued isometric maximum voluntary exertion force. The maximum finite-time Lyapunov exponent, λMax, was used to quantify the dynamic stability. Values of λMax increased with fatigue, suggesting dynamic stability of the torso decreases with muscle fatigue. Fatigue-by-task asymmetry interactions did not influence spinal stability.
The purpose of the second part of this dissertation was to predict time-dependent muscle forces and spinal loads during symmetric flexion-extension movements. A 2-dimensional sagittal plane, lumped parameter model was built with one thorax and five lumbar vertebrae stacked upon a stationary pelvis. Kinematics driven optimization was used to estimate time-dependent muscle forces. Muscle forces were determined by minimizing the metabolic power while satisfying the equations of motion. Spinal loads were calculated as the vector sum of the muscle forces and the trunk weight. Abdominal activity was observed at the onset of flexion and at the end of extension. The multifidus and psoas muscles played a major role in the spine dynamics. The compressive spinal loads were found to reach highest values at the onset of flexion, while the shear loads reached the highest values at large flexion angles.
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