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The Effect of Speed on Kinematic Variability and Dynamic Stability of Trunk in Subjects with and without Nonspecific Low back Pain during a Sagittal Repetitive Flexion Extension Movements

Asgari, Morteza | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45737 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Parnianpour, Mohammad; Narimani, Rouya; Sanjari, Mohammad Ali
  7. Abstract:
  8. Low back pain is one the most prevalent disease and major economic issue facing modern countries. Epidemiological studies suggest that maximum trunk flexion, the angular velocity of trunk and the rate of repetitive movements (such as flexion-extension), are associated with low-back disorders. From biomechanical point of view, lack of stability during dynamic repetitive movements, increases the risk of injuries. On the other hand, some researchers suggest increasing motor variability could be an intrinsic factor to intervene muscuskeletal disorders during repetitive movements. Pace of repetitive occupational tasks could affect both, motor variability and dynamic stability. The goal of this study was to assess how varying speed affects, the amount and structure of kinematic variability and local stability in repetitive flexion extension movements among healthy and low back patients.Fourteen men volunteers with chronic nonspecific LBP and twelve healthy men were recruited to perform continuously repeated trunk flexion and extension movements following two targets in sagittal plane. Each subject performed repetitive movements at three different speeds, 20 cycles per minute, self-selected and 40 cycles per minute. Each subject paced his movement by a periodic tone from a metronome at each target, achieving the 20 and 40 cycles per minute. Upper-body kinematics were collected at 100 Hz using six cameras of VICON motion analysis system with four reflective markers were attached to the skin over seventh cervical vertebrae (C7), tenth thoracic vertebrae (T10), Clavicle and sternum. 3D coordinates of thorax were recorded during movements and then instantaneous rotation angles of thorax were computed. Thirty continuous cycles of flexion and extension movementswere selected to minimize the effects of fatigue. For assessing kinematic variability, the overall mean standard deviation computed at ithtime normalized (0-100%) points in the cycle of movement (MeanSD). Short and long-term maximum finite-time Lyapunov exponents describing responses to infinitesimal perturbation, were computed from measured trunk kinematics to determine local dynamic stability. Maximum Floquet multiplier were also calculated to quantify orbital stability of trajectories at 0, 25, 50 and 75 % of cycles. Analysis of variance (ANOVA) with mixed repeated design was performed to test the main and interaction effects of speed and group on the measures of variability and local and orbital stability.The results of the ANOVA revealed that main effect of speed was significant on MeanSD, Lyapunov exponents and Floquet multipliers. Long-term Lyapunov exponents were higher in control volunteers than the LBP patients. Local divergence exponents increased with speed but movement variability reduced. Long-term divergence and magnitude of maximum FM were smaller at slow speeds. These findings suggest slower flexion and extension movements lead to improved stability over short- and long-term intervals. In LBP group, trajectories divergence were less than healthy group over steady state behavior. Maximum FM were smaller than one at different speeds, therefore all subjects exhibited orbital stability during repetitive movements
  9. Keywords:
  10. Flexion/Extension ; Low Back Pain ; Variability ; Local Stability ; Orbital Stability

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