Browsing by Author "Shin, Gwanseob"

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    The effects of sloped ground on the hip, knee, and ankle joint kinetics and kinematics during manual lifting tasks.
    (2002-08-21) Shin, Gwanseob; Dr. Eric Klang, Committee Member; Dr. Carolyn Sommerich, Committee Member; Dr. Gary A. Mirka, Committee Chair
    The biomechanical effects of sloped ground on hip, knee, and ankle joint moments and lifting posture during sagittally symmetric manual lifting were investigated using a two-dimensional five-segment dynamic biomechanical model. Subjects' motions were traced and recorded at 60Hz by Flock of Birds magnetic tracking system as they lifted a 10 kg cubic box on five sloped grounds; two declined slopes (-20°, -10°), two inclined slopes (+20°, +10°), and flat ground (0°), using three lifting techniques; back lift, freestyle lift, and leg lift. Fifteen trials were tested and each trial involved repetitive lifting (6 to 9 lifts per trial) for 50 seconds. The kinetic and kinematic effects were examined by computing the peak net reactive moments at the hip, knee, and ankle joints, and measuring peak segment flexion angles of the trunk, thigh, and leg (shank). Results indicated that the peak joint moments and peak segment angles were significantly affected by slope angle and lifting technique (α = 0.05). The inclined slope angles (10° and 20°) caused up to 6.8 % and 14.3 % larger peak hip moments than flat ground during the freestyle and leg lifts, respectively. The lowest peak hip moment (236.48 Nm) was observed during the leg lift on flat ground and the largest peak hip moment (302.62 Nm) occurred during the back lifts on flat ground. The components contribution analyses showed that the two static components (vertical reaction static force on the shoulder joint and the trunk mass) were main contributors to the responses of peak hip moment to changes in slope angle. The leg lift technique produced significantly less peak joint moments than other lifting techniques regardless of slope angle. The mean peak hip moment was 16.0 % and 10.5 % less in the leg lift technique (251.0 Nm) than in the back (298.8 Nm) and freestyle lift (280.4 Nm) respectively. Specifically, trunk angular acceleration acted as a major contributor to the significant difference in peak hip moments between the back lift and the leg lift. The trunk angular acceleration, peak flexion angles of the trunk, thigh, and shank separated the leg lift from the back lift.
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    Viscoelastic Responses of the Lumbar spine during Prolonged Stooping
    (2005-08-15) Shin, Gwanseob; Elizabeth G. Loboa, Committee Co-Chair; Gary A. Mirka, Committee Co-Chair; David B. Kaber, Committee Member; Peter L. Mente, Committee Member
    There is considerable evidence that awkward postures of the low back are related to the incidence of low back disorders (LBDs). Specifically, the stooped or fully flexed posture maintained over a prolonged period of time has been known to lead to LBDs in many industrials tasks but the specific biomechanics/physiology of this link is not fully developed. This study combined empirical work with finite element analyses to explore this relationship. The empirical work focused on quantifying the time-dependent responses of the lumbar spine during a prolonged stooped posture by assessing the changes in the sagittal plane range of lumbar flexion and the electromyographic activity of the back extensor musculature in the isokinetic lifts during and after prolonged stooping. Ten healthy participants performed a regimen of a 10-minute stooping period followed by a 10-minute upright standing recovery period, with an isokinetic lift every 2.5 minutes. Results showed significant creep effects of the flexion angle and the increased activity of extensor muscles during stooping to compensate for the reduced extensor moment producing capability of the passive tissues. The 10-minute upright standing did not produce a full recovery of the lumbar spine tissues but a 30-second rest break in the middle of the stooping period moderated these viscoelastic responses. A three-dimensional finite element (FE) model of the lumbar spine was developed to predict the responses of the passive and active tissues of the low back during the prolonged stooping and recovery period. This model employed a nonlinear stress-strain relationship describing the viscoelastic material properties of individual components of the lumbar spine. The trunk flexion tasks that were performed in the in vivo empirical work were simulated in the FE model and the predicted results (range of motion, muscle activation levels, etc.) were compared with experimental results to validate the model. The predicted results by the FE model showed high correlation (R>0.9) with the in vivo experimental results, confirming the capability of the FE model as a potential tool for risk assessment of the prolonged stooping tasks. Results of the in vivo experiment suggested the importance of proper duty cycles in reducing LBD risks due to repetitive prolonged stooping in work-related tasks. The FE model of this study showed potential to simulate various prolonged stooped postures in occupational tasks and predict time-dependent stress/strain of individual spinal tissues. The data from these simulations can be used to design better work postures and duty cycles that can reduce the risks for LBDs, without sacrificing work productivity.