Boyi Hu

Date of Graduation

2016

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Industrial and Managements Systems Engineering

Committee Chair

Xiaopeng Ning

Committee Co-Chair

Fei Dai

Committee Member

Jaridi Majid

Committee Member

Ashish D Nimbarte

Committee Member

Feng Yang

Abstract

Previous studies have shown that working on uneven ground surfaces is linked to alternations of the lumbar active and passive tissue load sharing mechanism and reductions in spinal stability, which is highly associated with the risk of low back pain. The purpose of the current research was to investigate the changes of the lumbar flexion relaxation phenomenon and lumbar segmental stability while working on slanted ground surfaces. In experiment one, fourteen male participants performed sagittal plane, trunk flexion-extension tasks on three laterally slanted ground surfaces (flat ground, 15° and 30°) while their lumbar muscle activities and trunk kinematic performances were recorded. Results showed that flexion relaxation occurred up to 6.2° earlier among the ipsilateral lumbar muscles with an increase in laterally slanted ground angle; however, the contralateral side was not affected as much. The results of experiment one demonstrated that the uneven ground surface has the potential of changing the lumbar tissue load-sharing mechanism and affect lumbar biomechanical responses.;Based on the results of experiment one, a follow up experiment was conducted to further explore the effects of antero-posteriorly slanted ground surfaces and trunk asymmetry on spine biomechanics during trunk bending motion. More specifically, we investigated the influences of antero-posteriorly slanted ground surfaces, trunk asymmetry and their interaction on the lumbar extensor muscle flexion relaxation phenomenon during trunk flexion motion, as well as lumbar segmental stability performance in deep trunk bending postures. Fourteen healthy male participants performed sagittally symmetric and asymmetric trunk bending tasks on one flat and two antero-posteriorly slanted surfaces (--15° (uphill facing) and 15° (downhill facing)), while their lumbar muscle electromyography and trunk kinematics were recorded. Results showed that standing on a downhill facing slanted surface could delay the onset of lumbar muscle flexion relaxation phenomenon, while standing on uphill facing ground causes lumbar muscle flexion relaxation to occur earlier. During asymmetric trunk bending, flexion relaxation occurred earlier among the contralateral side of lumbar muscles; significantly smaller maximum lumbar flexion and trunk inclination angles were also observed.;Regarding lumbar segmental stability, our results demonstrated that the asymmetric condition significantly reduced lumbar segmental stability by enlarging C7, T12 and S1 segments' sway distance and sway velocity and these effects were more pronounced in the antero-posterial (AP) direction. Furthermore, results indicated AREA CE might be a more appropriate method to be applied to analyze lumbar segmental stability in the asymmetric conditions than other sway area methods (i.e. AREA CC, AREA SW, etc.).;In terms of lumbar segmental stability, results showed that uphill facing surface generated negative effects on lumbar segmental stability, and thus is the least desirable working condition. Downhill facing surface showed insignificant effects on lumbar segmental stability compared with the flat ground condition in most cases. Finally, when performing tasks on slanted surfaces with a deep bending posture, S1 segment demonstrated the worst segmental stability among all three segments tested in the current research. To summarize, our results confirmed that uneven ground surfaces and asymmetric working postures could negatively affect the trunk biomechanics performance, and thus possibly increase the risk of low back pain. Findings from the current research demonstrated the potential need of including ground working conditions to ergonomic risk assessment tools and biomechanical models.

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