Low back pain (LBP) is a common occupational problem and continues to be the leading cause of occupational disability. Among diverse known risk factors, sitting is commonly considered as an important exposure related to LBP. Both modern living and contemporary work involve increased sedentary lifestyles, including more frequent and prolonged sitting. At present, however, the causal role of sitting on LBP development is controversial due to the contribution of several moderating factors (e.g., task demands, duration of exposures, and presence of muscle fatigue). A few studies have assessed low back loads in seated postures, but none has investigated the effects of prolonged sitting or time-dependent variations on spinal structure and spinal loading. Adverse effects of muscle fatigue on low back pain are well documented, yet the specific relationship between muscle fatigue and sitting-related low back pain are not fully established. In addition to these fundamental limitations in our understanding of the physical consequences of sitting, there is also little evidence regarding the effects of task requirements on muscle fatigue and spine loading.
Therefore, the main objectives of this work were, in the context of sitting, to: 1) develop and evaluate a method to assess paraspinal muscle fatigue using electrical stimulation; 2) develop and evaluate a method (model) to quantify biomechanical loads on the lumbar spine in a seated posture; and 3) quantify the effects of prolonged seated tasks on low back loads, body discomfort, and localized muscle fatigue (LMF). The primary hypothesis was that exposure to sitting-related LBP risks is influenced by task requirements and sitting duration.
A muscle stimulation protocol was developed to measure stimulation responses in the lumbar extensors. A stimulation protocol, which included one conditioning train along with three 16-second stimulation train at 2 Hz, was recommended as appropriate to measure those muscles potentially fatigued during prolonged seated tasks. A three-dimensional, sitting-specific, fatigue-sensitive, time-dependent, electromyography (EMG)-based biomechanical model of the trunk was developed to investigate the effects of seated tasks and time-dependent variations on lumbosacral loading during sitting. Reasonable levels of correspondence were found between measured and predicted lumbosacral moments under a range of seated tasks. Lastly, the effects of prolonged sitting and psychosocial work stress on low back were quantitatively identified. Only prolonged sitting significantly increased trunk flexion angles and led to muscle fatigue. Relatively weak correlations were found between subjective and objective measures, though the two fatigue measurement methods (based on EMG and stimulated responses) showed a good level of correspondence.
Overall, this work provides a quantitative assessment of biomechanical exposures associated with seated tasks. The methods developed in this work make a contribution in terms of measurement/modeling approaches that can be used to assess LBP-relevant risks during prolonged sitting. The results of this work provide a better understanding of the effects of prolonged sitting on the risk of developing sitting-related LBP. Finally, results regarding the influences of prolonged sitting and psychosocial demands can be used to guide future job design. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/50546 |
| Date | 08 April 2013 |
| Creators | Jia, Bochen |
| Contributors | Industrial and Systems Engineering, Nussbaum, Maury A., Madigan, Michael L., Lockhart, Thurmon E., Granata, Kevin P., Agnew, Michael J., Perez, Miguel A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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