Physiotherapy - Theses
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ItemThe influence of trunk-thigh angle on the feasibility of maintaining a neutral lumbar spine in prolonged sitting( 2011)The aim of this study was to explore the feasibility of sitting with a neutral lumbar curve over a prolonged period as a prophylactic measure for low back pain. Low back pain is a major complaint in Western Society, and the shift towards a predominantly sitting posture for work and leisure has not helped to diminish the frequency of this ailment. Adopting a neutral sagittal lumbar spine posture during prolonged sitting, defined as a midrange lumbar curve, has been recommended. The neutral lumbar spine posture is favoured for minimising the deleterious effects that are proposed to accumulate with sitting in extremes of lumbar flexion or extension. The position of the thighs relative to the trunk i.e. the hip flexion angle is considered a major influence on the curvature of the lumbar spine during sitting. The mechanism referred to as ‘lumbofemoral’ rhythm indicates that in the sagittal plane, the thighs and lumbar spine move concurrently, with flexion of the hips being accompanied by flexion of the lumbar spine. Thus, the posture of the lumbar spine in sitting is dependent on the angle of the thighs with respect to the trunk. In conventional sitting with the thighs horizontal (trunk-thigh angle 90°), it was proposed that significantly more activity in the back extensor muscles would be required to hold a neutral lumbar curve against the influence of the lumbofemoral biomechanics than with the thighs lowered 30° from the horizontal (trunk-thigh angle 120°). As a result, subjects sitting in the 90° posture would experience more muscle fatigue, evidenced by a slump into lumbar flexion over time. Thus, whilst previous research has shown that a neutral lumbar curve can be adopted in sitting, it is as yet unknown whether this posture can be maintained for prolonged periods of time particularly when the thighs are horizontal. In this research it was hypothesized that participants sitting with a trunk-thigh angle of 90° would demonstrate a greater deviation in lumbar angle over time that when sitting with a trunk-thigh angle of 120°. An exploratory study with a two-way time series design was used to address this gap in the literature. A sample of convenience of 15 participants, aged 18-35 years was recruited, each fulfilling the eligibility criteria. Each participant was tested in the two sitting positions described; Test Position 1 was defined by a trunk-thigh angle of 90°, and Test Position 2 by a trunk-thigh angle 120°. Tests were held in alternate sequence, with each test lasting 15 minutes, interspersed with a short 5-minute rest. The use of two tri-axial accelerometers, attached to the skin over the midline spine (T12 and S2) of participants, provided continuous measurement of lumbar angle. Participants were instructed on how to adopt the neutral lumbar curve, and were asked to maintain this posture for the duration of the test, whilst watching a series of movie clips on a screen ahead. At the end of each trial participants recorded the level of effort required to maintain the starting neutral lumbar spine position. Statistical analysis showed that participants were able to adopt the neutral lumbar curve in both sitting positions. With a midpoint sagittal lumbar angle of 12.33 (±7.93°) in Test Position 1, and 15.57 (±8.04°) in Test Position 2, participants adopted a mean start lumbar angle of 10.30 (±7.84°) and 10.09 (9.58°) respectively. However, in both sitting positions, participants were unable to maintain the start position over the 15-minute period. Absolute values showed a mean maximal deviation in lumbar angle of 7.52 (±4.76°) in Test Position 1 and 5.87 (±6.31°) in Test Position 2. The difference in trunk-thigh angle did not lead to a significant difference in the postural behaviour, with a similar onset and magnitude of increased lumbar flexion (5°) occurring in both test positions. In addition, the difference in trunk-thigh angle was not reflected in the level of effort reported with participants scoring relatively low values for holding the posture in the two positions. Thus the hypothesis for this study was rejected. There were a number of limitations to this study, in particular the variations in lumbar angle that occurred within the small sample size. Apart from increasing the number of participants, future research should include subjects from populations defined by age, gender, and task/ workplace, and the time frame should be increased to allow any subtle, yet cumulative effects from sitting with a different trunk-thigh angle to emerge. The investigation would benefit from measurement of adjacent spinal regions to determine their effect on the sitting lumbar posture, and from the use of electromyography to monitor back muscle activity.