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Introduction: Low back pain remains a burden for society, since it can lead to sickness absence and work disability. Physical occupational risk factors can contribute to the development of back pain, yet little is known about any risks in sedentary jobs posed by sitting. The influence of psychosocial factors on back pain and sickness absence amongst sedentary workers is also unclear. The aim of this study was to measure work activities, lumbar movement characteristics, symptoms and psychosocial factors in order to determine associations with low back pain and sickness absence. Methods: Phase 1: involved validation of a fibre-optic goniometer system that attaches to the lumbar spine and hip to continuously measure: (1) activities (sitting, standing, walking); and (2) lumbar movement characteristics (notably sitting postures and kinematics). New questionnaires were also validated to measure aspects of low back discomfort. Phase 2: consisted of a cross-sectional survey of call centre workers (n=600) to collect data on: demographics, clinical and occupational psychosocial factors, and symptoms. An experimental sample (n=140) wore the goniometer system during work. Phase 3: involved a 6-month follow-up survey to collect back pain and sickness absence data (n=367). Logistic regression was used to determine associations (P<0.05) between data. Results: Workers spent 83% of work-time sitting, 26% of which was spent adopting a lordotic lumbar posture. Current back pain (>24hrs: yes/no) was associated with a kyphotic sitting posture (time spent with a lumbar curve ≥180°) (R2 0.05), although future back pain was not. Using multivariable models: limited variety of lumbar movement whilst sitting was associated with future (persistent) LBP, dominating other variables (R2 0.11); yet high levels of reported back discomfort, physical aggravating factors and psychological demand at work were stronger predictors of sickness absence, and dominated other variables (R2 0.24). Interpretation: Workers do not follow the advice from employers to maintain a lumbar lordosis whilst sitting, as recommended by statutory bodies. Furthermore, sitting with a kyphotic posture did not increase the risk of back pain, although a relative lack of lumbar movement did. Thus, ergonomic advice encouraging lumbar movement-in-sitting appears to be justified. Predictors of sickness absence were multi-factorial, and consideration of work-relevant biomedical and psychosocial factors would be more useful than adopting more narrow screening approaches.