Background: Researchers have measured exposure to sitting using self-reported questionnaires and observational analysis. Such methods are not a reliable measure of daily exposure or sensitive enough to take into account lumbar posture when seated. Recent innovations have produced a fibre-optic goniometer (FOG) that can continuously measure sagittal lumbar posture, although this single sensor is unable to identify if the user is sitting, standing or walking.

Methods: A new system was developed utilising a second FOG attached to the hip. Movement characteristics of the hip and lumbar spine were described and used to develop software to predict activity (sitting, standing, walking). Subsequently 10 participants were asked to wear the FOGs for 8 minutes whilst their behaviour was recorded using a video camera. MPEG video sequences were produced and each activity was coded at a point in time and compared against the 2 FOG software model.

Results: All Participants found the system comfortable to wear. Validation of the software against the MPEG files showed high sensitivity for sitting (90%), standing (98%), and walking (95%). Positive predictive value was high for sitting (93%), standing (89%) and walking (94%). The overall agreement between video analysis and the FOG software was 92%

Conclusions: Developing the FOG has produced a practical system capable of continuously measuring sedentary workers basic activity in terms of sitting standing and walking. This novel tool will now be used in a prospective study of sedentary workers to determine the influence of seated lumbar posture on the development of LBP.