ABSTRACT
Prolonged and static sitting postures at VDU workplaces arc discussed as risk factors for the musculoskeletal system. Manufacturers of office chairs have therefore created specific dynamic office chairs that contain structural elements to promote dynamic sitting and therefore to prevent musculoskeletal disorders. The aim of this study was to evaluate the effects of four specific dynamic chairs on erector spinae and trapezius EMG, postures/joint angles and physical activity intensity (P AI) compared to a conventional standard office chair. All chairs were instrumented with inertial sensors to measure chair parameters (backrest inclination, scat pan inclination forward and sideward) and tested in laboratory by 10 subjects
performing 7 standardized office tasks. Muscular activation showed no significant differences between the specific dynamic chairs and the reference chair. The analysis of postures/joint angles and P AI revealed only few differences among the chairs, whereas the performed tasks strongly affected the measured muscle activation, postures and kinematics. The characteristic dynamic elements of each specific chair yielded significant differences of the measured chair parameters, but these characteristics did not seem to affect the sitting dynamics of the subjects performing their office tasks.
