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Sitting, Dynamic, Posture, Measurement, Video, School.

School children spent a lot of time sitting. Some Primary Schools in Slovenia were interested to improve pupil’s working conditions by introducing more dynamic type of sitting. A standard school chair was substituted with a large gymnastic ball. In order to evaluate influence of this substitution on sitting dynamics we developed a video system capable of assessing sitting posture in sagittal plain during prolonged period.

We composed a video acquisition system with video camera (Blaupunkt, CCR 808), simple optical markers with LED diodes and robust image analysing software. To test it we measured the sitting posture of eight school children, who were sitting for 30 minutes on a large gymnastic ball and on a chair without a backrest and armrest with the acquisition rate 3 s -1. Each image was analysed to determine position of markers and then the Lumbar Lordosis angle (LL) and the Pelvis Inclination angle (PI) time courses were calculated.

We found a measurement system very convenient in the conditions outside the laboratory. The level of backscatter which could impair automatic marker location extraction from the recorded image was low during all sessions. The marker in the recorded image had 30±10 pixels with different intensity. We found that during first 6 minutes the posture is more upright on the ball as compared to the chair (PI: chair 17.0±7.2, ball 13.2 ±8.5, p<0.05; LL: chair -5.1±2.5, ball - 4.8±2.1, p>0.05).

A measurement system using consumer video camera, LED video markers and image analytics software is cost effective and reliable system which has minimal influence on students comfort during measurements outside the laboratory.