System to measure the use of the backrest in sitting-posture office tasks.

This paper presents an inexpensive and simple system to measure the way of use of the backrest. The system can be also used in field studies. It is based on a set of electrodes which, attached to the subject's back and the backrest, allows the contact area to be measured. A laboratory test was performed to validate the system. In the test the spontaneous use of the backrest in standard office chairs and tasks was studied. Four different types of backrest use have been detected, and it has been shown that they determine the lumbar curvature and pelvic inclination angles, as well as postural mobility. The comfort levels observed in the four types of backrest use were also different. Consequently, the system can be used as an indicator of back posture and comfort.