The EMG Evaluation of Moving Tri-Seat Pan Chair Preventing the Pelvis Backward Rotation

Abstract

Objective: The purpose of the study is to preliminarily investigate the function of moving Tri-seat pan chair, which is designed to reduce the low back muscle tension by preventing the backward rotation of the pelvis. Background: Currently, the most Ergonomic chairs have focused on the lumbar support to reduce the disc pressure of lumbar spine. And the seat pan was ergonomically considered only to reduce the pressure to improve the sitting comfort. However, the main cause of disc problem was due to anatomical disruption of normal lordosis angle when the pelvis rotates backwardly during sitting. Therefore, it is meaningful investigation to measure the Tri-seat pan’s efficacy preventing pelvis backward rotation to minimize the disc pressure. Method: This study measured the muscle tension level of lumbar spine of subjects sitting on average school chair and the Tri-seat pan chair. Four subjects were tested for pilot study. Surface EMG was used to measure the static muscle activity from the right and left erector spine muscle. RMS value of EMG was used to evaluate the muscle activity. Furthermore, the lordosis angle was measured from the lumbar spine area by using body protractor for comparison. Results: The normalized RMS value indicated that the muscle activity at average school chair was 1.6 times greater at left side and 1.5 times at right side compared to the Tri-seat pan chair sitting. And the radius of curvature of lordosis was longer in average school chair by 2620mm, which is the indication of disrupted lordosis angle. Conclusion: The moving Tri-seat pan help maintaining the lumbar lordosis angle in certain extent during sitting position. Application: The moving Tri-seat pan can be refined in terms of exterior design and adjustment of components to be used for school chair to minimize low back problem and bad posture. This tri-seat pan concept can be applied to various working chairs including Ergonomic office chair.