Influence of hip angle on muscle activity and lumbar posture in dentists during a dental screening task

Introduction: To avoid potentially painful end-range positions and to facilitate activation of trunk muscles, adopting neutral lumbar spine postures has been emphasized. Such a neutral posture is obtained through positioning the lower lumbar spine into slight anterior tilt and slight lumbar lordosis while relaxation of the thoracic spine is maintained. Maintaining this neutral posture was found to be easier while sitting with an open hip angle. Whereas in the past dental stools facilitated a 90° hip angle, recently different stools have been developed to allow a greater hip angle. Next to saddle stools, for dentistry also the Ghopec stool has been developed. The latter stool comprises a seat pan consisting of a horizontal rear part for the pelvis and an inclinable sloping down front part for the upper legs, with a vertically and horizontally adjustable back rest. Aim: to evaluate the influence of different sitting modes on muscle activity and lumbar posture in dentists during work. M&M: This study compared muscle activity and lumbar posture on a standard stool with, a saddle stool without and the Ghopec with back rest. Twenty five participants completed a dental screening task on all stools in one session. Muscle activity was assessed with surface electromyography and lumbar posture using the BodyGuardTM. Results: Lumbar posture was most close to neutral on the Ghopec stool, whereas sitting on a standard or saddle stool resulted in a respectively more flexed or extended posture. Generally, sitting with a 90° hip angle (standard stool) resulted in higher activation of back muscles while sitting with a 125° hip angle (saddle stool and Ghopec) activated abdominal muscles to a higher degree, although less in the presence of a backrest (Ghopec). Conclusion: To maintain neutral posture, the Ghopec is considered the most suitable of the 3 stools investigate