Decoupled pelvis adjustment to induce lumbar motion: A technique that controls low back load in sitting

Static sitting in confined settings have been associated with low back pain in sedentary occupations such as office works and car driving. To prevent lumbar discomfort in prolonged static sitting, periodic motion of the lumbar spine is needed. Because the pelvis forms the basis for lumbar spine curvature, a passive motion technique was developed, which adjusts pelvis orientation independent from the trunk. This study uses a computer-aided simulator chair instrumented with a mechanism for decoupled pelvis adjustment and investigates the effects on low back load in eighteen healthy male individuals. Experiments involved measurement of body segments orientation, interface back pressure distribution and seat reaction forces during quasi-static actuated pelvis rotation in the sagittal and frontal plane. Joint forces and torques were estimated in the lumbosacral spine region. In sagittal pelvis adjustment, the pelvis rotated 19 ± 3 degrees and strong relations (r 2 > 0.8) were found with centre of back pressure in upward direction (cp z, r 2 = 0.90), lumbosacral shear force in forward direction (F ly, r 2 = 0.91), lumbosacral normal force in axial direction (F lz, r 2 = 0.80), lumbosacral torque around lateral direction (T lx, r 2 = 0.87) and interface pressure at the lower back (P lb, r 2 = 0.88). In frontal pelvis adjustment, the pelvis rotated 9 ± 1 degrees and strong relations were found with centre of back pressure in lateral direction (cp x, r 2 = 0.96), lumbosacral torque around forward direction (T ly, r 2 = 0.98) and lumbosacral torque around axial direction (T lz, r 2 = 0.95). These findings indicate that decoupled pelvis adjustment could be an applicable intervention to control low back load in prolonged static sitting. Decoupled pelvis adjustment might be an applicable technique to induce periodic lumbar motion which potentially improves tolerance for prolonged static sitting.