Thoracic and lumbar posture behaviour in sitting tasks and standing: Progressing the biomechanics from observations to measurements.

Few studies quantify spinal posture behaviour at both the thoracolumbar and lumbar spinal regions. This study compared spontaneous spinal posture in 50 asymptomatic participants (21 males) during three conditions: 10-min computer task in sitting (participants naïve to the measure), during their perceived 'correct' sitting posture, and standing. Three-dimensional optical tracking quantified surface spinal angles at the thoracolumbar and lumbar regions, and spinal orientation with respect to the vertical. Despite popular belief that lordotic lumbar angles are 'correct' for sitting, this was rarely adopted for 10-min sitting. In 10-min sitting, spinal angles flexed 24(7-9)deg at lumbar and 12(6-8)deg at thoracolumbar regions relative to standing (P < 0.001). When participants 'corrected' their sitting posture, their thoracolumbar angle -2(7)deg was similar to the angle in standing -1(6)deg (P = 1.00). Males were flexed at the lumbar angle relative to females for 10-min sitting, 'correct' sitting and standing, but showed no difference at the thoracolumbar region.