PURPOSE : The purpose of this study is to compare sagittal spinal alignment and mobility among standing and sitting (which are fundamental postures in daily activities), and four point kneeling (FPK: the imitation of quadrupedal animal posture).METHODS : Fifty three healthy young men have participated in this study. Spinal alignment is measured using a non-invasive skin surface measurement device (Spinal Mouse®: Index Ltd, Japan). The spinal alignment is measured in 3 positions: upright, flexion, and extension, in each posture (standing, sitting, and FPK), and then the thoracic and lumbar curvature and sacral slope are analyzed.RESULTS : Even between 2 fundamental positions, upright standing and sitting, the lumbar lordosis is statistically different (17.1±8.9° at upright standing, 3.5±10.0° at upright sitting, p<0.001). But the sacral slope is not different between those 2 positions. The lumbo-pelvic rhythm (lumbar-hip or lumbar-pelvis flexion ratio) is also different among the 3 postures, especially in FPK posture. In this posture the lumbar spine and pelvis (sacrum) move to opposite direction each other; this phenomenon is not observed at standing and sitting postures. CONCLUSION : The spinal alignment and mobility are different in many segments among standing, sitting, and FPK.