Human beings are the only vertebrates to maintain an upright, totally vertical, bipedal position submitted to the law of gravity. Unlike other vertebrates, the human spine comprises successive, opposing curves which allows the trunk to maintain an erect position. Lumbar lordosis is found in no other species. Bipedal locomotion in nonhuman primates is extremely limited. Those species often use their long forelimbs in pronation position to keep balance when trying to perform a bipedal displacement. Erect position is linked with pelvic rotation and enlargement, associated with modifications of the spine sagittal curvatures and muscle adaptation [1]. Human bipedalism is exclusive, stable and ergonomic. In order to maintain this posture for prolonged periods, the erect position should be economical in terms of energy expenditure. To correctly analyze the erect posture, it is necessary to define spinal and pelvic parameters, and to correlate those parameters with global parameters in full standing position. .
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