Minimum PC S Aof the global musculature to guarantee self-stability at each of the five lumbar spinal segments, depending on the geometrical arrangement of the spine, according Equation 1. Position A - symmetrical arrangement with no eccentricity and no spinal curvature. Position B - introducing an eccentricity without a spinal curvature. Position C - physiological situation in the sagittal plane with an eccentricity and a spinal curvature. Position D - introducing a curvature in a symmetrical arrangement.