A. The spine model. Blue dots indicate the joints between the lumbar vertebrae ( L
) and the sacrum ( S
). Blue and red lines indicate the locations of the straight and oblique global muscle fibers between the thoracic cage and pelvis (horizontal grey bars). The midline between the global muscles (dashed line) crosses the origin (horizontal position 0) and the point-mass m for the upper body. E is the eccentricity of thoracic and pelvis joints with respect to the origin; is the spinal curvature. B. Schema of spinal segment L2 L3. r is the distance between the CoR and m, α is the angle between r and the vertical. M
is the sum of the torques generated by the global muscles on this segment. M
is the external moment, and CT is the local counter torque.