Duval-Beaupère G, Schmidt C, Cosson P. A Barycentremetric Study of the Sagittal Shape of Spine and Pelvis: The Conditions Required for an Economic Standing Position. Annals of Biomedical Engineering July 1992; 20(4):451-462.
This study used standing full spine radiographs. The following quote concerns standing radiographs.
“Biomechanical studies must take into account not only the physical interrelation of the skeletal elements, but also the gravitational and antigravitational forces exerted upon them [ed: the need for gravitational, standing x-rays in order to properly study spinal biomechanics].