Appendix S1 - Functional Synergies Underlying Control of Upright Posture during Changes in Head Orientation

Geometric model relating the joint configuration to the center of mass position. The geometric model relating the joint configuration to the center of mass position (dCMPOS) in the sagittal plane (AP) was formulated in terms of ankle, knee, hip and L5-S1 joint angles, with the addition of C7-T1 and atlanto-occipital (AO) joint angles, or leg and trunk segment angles with the horizontal. The model with 6 joint angles (θi) is provided here, including 6 limb segment lengths (lj), the proportion of total body mass for each of these segments (mj), and the distance of the individual segment masses from the disital end where the mass of that segment is concentrated (dj), where i = {ankle, knee, hip, L5-S1, C7-T1 and AO} joint angles, and j = {shank, thigh, pelvis, trunk, neck, head} segments [20]. (DOCX)