Key words Coordination · Posture · Movement ·

Abstract The whole-body center of mass (CoM) has been classically regarded as the stabilized reference val-ue for human voluntary movements executed upon a fixed base of support. Axial synergies (opposing dis-placements of head and trunk with hip segments) are be-lieved to minimize antero-posterior (A/P) CoM displace-ments during forward trunk movements. It is also widely accepted that anticipatory postural adjustments (APAs) create forces of inertia that counteract disturbances aris-ing from the moving segment(s). In the present study, we investigated CoM stabilization by axial synergies and APAs during a whole-body reaching task. Subjects reached towards an object placed on the ground in front of them in their sagittal plane using a strategy of coordi-nated trunk, knee, and hip flexion. The reaching task im-posed constraints on arm-trajectory formation and equi-librium maintenance. To manipulate equilibrium con-straints, differing conditions of distance and speed were imposed. The comparison of distance conditions sug-gested that axial synergies were not entirely devoted to CoM stabilization: backward A/P hip displacements re-duced as head and trunk forward A/P displacements in-creased. Analysis of upper- and lower-body centers of mass in relation to the CoM also showed no strict mini-mization of A/P CoM displacements. Mechanical analy-sis of the effects of APAs revealed that, rather than act-ing to stabilize the CoM, APAs created necessary condi-tions for forward CoM displacement within the base of support in each condition. The results have implications for the CoM as the primary stabilized reference for pos-ture and movement coordination during whole-body reaching and for the central control of posture and volun-tary movement