Reaching for objects are a natural and common behavior. The proposed work is based on the unexpected finding in a series of preliminary studies that extremely large Coriolis forces are generated on the arm by the trunk rotation that normally accompanies reaching to laterally placed objects. Contrary to intuition, when we turn and reach for an object, the Coriolis force generated by the torso motion on the extending arm is an order of magnitude greater than the interaction forces generated during simple reaches not involving trunk rotation. This suggests that to understand normal unconstrained reaching it will be critical to understand the forces generated by truncal movements and how they are controlled. We have developed a set of paradigms designed to isolate the contribution of torso rotation to the force profiles associated with natural reaching movements. Our goal is to contribute to the understanding of human movement control by identifying the sensory and motor signals involved in the representation of self-motion used for a) generating anticipatory compensations to maintain movement accuracy despite self-generated Coriolis forces, b) generating on-line compensations, and c) allowing adaptation plasticity for self-generated Coriolis torques. In Aim 1, we propose to determine the role of vestibular signals in compensations for interaction torques during natural turn and reach movements. In Aim 2, we will assess the role of vestibular signals in on-line compensations for interaction torques generated by reaching movements during passive rotation. In Aim 3, we will assess the plasticity of compensation for interaction torques during turn and reach movements. The experimental program will involve kinematic measurements of the arm segments for reaching movements made during both voluntary and passive torso rotation. The associated joint torques will be computed through inverse dynamics modeling. The results will provide a better understanding of the interaction forces associated with natural reaching movements involving simultaneous movements of the whole body and of how they are controlled. We will learn how the nervous system parcels the net force field into a subcomponent mechanically caused by self-rotation and maintains sensory-motor adaptation attuned to this type of load component. The results should have broad significance for normal movement control as well as for disorders of movement control.