Dynamics of Posture and Reaching

Brandeis University, Waltham MA

Investigators

Abstract

An essential issue in the movement sciences is to understand how people maintain upright posture and balance. In everyday life, people often simultaneously turn and reach to pick up objects or to place objects. Such movements are typically accurate and seem virtually effortless. However, when an arm movement is made during ongoing trunk rotation large inertial forces are generated on the reaching arm. These forces are so large that huge errors in reaching and destabilization of posture would occur if the central nervous system (CNS) did not take them into account. In this program of research, two series of experiments will examine the interaction of the control of self-rotation and of arm-torso dynamics. Series 1 will evaluate the kinematics of reaching and turning, postural sway, arm joint torques, and ground reaction forces at the feet. Series 2 will assess these variables in tasks involving active and passive torso rotation and reaching. The results will indicate whether the CNS control of trunk rotation and arm reaching are a) parallel and independent, b) hierarchical with information about intended trunk rotation contributing to separate control of torso and arm movements, or c) distributed with a single internal model for reaching and turning. Falling in the elderly is a major health problem. Neurological diseases that affect torso and or limb movement control (e.g., Parkinson's disease) also increase the likelihood of falls. This research should provide a scientific basis for developing rehabilitation strategies that compensate for trunk-generated forces on the limbs and minimize the likelihood of falling.