Optimal Control of Non-ballistic Muscular Movements: A Constraint-Based Performance Criterion for Rising From a Chair

[+] Author and Article Information
M. G. Pandy

Department of Kinesiology and Health Education; Department of Mechanical Engineering, The University of Texas at Austin Austin, TX 78712

B. A. Garner, F. C. Anderson

Department of Mechanical Engineering, The University of Texas at Austin Austin, TX 78712

J Biomech Eng 117(1), 15-26 (Feb 01, 1995) (12 pages) doi:10.1115/1.2792265 History: Received August 28, 1992; Revised January 10, 1994; Online October 30, 2007


To understand how humans perform non-ballistic movements, we have developed an optimal control model to simulate rising from a chair. The human body was modeled as a three-segment, articulated, planar linkage, with adjacent links joined together by frictionless revolutes. The skeleton was actuated by eight musculotendinous units with each muscle modeled as a three-element entity in series with tendon. Because rising from a chair presents a relatively ambiguous performance criterion, we chose to evaluate a number of different performance criteria, each based upon a fundamental dynamical property of movement: muscle force. Through a quantitative comparison of model and experiment, we found that neither a minimum-impulse nor a minimum-energy criterion is able to reproduce the major features of standing up. Instead, we introduce a performance criterion based upon an important and previously overlooked dynamical property of muscle: the time derivative of force. Our motivation for incorporating such a quantity into a mathematical description of the goal of a motor task is founded upon the belief that non-ballistic movements are controlled by gradual increases in muscle force rather than by rapid changes in force over time. By computing the optimal control solution for rising from a static squatting position, we show that minimizing the integral of a quantity which depends upon the time derivative of muscle force meets an important physiological requirement: it minimizes the peak forces developed by muscles throughout the movement. Furthermore, by computing the optimal control solution for rising from a chair, we demonstrate that multi-joint coordination is dictated not only by the choice of a performance criterion but by the presence of a motion constraint as well.

Copyright © 1995 by The American Society of Mechanical Engineers
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