Examining contemporary motor control theories from the perspective of degrees of freedom.
ABSTRACT Occupational therapy aims to restore independent living skills and to improve social participation for clients; therefore, optimising motor ability can be a major goal during intervention in clinical practice. Choosing the adequate approach for each client is critical to achieve treatment goals. As frame of reference is based on contemporary theories related to human behaviours, it is crucial to synthesise current theories of motor control for clinical application. In this review, four motor control theories were examined by the Bernstein's classical question: redundant degrees of freedom. By addressing the central issue in motor control theories, the strengths and weaknesses for each theory were discussed in detail.
Classical literatures were selected for each theory and related references were reviewed as evidence to support the potential biological plausibility.
The research of motor control theories have been developed for over centuries, researchers still strive to discover how human beings execute movements. To date, motor control theories were mainly proposed by three disciplines: biology, psychology and engineering. Each discipline has unique perspective to develop solutions for understanding the processes behind the execution of movement.
For occupational therapists in clinics, it is imperative to integrate current knowledge and motor control theories into practice and to explore new approaches to treat clients with motor disability.
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ABSTRACT: This paper presents studies of the coordination of voluntary human arm movements. A mathematical model is formulated which is shown to predict both the qualitative features and the quantitative details observed experimentally in planar, multijoint arm movements. Coordination is modeled mathematically by defining an objective function, a measure of performance for any possible movement. The unique trajectory which yields the best performance is determined using dynamic optimization theory. In the work presented here, the objective function is the square of the magnitude of jerk (rate of change of acceleration) of the hand integrated over the entire movement. This is equivalent to assuming that a major goal of motor coordination is the production of the smoothest possible movement of the hand. Experimental observations of human subjects performing voluntary unconstrained movements in a horizontal plane are presented. They confirm the following predictions of the mathematical model: unconstrained point-to-point motions are approximately straight with bell-shaped tangential velocity profiles; curved motions (through an intermediate point or around an obstacle) have portions of low curvature joined by portions of high curvature; at points of high curvature, the tangential velocity is reduced; the durations of the low-curvature portions are approximately equal. The theoretical analysis is based solely on the kinematics of movement independent of the dynamics of the musculoskeletal system and is successful only when formulated in terms of the motion of the hand in extracorporal space. The implications with respect to movement organization are discussed.Journal of Neuroscience 08/1985; 5(7):1688-703. · 6.91 Impact Factor
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ABSTRACT: This paper presents a mathematical model which predicts both the major qualitative features and, within experimental error, the quantitative details of a class of perturbed and unperturbed large-amplitude, voluntary movements performed at intermediate speed by primates. A feature of the mathematical model is that a concise description of the behavioral organization of the movement has been formulated which is separate and distinct from the description of the dynamics of movement execution. Based on observations of voluntary movements in primates, the organization has been described as though the goal were to make the smoothest movement possible under the circumstances, i.e., to minimize the accelerative transients. This has been formalized by using dynamic optimization theory to determine the movement which minimizes the rate of change of acceleration (jerk) of the limb. Based on observations of muscle mechanics, the concept of a "virtual position" determined by the active states of the muscles is rigorously defined as one of the mechanical consequences of the neural commands to the muscles. This provides insight into the mechanics of perturbed and unperturbed movements and is a useful aid in the separation of the descriptions of movement organization and movement execution.Journal of Neuroscience 12/1984; 4(11):2745-54. · 6.91 Impact Factor
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ABSTRACT: This paper presents some elementary principles regarding constraints on movements, which may be useful in modeling and interpreting motor control strategies for skilled movements. Movements which are optimum with respect to various objectives, or "costs", are analyzed and compared. The specific costs considered are related to movement time, distance, peak velocity, energy, peak acceleration, and rate of change of acceleration (jerk). The velocity patterns for the various minimum cost movements are compared with each other and with some skilled movement patterns. The concept of performance trade-offs between competing objectives is used to interpret the distance-time relationships observed in skilled movements. Examples of arm movements during violin bowing and jaw movements during speech are used to show how skilled movements are influenced by considerations of physical economy, or "ease", of movement. Minimum-cost solutions for the various costs, which include the effect of frictional forces, are given in Appendices.Biological Cybernetics 02/1983; 46(2):135-47. · 2.07 Impact Factor