The voluntary control of movement is perhaps the most important of human skills since neither actions, nor ideas nor emotions can be expressed in its absence. Clinically significant deficits of motor control are all too common results of trauma and disease and are the source of enormous individual suffering and public as well as private expense. Our understanding of how neural mechanisms control human movements is founded in decades (or even centuries) of observation of behavior in both normal and impaired subjects. This can be thought of as an extensive but patchy record of what humans do in the course of performing motor tasks. What we are aiming for here is to better define the envelope of behaviors defined by what humans can do (rather than the subset of what they do by experimentally investigating the kinds of uniformities of behavior that are maintained across modifications of motor tasks. From observations of such uniformities or invariances, we infer rules for control of muscle contraction that are used by the motor system. We characterize sets of such rules as a strategy. Strategies are qualitative changes in the way muscle forces are developed in response to circumstances surrounding the performance of motor tasks to generate different kinds of movements. For example, we have identified two strategies for single-joint elbow movements called """"""""speed insensitive"""""""" and """"""""speed sensitive"""""""" which distinguish two patterns of behavior in response to changes in movement distance, load, accuracy and speed. Strategies predict kinetic, kinematic and myoelectrical aspects of behavior to provide both a succinct description as to what subjects do and prediction of what subjects should do. The development of these ideas has led us to try to fit them into general theories of voluntary movement. This leads to normative patterns which the strategies predict and we will try to apply these ideas to develop a model for studying motor learning and test an hypothesis on spontaneous falling in the elderly. The specific experiments to be performed in this study focus on extending our single joint approach to progressively more natural and unconstrained movements. Its goal is a description of behavior and a model for control of normal, everyday movement tasks.
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