Human mechanisms for control of posture and motion are normally optimized to perform in Earth's 1-G environment. The mechanisms by which the central nervous system controls and integrates posture and movement are the subject of considerable controversy and ongoing study. The control of jump landings is particularly interesting and complex for several reasons: (1) the control algorithm clearly involves elements of preplanned trajectory formulation as well as generation of commands based on feedback information; (2) dynamic interaction with the environment must be addressed; (3) the jump landing involves dynamic discontinuities; (4) multiple distinct modes of sensory information with different timing characteristics must be integrated into an adequate characterization of the system state; and (5) the controller exhibits rapid adaptation in the face of changes in environmental or perturbation conditions. When modeling the human control mechanisms, these issues must all be accounted for at various levels of detail.
The adaptive effects of exposure to microgravity on astronaut subjects provide a novel opportunity to test and refine models of human full-body motion control. The microgravity environment alters the dynamic equations of body motion, placing considerably different demands on the controller. Furthermore, microgravity alters the composition of sensory input, especially in terms of vestibular and proprioceptive information. When astronauts adapt to the microgravity of spaceflight, they exhibit quantitatively different control strategies, often measured as postflight degradation in performance for balance, locomotion, and jumping tasks. This research proposal centers on the development of a full-body, multisegment dynamic model of postural and motion control for human jumping, including simplification and integration of physiological subsystem descriptions.
This model will provide a framework for testing three hypotheses:
1.Jump landings can be described in terms of a limited number of full-body motion patterns, which correspond to specific muscle activationsynergies.
2.Patterns of motion and muscle activation result from (a) constraints imposed by musculo-skeletal dynamics, and (b) specific control strategies invoked by the central nervous system.
3.Alterations in astronaut jumping performance postflight result from adaptive adjustments to these control strategies due to altered system dynamics and sensory feedback information in zero-G.
The proposed research will identify control strategies by considering three main components. First, hierarchical control architectures will be examined, since research into postural stability in both humans and legged robots has shown that various levels of control may be invoked effectively depending on the nature of disturbances or environmental properties. Second, the modulation of musculoskeletal impedance as an important component of multisegment postural and motion control will be studied, including adaptive modulation of open-loop behavior. Finally, the dynamics of feedback pathways, especially for vestibular and proprioceptive cues, must be described to understand closed-loop control strategies. Prior studies have indicated that exposure to microgravity may result in significant modifications in each of the above three areas.
Models will be validated using data collected at MIT, the Massachusetts General Hospital, and Johnson Space Center. A large database of full-body motion and EMG measurements from approximately thirty shuttle astronauts during jumping and locomotion has already been amassed at JSC's Neuroscience Laboratory. Supplementary ground experiments have been initiated at MGH, while further tests will be designed to evaluate model predictions for human full-body motor control and adaptive processes in altered gravitational environments.
© 1998 Professor Dava Newman. All rights reserved.