In addition to its intrinsic importance during quiet standing, posture also serves as
the background for a wide variety of other critical motor tasks. The hierarchical nature of
the motor control system suggests that the different layers may be responsible for
different aspects of posture. I tested the hypothesis that spinal reflexes are organized
according to optimal principles of stability, control accuracy, and energy. I found that
there were no globally stable muscle activation patterns for muscles operating near
optimal fiber length, suggesting that the intrinsic viscoelastic properties of muscle are
insufficient to provide limb stability. However, for stiffer muscles a stable limb could be
created by selectively activating muscles based on their moment-arm joint angle
relationships. The optimal organization of length and velocity feedback to control and
stabilize the endpoint position of a limb could not be produced from a purely muscle
controller, but required neural feedback to improve endpoint performance, reduce
energetic cost, and produce greater coordination among joints. I found that while
muscles at near optimal fiber length were insufficient to provide limb stability, the length
feedback provided by the autogenic stretch reflex was sufficient to stabilize. Length
feedback was also sufficient to produce the directional tuning of muscle activity and
constrained ground reaction forces as is observed in experiments. These results have
implications for controlling powered prosthetic devices, suggesting that subdividing the
responsibility for stability among hierarchical control structures will simultaneous
improve stability and maneuverability of the devices.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/22634 |
| Date | 01 April 2008 |
| Creators | Bunderson, Nathan Eric |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Detected Language | English |
| Type | Dissertation |
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