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Neuro-Motor Responses to Daily Centrifugation in Bed-Rested SubjectsIt is well known from numerous space flight studies that exposure to micro-g produces both morphological and neural adaptations in the major postural muscles. However, the characteristics and mechanism of these changes, particularly when it may involve the central nervous system are not defined. Furthermore, it is not known what role unloading of the muscular system may have on central changes in sensorimotor function or if centrifugation along the +Gz direction (long body axis) can mitigate both the peripheral changes in muscle function and modification of the central changes in sensorimotor adaptation to the near weightless environment of space flight. The purpose of this specific effort was, therefore, to investigate the efficacy of artificial gravity (AG) as a method for maintaining sensorimotor function in micro-g. Eight male subjects were exposed to daily 1 hr centrifugation during a 21 day 6 degree head-down bed rest study. Seven controls were placed on the centrifuge without rotation. The radius and angular velocity of the centrifuge were adjusted such that each subject experienced a centripetal acceleration of 2.5g at the feet, and approximately 1.0g at the heart. Both the tendon (MSR) and functional stretch reflexes (FSR) were collected using an 80 lb. ft. servomotor controlled via position feedback to provide a dorsiflexion step input to elicit the MSR, and the same step input with a built in 3 sec hold to evoke the FSR. EMG data were obtained from the triceps surae. Supplementary torque, velocity and position data were collected with the EMG responses. All data were digitized and sampled at 4 kHz. Only the MSR data has been analyzed at this time, and preliminary results suggest that those subjects exposed to active centrifugation (treatment group) show only minor changes in MSR peak latency times, either as a function of time spent in bed rest or exposure to centrifugation, while the control subjects show delays in the MSR peak latencies that are typical of bed rested subjects. There also appears to be a trend in the treatment group where centrifugation results in peak latencies that are shorter than the control group. This trend is supported by the observation that peak reflex amplitudes are larger (up to 40% in magnitude)than those of the control subjects. Furthermore, centrifugation tends, by day 21 of bed rest, to normalize the peak amplitudes to the amplitudes observed prior to bed rest or centrifugation. From a preliminary point of view, centrifugation appears to have a positive effect on the sensorimotor system, and specifically on those muscles that provide anti-gravity and postural support.
Document ID
20070009992
Acquisition Source
Johnson Space Center
Document Type
Abstract
Authors
Reschke, Millard F.
(NASA Johnson Space Center Houston, TX, United States)
Somers, Jeffery T.
(Wyle Labs., Inc. Houston, TX, United States)
Krnavek, Jody
(Wyle Labs., Inc. Houston, TX, United States)
Fisher, Elizibeth
(Wyle Labs., Inc. Houston, TX, United States)
Ford, George
(Wyle Labs., Inc. Houston, TX, United States)
Paloski, William H.
(NASA Johnson Space Center Houston, TX, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2007
Subject Category
Aerospace Medicine
Meeting Information
Meeting: 28th Annual International Gravitational Physiology Meeting
Location: San Antonio, TX
Country: United States
Start Date: April 8, 2007
End Date: April 13, 2007
Distribution Limits
Public
Copyright
Other

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