Objectives
Gravity supplies a frame of reference for the human sensory-motor response. In the absence of gravity, such as during space flight, several systems are hindered. These disturbances are compensated for by the brain, and ultimately, the body adapts to the weightless environment. Balance and locomotion are temporarily disturbed after return to Earth, but eventually return to preflight levels. Postural problems reported by crewmembers include increased sway while standing, difficulty in rounding corners and increased body movement during locomotion. This investigation assessed the impact of microgravity on neuromuscular anticipatory postural activity and examined the changes, intending to provide a better understanding of balance and locomotion in humans and to design countermeasures which could reduce the time course of re-adaptation to gravity on Earth.
Five objectives were examined during this study. These were:
(1) to determine how long-duration space flight altered the anticipatory neuromuscular activity associated with arm movement,
(2) to determine whether foot sensory input modified neuromuscular responses during space flight,
(3) to determine the time course of adaptation during long-duration space flight to foot sensory input as measured by patterns of neuromuscular activation,
(4) to determine whether long-duration space flight modified anticipatory neuromuscular postural activity in the immediate postflight period,
(5) to determine whether modifications in anticipatory neuromuscular postural activity associated with long-duration space flight were correlated with postural instability immediately after landing and during the recovery period.
Shuttle-Mir Missions Approach
During preflight and postflight testing, subjects performed arm raises while standing on a force plate to obtain ground reaction forces and center of pressure (COP) measures. Body segment kinematic measures were also obtained. These measurements enabled determination of the degree of postflight postural instability associated with voluntary arm movement.
Results
The important finding stemming from the inflight data was that the addition of foot sensory input (i.e. provided by pressure to the feet) resulted in neuromuscular activation not normally present without foot pressure. These results strongly suggested that inflight foot pressure may be used as a form of a countermeasure to retard muscle atrophy and maintain the health of neuromuscular reflex loops. Muscle activation patterns associated with the "bungeed to treadmill condition" were dissimilar to those observed during arm movements made in unit gravity. This is an important finding because the bungee cords were calibrated to create a load equivalent to the subject's body weight (i.e., 1-G loading), but the altered activation patterns suggested that bungee loading is not equivalent, biomechanically speaking, to a unit gravity condition. Thus, for movement tasks, it would be inappropriate to compare responses observed during inflight bungee loading with those observed on Earth. Additionally, the adaptations in neuromuscular activation patterns associated with different inflight support conditions indicated that the sensory-motor system maintained it's response flexibility even after 100 days in microgravity.
Earth Benefits Publications
Layne, C.S., McDonald, P.V., Mulavara, A.P., Kozlovskaya, I.B., and Bloomberg, J.J. Adapting neuromuscular synergies in microgravity. Bernstein's Traditions in Motor Control Conference, Pennsylvania State University, University Park, PA, August, 1996.
Layne, C.S., McDonald, P.V., Pruett, C.J., Mulavara, A., Kozlovskaya, I.B., Voronov, A.V., and Bloomberg, J.J. The impact of space flight on anticipatory muscle activation. Annual Meeting of the American Institute of Aeronautics and Astronautics, Houston, TX, March, 1996.
Layne, C.S., Mulavara, A.P., McDonald, P.V., Pruett, C.J., and Bloomberg, J.J. Somatosensory input enhances neuromuscular activation during movements performed while free-floating in microgravity. Society for Neuroscience Annual Meeting, Washington, D.C. November, 1996.
Mulavara, A.P., McDonald, P.V., Layne, C.S., Poliner, J., Pruett, C.J., and Bloomberg, J.J. Quantifying adaptive preparatory postural adjustments that occur following space flight. 14th Annual Houston Conference on Biomedical Engineering Research, Houston, TX, February, 1996.
Layne, C.S., Spooner, B.S. Microgravity effects on "postural" muscle activity patterns. Adv. in Space Res. 1994 (in press).
Layne, C.S., McDonald, P.V., Mulavara, A.P., and Bloomberg, J.J. ''Adaptations in movement control after space flight..'' Annual Meeting of the North American Society for Psychology of Sport and Physical Activity, St. Charles, IL, June, 1998.
Layne, C.S., Mulavara, A.P., McDonald, P.V., Pruett, C.J., Kozlovskaya, I.B., and Bloomberg, J.J. ''The impact of long-duration space flight on upright postural stability during unilateral arm raises.'' Annual Meeting of the Society for Neuroscience, New Orleans, LA, October, 1997.
Layne, C.S., Mulavara, A.P., Pruett, C.J., McDonald, P.V., Kozlovskaya, I.B., and Bloomberg, J.J. ''The use of inflight foot pressure as a countermeasure to neuromuscular degradation.'' Acta Astronautica, vol. 42, no. 1-8, 231-246 (1998).
Principal Investigators
Inessa B. Koslovskaya, M.D. Co-Investigators
STS-71/Mir-18, STS-74/Mir 19
Inflight testing consisted of four arm-raising conditions designed to vary the degree of foot sensory input. Arm movements were completed while the subject free-floated, free-floated with the addition of foot pressure, was secured passively at the feet using Velcro to the Mir or Shuttle's support surface, and while connected via bungee cords to the support surface. Electrical activity (EMG) from selected arm, trunk and leg muscles and arm acceleration was monitored. Changes in the neuromuscular activation characteristics associated with the experimental conditions were recorded.
All subjects demonstrated decrements in postural control associated with voluntary arm movements. Center of pressure (COP) measures indicated that two postural control strategies were evident after space flight. Some subjects increased the magnitude of COP motion despite decreased arm acceleration features. This increased COP motion brought these subjects closer to the limits of their base of support, thus jeopardizing their stability. Other subjects displayed compression of the COP motion after space flight. This fact, combined with the decreased arm acceleration suggested that these subjects chose to minimize their COP motion in order to remain well clear of their base of support boundary. For all subjects the data indicated that the precise neuromuscular activation patterns necessary for optimal arm movement were not produced after space flight.
This project has the potential to increase the understanding of processes whereby sensory input results in neuromuscular activation. It is suggested that many of the processes that contribute to muscle atrophy on Earth also contribute to the atrophy associated with space flight. It is anticipated that foot pressure will be regularly used to lessen lower limb muscle atrophy and maintain the functional state of muscles in bedridden patients.
Layne, C.S., Bloomberg, J.J., McDonald, P.V., Mulavara, A.P., and Pruett, C.J. The use of foot pressure to enhance neuromuscular activation during space flight. Annual Meeting of the American Institute of Aeronautics and Astronautics, Houston, TX, March, 1996.
Charles S. Layne, Ph.D.
University of Texas at Austin
Institute of Biomedical Problems
Jacob J. Bloomberg, Ph.D.
Vernon P. McDonald, Ph.D.
Andrei A. Voronov, Ph.D.
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Curator:
Julie Oliveaux
Responsible NASA Official: John Uri |
Page last updated: 07/16/1999
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