Characteristics of postural corrective responses before and after long-term spaceflights |
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Authors: | D G Sayenko A A Artamonov I B Kozlovskaya |
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Institution: | 1.Toronto Rehabilitation Institute,Toronto,Canada;2.Institute of Biomedical Problems,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | Balance function is dramatically deteriorated after exposure to microgravity. The purpose of the present study was to investigate
the role and the contribution of different gravity sensory systems to the development of balance impairment after long-term
spaceflights. Postural perturbations (pushes to the chest) of the threshold, medium, and sub-maximal intensities were produced
in eight cosmonauts before, and on the day 3, 7, and 11 following spaceflight. Postural corrective responses were analyzed
by anterior-posterior body sway fluctuation and electromyographic activity of leg muscles. The characteristics of the postural
corrective responses changed significantly on the day 3 following spaceflight: the amplitude of posterior sway caused by perturbation
of threshold intensity was increased reaching 135% of preflight value; the corrective responses lasted more than 6 s in 50%
of all trials, while it did not last more than 4 s in 96% before spaceflight. The EMG responses were characterized by increased
contribution of medium- and long-latency reactions. On the day 11 following spaceflight, most of the characteristics of postural
corrective responses were close to preflight values. We assumed that the balance alterations after spaceflight are caused
by changes in weightlessness of functions of two main gravity sensory systems, namely, weight-bearing and vestibular one.
The deficit of weight-bearing afferentation triggers a decline of the extensors’ muscle tone, while changes of vestibular
function cause a decline of accuracy of postural corrections. |
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