EMG activity of three rat hindlimb muscles during microgravity and hypergravity phase of parabolic flight.
BACKGROUND
In man, quantifications of the motor activity have mainly been performed to study changes in posture and locomotion after space-flight. On the contrary, physiological data relative to the motor activity have never been obtained in animals in real microgravity.


OBJECTIVE
The purpose of this study was to evaluate, in rats, the immediate effect of real microgravity on the neuromuscular activity of three hindlimb muscles.


METHODS
Under aseptic conditions, the soleus (SOL), lateral gastrocnemius (LG) and tibialis anterior (TA) muscles of rat hindlimb were implanted each with a pair of electrodes. Their electromyographic (EMG) activity was analyzed before, during, and after parabolas, a parabola being composed of two 2 G episodes separated by one 0 G episode. Each episode lasted about 25 s.


RESULTS
Our results showed that, when compared to normal gravity (1G), hypergravity increased the EMG activity in the ankle extensors SOL and LG, whereas microgravity immediately induced a redistribution in the motor activity between the two antagonists, SOL and TA.


CONCLUSIONS
An immediate adaptation occurred in the motoneuronal recruitment of rat hindlimb muscles at the onset of changes in gravity level. This could be interpreted in terms of a short-term adaptative process involving peripheral mechanisms initiated by changes in activity of muscle spindles.
Leterme
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Laboratoire de Plasticité Neuromusculaire, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France.
Falempin
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D000222:Adaptation, Physiological / Q000502:physiology; D000337:Aerospace Medicine; D000818:Animals; D001522:Behavior, Animal; D004567:Electrodes, Implanted; D004576:Electromyography; D006614:Hindlimb / Q000502:physiology*; D018471:Hypergravity / Q000009:adverse effects*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D014743:Videotape Recording; D014893:Weightlessness / Q000009:adverse effects*