Human corticospinal excitability in microgravity and hypergravity during parabolic flight.
BACKGROUND
Spontaneous electromyographic (EMG) activity in the soleus muscle of the rat varies with the changing gravitational force in parabolic flight, presumably in an appropriate way to resist the load. We investigated how decreased and increased gravitational force affects EMG in human back and arm muscles and to what extent the motor cortex is responsible for any modulation seen.


METHODS
Three healthy subjects stood during 10 parabolas consisting of periods (duration 20-25 s) of 1.8 G, then 0 G, and then 1.8 G. EMG recordings were made from right deltoid and left and right erector spinae (ES) muscles and transcranial magnetic stimulation (TMS) was applied to the motor cortex to produce motor evoked potentials (MEPs) in target muscles.


RESULTS
In one exemplary subject, EMG levels and MEP areas increased in the left ES and right ES during periods of 0 G, which was less pronounced with the arm abducted. No significant changes were seen in EMG levels or MEP areas during periods of 1.8 G. Pooled data from the three subjects showed a similar pattern, revealing a facilitation of MEP responses in left and right ES muscles in periods of 0 G.


CONCLUSIONS
EMG levels and MEP areas in ES muscles increased during periods of 0 G, suggesting that back muscle activity is "turned on" to stabilize the axial skeleton when the vertical compression forces present on Earth are removed. Further analysis suggested that microgravity produced activation of ES muscles through an increase in corticospinal excitability.
Davey
Nick J
NJ
Department of Sensorimotor Systems, Division of Neuroscience & Psychological Medicine, Imperial College London, Charing Cross Hospital, London, UK. n.davey@imperial.ac.uk
Rawlinson
Steve R
SR
Nowicky
Alex V
AV
McGregor
Alison H
AH
Dubois
Kitsou
K
Strutton
Paul H
PH
Schroter
Robert C
RC
D000054:Acceleration; D004576:Electromyography; D005260:Female; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D011712:Pyramidal Tracts / Q000502:physiology*; D013026:Space Flight; D014893:Weightlessness / Q000009:adverse effects*