Human corticospinal excitability in microgravity and hypergravity during parabolic flight.

Area of Science:

• Human physiology
• Neuroscience
• Space adaptation

Background:

• Gravitational force significantly influences muscle activity, as observed in rat soleus muscle.
• Understanding human responses to altered gravity is crucial for space travel and terrestrial applications.

Purpose of the Study:

• To investigate the effects of decreased (0 G) and increased (1.8 G) gravitational forces on human back and arm muscle electromyographic (EMG) activity.
• To determine the role of the motor cortex in modulating muscle activity during altered gravitational conditions.

Main Methods:

• Three healthy subjects underwent parabolic flight, experiencing 1.8 G, 0 G, and 1.8 G phases.
• Electromyographic (EMG) recordings were taken from erector spinae (ES) and deltoid muscles.
• Transcranial magnetic stimulation (TMS) was used to assess motor cortex output via motor evoked potentials (MEPs).

Main Results:

• EMG levels and MEP areas in the erector spinae (ES) muscles increased during 0 G periods.
• This increase was less pronounced when the arm was abducted.
• No significant changes in EMG or MEPs were observed during 1.8 G periods.

Conclusions:

• Increased ES muscle activity and corticospinal excitability occur during 0 G, suggesting a mechanism to stabilize the axial skeleton.
• The motor cortex plays a role in activating back muscles during microgravity.
• These findings provide insights into neuromuscular adaptation to altered gravitational environments.