Interplanetary space flight compared with fetal/neonatal motor strategy: Theoretical and practical implications

Area of Science:

• Human physiology
• Space medicine
• Motor control

Background:

• Microgravity (G∼0) during spaceflight resembles intrauterine conditions, characterized by heating and hypoxia.
• Fetal development involves fast muscle fiber dominance as an adaptive strategy for survival in utero.
• Adults also adapt to microgravity, heat stress, and hypoxia by shifting muscle fiber properties towards faster types.

Purpose of the Study:

• To propose a specific motor strategy (fetal/microgravity, or FM-strategy) induced by microgravity or hypogravity.
• To define the 'Earth' adaptive motor response (gravitation/Earth, or GE-strategy) to postnatal conditions.
• To explore the 'slow Jupiter' (SJ-strategy) motor response in aging and its relation to hypergravity (G>1).

Main Methods:

• Comparative analysis of physiological conditions: intrauterine immersion vs. microgravity.
• Analysis of adaptive responses to different gravitational and environmental conditions (heat, hypoxia, normoxia, cold).
• Speculative modeling of motor strategies based on muscle fiber properties and motor unit activity.

Main Results:

• Microgravity and fetal immersion share adaptive motor responses favoring fast muscle fibers.
• Postnatal conditions (gravity, cooler temperature, normoxia) induce an 'Earth' adaptive motor response (GE-strategy).
• Aging and hypergravity (G>1) lead to slow muscle fiber dominance and reduced motor unit activity (SJ-strategy).

Conclusions:

• Specific sensory inputs and conditions can substitute each other due to equivalent effects on the motor system.
• Cold exposure acts as a 'surrogate' for gravity, stimulating muscle tone and potentially counteracting weightlessness.
• Combining cooling with vibration and sensory afferent stimulation may enhance anti-microgravity countermeasures.