Cold for gravity, heat for microgravity: A critical analysis of the “Baby Astronaut” concept

Abstract

The existing literature suggests that temperature and gravity may have much in common as regulators of physiological functions. Cold, according to the existing literature, shares with gravity common effects on the neuromuscular system, while heat produces effects similar to those of microgravity. In addition, there are studies evidencing unidirectional modification of the motor system to heat and hypoxia. Such agonistic relationship in a triad of “microgravity, heat, and hypoxia” and in a pair of “cold and gravity” in their effect on the neuromuscular system may have evolutionary origins. To address this problem, ten years ago, we came up with a concept with the working name Baby Astronaut hypothesis, which posed that “Synergetic adaptation of the motor system to different environments comes from their ontogenetic synchronicity.” More specifically, the synchronicity of microgravity (actually, the “wet immersion” model of microgravity), higher temperature, and hypoxia are the characteristics of the intrauterine environment of the fetus. After childbirth, this group of factors is rapidly replaced by the “extrauterine,” routine environment characterized by Earth gravity (1 G), normoxia, and lower ambient temperature. The physiological effect of cold and gravity on the motor system may well be additive (synergistic). We earlier estimated a “gravity-substitution” potential of cold-induced activity and adaptation to cold as 15–20% of G, which needs further validation and correction. In this study, we sought to critically analyze the interaction of temperature and gravity, based on the concept of Baby Astronaut, using data from the new academic literature. We have come to the conclusion that the concept of Baby Astronaut can be regarded as valid only for species such as a rat (immature, altricial species), but not for a human fetus. Several confirmatory experiments were suggested to verify (or falsify) the concept, which would allow us to consider it as empirical. In addition, the interaction of temperature and gravity may be of practical interest in the fields of neurorehabilitation and habilitation in childhood for constructing a physical environment, which would help strengthen or weaken muscle tone in specific muscles.

Are We Astronauts Before Birth? A Miracle of Intrauterine Life

“…Cold-induced activity and adaptation to cold can substitute 15 to 20% of the gravity and induce the activity of slow muscular fibers (type I) (Meigal & Gerasimova-Meigal 2022). After we were born or in other words while we landed from the universe and were exposed to cold, high oxygen concentrations and gravity, we stopped being astronauts and continued life as humans whose first year of development was marked by the tyranny of gravity and the replacement of fast muscle fibers by slow ones (Stanojevic et al 2011, 2012, Meigal & Gerasimova-Meigal 2022) . The question is whether the intrauterine environment is a sign that man, as part of the living world, originates from space.…”

“…According to recent research, Meigal and Gerasimova-Meigal (2022) hypothesize that heat exerts similar effects on the neuromuscular system as microgravity, while the cold shares common effects on neuromuscular system as gravity (Meigal & Gerasimova-Meigal 2022). They claimed that relationship of the triad "microgravity, heat and hypoxia" and the dyad "cold and gravity" on neuromuscular system may have evolutionary origins and concluded that "synergistic adaptation of the motor system to different environments comes from their ontogenic synchronicity" (Meigal & Gerasimova-Meigal, 2022).…”

“…They claimed that relationship of the triad "microgravity, heat and hypoxia" and the dyad "cold and gravity" on neuromuscular system may have evolutionary origins and concluded that "synergistic adaptation of the motor system to different environments comes from their ontogenic synchronicity" (Meigal & Gerasimova-Meigal, 2022). They produced the so called "wet immersion model" of microgravity in utero affecting fetal behavior which is mirroring the phylogenetic development of neurologic and motoric systems (Meigal & Gerasimova-Meigal 2022). From the evolutionary point of view temperature (either cold, hot or thermoneutral) and gravity (microgravity, or 1G Earth gravity) belong to controlling mechanisms of the origin and evolution of life on Earth (Islas 2014, Nadezhdin et al 2021).…”

Cerebral Circulation and Brain Temperature during an Ultra-Short Session of Dry Immersion in Young Subjects

“…Growth of brain temperature during DI, therefore, can theoretically contribute to some well-known effects of DI, for example, skeletal muscle hypotonia. The interactive effects of temperature and gravity on muscle tone is currently under discussion in academic community [ 26 ]. Furthermore, we aware of the fact that supraorbital temperature strongly relates to brain temperature, but it is not necessarily identical with it.…”

“…There are several reasons for brain temperature to increase in healthy and diseased conditions [ 20 ]. Several studies have shown that hyperthermia, either during exercise-induced heat stress or passive heating, exerts an effect on the neuromuscular and cardiovascular systems [ 21 , 22 , 23 , 24 , 25 , 26 ]. For example, heat stress can reduce central nervous activation of muscles and impair afferent feedback from them [ 21 ].…”