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Biological rhythms are one of the key mechanisms regulating the functions of living organisms. Work on studying circadian rhythms in space flight (SF) conditions began in the 1960s. One of the first experiments conducted on Biosatellite III (W.R. Adey, 1971) convincingly demonstrated a change in the phase angle between the circadian rhythm and the environment light cycle. However, to date, very little attention has been paid to the chronobiological aspects of the SF influence on human body. Apparently, this is due to the fact that chronobiology is an exact science and requires appropriate methodological approaches that are difficult to implement directly in SF conditions.
The largest number of works in the field of studying human and animal circadian rhythms under the influence of space flight factors are devoted to the study of the sleep-wake cycle (Alyakrinsky, Stepanova, 1985; Dijk D.J., 2001; Stepanova 2008, 2023; Zhang C., 2023; Grant L.K., 2024). Circadian rhythms also have a humoral pathway of regulation, so a number of studies are devoted to the study of the hormones rhythmicity under the influence of space flight factors. Thus, studies were conducted with a change in the light load in astronauts before SF, and asynchronous rhythms of cortisol and melatonin were revealed (Whitson P.A., 1995). In experiments on board the Mir station (MIR-NASA program), 60-day cycles of cortisol secretion were revealed (Larina I.M., 1999). The NASA Human Exploration Research Analog experiments investigated cognitive abilities and assessed melatonin acrophases under experimental dynamic and standard static lighting schedules (Rahman S.A., 2022). A series of experiments to study the effects of weightlessness on human thermoregulation were conducted on the International Space Station during long-term space missions (Gunga H.-C., Smith S.M., 2017); changes in the circadian rhythm of body temperature were also studied in 60-day head-down tilt bedrest (HDT) (Gunga H.-C., 2022). An experiment with 45-day HDT showed changes in the circadian rhythms of a number of physiological functions, including urination and defecation (Xiaodi Liang, 2012). Studies on mice have shown that spaceflight promotes asynchrony in the expression of clock genes in peripheral tissues (Gunga H.-C., 2022).
Thus, the obtained data confirm the need for more in-depth studies of the impact of changes in circadian rhythms during space flight on the state of the human physiological systems, and the search for means and methods for preventing disorders in order to maintain the physical and psychological health and performance of astronauts.
The work was carried out within Basic Topics of the RAS FMFR-2024-0039