Long-Term Bed Rest Delays the Circadian Phase of Core Body Temperature

Spaceflight can be associated with sleep loss and circadian misalignment as a result of non-24 h light-dark cycles, operational shifts in work/rest cycles, high workload under pressure, and psychological factors. Head-down tilt bed rest (HDBR) is an established model to mimic some of the physiological and psychological adaptions observed in spaceflight. Data on the effects of HDBR on circadian rhythms are scarce. To address this gap, we analyzed the change in the circadian rhythm of core body temperature (CBT) in two 60-day HDBR studies sponsored by the European Space Agency [n = 13 men, age: 31.1 ± 8.2 years (M ± SD)]. CBT was recorded for 36 h using a non-invasive and validated dual-sensor heatflux technology during the 3rd and the 8th week of HDBR. Bed rest induced a significant phase delay from the 3rd to the 8th week of HDBR (16.23 vs. 16.68 h, p = 0.005, g = 0.85) irrespective of the study site (p = 0.416, g = −0.46), corresponding to an average phase delay of about 0.9 min per day of HDBR. In conclusion, long-term bed rest weakens the entrainment of the circadian system to the 24-h day. We attribute this effect to the immobilization and reduced physical activity levels associated with HDBR. Given the critical role of diurnal rhythms for various physiological functions and behavior, our findings highlight the importance of monitoring circadian rhythms in circumstances in which gravity or physical activity levels are altered.

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Circadian rhythms in bed rest: Monitoring core body temperature via heat-flux approach is superior to skin surface temperature

Chronobiology International ◽

10.1080/07420528.2016.1224241 ◽

2016 ◽

Vol 34 (5) ◽

pp. 666-676 ◽

Cited By ~ 16

Author(s):

Stefan Mendt ◽

Martina Anna Maggioni ◽

Michael Nordine ◽

Mathias Steinach ◽

Oliver Opatz ◽

...

Keyword(s):

Heat Flux ◽

Body Temperature ◽

Circadian Rhythms ◽

Surface Temperature ◽

Core Body Temperature ◽

Bed Rest ◽

Skin Surface ◽

Skin Surface Temperature ◽

Core Body

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Regular exercise counteracts circadian shifts in core body temperature during long-duration bed rest

npj Microgravity ◽

10.1038/s41526-020-00129-1 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Stefan Mendt ◽

Hanns-Christian Gunga ◽

Dieter Felsenberg ◽

Daniel L. Belavy ◽

Mathias Steinach ◽

...

Keyword(s):

Body Temperature ◽

Core Body Temperature ◽

Space Station ◽

Bed Rest ◽

Resistive Exercise ◽

Long Duration ◽

Human Exploration ◽

Core Body

AbstractWith NASA’s plans for the human exploration of Mars, astronauts will be exposed to mission durations much longer than current spaceflight missions on the International Space Station. These mission durations will increase the risk for circadian misalignment. Exercise has gained increasing interest as a non-pharmacological aid to entrain the circadian system. To assess the potential of exercise as a countermeasure to mitigate the risk for circadian disorders during spaceflight, we investigated the effects of long-term head-down tilt bed rest (HDBR) with and without exercise on the circadian rhythm of core body temperature. Core body temperature was recorded for 24 h using a rectal probe in sixteen healthy men (age: 30.5 ± 7.5 years (mean ± SD)) after 7 days and 49 days of HDBR. Five participants underwent HDBR only (CTR), five participants underwent HDBR and performed resistive exercises (RE), and six participants underwent HDBR and performed resistive exercises superimposed with vibrations (RVE). The exercise was scheduled three times per week. CTR showed a phase delay of 0.69 h. In contrast, both exercise groups were characterized by a phase advance (0.45 h for RE and 0.45 h for RVE; p = 0.026 for interaction between time and group). These findings suggest that resistive exercise (with or without vibration) may also serve as a countermeasure during spaceflight to mitigate circadian misalignments. The results could also be important for increasing awareness about the role of circadian disorders in long-term bedridden patients.

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