Human sleep exhibits adaptive reorganization under combined thermal and photic stress during an Antarctic summer expedition, with enhanced slow-wave sleep supporting physiological restoration in cold, high-variability environments.
Key Findings
Results
Slow-wave sleep (deep sleep) increased significantly during the Antarctic expedition phase compared to the pre-expedition phase.
Slow-wave sleep was 17.8 ± 4.1% pre-expedition versus 20.2 ± 4.3% during the expedition.
The increase was statistically significant (p<0.001).
Ten expedition members were monitored continuously using validated wearable sensors.
Monitoring occurred across three phases: pre-expedition, Antarctic, and post-expedition.
Linear mixed-effects models were used to assess phase-related differences.
Results
Light sleep decreased significantly during the Antarctic expedition phase.
The decrease in light sleep was statistically significant (p=0.002).
This change occurred alongside the increase in slow-wave sleep, suggesting a reorganization of sleep architecture.
The expedition took place at James Ross Island during the 2025 Czech Antarctic Expedition.
The Antarctic environment was characterized by continuous daylight, low ambient temperatures, and high solar radiation variability.
Results
Higher outdoor temperatures predicted a greater proportion of deep sleep.
The regression coefficient for outdoor temperature predicting deep sleep proportion was β=2.00 (p<0.001).
Environmental variables including air temperature, relative humidity, and global radiation were logged concurrently indoors and outdoors.
This association was identified using linear mixed-effects models.
Results
Lower outdoor relative humidity was associated with increased deep sleep.
The regression coefficient for humidity predicting deep sleep was β=-1.04 (p=0.046), indicating an inverse relationship.
Both temperature and humidity were among the environmental variables continuously logged during the expedition.
The finding suggests that multiple environmental parameters independently modulate sleep architecture.
Results
Resting heart rate rose during the expedition and declined significantly after it, indicating autonomic recovery post-expedition.
Heart rate was recorded continuously using validated wearable sensors alongside sleep stage data.
The post-expedition decline in resting heart rate was described as significant, suggesting autonomic stress during the Antarctic phase.
Respiratory rate was also recorded as part of the wearable sensor data.
The authors interpret this pattern as evidence of thermoregulatory coupling between environmental conditions and autonomic balance.
Methods
The study monitored ten expedition members continuously across three distinct phases using wearable sensors in a naturalistic field setting.
The sample consisted of ten Czech Antarctic Expedition members at James Ross Island during 2025.
Wearable sensors were described as validated and recorded sleep stages, heart rate, and respiratory rate.
Three phases were defined: pre-expedition, Antarctic, and post-expedition.
Environmental data (air temperature, relative humidity, global radiation) were logged both indoors and outdoors concurrently with physiological data.
Linear mixed-effects models were the primary statistical approach.
What This Means
This research suggests that spending time in the extreme environment of Antarctica — with its constant summer daylight, cold temperatures, and variable solar radiation — changes how people sleep. Specifically, members of a Czech Antarctic expedition spent more time in deep, restorative sleep (called slow-wave sleep) while in Antarctica compared to before they left, and they spent less time in lighter sleep stages. These changes were linked to environmental conditions: warmer outdoor temperatures and lower humidity on a given day were associated with more deep sleep that night, pointing to a connection between the body's temperature-regulation system and how sleep is organized.
The study also tracked participants' resting heart rate as a measure of the body's automatic nervous system. Heart rate went up during the expedition and then dropped back down significantly afterward, suggesting the body was under physiological stress in Antarctica and recovered once participants returned home. This pattern of autonomic changes alongside shifts in sleep stages points to the body making coordinated adjustments to cope with the harsh polar environment.
This research matters because it provides rare, real-world evidence — collected during an actual expedition rather than in a laboratory — that human sleep is actively shaped by environmental temperature and light conditions. The findings help explain how the body might use deeper sleep as a restorative strategy when facing physical stress from cold and unusual light exposure. This could have implications for understanding how people adapt to extreme environments, including polar expeditions, nightshift work in cold climates, or other situations involving disrupted light-dark cycles and temperature challenges.
Sokol M, Volf P, Holuša J, Matějka M, Hejda J, Kutílek P. (2026). Thermal and photic modulation of human sleep architecture and autonomic adaptation during an Antarctic summer expedition.. Journal of thermal biology. https://doi.org/10.1016/j.jtherbio.2026.104403