Thermal and photic modulation of human sleep architecture and autonomic adaptation during an Antarctic summer expedition

Human sleep is strongly influenced by thermoregulatory and circadian processes, both of which are challenged in polar environments characterized by continuous daylight, low ambient temperatures, and high variability in solar radiation. This study examined how thermal and photic conditions modulate sleep architecture and autonomic function during the 2025 Czech Antarctic Expedition at James Ross Island. Ten expedition members were continuously monitored using validated wearable sensors that recorded sleep stages, heart rate, and respiratory rate across pre-expedition, Antarctic, and post-expedition phases. Environmental variables, including air temperature, relative humidity, and global radiation, were concurrently logged indoors and outdoors. Linear mixed-effects models revealed that the Antarctic phase was associated with a significant increase in slow-wave sleep (17.8 ± 4.1% pre-expedition vs. 20.2 ± 4.3% during expedition, p<0.001) and a decrease in light sleep (p=0.002). Higher outdoor temperatures predicted a greater proportion of deep sleep (β=2.00, p<0.001), and lower humidity was associated with increased deep sleep (β=-1.04, p=0.046). The resting heart rate rose during the expedition and then declined significantly afterward, indicating autonomic recovery. These findings suggest that human sleep exhibits adaptive reorganization under combined thermal and photic stress, with enhanced slow-wave sleep supporting physiological restoration in cold, high-variability environments. The results provide novel evidence of thermoregulatory coupling between environmental conditions, sleep architecture, and autonomic balance in situ.