Physiological Responses to Antarctic Conditions: Stress, Sleep Duration, and Physical Activity of Participants in the 34th Bulgarian Antarctic Expedition

Antarctic expeditions expose individuals to multiple and interacting stressors that may affect physiological regulation, sleep, and physical activity. This study investigated physiological responses in 28 male participants during the 34th Bulgarian Antarctic Expedition, who spent 30 days at the Antarctic research base. Physical activity and sleep duration were continuously monitored using three-dimensional inertial sensors. Salivary biomarkers of physiological responses associated with stress, cortisol, K+, Na+, the K+/Na+ ratio, total protein, and α-amylase activity, were measured before the expedition, weekly during deployment, and after return. Sleep duration increased significantly during Weeks 2 and 3 compared to Week 1. Light -intensity activity predominated over moderate-intensity activity and declined significantly over the monitoring period, whereas moderate-intensity activity decreased significantly during Week 3 compared with Week 1. Cortisol concentrations were significantly lower after return than during the pre-expedition period. Salivary K+ concentrations increased significantly during the Week 2 and subsequently decreased significantly after return, whereas Na+ concentrations remained stable throughout the mission but decreased after return. The K+/Na+ ratio declined significantly during the Weeks 2 and 3 and after expedition. Total salivary protein concentration and α-amylase activity increased at the Weeks 4 and 3, respectively, and both approached baseline following the participants’ return. The longitudinal changes in salivary biomarkers, together with alterations in physical activity and sleep duration, indicate dynamic physiological responses during and after Antarctic expedition. This minimally invasive, integrated approach may support further research on individual patterns of physiological adjustment and early deviations from adaptation, and may contribute to the development of personalized health monitoring strategies and timely preventive interventions during future Antarctic and other missions in extreme environments.