At intermediate altitude (2100 m), nocturnal SpO2 and heart rate show sleep-stage-specific dynamics, so acclimatization is not uniform across sleep stages, and wearable EEG-oximetry offers an ecologically valid index of central nervous system acclimatization.
Total sleep time was unchanged during the altitude camp despite altitude exposure.
Sleep architecture shifted across the first week at altitude: %N3 decreased and %REM increased, both logarithmically.
Nocturnal SpO2 was lower at altitude than in normoxia.
Overnight heart rate was higher at altitude than the habitual normoxic value.
SpO2 recovery over the first week was stage specific, with faster recovery in N1 and REM than in Wake.
Heart rate decline across nights also differed by sleep stage.
The authors conclude that acclimatization is not uniform across sleep stages and that the first 2 nights may capture the most rapid adjustments.
This study followed 17 elite mogul skiers (seven women) during a two-week training camp at 2100 m in the French Alps. During the first week and on the last night, the athletes wore a ring that measured blood oxygen levels and a headband that recorded brain activity to identify sleep stages. Total sleep time stayed about the same (around 7 hours), but the make-up of sleep changed. Over the first week, deep sleep (N3) decreased and REM sleep increased. Oxygen levels during sleep were lower than at sea level (about 95% versus 98%), and heart rate overnight was about 7 beats per minute higher. Over the first week, oxygen levels rose and heart rate fell, but at different rates depending on the sleep stage; oxygen recovered faster in light sleep (N1) and REM sleep than during wakefulness. This research suggests that adapting to moderate altitude does not happen evenly across the night, and that the first two nights may show the quickest changes. The findings may help in using wearable sleep and oxygen trackers to monitor how athletes adjust to altitude. The study was observational and small, in elite athletes only, so it cannot show that these patterns apply to other people.
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Upload Your LabsVaresco G, Van Cutsem J, Pattyn N, Bourrel N, Bieuzen F, Simonelli G. (2026). Dynamics of Sleep Architecture and Nocturnal Oxygen Saturation During Acclimatization at Intermediate Altitude: A Longitudinal Observational Study in Elite Athletes.. Journal of integrative neuroscience. https://doi.org/10.31083/JIN52881