Active Ascent Does Not Increase Sleep Disturbances Compared To Passive Ascent To 3600 m

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PURPOSE: Physical activity has been reported to both improve and hinder sleep quality and quantity at high altitude (HA). The purpose of this study was to examine the magnitude and time course of sleep disturbances following active and passive ascent to 3600 m. METHODS: Forty-one healthy unacclimatized soldiers (n = 41, mean ± SD, age = 26 ± 5 yr; body weight = 83.5 ± 11.6 kg) were tested at sea level (SL), flown to Taos Ski Valley, NM (2845 m) where they arrived around 1400, and then either hiked (n = 21; 5.0 km, 15.5% mean grade) or were driven (n = 20; 30-min drive) to a high altitude (HA) ski patrol facility located at 3600 m. Energy expenditure was measured with an ankle accelerometer. While sleeping for one night at sea level (SL) and three nights at HA (HA1, HA2, HA3), an actigraph was used to estimate total sleep time (SLP, min), total time in bed (TIB, min), onset latency (OL, min), and awakenings (Awak, events/h). Sleep Efficiency (Eff, %) was calculated as SLP/TIB*100. A pulse oximeter was used to determine mean pulse oxygen saturation (SpO2) and desaturations (DeSHr, events/hr). RESULTS: The active group expended a greater (P < 0.05) amount of energy (745 ± 435 kcal) than the passive group (55 ± 10 kcal) during ascent. There were no differences between groups in terms of sleep disturbances so data were combined. Eff (%) did not change from SL (85 ± 5) to HA1 (85 ± 7) but decreased (P < 0.05) from HA1 to HA2 (81 ± 6) and returned to baseline at HA3 (82 ± 7). OL (min) was unchanged from SL (20 ± 19) to HA1 (14 ± 15), increased (P < 0.05) from HA1 to HA2 (35 ± 25) and remained unchanged at HA3 (34 ± 36). Awak (events/hr) remained unchanged throughout the study but were shorter at SL compared to HA. SpO2 decreased (P < 0.05) from SL (94.8 ± 1.1) to HA1 (78.0 ± 4.7), increased (P < 0.05) from HA1 to HA2 (80.6 ± 4.2), and remained unchanged from HA2 to HA3 (80.7 ± 4.7). DeSHr (events/hr) increased (P < 0.05) from SL (1.7 ± 1.5) to HA1 (32.0 ± 28.5), decreased (P < 0.05) from HA1 to HA2 (25.1 ± 26.9), and remained unchanged from HA2 to HA3 (22.6 ± 24.9). CONCLUSION: Sleep quality and quantity were not impacted by active ascent to HA. Ventilatory acclimatization (increased SpO2) occurred during sleep over the three days at HA which likely contributed to improved sleep efficiency and less desaturations at HA3 compared to HA1. Authors’ views not official U.S. Army or DoD policy. Funding: USAMRDC

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