Active Ascent Accelerates The Time Course But Not Severity Of Acute Mountain Sickness At 3600 m

PURPOSE: Acute mountain sickness (AMS) typically peaks following the first night at high altitude (HA) and resolves over the next 2 to 3 days. The purpose of this study was to examine the severity and time course of AMS 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; VO2max = 47.9 ± 5.5 ml · kg−1 · min−1) were tested at sea level (SL) in Ft. Leonard Wood, MO, 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 HA ski patrol facility located at 3600 m where they resided for the next 4 days. Energy expenditure during ascent was assessed using an ankle accelerometer (Actical, Respironics, Inc.). AMS was assessed at least an hour following any exercise using the Environmental Symptoms Questionnaire and if AMS-C was ≥0.7, individuals were considered sick. AMS measurements were made at 2000 and 2200 on day 1 (HA1), at 0600, 1000, 1400, 2000, and 2200 on day 2 (HA2) and 3 (HA3), and then at 0600 on day 4 (HA4). The peak AMS-C score and prevalence was recorded on each day at HA. 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. Peak AMS-C scores did not differ between active and passive ascent groups, respectively, on HA1 (0.85 ± 0.99 vs. 0.62 ± 0.69), HA2 (1.01 ± 1.03 vs 0.99 ± 0.92), HA3 (0.74 ± 0.51 vs 0.34 ± 0.83) and HA4 (0.50 ± 0.36 vs. 0.21 ± 0.72). AMS prevalence, however, was higher (P < 0.05) in active versus passive ascent groups, respectively, on HA1 (53 vs. 35%), did not differ on HA2 (50 vs. 53%) or HA3 (35 vs. 19%), and was lower (P < 0.05) on HA4 (9 vs. 25%). When only AMS-susceptible individuals were analyzed, there were 11 sick individuals in both groups but 8/11 actives vs. 2/11 passives demonstrated peak AMS scores on HA1 (P < 0.05), 3/11 actives vs. 5/11 passives on HA2, 0/11 actives vs. 4/11 passives on HA3 (P < 0.05), and no individuals demonstrated peak AMS scores on HA4. CONCLUSIONS: Active ascent accelerated the time course but not the severity of AMS with more individuals sick within the first 4 hours at HA and less individuals sick after 2 to 3 days at HA. Authors’ views not official U.S. Army or DoD policy. Funding: USAMRDC