Daily prevalence of AMS-associated symptoms in the AMS and non-AMS groups.

<p>A—Day 1 (Qika Hut, 2,460 m): 26% of the subjects in the AMS group experienced headache and dizziness. Fewer than 7% of the non-AMS group experienced AMS symptoms, and none experienced GI symptoms at this altitude. B—Day 2 (Sanliujiu Hut, 3,100 m): headache was the most prevalent symptom (82.5%) in the AMS group, followed by sleep disturbance. In the non-AMS group, the main symptom was sleep disturbance (46%) followed by dizziness, headache, and fatigue (prevalence < 30% for all). C—Day 3 (Sanliujiu Hut, 3,100 m, after reaching the summit of Xue Mountain, 3,886 m): more than 50% of the AMS group experienced headache, dizziness, fatigue, and sleep disturbances. Sleep disturbance was the most prevalent symptom in both groups. All AMS symptoms were significantly more prevalent in the AMS than the non-AMS group on all 3 days. The sleep disturbance score reflected the sleep quality during the night before evaluation, but the sleep disturbance score on Day 1 was not considered in the analysis because all subjects slept at home (near sea level) on the night before trekking. McNemar’s test was used for within-group comparisons of prevalence, and the chi-squared test was used for between-group comparisons. <i>P</i>-values < 0.05 were considered statistically significant. * <i>p</i> < 0.05. AMS, acute mountain sickness; GI symptoms, gastrointestinal symptoms (nausea, vomiting, poor appetite).