Objectives Acute mountain sickness (AMS) is a significant health problem in high altitude setting. Maximal and submaximal exercise at very and extreme high altitude can increase the AMS incidence. But the effect of moderate activities at moderate high altitude on AMS is unclear.

Methods 91 healthy unacclimatised volunteers were enrolled in this prospective study. They traveled from sea level (345 m) to Golmud city (3200 m), Qinghai province, PRC, by train and bus. After 2 nights exposure 3200m, AMS LLS Questionnaires, blood pressure and oxygen saturation was administered to 91 subjects before and after walking 5 kilometers with a 10 kilograms load.

Results Total 91 participators complete the exercise. 7 of them were excluded from analyses because of incomplete data. The incidence of AMS before and after exercise was 20.24% (n = 17/84) and 11.90% (n = 10/84) respectively. After a 5 kilometer walk, the heart rate increased from 73.83 ± 9.96 to 84.31 ± 12.55 (P<0.05), Systolic BP decreased from 128.86 ± 13.93 mmHg to 124.48 ± 13.13 mmHg (P<0.05), and the SpO₂ level decreased from 92.80% ± 2.25% to 89.94% ± 2.45% (P < 0.05). Diastolic BP was slightly decreased (P > 0.05). There is no relation with SpO₂ with AMS scores, neither before nor after exercise.

Conclusions After 2 nights exposure 3200 m, 5 kilometer walking at 3200m altitude might improve the headache symptom, decrease SpO₂ and elevate heart rate, decrease the incidence of AMS.