The differences between the measured heart rate (HR) published in the respective references and predicted heart rate (HR) calculated by method used in this study.

HR = heart rate; m = meter;aThe data were cited from the Reference #19. Predict HR at camp 2 = measured HR at base camp × 6300 m/5400 m; % of difference = percentage of the difference between measured HR and predict HR.bThe data were cited from the Reference #22. Predict HR at camp 4 = measured HR at camp 2 × 8000 m/6550 m.#The heart rates under various conditions were measured, including without O2 supplement (regular air), 1L O2 supplement, or 2L O2 supplement.