SDRR CVRR TP VLFP LFP HFP nVLFP nLFP nHFP LHR 30 MASL 0.005 R= -0.394 0.003 -0.42 0.017 -0.34 0.191 0.0634 0.0149 R= -0.346 0.003 R= 0.410 0.421 0.0537 0.361 520 MASL 0.006 R= -0.383 <0.001 R= -0.467 0.023 R= -0.323 0.242 0.019 R= -0.334 0.0496 R= -0.282 <0.001 R= 0.541 0.0536 0.0722 0.903 1080 MASL 0.0121 R= -0.356 0.002 R= -0.430 0.0141 R= -0.349 0.626 0.0477 R= -0.284 0.008 R= -0.375 <0.001 R= 0.587 0.351 0.002 R= -0.424 0.082

Table 4: The p values and Pearson correlation coefficients of linear correlation between the age and the HRV measures of the subjects at 3 altitudes (n=49) SDRR: Standard deviation of RRI; CVRR: Coefficient of variation of RRI; TP: Total power; VLFP: Very-low-frequency power; LFP: Low-frequency power; HFP: High-frequency power; nVLFP: Normalized VLFP; nLFP: Normalized LFP; nHFP: Normalized HFP; LHR: Low-/high-frequency power ratio.