- Statistical analysis. Data will be reported as means ± SD. Data management and analysis will be performed with SPSS version 13.0 (SPSS Inc, Chicago, IL, USA). Differences among groups, changes over time within each group (time effect), and any interaction (differing trends over time among groups), will be assessed by two-way repeated measures ANOVA with unpaired Student's t-test with Bonferroni correction whenever needed. For all parameters during cardiopulmonary exercise test, mean values will be computed over 20 seconds. Spearman correlations will be used to assess the relationship between peak VO2 and other respiratory and haemodynamic variables at altitude. A P level of < 0.05 was considered statistically significant.