Overview of the study design separated by weeks (W.) and in order of the testing altitude, including the six months before the lead-in period where the training loads were assessed, the lead-in, the LHTL camp of 18 days, and the lead-out period.

<p>Testing included 3-km test  =  the 3-km running tests on the track near sea level; Pre-, Post-, Post-7 and Post-21  =  testing sessions; LHTL =  Live High-Train Low training camp for normobaric hypoxia (NH) and hypobaric hypoxia (HH), where athletes were exposed to both higher altitude for living and sleeping and lower altitude for training.</p

A. Daily objective training (D01-D18: day 01 to day 18) loads during the Live High-Train Low (LHTL) camp for normobaric hypoxia (NH) and hypobaric hypoxia (HH) groups.

<p><b>B</b>. Weekly objective training loads during the six months before the intervention for NH and HH groups.</p

A. Daily values of inspired pressure of oxygen (P_iO₂ in mmHg) during the Live High-Train Low (LHTL) camps for the normobaric hypoxia (NH) and hypobaric hypoxia (HH) groups.

<p><b>B</b>. Mean values of night oxygen pulse saturation (S_pO₂). Data are presented in mean ± standard error. Pre1-Pre2: measurements before the camps (1150 m, Prémanon, France); D01-D18: measurement during the camps (NH: hypoxic room in Prémanon, France; HH: Fiescheralp, Switzerland). ^#P<0.05, ^###P<0.001 for differences between groups.</p