All procedures were conducted in accordance with the Declaration of Helsinki as amended by the 59th WMA General Assembly, in Seoul, Korea, October 2008 and the IJSM’s ethical standards [28]. This study obtained approval of the Comité de Bioética de la Universitat de Barcelona (Institutional Review Board IRB0003099, Resolution 30/06/2010). According to the results of the initial test, subjects were divided into two groups in order to establish a balanced fitness composition between the group training at sea level (NOR) composed by 6 men and 1 women (aged 24 ± 4.5 years) and that training at a simulated altitude of 2500 m (HYP) composed by 3 men and 2 women (mean age: 23.8 ± 4 years). The participants did not receive financial compensation or any other kind of reward.