To further complicated matters, in a 2009 study from van Hall’s group (129), lowlanders who were taken to 4100 m altitude had the same elevated lactate response during exercise upon acute exposure to that altitude, and after two weeks and eight weeks of acclimatization (compared to sea level). They showed that the muscle lactate concentration was the same at exhaustion across all conditions, from sea level to eight weeks of chronic hypoxia. Further the epinephrine and norepinephrine concentrations were increased above sea-level values in acute hypoxia, and were further increased after weeks of acclimation, signifying a normal sympathetic nervous system response to exercise. Last, the ADP concentration in muscle was not different across conditions. These findings are obviously at odds with the Pronk et al. study (98) and other proponents of the lactate paradox. Although the pros and cons have already been debated (132, 138), we are sure to hear more in the years ahead.