"Live high, train low" You do need good oxygen supply during training in order to fully utilize (and grow) the muscles. Low oxygen (such as found at high alti

"Live high, train low" You do need good oxygen supply during training in order to fully utilize (and grow) the muscles. Low oxygen (such as found at high altitude) is good for the non-training periods (e.g. during sleep), where it induces a hypoxia-adaptation reaction that consists among others in increased erythropoietin (EPO), resulting in increased hemoglobin, etc.