Altitude training has been used regularly for the past five decades by elite endurance athletes with the goal of improving performance at sea level. With the traditional live high-train high altitude training, many studies have shown that aerobic performance may not increase. It has therefore been hypothesized that the positive effects of altitude acclimatization like the increase in endogenous erythropoietin followed by an augmented hemoglobin mass (Hb_mass) as well as other factors associated with increased muscle efficiency where reversed by the negative effects of reduced absolute training intensity at altitude. This reduction in absolute training intensity is mainly due to the reduction in VO_2max by about 6-8% per 1000m increasing altitude from sea level to 3000m in acute hypoxia. With two weeks of acclimatization, this reduction can only be reduced by one half. In order to optimize altitude training, the live high-train low (LHTL) altitude training concept was developed in the early 1990s with the goal to combine the positive acclimatisation effects with simultaneously reducing the negative training effects. With allowing the athletes to "train low" with sea-level intensity and oxygen flux, beneficial metabolic and neuromuscular adaptations can be maintained. Since then, several LHTL studies have shown that with a sufficient "hypoxic dose", spending more than 300 - 400 hours at altitudes higher than 2300m, Hb_mass can be increased by about 5%, what in combination with "sea level" training increases endurance performance in elite endurance athletes. However, the importance of the underlying mechanisms are debated. In addition, the result of improved performance were possibly confounded by effects like placebo, training modalities, differences in peaking and tapering as well as training camp effects. The influences of these factors on endurance performance after LHTL should therefore be in the focus of future research.