Effect of hypoxic "dose" on physiological responses and sea-level performance

Live high-train low (LH + TL) altitude training was developed in the early 1990s in response to potential training limitations imposed on endurance athletes by traditional live high-train high (LH + TH) altitude training. The essence of LH + TL is that it allows athletes to "live high" for the purpose of facilitating altitude acclimatization, as manifest by a profound and sustained increase in endogenous erythropoietin (EPO) and ultimately an augmented erythrocyte volume, while simultaneously allowing athletes to "train low" for the purpose of replicating sea-level training intensity and oxygen flux, thereby inducing beneficial metabolic and neuromuscular adaptations. In addition to "natural/terrestrial" LH + TL, several simulated LH + TL devices have been developed to conveniently bring the mountain to the athlete, including nitrogen apartments, hypoxic tents, and hypoxicator devices. One of the key questions regarding the practical application of LH + TL is, what is the optimal hypoxic dose needed to facilitate altitude acclimatization and produce the expected beneficial physiological responses and sea-level performance effects? The purpose of this paper is to objectively answer that question, on the basis of an extensive body of research by our group in LH + TL altitude training. We will address three key questions: 1) What is the optimal altitude at which to live? 2) How many days are required at altitude? and 3) How many hours per day are required? On the basis of consistent findings from our research group, we recommend that for athletes to derive the physiological benefits of LH + TL, they need to live at a natural elevation of 2000-2500 m for ≥ 4 wk for ≥ 22 h·d^-1.