Levine & Stray-Gundersen 1997, Living high-training low

J Appl Physiol 83:102-112. The founding live-high, train-low (LHTL) trial. Trained collegiate runners, three 4-week arms: live high/train low (2,500 m / 1,250 m), live high/train high (~2,500 m), and a sea-level control. Both altitude groups raised red cell mass ~9% and VO2max ~5%, but only the LHTL group improved 5,000 m time (~13 s). The direct demonstration that training low preserves the intensity that living high otherwise degrades. Moderate (small, not placebo-controlled, foundational).