Chapman et al. 2014, How high to live for optimal sea-level performance

J Appl Physiol 116:595-603. Runners lived four weeks at 1,780, 2,085, 2,454 or 2,800 m, training low. The 3,000 m time-trial improved for the 2,085 m and 2,454 m groups but not at 1,780 m (too low to drive enough red cell mass) or 2,800 m (too high: performance worsened despite a ~7% red cell volume gain, blamed on disrupted training and ventilatory de-acclimatisation). Brackets the practical living-altitude window at roughly 2,000-2,500 m. Moderate.