We quantified the effect of an extended live high-train low (LHTL) simulated altitude exposure followed by a series of training camps at natural moderate altitude on competitive performance in seven elite middle-distance runners (Vo2max 71.4 +/- 3.4 mL.min-1.kg-1, mean +/- SD). Runners spent 44 +/- 7 nights (mean +/- SD) at a simulated altitude of 2846 +/- 32 m, and a further 4 7- to 10-d training at natural moderate altitude (1700-2200 m) before racing. The combination of simulated LHTL and natural altitude training improved competitive performance by 1.9% (90% confidence limits, 1.3-2.5%). Middle-distance runners can confidently use a combination of simulated and natural altitude to stimulate adaptations responsible for improving performance.