To determine whether ischaemic preconditioning (IPC) administered prior to an altitude training camp could enhance aerobic fitness and endurance performance in athletes. In a randomized controlled trial, 19 competitive (Tiers 3–5) cross-country (XC) skiers (V˙ O2peak 69.1 ± 6.4 ml.min−1.kg−1) performed a 6-day IPC block ( n = 10) or placebo compressions (n = 9) before a 21-day altitude camp in Park City, Utah (2,200 m) during their pre-competition season. Measures of performance and laboratory outcomes included a 3000-m track time trial, peak treadmill speed, peak O2 uptake, muscle oxygenation, ventilatory thresholds and haematological markers. V˙ O2peak improved only in IPC (2.9 ml.min−1.kg−1, 4%, p = 0.002), in direct proportion to the increase in quadriceps muscle deoxygenation ( 17%, r = 0.84, p textless 0.05). Both groups improved red cell count (3.6%, p = 0.006), peak treadmill speed (1.0 km.h−1, p textless 0.001) and 3000-m track time (−2.4 s, p = 0.032) to the same extent. In IPC, the reduction in track time inversely correlated with the increase in V˙ O2peak (r = −0.67, p textless 0.05). Six days of IPC enhance the V˙ O2peak gain from an altitude training camp in trained XC skiers, concomitant with greater muscle deoxygenation, and from similar training load. IPC may be considered as an effective and sustainable strategy for developing maximal aerobic fitness in a ‘live high-train high’ paradigm.