Acute Effects of Hypoxic Cycling Warm-Up on Subsequent Normoxic Running Performance: A Randomized Crossover Study

Simulated normobaric hypoxia may serve as a pre-exercise conditioning strategy, but its acute effects during warm-up remain unclear in endurance runners. This study examined whether a 20-min cycling warm-up under normoxia (nominal FiO2 ≈ 20.9%) or simulated altitudes of ≈2500 m (nominal FiO2 ≈ 15.5%) and ≈3500 m (nominal FiO2 ≈ 14.5%) altered physiological responses and performance during a subsequent incremental treadmill test in normoxia. Twelve competitive endurance runners (10 men and 2 women) completed the three conditions in a randomized, counterbalanced crossover design. Speed at the second ventilatory threshold (vVT2) was the primary outcome; heart rate, blood lactate, oxygen uptake, perceived exertion, and other threshold-related variables were exploratory outcomes. Oxygen saturation during warm-up differed significantly among conditions (p < 0.001; η2p = 0.64), supporting a greater desaturation under both nominal hypoxic settings than under the control setting, although the two hypoxic levels did not differ. No significant condition effects were observed for vVT2 or other performance variables, heart rate (p = 0.228; η2p = 0.13), or post-test lactate (p = 0.279; η2p = 0.11). Thus, this specific hypoxic cycling warm-up showed no evidence of improving subsequent normoxic running performance. Wide confidence intervals and the small sample preclude definitive conclusions.