Comparison of adaptations to four weeks of continuous hypoxic training between healthy men with lower and higher initial aerobic fitness.

Background: Continuous hypoxic treadmill training increases the physiological load of aerobic exercise, but it remains unclear whether baseline aerobic fitness influences short-term adaptation. This study compared the responses of healthy men with lower and higher initial aerobic fitness to four weeks of continuous treadmill training performed in normobaric hypoxia equivalent to a simulated altitude of 2500 m. Methods: Twenty-two healthy adult men were classified into lower- group (LF) and higher-fitness groups (HF) according to baseline treadmill graded exercise test performance. All participants completed the same four-week hypoxic treadmill training program and the same pre- and post-intervention tests, including a graded treadmill test with cardiorespiratory and oxygenation monitoring and a Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IR1). Results: Both groups improved after training, but the changes were consistently larger in the LF group. Compared with the HF group, the LF group showed larger percentage improvements in relative VO Conclusions: Four weeks of continuous hypoxic treadmill training were associated greater improvements in aerobic and threshold-related outcomes in men with lower initial aerobic fitness. The oxygenation outcomes provide descriptive physiological information only and should not be interpreted as evidence of hematological adaptation.