Effects of Six Weeks of Sub-High-Altitude Training on the Physical Performance and Psychological State of Adolescent Swimmers

Inclusion Criteria: 1. Age 12-18 years; 2. At least 3 years of systematic swimming training; 3. No history of severe lower-limb sports injuries within the past 6 months (defined as injuries resulting in a training hiatus of ≥4 weeks); 4. No participation in any form of hypoxic training during the 2 months prior to the experiment. Exclusion Criteria: 1. Presence of any cardiovascular, metabolic, or musculoskeletal disorders that may affect testing or training; 2. Inability to guarantee attendance during the experiment (expected number of absences \> 2)