High-intensity interval versus moderate-intensity continuous freestyle swimming in obese college students: A randomized controlled study protocol examining glycolipid and vascular endothelial responses

BACKGROUND: Obesity among college students may be accompanied by early metabolic and endothelial abnormalities before overt cardiometabolic disease develops. Freestyle swimming combines whole-body energy expenditure with low weight-bearing load. This randomized controlled trial will compare high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) freestyle swimming and examine the relationships between changes in glycolipid markers and vascular endothelial markers. METHODS: A total of 108 obese college students will be randomized in a 1:1:1 ratio to HIIT, MICT, or a usual-activity control group (36 participants per group). The exercise groups will complete supervised 30-min freestyle swimming sessions three times weekly for 6 months. Total cholesterol (TC) at 6 months, adjusted for baseline TC, will be the single primary outcome. Secondary glycolipid, endothelial, anthropometric, adherence, and safety outcomes will be assessed at baseline and at 2, 4, and 6 months. The primary comparison will use analysis of covariance under the intention-to-treat principle. Longitudinal mixed-effects models and multiple imputation sensitivity analyses will characterize outcome trajectories. Multivariable linear regression will examine the relationships between changes in individual glycolipid markers and changes in ET-1 and NO. DISCUSSION: This trial will clarify whether HIIT and MICT freestyle swimming differ in their effects on TC and other glycolipid and endothelial outcomes in obese college students and whether improvements in glycolipid markers are accompanied by changes in ET-1 and NO. The findings may inform safe and more precise exercise prescriptions for young adults with obesity. CLINICAL TRIAL REGISTRATION: The trial was prospectively registered in the Chinese Clinical Trial Registry (ChiCTR2600121931) on April 7, 2026.