Effects Of High-Intensity Interval Training On Cardiorespiratory Fitness And Muscular Endurance In University Athletes: A Randomized Controlled Trial

High-intensity interval training (HIIT) has emerged as a time-efficient exercise modality; however, its dose-response relationship on multiple fitness components in collegiate athletes remains insufficiently characterized. Objectives: This study aimed to evaluate the effects of an 8-week HIIT programme on cardiorespiratory fitness (VO₂max), muscular endurance, lactate threshold, and body composition in university-level athletes compared to moderate-intensity continuous training (MICT). Methods: Sixty-four (n = 64) university athletes (mean age 20.3 ± 1.8 years) were randomly assigned to HIIT (n = 32) or MICT (n = 32) groups. The HIIT protocol consisted of 4 × 4-minute intervals at 90-95% HRmax with 3-minute active recovery periods, 3 sessions per week. Primary outcomes included VO₂max (ml·kg⁻¹·min⁻¹), muscular endurance index (MEI), and blood lactate concentration. Pre- and post-intervention assessments were conducted under standardized laboratory conditions. Results: The HIIT group demonstrated significantly greater improvements in VO₂max (Δ+5.6 ml·kg⁻¹·min⁻¹, 95% CI: 4.2-7.0, p