Background: Non-communicable diseases linked to sedentary lifestyles represent a global public health burden. High-intensity interval training (HIIT) has been proposed as a time-efficient alternative to traditional moderate-intensity continuous training (MICT) for improving cardiovascular fitness and body composition; however, comparative evidence in sedentary young adult populations is incomplete.

Objective: To compare the effects of 12-week HIIT versus MICT programmes on VO₂max, resting heart rate, body mass index (BMI), and waist circumference in sedentary young adults.

Method: A three-arm randomized controlled trial assigned 90 sedentary adults (18–30 years; 48 female, 42 male) to HIIT (n = 30), MICT (n = 30), or a no-exercise control group (n = 30). Exercise sessions were three times per week, with HIIT sessions lasting 20 minutes and MICT sessions lasting 45 minutes. VO₂max was assessed by incremental treadmill ergometry; body composition by DEXA scan. SPSS v.28 was used for ANCOVA analysis. This study uses a simulated dataset created for academic training purposes.

Key Results: HIIT produced significantly greater VO₂max improvements than MICT (Δ+5.8 vs. Δ+3.9 mL/kg/min; p = 0.031) with less total exercise time (240 vs. 540 min/month). Both exercise groups significantly reduced BMI and waist circumference compared to controls (p < 0.01), with no significant difference between HIIT and MICT for body composition outcomes.