Effects of Whole-Body High-Intensity Interval Training on Fitness in Overweight Adults

This study investigates the physiological, functional, and metabolic effects of a supervised whole-body high-intensity interval training (WB-HIIT) program conducted entirely in person in adults with overweight and obesity.

Overweight and obesity are associated with decreased cardiorespiratory fitness, metabolic impairments, and increased risk of chronic diseases. In contrast, regular physical activity is known to improve cardiorespiratory fitness, metabolic health, body composition, strength, and quality of life. WB-HIIT, which involves body-weight exercises performed at high intensity with controlled recovery intervals, provides a time-efficient, equipment-free training modality that can be adapted for individuals with excess body weight.

A total of 40 adults aged 18 to 55 years with a BMI between 25 and 35 kg/m² will be recruited and allocated to an intervention and control group. In the intervention group, participants will complete a 10-week supervised WB-HIIT program consisting of 2 to 3 sessions per week. Training sessions will include 8 to 12 whole-body exercises targeting major muscle groups, performed in intervals lasting 20 to 60 seconds with recovery periods adjusted according to participant progression. Intensity will be monitored through heart rate and perceived exertion (Borg CR-10 scale), and progression will be achieved by modifying the number of sets, exercise complexity, and work-to-rest ratio.

All participants will undergo comprehensive pre- and post-intervention evaluations. Body composition will be measured using DXA, and anthropometric measurements will include waist circumference and BMI. Cardiometabolic health will be assessed through fasting blood sampling measuring glucose, insulin, HbA1c, lipid profile, hepatic markers, and additional exploratory biomarkers. Cardiorespiratory fitness will be evaluated using a maximal graded treadmill test with gas exchange analysis to determine VO₂peak and the Chester step test. Functional performance will be assessed through the 30-second chair-stand test, arm-curl test, and 6-minute walk test. Muscular strength will be evaluated through 3-repetition maximum (3-RM) testing and fatigue protocols at 60% of 1-RM for the leg-press and bench-press exercises. Physical activity and dietary habits will also be evaluated before and after the intervention.

The primary outcomes of the study are the changes in VO₂peak and muscle strength following the intervention. Secondary outcomes include changes in body composition, metabolic parameters, and functional capacity. Statistical analyses will include repeated-measures ANOVA and between-group comparisons using parametric or non-parametric methods as appropriate.

This study aims to deepen understanding of the effects of supervised WB-HIIT in overweight adults and to identify practical, scalable training methods that can be implemented in community or clinical settings. The findings may guide the development of accessible exercise-based health strategies for improving fitness and metabolic health in this population.

Inclusion criteria

• Adults aged 18 to 55 years.
• Body mass index (BMI) between 25 and 35 kg/m².
• Able to provide written informed consent.
• Able to safely participate in high-intensity interval training.
• For participants with BMI > 30 kg/m²: medical clearance from their general practitioner.

Exclusion criteria

• BMI < 25 or > 35 kg/m².
• Presence of any chronic medical condition other than overweight/obesity.
• Known cardiovascular, metabolic, respiratory, or musculoskeletal disease that contraindicates high-intensity exercise.
• Pregnancy.
• Inability to perform exercise testing or complete the WB-HIIT program.
• Any condition judged by investigators to interfere with participation or data interpretation.