This study proposes a single-blind randomized clinical trial designed to evaluate the effects of high-intensity interval training (HIIT) on liver health in adults with overweight or obesity, while also assessing the usefulness of FibroScan as a tool for detecting and monitoring hepatic changes. The study is grounded in the idea that HIIT may improve liver status in individuals with metabolic dysfunction-associated steatotic liver disease, even in the absence of major weight loss, and that FibroScan could serve not only as a diagnostic method but also as a follow-up instrument during conservative treatment.

The sample will include 30 adults from the Los Ríos Region, aged 18 to 59 years, with BMI >25 kg/m² and chronic noncommunicable conditions such as dyslipidemia, diabetes, or hypertension, provided they are fit for exercise. Participants will be randomly assigned to either an intervention group (HIIT, n=15) or a non-trained control group (n=15). Recruitment will be community-based, using posters and social media, and eligibility will be screened with the PAR-Q+ questionnaire. Individuals with excessive alcohol intake, liver disease of other etiologies, pregnancy, or contraindications to exercise will be excluded.

The HIIT intervention will last 8 weeks, with 2 to 3 sessions per week, each session lasting 30 minutes. The protocol consists of five 2.5-minute bouts at 80% of heart rate reserve, interspersed with 2.5-minute active recovery periods at 20% of heart rate reserve. The training will be supervised by a physical therapist experienced in cardiometabolic exercise prescription, and the control group will receive training after the study is completed for ethical reasons.

Before and after the intervention, participants will undergo a comprehensive evaluation including blood sampling, anthropometry, body composition, and physical fitness assessment. Blood markers will include transaminases, lipid profile, glucose, and HbA1c. Liver health will be assessed by FibroScan through controlled attenuation parameter (CAP) for steatosis and liver stiffness for fibrosis. Additional variables such as waist circumference, muscle mass, fat mass, handgrip strength, and prior physical activity level will also be recorded.

Statistically, the study will compare baseline differences between groups and evaluate pre-post changes after the intervention using parametric or nonparametric tests according to data distribution, along with correlation and multiple regression analyses. The expected outcome is that HIIT will improve liver-related parameters, and that FibroScan will be sensitive enough to detect these changes, supporting its value as a regional clinical tool for the identification and follow-up of hepatic steatosis and fibrosis in people with overweight or obesity.

Inclusion Criteria:

• 18 to 59 years from the Los Ríos Region
• Overweight or obesity (BMI >25 kg/m²)
• Diagnosis of a chronic noncommunicable disease such as insulin resistance, and type 2 diabetes
• Fit to perform physical activity/exercise
• Exercise readiness will be confirmed using the PAR-Q+ questionnaire

Exclusion Criteria:

• Excessive alcohol consumption
• Liver diseases of other etiologies
• Musculoskeletal and/or cardiovascular conditions that contraindicate exercise - Inability to attend in-person exercise sessions, or pregnancy

Considering that the investigators will collect personal information of each participant, for Ethical reasons, the investigators will share only group data, such as means and standard deviation.