The goal of this clinical trial is to learn if the "Move Sapiens" exergame in Virtual Reality (VR), incorporated with a short model of High-Intensity Interval Training (HIIT), works as an intervention tool for adolescents with Attention-Deficit Hyperactivity/Disorder (ADHD). It will also assess the safety and effectiveness of this intervention.

The main questions it aims to answer are: Does interacting with HIIT "Move Sapiens®" in VR improve attention and executive function in adolescents with ADHD? Does this intervention reduce other symptoms such as sleep problems and anxiety? Researchers will compare the HIIT VR exergame to a control condition.

Participants will: Engage with "Move Sapiens®" in VR (intervention group) or participate in a control condition with an adapted version of the exergame without physical exercise (control group) (five times a week for 4 weeks). Visit the clinic for assessments and tests. The analysis will involve comparing group means using a mixed model and calculating effect sizes with Cohen's d to determine the clinical relevance of the results

Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by inattention, hyperactivity, and impulsivity, affecting 3-5% of the global school-age population. Literature data show that high-intensity interval training (HIIT) is a potential intervention for ADHD inattentive symptoms and cognitive functioning deficits. These neuromodulatory effects have great potential to enhance neural plasticity and improve the executive functions of patients with ADHD. Furthermore, virtual reality (VR) can increase motivation for general activities, being a possible interesting tool, especially for people with ADHD.

Therefore, this study will investigate the potential of the 'Move Sapiens®' exergame in VR as an intervention tool for adolescents with ADHD. The primary objective is to assess whether interacting with 'Move Sapiens®' in VR can induce observable improvements in executive function and attention, a secondary objective is investigating a possible reduction in symptoms such as sleep problems and anxiety. Data will be obtained through validated questionnaires, in evaluation sessions conducted by clinicians and neuropsychologist, before and after the intervention. Ninety-eight participants, aged 12 to 17 with ADHD, will be randomly allocated in two groups that will interact with two versions of the VR 'Move Sapiens®' (with and without HIIT) during 20 sessions over 4 weeks. The four initial sessions and the last session will be performed in the laboratory. In these sessions, heart hate will also be monitored. Other sessions will be done at home with remote supervision. In all sessions, the game score will be monitored. The experimental group will practice the exergame, which incorporates a short model of HIIT, consisting of 12 cycles that include 16 seconds of maximum effort followed by 20 seconds of rest (total: 7 minutes and 12 seconds). In the control group, participants will engage in an adapted version of the Move Sapiens exergame without physical exercise, interacting through the joystick. This randomized clinical trial will be conducted in two centres: the Hospital de Clínicas de Porto Alegre (HCPA), and the Centro de Escola de Especialidades Médicas (CEEM - UniEduk/UniMax).

Furthermore, in a small convenience subsample of 30 participants (15 intervention and 15 control group) from the Porto Alegre-RS, we will explore a possible biological mechanism ("brain signature") associated with improved attention, detectable by fMRI, suggesting potential changes in brain function detectable through neuroimaging.

Inclusion Criteria:

• participants with diagnosis of ADHD according to DSM-5;
• age between 12 and 17 years;
• no prior use of ADHD medication or have not been using ADHD medication for at least one month.

Exclusion Criteria:

• participants with conditions and comorbidities that prevent the execution of HIIT in VR, such as severe additional psychiatric and physical conditions and a history of seizures;
• inattention score below 12 on the SNAP-IV inattention subscale;
• IQ below 70;
• recreationally active people who engage in intense, systematic physical activity more than two times a week.

For the MRI assessment, the following exclusionary criteria are added:

• participants with non-compatible aneurysm clips, cochlear implants, pacemakers, metal fragments in the body or eyes, or non-removable piercings;
• internal metal residues that interfere with image acquisition and analysis;
• severe claustrophobia;
• respiratory difficulties that prevent cooperation;
• inability to remain still due to hyperactivity;
• body weight and size exceeding device limits;
• excessive involuntary movement;
• anatomical abnormalities.

This study will be a single-blind clinical trial; the evaluators of the primary outcomes will be blinded, unaware of the group allocation to ensure the objectivity of the assessments. The data analysis will remain blinded to ensure that the researcher in charge is unaware of the experimental conditions, thus maintaining the impartiality of the analysis. However, the participants will be aware of their allocation group, as they will experience the different versions of the VR game 'Move Sapiens®'; one group will perform the exergame, with HIIT physical exercise, while the other will participate using a joystick, without physical exercise, which will prevent blinding of the volunteers. The training monitoring team, due to operational necessity, will also not be blinded.