The main aim of the MENTALFIT project is to test the effectiveness of physically active teaching methodologies to reduce mental fatigue and optimize cognitive, emotional, and motivational processes in secondary school students. Specifically, the study aims to examine differences depending on the type of physically active strategy implemented (physically active learning, active breaks, and active recesses) on students' mental fatigue, cognitive function, group dynamics, and motivational processes. Furthermore, the project aims to compare whether learning and academic performance are similar in traditional classes versus classes employing a physically active teaching methodology. Finally, a secondary objective of the project is to create and validate new instruments to assess the different psychobiological and educational processes included in this project.

Background and Rationale Mental Fatigue (MF) is a dynamic psychobiological state induced by prolonged cognitive and emotional demands. In educational contexts, particularly in secondary education, it manifests as a cascading deterioration affecting attention, executive function, emotional regulation, and learning capacity. Despite its relevance, MF remains understudied in adolescents. Secondary school students face substantial sedentary demands, spending an average of 78% of the school day in sedentary activities. These schedules, characterized by extended periods of continuous instruction with minimal breaks, create conditions conducive to MF development. The MENTALFIT project aims to address this by reintegrating movement into school routines to counteract MF and its associated cognitive decrements.

Study Design and Methodology This quasi-experimental study (Study 3 of the MENTALFIT overarching protocol) employs a multifactorial design to evaluate the differential effectiveness of three physical activity (PA) interventions. The study is conducted over a full academic year (2024-2025) across several secondary schools in Extremadura, Spain. The sample comprises adolescents in their 3rd and 4th year of secondary education (aged 13-17).

The sample is divided into four groups: one control group ("business as usual") and three experimental groups. To compare the effectiveness of different approaches, each experimental center implements three distinct physically active strategies in a counterbalanced rotation across the three trimesters. This ensures that each experimental group receives every type of intervention while controlling for order effects.

Intervention Components

The multicomponent intervention includes:

Physically Active Lessons (PAL): Integrating motor activities with curriculum content.

Active Breaks (AB): Short bouts of physical activity delivered between or during lessons.

Active Recess (AR): Structured opportunities for physical activity during break times.

Data Collection Data are collected at six measurement points throughout the academic year (at the beginning and end of each trimester). Assessments include standardized self-report measures evaluating mental fatigue perception, academic burnout, school engagement, academic motivation, and well-being. Furthermore, objective measures are collected, including academic grades (GPA), computerised neuropsychological batteries (Stroop, PASAT, PVT-B), continuous heart rate and physical activity monitoring via Fitbit devices, and brain activity via Electroencephalography (EEG) in a selected subsample to capture objective neural correlates of mental fatigue.

Inclusion Criteria:

• Enrolment in the 3rd or 4th year of compulsory secondary education (Educación Secundaria Obligatoria).
• Attending one of the participating secondary schools.
• Providing written informed consent from parents/guardians and verbal assent from the students.

Exclusion Criteria:

• Medical or physical inability to participate in the physically active interventions.
• Refusal to participate or lack of parental consent.
• Schools participating in any other physical activity or health promotion program

De-identified individual participant data (IPD) that underlie the results reported in the published article will be shared. This includes data regarding self-reported mental fatigue, cognitive performance, psychosocial variables, and objective physical activity metrics, after removing any identifying information to protect the privacy of the adolescent participants.

Data will become available beginning 6 months following the publication of the main study findings and will remain accessible for up to 5 years after publication.

Access to the de-identified IPD will be granted to qualified academic researchers who submit a methodologically sound proposal. Proposals must be directed to the Principal Investigator or the corresponding author of the published manuscript. To gain access, data requestors must sign a formal data access agreement confirming that the data will only be used for the approved research purposes and that no attempts will be made to re-identify the participants.