Project which objective is to test the effectiveness of an extracurricular physical activity intervention based on high intensity interval training (MOVI-daFit!) on improving cardiorespiratory fitness (CRF), cardiometabolic risk, executive function, and academic performance.

In the last decade, this research group has tested the effectiveness of three interventions following this model. The first one (MOVI) was carried out in peripuberal age children (4th and 5th year of primary education, 8-11 years) and showed a moderate effect in reducing the adiposity of schoolchildren with higher BMI, an improvement of the lipid profile, without significantly improving the global cardiometabolic risk because it did not produce a reduction in insulinemia.

The second edition (MOVI-2), carried out at schoolchildren of the same age range, increased the duration and intensity of the sessions, and was focused on the development of muscular strength in order to improve insulinemia levels. The intervention showed proved effectiveness; in addition, the data from this intervention showed a modest improvement in girls' aerobic capacity, but not in boys.

The last edition (MOVI-KIDS) was aimed at children aged 4 to 7 years to test the hypotheses that vigorous physical activity at early ages could produce lifelong cardio-metabolic benefits. Data submitted for publication in this study show that, as in the case of the IDEFICS study in children of similar age, the intervention was not effective in improving fitness.

This new edition (MOVI-daFit!) has been designed as controlled cluster-randomized trial including 10 schools from Cuenca province, Spain. Five schools will be randomized to intervention group (IG), in which the intervention MOVI-daFit! will be conducted for children in fourth and fifth school grades (9-11 years old). The other five schools will be allocated to the control group (CG).

During an academic year the 4th and 5th schoolchildren allocated to IG will be carry out, in out of school hours, four times by week, one hour sessions of a standardized recreative, non competitive, physical activity intervention based on games adapted to high intensity interval training methodology (MOVI-daFit!). In the CG regular physical activity will continue.

At the end of the school year the researchers will determine main outcome variables: changes in VO2max, body fat by bioimpedance, reactive hyperemia index, academic achievement, executive function, and biochemical analytic procedures including lipid profile, insulin, HbA1, C ultrasensitive reactive protein and BDNF.

The hypotheses of this new edition will be that the MOVI-daFit! based on high intensity interval training (HITT) adapted for the 4th and 5th schoolchildren, will:

1. Increase the aerobic capacity (VO2max).
2. Reduce the percentage of body fat in the GI versus the GC by 6%.
3. Improve executive function and academic performance.
4. Improve subclinical markers of atherosclerosis (endothelial function and carotid intima-media thickness).

Inclusion criteria:

• Schools must have at least one full classrooms for both the 4th and 5th grade of primary school.
• The approval of boards of governors will be necessary.
• Children's parents or legal representatives will sign an informed consent to participate.
• Parents will be invited to collaborate by filling in questionnaires with regard to family leisure habits, sleeping, eating and getting around town.

Exclusion criteria:

• Severe Spanish language learning difficulties.
• Serious physical or mental disorders identified by parents or teachers that would impede participation in the programme's activities.
• Children diagnoses of chronic disorders, such as heart disease, diabetes or asthma, which in the opinion of their paediatricians would prevent their participation in the programme's activities (MOVI-daFit!).