Project which objective is a) to test the effectiveness, in preschool children, of an integrated physical activity intervention in the classroom based on intervallic training (MOVI-HIIT) on improving executive function, body composition, cardiorespiratory fitness and b) to evaluate teachers' perceptions of barriers and facilitating elements for the implementation and monitoring of MOVI-HIIT interventions in the classroom.

In the last decade, this research group has tested the effectiveness of five interventions in school settings. The first one (MOVI) was carried out in children 8 to 11 years children (4th and 5th year of primary education) and showed a moderate effect in reducing adiposity of schoolchildren with higher body mass index (BMI), and 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 with 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 proved to be effective; in addition, data from this intervention showed a modest improvement in girls' aerobic capacity, but not in boys.

The third 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. 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.

The fourth edition (MOVI-da10!) was carried out at schoolchildren of the same age range, but focusing on active breaks designs, and as a controlled cluster-randomized trial, to test the effectiveness of a classroom-based physical activity intervention on improving, body composition, cardiorespiratory fitness and executive function.

The fifth edition (MOVI-daFit!) was carried out with 9 to 11 years schoolchildren, and consisted in a standardized recreative, non-competitive, physical activity intervention based on games adapted to high intensity interval training methodology (out of school hours, four times by week, one hour session). The aim was to test the effectiveness of an extracurricular physical activity intervention based on high intensity interval training (MOVI-daFit!) on improving cardiorespiratory fitness, cardiometabolic risk, executive function, and academic performance.

The results from these last two editions are currently under process of publishing.

The new edition (MOVI-HIIT) has been designed controlled cluster-randomized trial including 10 schools from Ciudad Real province, Spain. It will include two arms (one intervention and one control arm), in which 5 schools will be randomly assigned to the group in which a physical activity intervention will be performed (MOVI-HIIT), and another 5 schools to the control group in which the usual tasks will be performed.

With the MOVI-HIIT intervention, based on high intensity interval training integrated into the classroom for children of 2nd and 3rd grade of preschool education of one year of duration:

1. Cardiorespiratory fitness (VO2max) will increase in the intervention group (IG) whose values are below the 50th percentile for their age and sex compared to those with the same condition in the control group (CG), with an effect size (standardized mean difference) of 0.3 (moderate). This hypothesis will be used to calculate the sample size in this proposal. Considering only half of schoolchildren with lower cardiorespiratory fitness in IG and CG is due to the fact that VO2 max cannot be increased in trained subjects, and it is possible to increase it very little (less than 2%) in those with acceptable levels of aerobic capacity.
2. It will reduce the percentage of body fat in the IG versus the CG by 6%.
3. It will improve the executive function.

Inclusion Criteria:

• Schools in the province of Ciudad Real with at least one class (classroom) at each level (2nd and 3rd of preschool education), and in which the School Board gives its approval to the interventions and to the basal and final evaluations.
• The participating schoolchildren must belong to the 2nd and 3rd year of preschool education, not have any malformation that prevents them from learning the Spanish language (or Spanish sign language), not have any type of physical or mental disorder that parents and/or teachers have identified that prevents the performance of physical activities, not suffer from any chronic disease such as heart disease, diabetes or asthma that, according to the criteria of their pediatrician - after analysis of the program of activities - prevents their participation in them.
• As this is an intervention in the classroom, the school faculty will include the active breaks proposed in the center's programming, for which reason the intervention will be received by all the children in each IG school. However, we will consider school participants to be those who have the consent of the parent or guardian for participation in the study. In addition, schoolchildren must verbally express their willingness to participate in the baseline and final physical examinations.

Exclusion Criteria:

• Children with severe Spanish language learning difficulties.
• Children with 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-HIIT).