## 2 Materials and Methods
### Instruments (Stages 2 and 4)
#### 2.3.1 Instruments for Students (Stages 2 and 4)
* Psychosocial aspects  
These variables will be measured by means of a questionnaire:  
(1) _Academic Motivation Questionnaire_ (PLOC): to measure the student's academic motivation, the version translated and validated into Spanish [43] of the Perceived Locus of Causality (PLOC) Scale is used in an adapted way [44], adapted in turn from the Self-Regulation Questionnaire of [PERSON] and [PERSON] [45]. The instrument consists of 20 items, preceded by the phrase \"I participate in this class,\" and distributed into five subscales with four items: amovitation, external regulation, introjected regulation, identified regulation, and intrinsic motivation;  
(2) _Questionnaire for the analysis of the levels of personal and social responsibility_ (PSRQ): it is a scale to measure responsibility that has been adapted to the school context by [PERSON] et al. [46] and into Spanish by [PERSON] et al. [47]. This questionnaire consists of 14 items grouped into 2 dimensions: social responsibility and personal responsibility;  
(3) _Questionnaire for the analysis of basic psychological needs_ (PMSE): to measure basic psychological needs, the Spanish version of the Psychological Need Satisfaction in Exercise Scale (PMSE) by [PERSON] and [PERSON] [48] and [PERSON] et al. [49], validated in the educational context by [PERSON] et al. [50]. This questionnaire is made up of 12 items that refer to the need for autonomy, competence and relationship with others;  
(4) _Classroom Social Climate Assessment Questionnaire_: to measure the social climate in the classroom, the scale developed by [PERSON] et al. [51] that consists of 14 items grouped into 4 levels: interest, satisfaction, relationship, and communication;  
(5) _Measure of the Intention to be Physically Active_ (IPAS): the version adapted and translated into Spanish [52] of the Intention to be Physically Active Scale (IPAS) by [PERSON] et al. [53] will be used. The scale is composed of five items to measure the subject's intention to be physically active (e.g., \"I usually play sports in my free time\") with a single dimension. * Health  
(1) _Level of physical activity_: to measure the level of physical activity, a subsample of 150 participants belonging to the CG and EG will be randomly and equally selected and accelerometers (Actigraph wGT3X-BT) will be used. The instrument has been previously tested for its validity and reliability in measuring physical activity [54; 55];  
(2) _Anthropometry_: the weight will be measured twice with the Seca(r) 861 weighing scale, in which the students must wear light clothing and no footwear. Regarding height, it will be measured twice with a stadiometer (Seca(r) 222) in which the children will stand barefoot, upright and sagittal, touching the wall;  
(3) _Body composition_: the body mass index (BMI) of the participants will be calculated as the difference of weight by height squared (Kg/cm\({}^{2}\));  
(4) _Physical condition_: to measure physical condition variables related to health, the Alpha Fitness Battery tests will be used [56; 57]. _Aerobic capacity_ will be assessed by the Course Navette Test, which has been validated to measure maximal aerobic capacity. _Muscular strength_ will be measured using dynamometry (Takey(r), TKK 5401 Grip-D) and the standing broad jump to measure upper and lower body explosive strength. _Flexibility_ will be assessed using the sit and reach test [58] which measures the maximum distance that participants can reach their fingertips by flexing the trunk without bending the knees. Teenagers will have three attempts [59]. In addition, the Chales Dillman Hexagon Test will be used to assess _cordinative agility_[41]. There will be two attempts and the best result will be recorded [60];(5) _Life habits_: to measure healthy habits, the Youth Activity Profile-Spain (YAP-S) questionnaire will be used, which provides information on physical activity and sedentary behavior of adolescents.