Rationale, Design and Methods of a Study on Physical Activity, Sedentarism, Physical Fitness, and Brain , Cognitive Performance and Academic Achievement in School Children. The Cogni-Action Project

Regarding the study (i.e., crossover-randomized trial), children will be randomized to each protocol session, participating in all of them with two-weeks apart . Thus, they will assist to our gym to perform one of the three protocol and subsequently they will be move to a laboratory where they will undergo EEG and eye-tracking measurements during resting state condition and during two different cognitive tasks More details can be found in following sections.

The design of the project will consist of a counterbalanced cross-over trial where the participants will perform, on different days, three different PA training protocols in a random order. Each child will visit our laboratory three times, every two weeks to ensure a "wash-out" period with the purpose of mitigating the PA effect from each protocol. Participants will assist to the three different sessions at the same weekday (e.g., Monday) and at the same daytime to avoid differences in preceding school activities or circadian rhythms. Participants will undergo a "Sedentary condition" (SC), sitting and watching a documentary on TV as has been used previously, and two different PA protocols consisting in "Moderate-Intensity Continuous Training" (MICT), i.e., continuous outdoor walking, and "Cooperative High-Intensity Interval Training" (C-HIIT), composed of a circuit training with a partner (physical education teacher). These three protocols have been chosen in view of what corresponds to types of activities usually performed in schools. Thus, SC mimics the time spent during any academic lesson (i.e. mathematics or language lessons); MICT represents the typical activity in a PE class; and C-HIIT has been selected since it is postulated as an exercise protocol that could possibly be implemented in the PE class. The three protocols are designed so that energy expenditure is equivalent between them, to eliminate differences in the energy expenditure as a possible confounding factor. The energy expenditure calculation protocol is detailed on supplementary material.

After each PA protocol, the participants will undergo EEG and eye-tracking measurements as follows: 1st, resting state spontaneous brain activity will be assessed during 3 min with EEG only, and subsequently, eye-tracking will be registered in parallel with EEG while participants perform the cognitive tasks (a working memory task and a reading task). The measurements will start between 20 to 25 minutes after the end of each condition. In this way, we will emulate a school recess in the Chilean context, before the start of the next subject. All measures will be carried out in the "Laboratorio Lenguaje & Cognición ELV", which belongs to the Literature and Language Sciences Institute of the Pontificia Universidad Católica de Valparaíso. To avoid subjective influence of evaluator, when the participants go to the laboratory, the evaluator will be blinded according to which PA protocol participants performed.

Neuroelectric and eye-tracker measurements EEG measurement: A B-Alert X24 device for EEG (Advanced Brain Monitoring, California, United States) will be used, which consists of 24 active electrodes that minimize the noise of electrical devices outside the biological processes of interest, ensuring good signal quality. Two channels will be used to register electrooculographic activity, to better discriminate between true electroencephalographic and electrooculographic activity associated with eye movement and blinking. Recordings will be done at a sampling rate of 256 values per second, with a band-pass filter between 0.1 - 100 Hz, and a notch filter of 50 Hz to eliminate the noise of the surrounding alternating current in the room. It should be noted that this equipment is wireless, which makes it more convenient and faster to mount on participants. For this study the investigators will focus on the channels Fz, Cz, CPz, Pz, POz, Oz, O1 and O2.

Eye-tracker: A Tobii Pro TX300 (Tobii, Stockholm, Sweden) will be used to track eye movements directly through a light sensitive camera near the infrared spectrum. This equipment studies the visuomotor characteristics during the process of reading and the trajectories of the look around each word. In addition, it will serve to define the exact moments at which these words are read and thus be able to synchronize the EEG record to calculate an average signal (N400) that reflects the brain's processing of language. The same device records raw values of pupil size (diameter), saving all data with a sampling rate of 300 Hz.