The main result of the study was the large effect size that we identified in almost all tests, with the exception of the visual search test runtime. The cognitive function of the students who participated in the PAL increased, with significant improvement in correct answers and time reaction in the three cognitive test used. The only exception was the frequency of correct answers for the visual search, a high difficult test for which the participants showed improved in reaction time but not in correct answers. In all other cases it was possible to find mean differences in the expected directions: baseline with lower average number of correct answers and higher average time reactions than at other moments, showing a gradual improvement over time.
This improvement was higher in IG than CG as showed the lowers p-values and highers cohen-d values when compared the differences between base-line and all other moments in each group, and could be related with the classes with physically active lessons, due it was the children who underwent that intervention who showed the best improvement.
The majority of previous studies that associate physical activity and cognitive function were based on the possible isolated effects of physical activity practice, especially of moderate and vigorous intensity5,18. The most consistent evidence has shown that most interventions focus on increasing physical activity at these intensities (moderate and vigorous) outside the classroom, indicating positive outcomes related to cognitive performance12.. However, these positive results were generally found in developed countries, with full-time education and favorable socioeconomic conditions9. In contrast, our findings showed positive effects of physically active lessons in one of the five cognitive indicators evaluated.
Inhibitory control is an important cognitive function for the development and academic performance of children. Previous studies have found positive associations between academic performance and cognitive performance in tests that evaluate children's inhibitory control19. Suggest that inhibition enables proficient performance of other executive functions, which, in turn, influences the ability to produce behaviors aimed at new goals, in new situations. In this way, it is possible that the stimuli of physical activities in classes can promote effects on inhibitory control in children, by allocating neural resources of attention through an increase in the plasticity of the frontal regions of the brain20.
In this perspective, school plays a fundamental role in the integral development of students, demonstrating that this environment could be a possible enhancer of cognitive performance, even in less developed countries21. Furthermore, the level of evidence on the likely advantages of replacing sitting time with light physical activity integrated with the curriculum content on cognitive functions remains low or inconclusive8.
It is important to note that, besides the similarity of effects in most cognitive variables compared with the control group, the children's performance of the intervention group was not inferior in any variable during the two years of follow-up. This means, on the one hand, the intervention did not harm students’ learning. On the other hand, the more physically active lessons which also include more social interaction between students can, on long terms, contribute increasing their eagerness to learn. This is another aspect to be also investigated henceforth.
Considering the natural development of children, it is expected that cognitive performance will change based on the interaction with a set of factors, including the learning process in the school environment and other experiences in the family and social environment22. For this reason, the cognitive tests were adjusted in the second year of intervention (M4 and M5), making them more challenging, to minimize the possibility of a positive effect caused by children's predictable cognitive development23.
The recent review by Norris7 showed that the PAL observed with an average duration of 26 minutes per class, three to five days a week, and an average intervention time of six months did not indicate any noticeable effects on cognitive functions. Similarly, Watson18 found inconclusive effects on cognitive functions but noted that a possible explanation may be related to the variation in quality of the tests used. The tests used in the present study are well known and widely used and all measures in our study were administered by specialized professionals in the field of psychology, through computerized cognitive tests, adjusted for children of this age group. However, in this type of intervention, the teacher plays a fundamental role, because they are the ones who will impart the PAL in the classroom, and this is not common in the traditional culture of the school, where movement is generally not integrated into the curriculum components24–26. In this sense, it is essential to consider the more teachers are involved is the better the outcomes27.
In the current study, teachers were instructed to replace conventional lessons as often as possible, autonomously. Unlike other studies, in which teachers are directed to insert a rigid number of PAL, in the current study, teachers were free to insert the activities whenever they wanted, to preserve the external validity of this type of intervention. Despite this free choice, teachers reported applying the PAL three times a week, with an average time of approximately 45 minutes. However, because there was no daily control of how many times the activities were inserted, it is possible that the conduction of activities may have occurred at different frequencies and periods of time throughout the school year, in special due to the change of teachers after the grade transition. In this sense, interventions with PAL should be better reported in future studies, with detailed descriptions of how teachers carry out physically active lessons, as well as the evaluation of cognitive indicators7.
The variability in the applied cognitive tests is a factor to be considered, since different measures can show different outcomes28. However, this condition may be a strong point of our study, as validated tests were used, administered by trained evaluators. Evidence indicates that computerized tests provide greater consistency in administration and scoring, as well as greater precision in stimulus control and greater precision in measurement28. In addition, our main analysis eliminates the impact of sample loss, ensuring the quality of our results.
The limitations of the current study include the lack of information regarding behaviors performed outside the school environment during the intervention period. Other domains of cognitive functions should also be explored. In addition, studies are needed to qualitatively investigate the involvement of teachers in the intervention, and how the PAL are carried out, using a tool that makes it possible to observe the number of lessons administered per class.