Lifestyle Behaviours, Self-Esteem and Academic Performance in Primary Education Students—A Structural Equation Model According to Sex and School Type

Citation: Villodres, G.C.; Salvador-Pérez, F.; Chacón-Cuberos, R.; Muros, J.J. Lifestyle Behaviours, Self-Esteem and Academic Performance in Primary Education Students—A Structural Equation Model According to Sex and School Type. Children 2023,10, 1769. https://doi.org/10.3390/ children10111769 Academic Editor: Ferdinand Salonna Received: 4 October 2023 Revised: 25 October 2023 Accepted: 29 October 2023 Published: 31 October 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). children Article Lifestyle Behaviours, Self-Esteem and Academic Performance in Primary Education Students—A Structural Equation Model According to Sex and School Type Gracia Cristina Villodres 1, Federico Salvador-Pérez 2, Ramón Chacón-Cuberos 3and JoséJoaquín Muros 1,* 1Department of Didactics of Corporal Expression, Faculty of Education, University of Granada, 18071 Granada, Spain; [email protected] 2Department of Didactics of Social Sciences, Faculty of Education, International University of La Rioja, 26006 Logroño, Spain; [email protected] 3Department of Research Methods and Diagnosis in Education, Faculty of Education, University of Granada, 18071 Granada, Spain; [email protected] *Correspondence: [email protected]; Tel.: +34-958246350 Abstract: (1) Background: The present study aimed to examine the relationship between physical activity (PA), screen time (ST), maximal oxygen uptake (VO 2 max), Mediterranean diet (MD) adherence, self-esteem (SE) and academic performance (AP) in primary education students. In order to address this aim, an explanatory model was developed to examine the existing relationships between PA, ST, VO 2 max, MD adherence, SE and AP. Further, the proposed structural model was examined via multi-group analysis as a function of sex and school type. (2) Methods: A non-experimental, descriptive, comparative and cross-sectional study was designed with a total sample of 269 Spanish students (11.29 ± 0.62). Validated questionnaires were administered to collect data on study variables. (3) Results: Relative to boys, girls reported better academic grades and showed a stronger positive relationship between MD adherence and AP, MD adherence and PA, and VO 2 max and SE. Likewise, girls showed a stronger negative relationship between ST and VO 2 max, and ST and MD adherence. At the same time, mixed funding school (MFS) students reported higher PA engagement than state school (SS) students. However, SS students reported better MD adherence, ST and AP than MFS students. Further, a stronger positive relationship was found in SS students between MD adherence or VO 2 max and SE than in MFS students. Also, within the former group, ST was more negatively related to MD adherence and VO 2 max. (4) Conclusions: Scientific and educational communities must develop future strategies that consider potential determinants in order to target more desirable outcomes. Keywords: physical activity; Mediterranean diet adherence; screen time; maximal oxygen uptake; self-esteem; academic performance; children; preadolescence; structural equation model 1. Introduction Pre-adolescence is an important developmental period characterised by the establishment of behavioural habits which can affect children’s health both now and in the future [1]. Physical activity (PA) has been defined as any exercise performed using the skeletal muscles and involving energetic expenditure [ 2 ]. According to World Health Organization (WHO) recommendations, children and adolescents should engage in at least 60 min of moderate-to-vigorous PA per day. Further, it is recommended not to spend more than two hours per day in front of screens or devices [ 3 ]. Overwhelming evidence associates PA with a reduction in cardiovascular diseases, hypertension, different cancers, etc. [ 4 ]. Also, PA engagement translates into physical and mental benefits—such as improved maximal oxygen Children 2023,10, 1769. https://doi.org/10.3390/children10111769 https://www.mdpi.com/journal/children Children 2023,10, 1769 2 of 16 uptake (VO 2 max), self-esteem (SE) [ 5 , 6 ], cognitive functioning and academic performance (AP) [7]. In the majority of scientific studies, children reporting greater PA engagement also report adequate Mediterranean diet (MD) adherence and less screen time (ST) [ 8 ]. In addition to PA engagement, greater cardiorespiratory fitness is associated with optimal MD adherence in children aged between six and 13 years [ 9 ]. MD is characterised by a low intake of saturated fats and red meat and a limited amount of wine in adults, while emphasising a high consumption of plant-based foods like fruits, vegetables, whole grains, nuts and seeds. A MD also includes olive oil, dairy products such as cheese and yogurt, eggs, and a moderate consumption of fish and poultry [ 10 ]. It is characterised by low levels of saturated fats and elevated levels of monounsaturated fats, alongside abundant fibre, complex carbohydrates and antioxidants [ 11 ]. It is also known that following a traditional MD helps to maintain a healthy body weight [ 12 ] and general health-related quality of life in children and adolescents [ 13 ]. Further, poor MD adherence in children is associated with a higher risk of suffering cognitive issues and mental illnesses such as attention deficit hyperactivity disorder (ADHD) [14,15] Previous research also highlights that health promotion interventions targeting physical fitness and sound nutrition in children benefit not only physical and mental health, such as SE, but also cognitive health [ 16 ], such as AP [ 17 ]. Black et al. [ 18 ] observed that a multiple micronutrient-fortified diet increased school children’s cognition with improved expressive language and inhibitory control. At the same time, Ludyga et al. [ 19 ] found that a PA programme run during school break time improved adolescents’ executive functions, such as inhibitory control. Likewise, a metanalysis conducted by Rasberry et al. [ 20 ] revealed a total of 251 associations between PA and AP, with AP being represented through measures of academic performance, cognitive skills, attitudes and academic grades in Mathematics. Although physical and mental health benefits are widely acknowledged, approximately 81% of adolescents aged 11–17 do not engage in enough PA. Among this group, girls are less active than boys, with 85% of girls failing to meet recommendations set by the WHO compared to 78% of boys [ 2 ]. Also, Spanish children and adolescents spend one hour and 13 min a day on weekdays and almost three hours a day on weekend days in front of a screen, exceeding screen recommendations, with ST being higher in boys [ 3 ]. According to the latest Pasos study [ 3 ], more than 12% of the Spanish population aged eight to sixteen years reported low MD adherence. Similar to the results seen with PA engagement, girls reported lower MD adherence than boys. Further, the present research team observed that confinement due to COVID-19 caused PA to decrease in Spanish children, whilst ST increased, negatively affecting SE. In this regard, it is essential to consider SE from early ages in order to improve health-related quality of life [ 21 ]. Also, SE is considered to be a main criterion for the diagnosis of mental disorders [ 22 ]. Specifically, girls and state school (SS) students were most affected during the pandemic [23]. Concern exists that these habits will continue into the future [24]. In line with that discussed above, Schlund et al. [ 25 ] concluded that sex effects are not reported in a suitable way for effective intervention programmes to be developed to improve healthy habits at school. A consideration of sex is imperative as it is key at every step of intervention planning, implementation and evaluation. Likewise, according to Muñiz and Suárez-Pandiello [ 26 ], students’ immediate settings, such as their school, can influence their health. In Spain, broad differences exist between mixed funding schools (MFS) and SS. Typically, students attending MFS tend to be predominantly Catholic and come from families with a higher socioeconomic status than SS students. The present study hypothesises that sex and setting could be influential factors in the health of children. Consequently, influential factors in the aforementioned relationships need to be considered in order to provide a scientific basis from which future intervention programmes targeting healthy habits can be developed. It is important to examine whether differences emerge as a function of sex and setting. Children 2023,10, 1769 3 of 16 Thus, the present study aimed to examine the relationship between PA, ST, VO 2 max, MD adherence, SE and AP in primary education students. In order to address this aim, the present study outlined the following objectives: Develop an explanatory model of the existing relationships between PA, ST, VO 2 max, MD adherence, SE and AP in primary education students; Analyse the associations between the variables included in the model according to sex and school type through multi-group analysis. 2. Materials and Methods 2.1. Design and Participants A non-experimental, descriptive, comparative and cross-sectional study was designed. Three hundred and thirty-one children were initially recruited to the study. Of these, questionnaires completed by 62 participants were discarded due to incorrect completion or missing data. Thus, 269 students formed the final sample. The sample was made up of 125 girls (46.50%) and 144 boys (53.50%), with an average age of 11.29 ± 0.62 years. All participants came from two state schools (SS) and three mixed-funding schools (MFS) in Granada, Spain. The sampling process was non-random, as participants were chosen based on convenience. All students willingly took part in the study, with the prior consent of their parents or legal guardians. The study was authorised by participating schools and parents’ associations. 2.2. Instruments A Spanish version of the PA questionnaire for children (PAQ-C) that has been crossculturally adapted and validated in children aged between eight and fourteen years was used to evaluate PA engagement [ 27 , 28 ]. This tool has been shown to be valid and reliable, producing an intraclass correlation coefficient (ICC) greater than 0.73 and an internal consistency of α = 0.86. This self-report instrument comprises 10 questions aimed at gauging involvement in moderate and vigorous PA over the week prior to completion. An overall PA score is determined by calculating average scores from responses to the first nine questions, which are rated on a five-point scale. The tenth question serves as a validity check, in which respondents indicate whether any personal obstacles hindered their regular PA during the seven days evaluated by the questionnaire. None of the respondents mentioned facing such hindrances. VO 2 max was estimated using the 20 m incremental maximum effort shuttle run field test, employing the equation proposed by Léger et al. [ 29 ]. In order to complete this test, participants must run back and forth between two lines placed 20 m apart. Participants start at an initial velocity of 8.5 km/h and increase their speed by 0.5 km/h/min. When participants can no longer reach the line within the time provided on two consecutive occasions or can no longer maintain the physical effort required to continue, they stop and finish the test. The latest updated version by Altavilla et al. [ 30 ] of the KIDMED [ 31 ] was used to evaluate MD adherence. This test consists of 16 yes-or-no items that evaluate MD adherence in children and adolescents. Twelve questions are phrased positively, where a ‘yes’ response is scored as +1. Conversely, four questions are phrased negatively, where a ‘yes’ response is scored as − 1. All ‘no’ responses are scored as 0. The maximum possible score is 12, whilst the lowest possible score is − 4. Based on the total KIDMED score, children’s diets are categorised as either optimal quality ( ≥ 8), needing improvement (4–7) or poor quality (≤3). An ad hoc and bespoke questionnaire was developed to collect the sociodemographic data of sex and date of birth. Also, ST was evaluated. Children reported the number of hours spent daily on screen-based leisure activities such as watching television, playing video games, using a mobile phone, using a computer, etc., on weekdays and weekends. An overall summary score was calculated from the mean number of hours reported over the seven days examined (week and weekend days). Children 2023,10, 1769 4 of 16 AP was evaluated according to academic grades. Schools provided recorded grades for nine different subjects: Natural Sciences, Social Sciences, Spanish Language and Literature, Mathematics, English, Religion/Values, Art Education, Physical Education and French. Grades for these subjects pertained to the first term of the school year in which the research was carried out (2022–2023). Previous studies have also used these indicators to assess AP [7]. An adapted, translated and validated Spanish version of the Rosenberg self-esteem scale was used for the evaluation of personal SE [ 32 , 33 ]. This adapted version has demonstrated both validity and reliability, with an internal consistency of α = 0.80. The scale comprises ten items designed to gauge an individual’s SE levels. The first five items are phrased positively, with responses graded from A to D and assigned scores ranging from 4 to 1. The remaining five items are negatively phrased, and for these questions, responses are listed from A to D, with scores ranging from 1 to 4. This design helps account for potential acquiescence bias in self-administered assessments. Total scores are computed by summing scores for each specific item, resulting in a maximum possible score of 40 and a minimum score of 10. Final scores are categorised as follows: low SE, indicating significant SE issues (10–25); medium SE, suggesting room for improvement (26–29); and high SE, reflecting a normal level of SE (30–40). The Spanish translation of the most recent version of the family affluence scale (FAS III) was used to evaluate social economic status (SES) [ 34 , 35 ]. This scale has been shown to be valid and reliable, with an internal consistency of between α = 0.76 and 0.91. This scale consists of six items that are designed to evaluate family purchasing power based on material goods. All items were scored between 0 and 3. The sum of individual scores was used to evaluate total SES. The highest possible score is 13 and the lowest possible score is 0 [ 36 ]. SES was classified as low (0–2), medium (3–5) or high ( ≥ 6). In this case, all participants showed a high socioeconomic level. 2.3. Procedure Two sets of informational packages were developed to ensure informed consent. The first was directed towards educational centre directors, while the second was intended for the parents or legal guardians of participating students. These packages contained comprehensive details regarding the study’s attributes and prerequisites. Furthermore, a research assistant was available to offer assistance and guidance regarding the performance of physical testing. Participants were instructed on the correct completion of questionnaires and tests. All tests were conducted during school time. Ethical approval was granted by the Ethics Committee of the University of Granada (2796/CEIH/2022). Data collection was carried out during the months of April and May 2023. 2.4. Data Analysis Data were analysed using IBM SPSS 25.0 statistical software. Categorical data such as sex, school year and school type are represented as percentages. For numerical data, means and standard deviations are presented. Sample distribution was evaluated using the Kolmogorov–Smirnov test. Upon confirming a non-normal distribution, the Mann– Whitney U test was employed to compare two independent groups and the Kruskal–Wallis test was used to compare more than two groups. IBM AMOS ® 24.0 software was used to perform structural equation modelling (SEM). SEM enables connections to be established between the variables outlined in the theoretical model (Figure 1). In this instance, the model was constructed with six observed variables. These observed variables included the four endogenous variables, SE, AP, MD adherence and VO 2 max, and the two exogenous variables, PA and ST. Endogenous variables have associated error terms which are visually depicted by a circle, whilst exogenous variables lack error terms and are represented by two-way arrows. SEM was employed to determine Children 2023,10, 1769 5 of 16 the relationships between the variables in the theoretical model as a function of sex (boys and girls) and school type (SS and MFS). Figure 1. Structural equation model. Note: physical activity (PA), screen time (ST), Mediterranean diet (MD), maximal oxygen uptake (VO2max), self-esteem (SE), academic performance (AP). In order to evaluate the fit of the developed structural equations model (SEM) with the actual data, various indices were used to evaluate model adequacy. The goodness of fit should be assessed on the basis of a chi-square test. Non-significant p-values indicate a good model fit. According to Byrne [ 37 ], it is also important to use additional fit indices because the mentioned statistic can be highly influenced by the sample size. Comparative fit index (CFI), incremental fit (IFI), normalised fit (NFI) and the Tucker–Lewis (TLI) indices were used. In order to be able to conclude that model fit is acceptable, values should exceed 0.90, with excellent model fit being indicated by values higher than 0.95. In addition, root mean squared error of approximation (RMSEA) analysis was performed, with values below 0.08 signifying acceptable fit and values below 0.05 indicating excellent fit. 3. Results Descriptive characteristics of the study sample are presented in Table 1. Table 1. Sample characteristics according to sex and school type. Characteristics n % PA pST pMD pVO2max pSE pAP p Total 269 100 3.49 ± 0.88 2.31 ± 1.54 6.43 ±2.74 39.79 ± 6.46 30.48 ± 5.99 7.85 ± 1.21 Sex Boys 144 53.5 3.65 ± 0.90 <0.001 2.39 ± 1.66 0.628 6.41 ±2.74 0.820 41.82 ± 6.37 <0.001 30.94 ± 5.55 0.280 7.77 ± 1.22 <0.001 Girls 125 46.5 3.29 ± 0.82 2.21 ± 1.39 6.43 ±2.74 37.45 ± 5.74 29.94 ± 6.43 8.15 ± 1.16 School Type SS 114 42.4 3.17 ± 0.85 <0.001 1.82 ± 1.51 <0.001 7.12 ±2.51 <0.001 40.27 ± 6.73 0.684 30.04 ± 6.83 0.733 8.21 ± 1.20 <0.001 MFS 155 57.6 3.72 ± 0.82 2.68 ± 1.46 5.92 ±2.8 39.43 ± 6.51 30.81 ± 5.28 7.75 ± 1.8 Note: physical activity (PA), screen time (ST), Mediterranean diet (MD), maximal oxygen uptake (VO 2 max), self-esteem (SE), academic performance (AP), state school (SS), mixed funding school (MFS). Of the total number of students, 53.5% were boys and 46.5% were girls. Boys reported significantly higher PA engagement (3.65 ± 0.90 vs. 3.29 ± 0.82; p< 0.001) and VO 2 max Children 2023,10, 1769 6 of 16 than girls (41.82 ± 6.37 vs. 37.45 ± 5.74 mL/kg/min; p< 0.001). However, girls achieved significantly higher academic grades (8.15 ±1.16 vs. 7.77 ±1.22; p= 0.014) than boys. No significant differences were found with regard to ST, MD adherence and SE. In addition, 42.4% attended SS, whilst 57.6% of participating students attended MFS. Statistically significant differences were observed in relation to ST, with this being higher in MFS students (2.68 ± 1.46 vs. 1.82 ± 1.51 h; p< 0.001). Likewise, students belonging to MFS reported higher PA engagement (3.72 ± 0.82 vs. 3.17 ± 0.85; p< 0.001). However, SS students reported higher MD adherence (7.12 ± 2.51 vs. 5.92 ± 2.8; p< 0.001) and AP (8.21 ±1.20 vs. 7.75 ±1.8; p< 0.001) than MFS students. No significant differences were found with regard to VO2max and SE. Important differences are revealed according to sex and school type. For this reason, a structural equation model was carried out in order to better understand the relationship between study variables and the influence of student groupings on outcomes. The structural model developed showed good fit indices for the multi-group analysis. The chi-squared test produced statistically significant outcomes ( χ2 = 4.1; df = 5; p= 0.539). This meant that the null hypothesis was accepted. The model could also be concluded to be homogeneous. However, Byrne (2016) urges the need to use other goodness of fit indices, given the sensitivity to sample size that is presented by this statistic. In this sense, NFI, IFI, TLI and CFI values were all excellent, being 0.97, 1.007, 1.023 and 1.00, respectively. Likewise, the RMSEA value was 0.000, which was also excellent. Thus, an excellent fit was demonstrated between the SEM developed and the gathered empirical data. Table 2and Figure 2present the regression weights and standardised regression weights pertaining to the SEM developed for the overall sample. These outcomes make it possible to determine existing associations between PA, ST, VO 2 max, MD adherence, SE and AP. Positive relationships were observed between PA and VO 2 max (b = 0.278; p< 0.005) and PA and MD adherence (b = 0.325; p< 0.005). With regard to ST, negative relationships were observed between ST and VO 2 max (b = − 0.188; p< 0.001) and ST and MD adherence (b = − 0.288; p< 0.005). MD adherence was positively related to AP (b = 0.272; p< 0.005) and SE (b = 0.173; p= 0.004). Likewise, VO 2 max was positively related to SE (b = 0.162; p= 0.006). Table 2. Regression weights for the overall sample. Association between Variables RW SRW Estimation SE CR pEstimation VO2max ←PA 2.043 0.423 4.831 *** 0.278 VO2max ←ST −0.788 0.240 −3.276 0.001 −0.188 MD ←PA 1.016 0.180 5.655 *** 0.325 MD ←VO2max −0.016 0.025 −0.642 0.521 −0.038 MD ←ST −0.512 0.100 −5.118 *** −0.288 AP ←MD 0.120 0.026 4.632 *** 0.272 SE ←MD 0.376 0.130 2.898 0.004 0.173 SE ←VO2max 0.150 0.055 2.726 0.006 0.162 AP ←VO2max 0.014 0.011 1.290 0.197 0.076 PA ↔ST −0.080 0.082 −0.976 0.329 −0.060 Note: regression weight (RW), standardised regression weight (SRW), standard error (SE), critical ratio (CR), maximal oxygen uptake (VO 2 max), physical activity (PA), screen time (ST), Mediterranean diet (MD), self-esteem (SE), academic performance (AP). *** p< 0.005. Table 3and Figure 3present the regression weights and standardised regression weights pertaining to the SEM developed for boys. The chi-squared test produced a statistically significant outcome ( χ2 = 2.0; df = 5; p= 0.844). As before, the NFI value obtained was 0.962, the IFI value was 1.061, the TLI value was 1.228 and the CFI value was 1.00, with all of these being excellent. Likewise, the RMSEA obtained a value of 0.000, which was also excellent and demonstrated an appropriate level of fit of the SEM. In this case, PA was positively related to VO 2 max (b = 0.222; p= 0.006) and MD adherence (b = 0.291; p< 0.005). With regard to ST, negative relationships were observed between ST Children 2023,10, 1769 7 of 16 and VO 2 max (b = − 0.160; p= 0.046) and ST and MD adherence (b = − 0.244; p= 0.002). In addition, MD adherence was positively related to AP (b = 0.202; p= 0.013) and SE (b = 0.206; p= 0.011). Figure 2. Structural equation model for the overall sample. Note: physical activity (PA), screen time (ST), Mediterranean diet (MD), maximal oxygen uptake (VO 2 max), self-esteem (SE), academic performance (AP). Table 3. Regression weights pertaining to the SEM developed for boys. Association between Variables RW SRW Estimation SE CR pEstimation VO2max ←PA 1.582 0.573 2.762 0.006 0.222 VO2max ←ST −0.615 0.308 −1.992 0.046 −0.160 MD ←PA 0.889 0.243 3.653 *** 0.291 MD ←VO2max −0.033 0.035 −0.939 0.348 −0.076 MD ←ST −0.402 0.130 −3.105 0.002 −0.244 AP ←MD 0.090 0.036 2.490 0.013 0.202 SE ←MD 0.418 0.165 2.531 0.011 0.206 SE ←VO2max 0.083 0.071 1.176 0.240 0.096 AP ←VO2max 0.025 0.016 1.581 0.114 0.128 PA ↔ST −0.123 0.124 −0.990 0.322 −0.083 Note: regression weight (RW), standardised regression weight (SRW), standard error (SE), critical ratio (CR), maximal oxygen uptake (VO 2 max), physical activity (PA), screen time (ST), Mediterranean diet (MD), self-esteem (SE), academic performance (AP). *** p< 0.005. Table 4and Figure 4present the regression weights and standardised regression weights pertaining to the SEM developed for girls. The chi-squared test produced a statistically significant outcome ( χ2 = 2.4; df = 5; p= 0.794). As before, the NFI value obtained was 0.975, the IFI value was 1.029, the TLI value was 1.097 and the CFI value was 1.00, with all of these being excellent. Likewise, the RMSEA obtained a value of 0.000, which was also excellent and demonstrated an appropriate level of fit of the SEM. In this case, PA was positively related to VO 2 max (b = 0.226; p= 0.006) and MD adherence Children 2023,10, 1769 8 of 16 (b = 0.370; p< 0.005). With regard to ST, negative relationships were observed between ST and VO 2 max (b = − 0.318; p< 0.005), and ST and MD adherence (b = − 0.329; p< 0.005). MD adherence was positively related to AP (b = 0.342; p< 0.005). Also, a positive relationship was observed between VO2max and SE (b = 0.204; p= 0.022). Figure 3. Structural equation model for boys. Note: physical activity (PA), screen time (ST), Mediterranean diet (MD), maximal oxygen uptake (VO 2 max), self-esteem (SE), academic performance (AP). Table 4. Regression weights pertaining to the SEM developed for girls. Association between Variables RW SRW Estimation SE CR pEstimation VO2max ←PA 1.588 0.578 2.747 0.006 0.226 VO2max ←ST −1.313 0.340 −3.861 *** −0.318 MD ←PA 1.248 0.266 4.688 *** 0.370 MD ←VO2max 0.018 0.040 0.450 0.653 0.038 MD ←ST −0.653 0.161 −4.061 *** −0.329 AP ←MD 0.144 0.036 4.044 *** 0.342 SE ←MD 0.299 0.207 1.439 0.150 0.128 SE ←VO2max 0.228 0.100 2.284 0.022 0.204 AP ←VO2max 0.030 0.017 1.729 0.084 0.146 PA ↔ST −0.066 0.102 −0.648 0.517 −0.058 Note: regression weight (RW), standardised regression weight (SRW), standard error (SE), critical ratio (CR), maximal oxygen uptake (VO 2 max), physical activity (PA), screen time (ST), Mediterranean diet (MD), self-esteem (SE), academic performance (AP). *** p< 0.005. Children 2023,10, 1769 9 of 16 Figure 4. Structural equation model for girls. Note: physical activity (PA), screen time (ST), Mediterranean diet (MD), maximal oxygen uptake (VO 2 max), self-esteem (SE), academic performance (AP). Table 5and Figure 5present the regression weights and standardised regression weights pertaining to the SEM developed for participants attending SS. The outcome of the chi-squared test was statistically significant ( χ2 = 1.5; df = 5; p= 0.918). As before, the NFI value obtained was 0.975, the IFI value was 1.066, the TLI value was 1.242 and the CFI value was 1.00, with all of these being excellent. Likewise, the RMSEA obtained a value of 0.000, which was also excellent and demonstrated an appropriate level of fit of the SEM. In this case, PA was positively related to VO 2 max (b = 0.247; p= 0.006) and MD adherence (b = 0.405; p< 0.005). With regard to ST, negative relationships were observed between ST and VO 2 max (b = − 0.181; p= 0.044) and ST and MD adherence (b = − 0.211; p= 0.014). MD adherence was positively related to SE (b = 0.231; p= 0.010). Also, a positive relationship was observed between VO2max and SE (b = 0.209; p= 0.019). Table 5. Regression weights pertaining to the SEM for participants attending state schools. Association between Variables RW SRW Estimation SE CR pEstimation VO2max ←PA 1.956 0.713 2.745 0.006 0.247 VO2max ←ST −0.804 0.400 −2.010 0.044 −0.181 MD ←PA 1.198 0.257 4.657 *** 0.405 MD ←VO2max −0.030 0.033 −0.904 0.366 −0.080 MD ←ST −0.351 0.142 −2.467 0.014 −0.211 AP ←MD 0.067 0.045 1.488 0.137 0.139 SE ←MD 0.628 0.243 2.585 0.010 0.231 SE ←VO2max 0.212 0.091 2.346 0.019 0.209 AP ←VO2max 0.001 0.017 0.052 0.958 0.005 PA ↔ST −0.190 0.121 −1.564 0.118 −0.149 Note: regression weight (RW), standardised regression weight (SRW), standard error (SE), critical ratio (CR), maximal oxygen uptake (VO 2 max), physical activity (PA), screen time (ST), Mediterranean diet (MD), self-esteem (SE), academic performance (AP). *** p< 0.005. Children 2023,10, 1769 16 of 16 43. Rutjes, A.W.; Denton, D.A.; Nisio, M.D.; Chong, L.Y.; Abraham, R.P.; Al-Assaf, A.S.; Anderson, J.L.; Malik, M.A.; Vernooij, R.W.; Martínez, G.; et al. Vitamin and mineral supplementation for maintaining cognitive function in cognitively healthy people in mid and late life. Cochrane Database Syst. Rev. 2018,12, CD011906. [CrossRef] 44. Bergier, J.; Ni´znikowska, E.; Bergier, B.; Acs, P.; Salonna, F.; Junger, J. Differences in physical activity, nutritional behaviours, and body silhouette concern among boys and girls from selected european countries. Hum. Mov. 2018,18, 19–28. [CrossRef] 45. Castro, M.; Ríos-Reina, R.; Ubeda, C.; Callejón, R.M. Evaluación de menús ofertados en comedores escolares: Comparación entre colegios públicos, privados y concertados. Rev. Nutr. 2016,29, 97–108. [CrossRef] 46. Constandt, B.; Thibaut, E.; De Bosscher, V.; Scheerder, J.; Ricour, M.; Willem, A. Exercising in Times of Lockdown: An Analysis of the Impact of COVID-19 on Levels and Patterns of Exercise among Adults in Belgium. Int. J. Environ. Res. Public Health 2020 , 17, 4144. [CrossRef] 47. Rogero-García, J.; Candelas, M.A. Representaciones sociales de los padres y madres sobre la educación pública y privada en España. Rev. Sociol. Educ.-RASE 2016,9, 46–58. 48. Sahli, H.; Ouerghi, N.; Jebabli, N.; Amara, S.; Sahli, F.; Makram, Z. Effects of Verbal Encouragements on Selected Measures of Physical Fitness and Subjective Effort Perception in Young High School Students. Int. J. Sport. Stud. Health 2022 ,4, e122590. [CrossRef] 49. Braun-Trocchio, R.; Williams, A.; Harrison, K.; Warfield, E.; Renteria, J. The Effects of Heart Rate Monitoring on Ratings of Perceived Exertion and Attention Allocation in Individuals of Varying Fitness Levels. Front. Sports Act. Living 2021 ,3, 798941. 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