Longitudinal reallocations of time between 24-h movement behaviours and their associations with inflammation in children and adolescents: the UP&DOWN study.

BACKGROUND: While there is evidence that physical activity, sedentary behaviour (SB) and sleep may all be associated with modified levels of inflammatory markers in adolescents and children, associations with one movement behaviour have not always been adjusted for other movement behaviours, and few studies have considered all movement behaviours in the 24-hour day as an exposure. PURPOSE: The aim of the study was to explore how longitudinal reallocations of time between moderate-to-vigorous physical activity (MVPA), light physical activity (LPA), SB and sleep are associated with changes in inflammatory markers in children and adolescents. METHODS: A total of 296 children/adolescents participated in a prospective cohort study with a 3-year follow-up. MVPA, LPA and SB were assessed by accelerometers. Sleep duration was assessed using the Health Behavior in School-aged Children questionnaire. Longitudinal compositional regression models were used to explore how reallocations of time between movement behaviours are associated with changes in inflammatory markers. RESULTS: Reallocations of time from SB to sleep were associated with increases in C3 levels (difference for 60 min/d reallocation [d60] = 5.29 mg/dl; 95% confidence interval [CI] = 0.28, 10.29) and TNF-α (d60 = 1.81 mg/dl; 95% CI = 0.79, 15.41) levels. Reallocations from LPA to sleep were also associated with increases in C3 levels (d60 = 8.10 mg/dl; 95% CI = 0.79, 15.41). Reallocations from LPA to any of the remaining time-use components were associated with increases in C4 levels (d60 ranging from 2.54 to 3.63 mg/dl; p < 0.05), while any reallocation of time away from MVPA was associated with unfavourable changes in leptin (d60 ranging from 3088.44 to 3448.07 pg/ml; p < 0.05). CONCLUSIONS: Reallocations of time between 24-h movement behaviours are prospectively associated with some inflammatory markers. Reallocating time away from LPA appears to be most consistently unfavourably associated with inflammatory markers. Given that higher levels of inflammation during childhood and adolescence are associated with an increased risk of chronic diseases in adulthood, children and adolescents should be encouraged to maintain or increase the level of LPA to preserve a healthy immune system.

Fitness, body composition, and metabolic risk scores in children and adolescents: the UP&DOWN study.

We aimed to analyse the longitudinal association between physical fitness (PF) and body composition (BC) with a metabolic risk score (Met4) in children and adolescents and to elucidate whether the association between PF and Met4 differs when using relativized or absolute fitness variables. A total of 188 children (86 females) and 195 adolescents (97 females) were included. Cardiorespiratory fitness (CRF) was determined by the 20-m shuttle run test, and muscular fitness (MF) was determined by hand grip and standing long jump tests. Height and weight were measured, and the body mass index (Kg/m2) was calculated. Triceps and subscapular skinfolds were assessed to compute body fat percentage. Met4 was computed from systolic blood pressure, triglycerides, high-density lipoprotein cholesterol, and glucose levels. Relative CRF was longitudinally and negatively associated with Met4 in female children (ß = -0.031, p = 0.025), while absolute CRF was positively associated with Met4 in male children and adolescents (ß = 0.000, p < 0.05). Relative upper and lower-body MF were longitudinally and negatively associated with Met4 in female adolescents (ß = -1.347, ß = -0.005, p < 0.05), while absolute lower-body MF was positively associated with Met4 in male children (ß = 0.000, p = 0.019). BC was longitudinally and positively associated with Met4 in male children (ß-ranging from 0.011 to 0.055, all p < 0.05) and male adolescents (ß-ranging from 0.011 to 0.046, all p < 0.05).  Conclusion: BC is more strongly associated with Met4 than PF in children and adolescents. An optimal body weight status should be considered the main objective of health-promoting programs at childhood and adolescence. Furthermore, the way of expressing the fitness variables determines the direction of the association with Met4. What is Known: • Physical fitness is an important health indicator in children and adolescents, with great amount of previous evidence supporting the preventive role of maintaining optimal levels of both cardiorespiratory and muscular fitness for future cardiometabolic issues. What is New: • The way of reporting physical fitness variables can affect the associations between physical fitness features and cardiometabolic outcomes. Since body composition variables have a great impact on both physical fitness and cardiometabolic health, relativizing physical fitness performance by body composition could lead to erroneous conclusions.

Objective measured physical activity and metabolic syndrome score in children and adolescents: The UP&DOWN longitudinal study.

INTRODUCTION: We aimed to analyze the cross-sectional and longitudinal association of physical activity (PA) levels and PA patterns with metabolic syndrome score (MetS) in children and adolescents. METHODS: A total of 175 children (82 females) and 188 adolescents (95 females) were included. Objective PA levels and patterns were determined by accelerometry. MetS was computed from waist circumference, systolic blood pressure, triglycerides, high-density lipoprotein cholesterol, and glucose levels. Different linear regression models were implemented to examine the associations of PA with MetS. RESULTS: Vigorous PA, moderate-vigorous PA, number of bouts per day in 10 min (N10), and total time in bouts per day in 10 min (T10) were negatively associated with MetS in male children and adolescents at cross-sectional level (ß ranging from -0.005 to -0.164, all p < 0.05). Total time in bouts per day in 20 min in male children, and vigorous PA and N10 in female children were longitudinally and negatively associated with MetS (ß ranging from -0.011 to -0.247, all p < 0.05). CONCLUSIONS: Associations of PA and MetS were observed at cross-sectional level in males and longitudinally in female children. The associations in PA patterns were found when patterns were grouped into bouts of 10 min. Therefore, for future studies of PA with health markers in the pediatric population, it would be advisable to choose bouts of shorter duration.

Longitudinal effects of FTO gene polymorphism on body composition, cardiorespiratory fitness, physical activity, inflammatory markers, and cardiovascular risk in children and adolescents. "The UP & DOWN study".

The role of polymorphism rs9939609 of the FTO gene has been related with fat mass and cardiovascular risk in adults, but it remains unclear in children and adolescents. Hence, the main aim of this study was to determine the FTO polymorphism effects on body composition, cardiorespiratory fitness (CRF), physical activity (PA), inflammatory markers, and cardiovascular risk both in cross-sectional analysis and after two-years of follow-up in children and adolescents. A total of 2129 participants were included in this study. The rs9939609 polymorphism was genotyped. Body composition measurements, CRF, and moderate-to-vigorous PA (MVPA) were determined at baseline and after two-year of follow-up. Moreover, plasma leptin and adiponectin were also determined as inflammatory markers. Furthermore, an index of cardiovascular disease risk factors (CVDRF-I) was calculated. Codominant (TT vs. TA vs. AA) and dominant (AA+AT vs. TT) models were applied for statistical analysis. The results showed a main effect of the FTO genotype on body composition measures in both first and third year (p < 0.05), with lower adiposity in TT compared with AA or AA+AT group. These differences were maintained after accounting for pubertal maturity, sex, age, VO2 max, and MVPA. Moreover, lower leptin level was observed in TT compared to AA+AT group in the third year. An interaction in Gene*Time*Sex was found in height and neck circumference in dominant model (p = 0.047; p = 0.020, respectively). No differences were found in CRF, MVPA nor CVDRF-I between groups. Hence, homozygous TT allele could be a protective factor against weight gain from early childhood.

European fitness landscape for children and adolescents: updated reference values, fitness maps and country rankings based on nearly 8 million test results from 34 countries gathered by the FitBack network.

OBJECTIVES: (1) To develop reference values for health-related fitness in European children and adolescents aged 6-18 years that are the foundation for the web-based, open-access and multilanguage fitness platform (FitBack); (2) to provide comparisons across European countries. METHODS: This study builds on a previous large fitness reference study in European youth by (1) widening the age demographic, (2) identifying the most recent and representative country-level data and (3) including national data from existing fitness surveillance and monitoring systems. We used the Assessing Levels of PHysical Activity and fitness at population level (ALPHA) test battery as it comprises tests with the highest test-retest reliability, criterion/construct validity and health-related predictive validity: the 20 m shuttle run (cardiorespiratory fitness); handgrip strength and standing long jump (muscular strength); and body height, body mass, body mass index and waist circumference (anthropometry). Percentile values were obtained using the generalised additive models for location, scale and shape method. RESULTS: A total of 7 966 693 test results from 34 countries (106 datasets) were used to develop sex-specific and age-specific percentile values. In addition, country-level rankings based on mean percentiles are provided for each fitness test, as well as an overall fitness ranking. Finally, an interactive fitness platform, including individual and group reporting and European fitness maps, is provided and freely available online (www.fitbackeurope.eu). CONCLUSION: This study discusses the major implications of fitness assessment in youth from health, educational and sport perspectives, and how the FitBack reference values and interactive web-based platform contribute to it. Fitness testing can be conducted in school and/or sport settings, and the interpreted results be integrated in the healthcare systems across Europe.

Comparison Between Cardiorespiratory Fitness and Functions of Cognitive Control in Adolescents: A Tracking Study of 3 Years.

PURPOSE: Compare tracking groups with cognitive control functions and plasma brain-derived neurotrophic factors concentrations from childhood to adolescence. METHODS: This is a prospective study with 3 years of follow-up. At baseline, data from 394 individuals were collected (11.7 y), and data were obtained from 134 adolescents (14.9 y) at the 3-year follow-up. At both time points, anthropometric and maximal oxygen uptake data were collected. Cardiorespiratory fitness (CRF) groups were classified into high or low CRF. At follow-up, cognitive outcomes were collected via the Stroop and Corsi block test; plasma brain-derived neurotrophic factors concentrations were also analyzed. RESULTS: Comparisons demonstrated that maintaining high CRF over 3 years results in shorter reaction time, better inhibitory control, and higher working memory values. Likewise, the group that moved from low to high CRF over 3 years presented better reaction time. Plasma brain-derived neurotrophic factors concentrations were higher for the group that increased its CRF over the 3 years in relation to the low-low group (90.58 pg·mL-1; P = .004). However, after scaling by an allometric approach, differences were only found for reaction time and working memory between high-high and high-low groups. CONCLUSION: Maintaining high CRF over 3 years was positively related to reaction time and working memory in relation to adolescents that decreased their levels of CRF.

Sedentary behaviour profiles and longitudinal associations with academic performance in youth: The UP&DOWN study.

The current study evaluated longitudinal associations between profile transitions of context-specific sedentary behaviour (SB) and changes in academic performance (AP) among school-aged youth. Participants were 466 children and 717 adolescents (50.8% males) aged 8-18 years (children = 7.92 ± 0.41 years; adolescents = 11.85 ± 1.53 years). Non-school SBs and AP were evaluated at baseline and two years later. General linear mixed models were implemented, controlling for age, region, parental education, body mass index, and cardiorespiratory fitness. Cross-sectionally, participants with an Educative-profile (i.e., highest scores in doing homework with/without computer and reading for fun) had higher AP when compared to other profiles. Longitudinally, males who changed from a Screen- to an Educative-profile had higher AP than males who changed from an Educative- to a Social- or Screen-SB profile (p < 0.01). No significant differences were found in females. These findings show the importance of analysing SB patterns from a qualitative perspective (i.e., context-specific for boosting school children AP) and highlighting time spent in educative as the most positive for AP, as well the need to implement interventions to reduce time on screen and social behaviours, especially targeting males.

Association between cardiorrespiratory fitness and cognitive control: is somatic maturity an important mediator?

BACKGROUND: Recently some articles presented information related to the possible effect of maturity over the cognitive control and cardiorespiratory fitness, however little is known about the real effects of maturity in the relation of these variables. In this sense, the purpose of this study was to examine the potential mediating role of somatic maturity on the association between cardiorespiratory fitness (CRF) and cognitive control. METHODS: This three-year longitudinal research comprises two data collection groups: a baseline conducted in 2016 with 394 adolescents (aged 11.7 ± 0.6 years) and a follow-up in 2019 with 134 adolescents (aged 14.9 ± 0.7 years). Anthropometry data, 20-m shuttle run test and peak height velocity (PHV) to determine the maximum oxygen uptake (VO2max) and somatic maturity, respectively, were collected at both sampling times. In parallel, the Sociodemographic and cognitive control function variables were included in the follow-up to evaluate the inhibitory control (by the Stroop test) and the visuo-spatial working memory (by the Corsi block-tapping test). Associations between CRF and cognitive functions were computed by multiple linear regression, with mediation as a function of PHV. RESULTS: CRF exhibited transversal associations with reaction time in congruent (ß = -0.004; p = 0.001) and incongruent (ß = -0.005; p = 0.004) stimulus-responses. Meanwhile, the variation in VO2max over the three year-study had a significant impact on the reaction time of congruent (ß = -0.006; p = 0.001) and incongruent (ß = -0.006; p = 0.012) responses at follow-up. However, PHV did not show a significant association with the cognitive functions, indicating no mediating role. CONCLUSIONS: Although the associations between CRF and the cognitive functions exhibited great transversal and longitudinal impacts, somatic maturity did not affect the cognitive control functions, associating exclusively with CRF.

[Association between educational level and suspicion of cognitive imparirment in Chilean older people]. / Asociación entre nivel educacional y sospecha de deterioro cognitivo en personas mayores chilenas: resultados de la Encuesta Nacional de Salud 2016-2017.

BACKGROUND: A low education level has been associated with cognitive impairment in older adults. AIM: To determine the association between educational attainment and suspicion of cognitive imparirment in older Chilean population. MATERIAL AND METHODS: Data from 2,005 adults aged ≥ 60 years assessed during 2016-2017 Chilean National Health Survey were included. Education was self-reported and categorized as primary: ≤ 8 years; secondary: 9 to 12 years and beyond secondary: > 12 years. suspicion of cognitive imparirment was assessed with the Mini-Mental questionnaire. RESULTS: Men and women with low education attainment had a higher prevalence of cognitive impairment (33% [95% confidence intervals (CI): 24; 41] and 27% [95% CI: 21; 33], respectively). Men who reported less schooling (≤ 8 years) were more likely to be at risk of suspicion of cognitive imparirment (Odds ratio (OR): 4.53 [95% CI: 1.10, 18.62]) compared to their peers. Women showed a substantially higher magnitude of association than men. The probability of suspicion of cognitive imparirment increased 9-times (OR: 9.96 [95% CI: 1.24; 79.6]) for 9-12 years and 18-times for ≤ 8 years of education (OR: 18.8 [95% CI: 2.42; 146.1]) compared to women with higher education. CONCLUSIONS: Older adults with low education attainment had an increased likelihood of developing suspicion of cognitive imparirment. However, the risk differs by sex, being higher in women than men.

[Handgrip strength as a predictor of adverse health outcomes]. / Fuerza de prensión manual. Un sencillo, pero fuerte predictor de salud en población adulta y personas mayores.

Muscle strength can be measured through different methods and handgrip strength is one of the most used techniques in epidemiological studies. Given its easy application, high reliability, and low cost, it is considered an important health biomarker. Handgrip strength is associated with adverse health outcomes such as mortality and risk of developing chronic diseases, cardiovascular, respiratory, cancer and dementia. There is a paucity of evidence in Chile about the association of handgrip strength with these health outcomes limiting its visibility and implementation in clinical settings. Therefore, this narrative review summarizes the scientific evidence about the association of grip strength with non-communicable chronic diseases and mortality in middle age and older adults.

Objectively measured physical activity and academic performance in school-aged youth: The UP&DOWN longitudinal study.

To examine the longitudinal relationships between objectively measured total volume and specific intensities of physical activity (PA) with academic performance in a large sample of youth aged 6-18 years. A longitudinal study of 1046 youth (10.04 ± 3.10 years) from Spain was followed over 2 years. PA (volume and intensity) was measured by accelerometry. Academic performance was assessed through grades reported on the transcript at the end of the academic year (Mathematics, Language, an average of these two core subjects, and grade point average [GPA]). Longitudinal relationships between PA and four indicators of academic performance were examined using covariance and regression analyses, adjusted for a variety of confounders. Youth Quartile 2 for PA volume at baseline obtained better scores than those who participated in Quartiles 1 or 4 volumes of PA in GPA 2 years later (p = 0.006). There were generally no longitudinal associations between specific PA intensities and any of the academic performance indicators (all p > 0.170). However, a change in light PA over 2 years was inversely associated with three academic indicators in youth (ßrange , -.103 to - 090; all P < 040). Findings suggest that participants in Quartile 2 volume of PA had a better GPA in comparison with Quartiles 1 and 4 volumes of PA during youth, but there was no association with changes in PA volume over time. PA intensity was generally unrelated to academic performance during youth. However, there was an inverted u-shape relationship between light PA changes and GPA.

Correlates of dual trajectories of physical activity and sedentary time in youth: The UP & DOWN longitudinal study.

Trajectories of physical activity and sedentary time (SED) may differ between subgroups of youth. The aim of this study was to identify group-based dual trajectories of physical activity and SED and explore individual, social, and environmental correlates of these trajectories. Longitudinal data (three time points, baseline 2011-2012) of Spanish youth (n = 1597, mean age = 11.94 ± 2.52, 50.9% boys) were used. Moderate-to-vigorous physical activity (MVPA) and SED were assessed objectively at each time point, and 21 potential correlates were self-reported at baseline. Parallel process growth mixture models identified shared categorical latent groups, adjusting for school and age. Multinomial logistic regression models identified baseline correlates of a given trajectory. Four shared categorical latent groups were identified: (1) stable MVPA and decreasing SED (4%); (2) stable MVPA and increasing SED (3%); (3) consistently higher MVPA (18%); and (4) stable low MVPA and slight increase in SED (75%). Multinomial logistic regression models with group 3 as reference found: negative affect (RRR = 0.90, 95% CI 0.84-0.97), parental screen-time rules (RRR = 1.15, 95% CI 1.00-1.33), and household media equipment (RRR = 1.17, 95% CI 1.05-1.30) predicted likelihood of group 1 membership; cons of reducing SED (RRR = 2.70, 95% CI 1.77-4.10) predicted likelihood of group 2 membership; and co-participation in physical activity with friends (RRR = 0.80, 95% CI 0.69-0.94), fathers' modeling of TV viewing (RRR = 1.22, 95% CI 1.02-1.47), and household media equipment (RRR = 1.16, 95% CI 1.02-1.31) predicted likelihood of group 4 membership. Results suggest that strategies to improve MVPA and SED behaviors among youth may need to be multifaceted, targeting all levels of influence.

Longitudinal associations of physical fitness and body mass index with academic performance.

No studies have analyzed the longitudinal associations of change in physical fitness components and obesity with academic performance. The aim of the study was to examine longitudinal associations of changes in physical fitness components and body mass index with academic performance among youth, and whether the physical fitness components are moderators of the longitudinal association between obesity and academic performance in youth. Longitudinal analyses (2 years) included 1802 youths. Physical fitness components were assessed following the ALPHA health-related fitness test battery. Academic performance was assessed via school records. Youth in the persistently high cardiorespiratory fitness and motor ability categories (ie, fit at baseline and at 2-year follow-up) had higher academic performance at follow-up than those in the persistently low category. Further, youth with normal weight at baseline and overweight/obesity at follow-up had lower academic performance scores at follow-up compared to those with normal weight. Also, cardiorespiratory fitness may ameliorate the negative influence of excess body mass index on academic performance at follow-up. Promoting physical activity programs at school that include both aerobic exercise and motor tasks to improve physical fitness and reduce body mass index may not only improve physical health, but also contribute toward successful academic development.

Active commuting to school among 36,781 Spanish children and adolescents: A temporal trend study.

This study examines trends in the rates of active commuting to school (ACS) in Spanish children (n = 18 343; 8.93 ± 1.68) and adolescents (n = 18 438; 14.11 ± 1.58) aged 6-18 years from 2010 to 2017. Given the study period included the economic crisis in Spain (2008-2013), the second aim of this study was to compare ACS rates during and after the economic crisis. Data were obtained from 28 studies conducted across Spain. The overall trends in ACS were evaluated using multilevel logistic regression analysis. Among Spanish children and adolescents, the rates of ACS to school ranged around 60% between 2010 and 2017. The rates of ACS in Spanish youth did not change significantly during the 2010-2017 period, except a sporadic increase in the rate of ACS in adolescents in 2012-2013. No significant association between the ACS and the economic crisis time period in youth was found. As conclusion, the ACS remains stable in Spain during the last decade, which is a promising result regarding the evidenced decreasing trend in many countries. Further educational and policy strategies are important to continue promoting this behavior in children and adolescents in the long term.

Physical fitness and its association with cognitive performance in Chilean schoolchildren: The Cogni-Action Project.

This study aimed to establish the association and differences in a diversity of cognitive domains according to cardiorespiratory fitness (CRF), muscular fitness (MF), and speed-agility fitness (S-AF) level in a large sample of Chilean schoolchildren. 1171 Chilean schoolchildren aged 10-14 years participated. CRF, MF, and S-AF were assessed through the ALPHA-fitness test battery. Cognition was evaluated through the NeuroCognitive Performance Test, which involved eight tests related to four main domains: cognitive flexibility (CF), working memory (WM), inhibitory control (IC), and intelligence (IN). Both global (multivariate) and individual (univariate) analyses were performed to determine the differences in cognitive functioning according to low-, middle-, and high-fitness level. The global analyses showed a significant main effect for CRF, F(16,940)  = 3.08, p ≤ .001 and MF groups, F(16,953)  = 2.30, p = .002, but not for S-AF, F(16,948)  = 1.37, p = .105. CRF shows a significant main effect in seven of eight tests, involving CF, WM, IC, and IN domains, whereas MF shows a significant main effect in five of eight tests without association with IN. SA-F shows a significant main effect only with IC. Statistical differences were found between the low- and middle/high-fitness groups but not between the middle- and high-fitness groups. At a global level, both CRF and MF seem to be associated with a higher cognitive profile in scholars; however, at an individual level, all fitness components show a favorable relationship to some cognitive domine. Then, future cognitive developing strategies should consider all fitness components, prioritizing those low-fitness schoolchildren.

Development of cardiorespiratory fitness standards for working memory using receiver operating curves in 15-year-old adolescents.

BACKGROUND: Working memory performance is associated with better academic achievements in children and adolescents, and it is positively related to CRF. However, what level of cardiorespiratory fitness (CRF) discriminates higher working memory performance is not known. The purpose of this study was to identify CRF thresholds linked to working memory in adolescents. METHODS: Data of 141 adolescents (53.2 % girls) were collected (14.9 years) from a cross-sectional study during the year 2019. CRF was assessed by the 20-m shuttle run test, and maximal oxygen uptake was calculated using the Mahar´s equation. Working memory was evaluated by the Corsi blocks test and performance was classified by percentiles. Receiver operating characteristic (ROC) curve analysis was used to identify CRF thresholds. RESULTS: The ROC analysis indicated that CRF could be used to discriminate working memory in adolescents. CRF thresholds of ≥45.03 ml.kg- 1.min- 1for boys and ≥36.63 ml.kg- 1.min- 1for girls were found to be indicative of "normal" working memory performance. CONCLUSIONS: CRF could discriminate low and normal working memory performance in 14-16- year-old adolescents. These thresholds could allow for earlier identification and intervention of low working memory performance using CRF.

A cross-sectional association of physical fitness with positive and negative affect in children and adolescents: the up & down study.

BACKGROUND: Affect and physical fitness play an important role in psychological and physical health; however, the association between those variables in youth remains unknown. The aim of the present study was to examine the influence of physical fitness on positive and negative affect in Spanish children and adolescents. METHOD: Healthy young Spanish people (n = 1,490) were recruited for the present study: 542 children (n = 272 girls; mean age 9.6 years) and 948 adolescents (n = 454 girls; mean age 14.1 years) with complete baseline data on health-related fitness tests (20 m shuttle run test, 4 × 10 m test, muscular fitness index, and physical fitness index), and positive and negative affect (Positive and Negative Affect Schedule). RESULTS: Higher performance on physical fitness components was associated with positive affect (ß = -0.176-0.118, all P < 0.05). There was no association between all physical fitness components and negative affect (ß = -0.100-0.15, all P > 0.05). There were differences on positive affect between the lowest and the highest quartile of the physical fitness index in boys (P = 0.037, Cohen's d 0.60) and girls (P = 0.004, Cohen's d = 0.69), and between the lowest and the highest quartile of muscular fitness index in girls (P < 0.001, Cohen's d = 0.76). CONCLUSIONS: Promoting physical activity during the school years, including strength exercises to increase muscular fitness, could improve positive affect levels and thus psychological health.

Changes in and the mediating role of physical activity in relation to active school transport, fitness and adiposity among Spanish youth: the UP&DOWN longitudinal study.

BACKGROUND: Longitudinal changes in child and adolescent active school transport (AST), and the mediating role of different intensities of daily physical activity (PA) levels in relation to AST and physical fitness and adiposity indicators is unclear. This study aimed to: 1) describe longitudinal changes in AST, light PA (LPA), moderate- to vigorous-intensity PA (MVPA), physical fitness and adiposity indicators over three time-points; and 2) investigate the mediating role of LPA and MVPA levels on associations between AST and physical fitness and adiposity indicators over three time-points among children and adolescents. METHODS: This longitudinal study comprised 1646 Spanish children and adolescents (48.8% girls, mean age 12.5 years ±2.5) at baseline, recruited from schools in Cádiz and Madrid. Mode of commuting to school was self-reported at baseline (T0, 2011-12), 1-year (T1) and 2-year follow-up (T2). PA was assessed using accelerometers. Handgrip strength, standing long jump and cardiorespiratory fitness (CRF) assessed physical fitness. Height, weight, body mass index, waist circumference, and triceps and subscapular skinfold thickness were measured. Multilevel linear regression analyses assessed changes in AST, PA levels, physical fitness and adiposity indicators over three time-points (T0-T1-T2). Additionally, longitudinal path analysis (n = 453; mean age [years] 12.6 ± 2.4) was used to test the mediating effects of LPA and MVPA levels on the association between AST and physical fitness and adiposity indicators. RESULTS: Multilevel analyses observed decreases in LPA between T0-T1 (ß = - 11.27; p < 0.001) and T0-T2 (ß = - 16.27; p < 0.001) and decreases in MVPA between T0-T2 (ß = - 4.51; p = 0.011). Moreover, changes over time showed increases in handgrip between T0-T1 (ß = 0.78; p = 0.028) and T0-T2 (ß = 0.81; p = 0.046). Path analyses showed that AST was directly positively associated with MVPA at T1 (all, ß ≈ 0.33; p < 0.001). MVPA at T1 mediated associations between AST and CRF at T2 (ß = 0.20; p = 0.040), but not the other outcomes. LPA did not mediate any associations. CONCLUSIONS: Results from longitudinal path analysis suggest that participation in more AST may help attenuate declines in MVPA that typically occur with age and improve CRF. Therefore, we encourage health authorities to promote AST, as a way to increase MVPA levels and CRF among youth.

Bidirectional associations between fitness and fatness in youth: A longitudinal study.

The aim was to examine the bidirectional association between cardiorespiratory fitness (CRF) and fatness in a 2-year longitudinal study conducted in young people. A total of 1082 children (512 females) and 727 adolescents (342 females) with complete data at baseline and follow-up were included. CRF was determined by the 20-m shuttle run test. Height and weight were measured, and body mass index and fat mass index (kg/m2 ) were calculated. Triceps and subscapular skinfolds were assessed to compute body fat percentage. Bidirectionality was tested by including CRF and each fatness index as exposures and outcomes, alternatively, in different regression models. CRF was prospectively associated with fatness index levels (ß from -0.186 to -0.528; P < .001), remaining significant in children after adjusting for baseline fatness indices. Fatness indices were prospectively associated with CRF (ß from -0.207 to -0.479; P < .001), with no substantial changes observed in children and female adolescents when baseline CRF was considered. Changes in CRF were prospectively associated with several fatness indices, regardless of body fatness at baseline (ß from -0.062 to -0.220; P < .05). Body fatness changes were associated with future CRF levels, independently of baseline CRF, especially in children of both sexes and male adolescents (ß from -0.079 to -0.260; P < .05). Overall, a bidirectional association was observed between CRF and fatness in children and adolescents. The attainment of optimal CRF and fatness levels in early ages should be promoted since it could result in favorable future fatness and CRF levels, respectively, which are two key determinants of health status.

Changes in the school and non-school sedentary time in youth: The UP&DOWN longitudinal study.

The aims of this study were (i) to examine the sedentary time (ST) during different time periods [i.e., weekend, out-of-school weekdays hours, school hours, recess, physical education classes (PEC)] in children and adolescents; (ii) to identify 2-year longitudinal changes in the ST for these periods; and (iii) to examine if ST at baseline is associated with ST 2 years later. This was a 2-year follow-up study with 826 (51.9% boys) children and 678 (50.7% boys) adolescents. Accelerometers were used to assess ST. Students spent more than 60% of their weekend, out-of-school hours and school hours in ST. During these periods, girls and adolescents were more sedentary than boys and children, respectively (p < 0.05). Over 2-year follow-up, ST increased during the weekend, out-of-school hours, school hours and recess in all subgroups studied (p < 0.001). ST during PEC declined 2% per year in children (p < 0.001) but it increased in adolescents (p < 0.05). ST during the periods analysed at baseline was lowly associated with ST during these periods 2 years later (intraclass correlations from <0.001 to 0.364). Interventions in these settings may be adequate if the intention is to avoid ST increase in students.