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Background and Aims: International reference values for cardiometabolic risk variables, to allow for standardization of continuous risk scores in children, are not currently available. The aim of this study was to provide international age- and gender-specific reference values for cardiometabolic risk factors in children and adolescents., Methods: Cohorts of children sampled from different parts of Europe (North, South, Mid and Eastern) and from the United States were pooled. In total, 22,479 observations (48.7% European vs. 51.3% American), 11,234 from girls and 11,245 from boys, aged 6-18 years were included in the study. Linear mixed-model regression analysis was used to analyze the associations between age and each cardiometabolic risk factor., Results: Reference values for 14 of the most commonly used cardiometabolic risk variables in clustered risk scores were calculated and presented by age and gender: systolic blood pressure (SBP), diastolic blood pressure (DBP), waist circumference (WC), body mass index (BMI), sum of 4 skinfolds (sum4skin), triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), TC:HDL-C ratio, glucose, insulin, homeostatic model assessment-score (HOMA-score), and cardiorespiratory fitness (CRF)., Conclusions: This study suggests a common standard to define cardiometabolic risk in children. Adapting this approach makes single risk factors and clustered cardiometabolic disease risk scores comparable to the reference material itself and comparable to cardiometabolic risk values in studies using the same strategy. This unified approach therefore increases the prospect to estimate and compare prevalence and trends of cardiometabolic risk in children when using continuous cardiometabolic risk scores., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Physical activity (PA) favorably affects metabolic health in children, but it is unclear how total volumes versus patterns (bouts and breaks) of PA relate to health. By means of multivariate pattern analysis that can handle collinear variables, we determined the associations of PA volumes and patterns with children's metabolic health using different epoch settings. A sample of 841 Norwegian children (age 10.2 ± 0.3 years) provided in 2014 data on accelerometry (ActiGraph GT3X+), using epoch settings of 1, 10, and 60 s and several indices of metabolic health used to create a composite metabolic health score. We created 355 PA indices covering the whole intensity and bout duration spectrum, and used multivariate pattern analysis to analyze the data. Findings showed that bouts of PA added information about childhood health beyond total volumes of PA for all epoch settings. Yet, associations of PA patterns with metabolic health were completely dependent on the epoch settings used. Vigorous PA was strongly associated with metabolic health, while associations of light and moderate PA were weak to moderate, and associations of sedentary time with metabolic health was non-existing. Short intermittent bursts of PA were favorably associated with children's metabolic health, whereas associations of prolonged bouts were weak. This study is the first to determine the multivariate physical activity association pattern related to metabolic health in children across the whole PA intensity and bout duration spectrum. The findings challenge our understanding of PA patterns, and are of major importance for the analysis of accelerometry data., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Background: Physical activity is a cornerstone for promoting good metabolic health in children, but it is heavily debated which intensities (including sedentary time) are most influential. A fundamental limitation to current evidence for this relationship is the reliance on analytic approaches that cannot handle collinear variables. The aim of the present study was to determine the physical activity signature related to metabolic health in children, by investigating the association pattern for the whole spectrum of physical activity intensities using multivariate pattern analysis., Methods: We used a sample of 841 children (age 10.2 ± 0.3 years; BMI 18.0 ± 3.0; 50% boys) from the Active Smarter Kids study, who provided valid data on accelerometry (ActiGraph GT3X+) and several indices of metabolic health (aerobic fitness, abdominal fatness, insulin sensitivity, lipid metabolism, blood pressure) that were used to create a composite metabolic health score. We created 16 physical activity variables covering the whole intensity spectrum (from 0-100 to ≥ 8000 counts per minute) and used multivariate pattern analysis to analyze the data., Results: Physical activity intensities in the vigorous range (5000-7000 counts per minute) were most strongly associated with metabolic health. Moderate intensity physical activity was weakly related to health, and sedentary time and light physical activity were not related to health., Conclusions: This study is the first to determine the multivariate physical activity signature related to metabolic health in children across the whole intensity spectrum. This novel approach shows that vigorous physical activity is strongest related to metabolic health. We recommend future studies adapt a multivariate analytic approach to further develop the field of physical activity epidemiology., Trial Registration: The study was registered in Clinicaltrials.gov (www.clinicaltrials.gov) 7th of April 2014 with identification number NCT02132494 .

Background: Knowledge of the reproducibility of domain-specific accelerometer-determined physical activity (PA) estimates are a prerequisite to conduct high-quality epidemiological studies. The aim of this study was to determine the reproducibility of objectively measured PA level in children during school hours, afternoon hours, weekdays, weekend days, and total leisure time over two different seasons., Methods: Six hundred seventy six children from the Active Smarter Kids study conducted in Sogn og Fjordane, Norway, were monitored for 7 days by accelerometry (ActiGraph GT3X+) during January-February and April-May 2015. Reproducibility was estimated week-by-week using intra-class correlation (ICC) and Bland-Altman plots with 95% limits of agreement (LoA)., Results: When controlling for season, reliability (ICC) was 0.51-0.66 for a 7-day week, 0.55-0.64 for weekdays, 0.11-0.43 for weekend days, 0.57-0.63 for school hours, 0.42-0.53 for afternoon hours, and 0.42-0.61 for total leisure time. LoA across models approximated a factor of 1.3-2.5 standard deviations of the sample PA levels. 3-6 weeks of monitoring were required to achieve a reliability of 0.80 across all domains but weekend days, which required 5-32 weeks., Conclusion: Reproducibility of PA during leisure time and weekend days were lower than for school hours and weekdays, and estimates were lower when analyzed using a week-by-week approach over different seasons compared to previous studies relying on a single short monitoring period. To avoid type 2-errors, researchers should consider increasing the monitoring period beyond a single 7-day period in future studies., Trial Registration: ClinicalTrials.gov, NCT021324947 . Registered on 7 April 2014.

Background/objectives: Physical activity (PA) and cardiorespiratory fitness (CRF) are independently associated with reduced cardiometabolic risk in children, and may affect risk through different pathways. This study aims to examine if CRF moderate the prospective association between PA, sedentary time, and cardiometabolic outcomes in 10-year-old children., Subjects/methods: In total, 718 children of 1129 (drop out n = 7) had valid measures of PA (accelerometry), CRF (the Andersen running test), and a cardiometabolic risk profile measured at baseline and follow-up 7 months later. Cardiometabolic outcomes were systolic blood pressure, waist circumference (WC), total cholesterol, high-density lipoprotein, triglycerides, glucose, and insulin (HOMA-IR). The cardiometabolic risk factors were analysed individually, and as a clustered risk score (z score). A linear mixed model was used to examine the prospective associations between different PA exposures (overall PA, sedentary time, moderate-to-vigorous PA (MVPA), vigorous PA) and cardiometabolic outcomes, including the interaction term PA × CRF in the model to assess moderation by CRF., Results: CRF modified the association for baseline overall PA (P < 0.039) and MVPA (min/day) with clustered cardiometabolic risk at follow-up (P < 0.023). Moreover, CRF modified the association between overall PA and MVPA with HOMA-IR independent of WC (P < 0.022). When stratified by CRF level (median split; high/low), MVPA predicted lower HOMA-IR [MVPA β -0.133 (95% CI: -0.223, -0.043); P = 0.004] and clustered cardiometabolic risk [MVPA β -0.094 (95% CI: -0.169, -0.019); P = 0.014] in children with low CRF, but not among their fitter peers (P > 0.232). There was neither direct association between sedentary time and cardiometabolic risk factors in any analyses, nor moderation by CRF., Conclusion: CRF significantly moderated the prospective association between PA and the clustered cardiometabolic risk, but not for time spent sedentary. The magnitude of association between MVPA and clustered cardiometabolic risk was stronger in children with low CRF, and no associations appeared present in their high-fit peers.

Background: There are many unresolved issues regarding data reduction algorithms for accelerometry. The choice of criterion for removal of non-wear time might have a profound influence on physical activity (PA) and sedentary time (SED) estimates. The aim of the present study was to compare 10 different non-wear criteria and a log of non-wear periods in 11-year-old children., Methods: Children from the Active Smarter Kids study performed 7-days of hip-worn accelerometer monitoring (Actigraph GT3X+) and logged the number of non-wear periods each day, along with the approximate duration and reason for non-wear. Accelerometers were analyzed using 10 different non-wear criteria: ≥ 10, 20, 30, 45, 60, and 90 min of consecutive zero counts without allowance for interruptions, and ≥60 and 90 min with allowance for 1 and 2 min of interruptions., Results: 891 children provided 5203 measurement days, and reported 1232 non-wear periods ranging from 0 to 3 periods per day: on most days children reported no non-wear periods (77.1% of days). The maximum number of non-wear periods per day was 2 for the 90-min criterion, 3 to 5 for most criteria, 7 for the 20-min criterion, and 20 for the 10-min criterion. The non-wear criteria influenced overall PA (mean values across all criteria: 591 to 649 cpm; 10% difference) and SED time (461 to 539 min/day; 17% difference) estimates, especially for the most prolonged SED bouts. Estimates were similar for time spent in intensity-specific (light, moderate, vigorous, and moderate-to-vigorous) PA, but varied 6-9% among the non-wear criteria for proportions of time spent in intensity-specific PA (% of total wear time)., Conclusions: Population level estimates of PA and SED differed between different accelerometer non-wear criteria, meaning that non-wear time algorithms should be standardized across studies to reduce confusion and improve comparability of children's PA level. Based on the numbers and reasons for non-wear periods, we suggest a 45 or 60-min consecutive zero count-criterion not allowing any interruptions to be applied in future pediatric studies, at least for children older than 10 years., Trial Registration: The study is registered in Clinicaltrials.gov with identification number NCT02132494 . Registered 7 April 2014.

Measurement of aerobic fitness by determining peak oxygen consumption (VO 2peak ) is often not feasible in children and adolescents, thus field tests such as the Andersen test are required in many settings, for example in most school-based studies. This study provides cross-validated prediction equations for VO 2peak based on the Andersen test in 10 and 16-year-old children. We included 235 children (n = 113 10-year olds and 122 16-year olds) who performed the Andersen test and a progressive treadmill test to exhaustion to determine VO 2peak . Joint and sex-specific prediction equations were derived and tested in 20 random samples. Performance in terms of systematic (bias) and random error (limits of agreement) was evaluated by means of Bland-Altman plots. Bias varied from -4.28 to 5.25 mL/kg/min across testing datasets, sex, and the 2 age groups. Sex-specific equations (mean bias -0.42 to 0.16 mL/kg/min) performed somewhat better than joint equations (-1.07 to 0.84 mL/kg/min). Limits of agreement were substantial across all datasets, sex, and both age groups, but were slightly lower in 16-year olds (5.84-13.29 mL/kg/min) compared to 10-year olds (9.60-15.15 mL/kg/min). We suggest the presented equations can be used to predict VO 2peak from the Andersen test performance in children and adolescents on a group level. Although the Andersen test appears to be a good measure of aerobic fitness, researchers should interpret cross-sectional individual-level predictions of VO 2peak with caution due to large random measurement errors., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

To evaluate changes in clustered cardiovascular disease (CVD) risk factors in 9-year-old children following a 2-year school-based physical activity intervention. In total, 259 children (age 9.3 ± 0.3 years) were invited, of whom 256 participated. The intervention group (63 boys, 62 girls) carried out 60-minute teacher-controlled daily physical activity over two school years. The control group (62 boys, 69 girls) had the curriculum-defined amount of physical education (45 minutes twice each week). Of these, 67% (171 total, 91 intervention) successfully completed both baseline and post-intervention of six CVD risk factors: systolic blood pressure (SBP), triglyceride (TG), total cholesterol-to-high-density lipoprotein cholesterol ratio (TC:HDL ratio), waist circumference (WC), the homeostasis model assessment for insulin resistance (HOMA), and peak oxygen uptake (VO 2peak ). All variables were standardized by sex prior to constructing a cluster score (sum of z scores for all variables). The effect of the intervention on the cluster score was analyzed using linear multiple regression. The cluster score improved after the intervention (ES = .29). Furthermore, the analyses showed significant effects in favor of the intervention group for systolic blood pressure (ES = .35), total cholesterol-to-HDL-c ratio (ES = .23), triglyceride (ES = .40), and VO 2peak (ES = .57). A teacher-led school-based physical activity intervention that is sufficiently long and includes a substantial amount of daily physical activity can beneficially modify children's clustered CVD risk profile., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Inconsistent findings exist for the effect of school-based physical activity interventions on academic performance. The Active Smarter Kids (ASK) study revealed a favorable intervention effect of school-based physical activity on academic performance in numeracy in a subsample of 10-year-old elementary schoolchildren performing poorer at baseline in numeracy. Aiming to explain this finding, we investigated the mediating effects of executive function, behavioral self-regulation, and school related well-being in the relation between the physical activity intervention and child's performance in numeracy. An ANCOVA model with latent variable structural equation modeling was estimated using data from 360 children (the lower third in academic performance in numeracy at baseline). The model consisted of the three latent factors as mediators; executive function, behavioral self-regulation, and school related well-being. We found no mediating effects of executive function, behavioral self-regulation or school related well-being in the relationship between the ASK intervention and academic performance in numeracy ( p ≥ 0.256). Our results suggest that the effect of the intervention on performance in numeracy in the present sample is not explained by change in executive function, behavioral self-regulation, or school related well-being. We suggest this finding mainly could be explained by the lack of effect of the intervention on the mediators, which might be due to an insufficient dose of physical activity. Trial registration: Clinicaltrials.gov registry, trial registration number: NCT02132494.

Active learning combines academic content with physical activity (PA) to increase child PA and academic performance, but the impact of active learning is mixed. It may be that this is a moderated relationship in which active learning is beneficial for only some children. This paper examine the impact of baseline academic performance and gender as moderators for the effects of active learning on children's academic performance. In the ASK-study, 1129 fifth-graders from 57 Norwegian elementary schools were randomized by school to intervention or control in a physical activity intervention between November 2014 and June 2015. Academic performance in numeracy, reading, and English was measured and a composite score was calculated. Children were split into low, middle and high academic performing tertiles. 3-way-interactions for group (intervention, control)∗gender (boys, girls)∗academic performance (tertiles) were investigated using mixed model regression. There was a significant, 3-way-interaction (p=0.044). Both boys (ES=0.11) and girls (ES=0.18) in the low performing tertile had a similar beneficial trend. In contrast, middle (ES=0.03) and high performing boys (ES=0.09) responded with small beneficial trends, while middle (ES=-0.11) and high performing girls (ES=-0.06) responded with negative trends. ASK was associated with a significant increase in academic performance for low performing children. It is likely that active learning benefited children most in need of adapted education but it may have a null or negative effect for those girls who are already performing well in the sedentary classroom. Differences in gendered responses are discussed as a possible explanation for these results., Trial Registration: Clinicaltrials.gov registry, trial registration number: NCT02132494., (Copyright © 2017 Elsevier Inc. All rights reserved.)

This study reveals the lipoprotein subclass pattern associated with cardiorespiratory fitness (CRF) in healthy children. Serum concentrations of lipoprotein subclasses and concentrations and average particle size of their main classes were quantified in 94 ethnic Norwegian children using high-performance liquid chromatography (HPLC). Twenty-four lipoprotein features were used as input to multivariate regression analysis with CRF measured either by peak oxygen consumption (VO2peak) using a continuous treadmill protocol or indirectly by the 10-minute Andersen intermittent running field test. By including BMI and gender as descriptors, a predictive cross-validated multivariate regression model was obtained for both CRF measures. CRF correlated positively with average particle size for high-density lipoprotein (HDL) and its subclasses of large HDL particles and negatively with very small HDL particles, chylomicrons, triglycerides, and average size and concentration of very low-density lipoprotein (VLDL) particles and VLDL subclasses of large particles (P<.05). BMI correlated negatively with both measures of CRF, but exhibited a stronger association with VO2peak than with the Andersen test. Our data showed a strong association between CRF measured either by VO2peak or by the Andersen test and a subclass lipoprotein pattern that is associated with cardiovascular (CV) health. Thus, our results show why high levels of CRF are beneficial for children's CV health. The Andersen test, being a practical field test that involves minimal equipment and, being less influenced by BMI than VO2peak, represents a good measure of CRF, and, accordingly, a proxy measure of cardiovascular health status in children., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Introduction: Knowledge of reproducibility of accelerometer-determined physical activity (PA) and sedentary time (SED) estimates are a prerequisite to conduct high-quality epidemiological studies. Yet, estimates of reproducibility might differ depending on the approach used to analyze the data. The aim of the present study was to determine the reproducibility of objectively measured PA and SED in children by directly comparing a day-by-day and a week-by-week approach to data collected over two weeks during two different seasons 3-4 months apart., Methods: 676 11-year-old children from the Active Smarter Kids study conducted in Sogn og Fjordane county, Norway, performed 7 days of accelerometer monitoring (ActiGraph GT3X+) during January-February and April-May 2015. Reproducibility was calculated using a day-by-day and a week-by-week approach applying mixed effect modelling and the Spearman Brown prophecy formula, and reported using intra-class correlation (ICC), Bland Altman plots and 95% limits of agreement (LoA)., Results: Applying a week-by-week approach, no variables provided ICC estimates ≥ 0.70 for one week of measurement in any model (ICC = 0.29-0.66 not controlling for season; ICC = 0.49-0.67 when controlling for season). LoA for these models approximated a factor of 1.3-1.7 of the sample PA level standard deviations. Compared to the week-by-week approach, the day-by-day approach resulted in too optimistic reliability estimates (ICC = 0.62-0.77 not controlling for season; ICC = 0.64-0.77 when controlling for season)., Conclusions: Reliability is lower when analyzed over different seasons and when using a week-by-week approach, than when applying a day-by-day approach and the Spearman Brown prophecy formula to estimate reliability over a short monitoring period. We suggest a day-by-day approach and the Spearman Brown prophecy formula to determine reliability be used with caution., Trial Registration: The study is registered in Clinicaltrials.gov 7th April 2014 with identification number NCT02132494.

Purpose: To examine the associations between cardiorespiratory fitness, muscle strength, physical activity and waist circumference with self-reported health-related quality of life (HRQoL) in children., Methods: We conducted a cross-sectional analysis that included 1129 school children aged 10 years from 57 schools in Sogn and Fjordane County, Norway. The HRQoL outcome was assessed by the self-reported KIDSCREEN-27 questionnaire, which covers five life domains. Independent variables were cardiorespiratory fitness assessed by the Andersen intermittent field running test, handgrip strength measured by a hand dynamometer, explosive strength in the lower body using a standing broad jump test, physical activity (counts per minute) using an accelerometer and abdominal adiposity measured by waist circumference. Statistical analyses were performed using linear mixed-effect models including school site as a random effect. Age and sex were entered as covariates., Results: Only cardiorespiratory fitness was positively associated with higher scores on all five KIDSCREEN-27 domains (P < 0.047 for all). Explosive strength in the lower body was positively associated with higher autonomy and parents scores (P = 0.018), while physical activity was positively associated with higher physical well-being scores (P = 0.008)., Conclusions: Improving cardiorespiratory fitness might be especially useful for improving HRQoL in children.

The aims of the present study were to provide reference values for time to exhaustion (TTE) on a modified Balke treadmill protocol, and to perform a cross-validation of TTE as a measure of maximal oxygen consumption (VO 2max ), in Norwegian men and women 20-85 years of age. Reference values for TTE were derived from a national sample of 765 subjects. An additional sample of 119 subjects was included in the cross-validation (total n = 884), where prediction equations for VO 2max was established. A decline in TTE was seen with increased age. Prediction of VO 2max in an independent dataset (n = 319) resulted in a R 2  = 0.78 and standard error of the estimate = 4.55 mL/kg/min. The observed-predicted bias was small (mean difference <1.24 mL/kg/min), whereas random error was considerable (95% limits of agreement ± 7.11-9.70 mL/kg/min) across age in both men and women. Despite limitations concerning the prediction of VO 2max on an individual level, TTE from the Balke protocol is a good measure of aerobic fitness in adults across a range of settings, and could be evaluated according to the suggested reference values., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Agreement between and classification accuracy of six different noninvasive composite scores and a cardiovascular disease (CVD) risk factor score were investigated in 911 (466 boys and 445 girls) 10-year-old Norwegian children. A CVD risk factor score (triglyceride, total cholesterol/HDL ratio, homeostasis model assessment of insulin resistance, systolic blood pressure (SBP), waist-to-height ratio (WHtR), and cardiorespiratory fitness) and six noninvasive risk scores (fitness+three different measurements of fatness (body mass index (BMI), WHtR, and skinfolds), with and without inclusion of SBP) were calculated (mean z-score by gender). Agreement was assessed using Bland-Altman plots. The ability of noninvasive scores to correctly classify children with clustered CVD risk was examined by receiver operating characteristic (ROC) analysis and Cohen's kappa coefficient (κ). For both sexes, the noninvasive scores without SBP showed excellent AUC values (AUC=0.93-0.94, 95% CI=0.88-0.98) and moderate kappa values (κ=0.49-0.64) and had limits of agreement of 0.0±0.78-0.89 (arbitrary unit). Inclusion of SBP increased AUC values (AUC=0.96-0.97, 95% CI=0.94-0.99), kappa values (κ=0.58-0.69), and reduced limits of agreement (0.0±0.68-0.76). Noninvasive scores that include fitness and fatness provide acceptable agreement and classification accuracy, allowing for widespread early identification of children that might be at risk for developing CVD later in life. SBP should be included in the noninvasive score to improve classification accuracy if possible., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Changes in cognitive function induced by physical activity have been proposed as a mechanism for the link between physical activity and academic performance. The aim of this study was to investigate if executive function mediated the prospective relations between indices of physical activity and academic performance in a sample of 10-year-old Norwegian children. The study included 1,129 children participating in the Active Smarter Kids (ASK) trial, followed over 7 months. Structural equation modeling (SEM) with a latent variable of executive function (measuring inhibition, working memory, and cognitive flexibility) was used in the analyses. Predictors were objectively measured physical activity, time spent sedentary, aerobic fitness, and motor skills. Outcomes were performance on national tests of numeracy, reading, and English (as a second language). Generally, indices of physical activity did not predict executive function and academic performance. A modest mediation effect of executive function was observed for the relation between motor skills and academic performance. Trial registration: Clinicaltrials.gov registry, trial registration number: NCT02132494.

Background: Cross-sectional data have suggested an inverse relation between physical activity and cardiometabolic risk factors that is independent of sedentary time. However, little is known about which subcomponent of physical activity may predict cardiometabolic risk factors in youths. Objective: We examined the independent prospective associations between objectively measured sedentary time and subcomponents of physical activity with individual and clustered cardiometabolic risk factors in healthy children aged 10 y. Design: We included 700 children (49.1% males; 50.9% females) in which sedentary time and physical activity were measured with the use of accelerometry. Systolic blood pressure, waist circumference (WC), and fasting blood sample (total cholesterol, high-density lipoprotein cholesterol, triglycerides, glucose, fasting insulin) were measured with the use of standard clinical methods and analyzed individually and as a clustered cardiometabolic risk score standardized by age and sex ( z score). Exposure and outcome variables were measured at baseline and at follow-up 7 mo later. Results: Sedentary time was not associated with any of the individual cardiometabolic risk factors or clustered cardiometabolic risk in prospective analyses. Moderate physical activity at baseline predicted lower concentrations of triglycerides ( P = 0.021) and homeostatic model assessment for insulin resistance ( P = 0.027) at follow-up independent of sex, socioeconomic status, Tanner stage, monitor wear time, or WC. Moderate-to-vigorous physical activity ( P = 0.043) and vigorous physical activity ( P = 0.028) predicted clustered cardiometabolic risk at follow-up, but these associations were attenuated after adjusting for WC. Conclusions: Physical activity, but not sedentary time, is prospectively associated with cardiometabolic risk in healthy children. Public health strategies aimed at improving children's cardiometabolic profile should strive for increasing physical activity of at least moderate intensity rather than reducing sedentary time. This trial was registered at clinicaltrials.gov as NCT02132494., (© 2017 American Society for Nutrition.)

High aerobic fitness is consistently associated with a favorable metabolic health profile in children. However, measurement of oxygen uptake, regarded as the gold standard for evaluating aerobic fitness, is often not feasible. Thus, the aim of the present study was to perform a clinical validation of three measures of aerobic fitness (peak oxygen consumption [VO 2peak ] and time to exhaustion [TTE] determined from a graded treadmill protocol to exhaustion, and the Andersen intermittent running test) with clustered metabolic health in 10-year-old children. We included 93 children (55 boys and 38 girls) from Norway during 2012-2013 in the study. Associations between aerobic fitness and three different composite metabolic health scores (including lipoprotein subgroup particle concentrations, triglyceride, glucose, systolic blood pressure, and waist-to-height ratio) were determined by regression analyses adjusting for sex. The relationships among the measures of aerobic fitness were r  = 0.78 for VO 2peak vs. TTE, r  = 0.63 for VO 2peak vs. the Andersen test, and r  = 0.67 for TTE vs. the Andersen test. The Andersen test showed the strongest associations across all markers of metabolic health ( r  = - 0.45 to - 0.31, p  < 0.002), followed by VO 2peak ( r  = - 0.35 to - 0.12, p  < 0.256), and TTE ( r  = - 0.28 to - 0.10, p  < 0.334). Our findings indicate that indirect measures of aerobic fitness do not stand back as markers of metabolic health status in children, compared to VO 2peak . This is of great importance as good field tests provide opportunities for measuring aerobic fitness in many settings where measuring VO 2peak are impossible.

Objective: To investigate the effect of a seven-month, school-based cluster-randomized controlled trial on academic performance in 10-year-old children., Methods: In total, 1129 fifth-grade children from 57 elementary schools in Sogn og Fjordane County, Norway, were cluster-randomized by school either to the intervention group or to the control group. The children in the 28 intervention schools participated in a physical activity intervention between November 2014 and June 2015 consisting of three components: 1) 90min/week of physically active educational lessons mainly carried out in the school playground; 2) 5min/day of physical activity breaks during classroom lessons; 3) 10min/day physical activity homework. Academic performance in numeracy, reading and English was measured using standardized Norwegian national tests. Physical activity was measured objectively by accelerometry., Results: We found no effect of the intervention on academic performance in primary analyses (standardized difference 0.01-0.06, p>0.358). Subgroup analyses, however, revealed a favorable intervention effect for those who performed the poorest at baseline (lowest tertile) for numeracy (p=0.005 for the subgroup∗group interaction), compared to controls (standardized difference 0.62, 95% CI 0.19-1.07)., Conclusions: This large, rigorously conducted cluster RCT in 10-year-old children supports the notion that there is still inadequate evidence to conclude that increased physical activity in school enhances academic achievement in all children. Still, combining physical activity and learning seems a viable model to stimulate learning in those academically weakest schoolchildren., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: The Norwegian version of the Kidscreen-27, a measure of generic health-related quality of life, has not yet been validated. Thus, the aim of this study was to investigate the reliability and validity of the Norwegian Kidscreen-27, in 10 year-old children., Methods: The Kidscreen-27 consists of five domains and was validated in a cross-sectional study of 1085 school children (52.5 % boys). In addition a subsample of 56 children also had repeated measures in order to study test-retest reliability., Results: Cronbach's alpha values ranged from 0.73 to 0.83, while intraclass correlation values over time ranged from 0.71 to 0.81. The domains of physical well-being, psychological well-being and autonomy & parents improved over time (Ps < 0.05), while social support and school environment domains did not. Confirmatory factor analysis showed an acceptable overall model fit: X (2) = 707; df = 310; P <0.001, root mean squared error of approximation = 0.037, the comparative fit index = 0.96 and the Tucker-Lewis index = 0.95. All factor loading were > 0.40. The Kidscreen-27 domains were significantly associated with general life satisfaction as measured with the Cantrils Ladder (Spearman rank correlations ranged from 0.29 to 0.59, Ps < 0.05)., Conclusion: The Norwegian version of Kidscreen-27 has good reliability and validity.

Background: Evidence is emerging from school-based studies that physical activity might favorably affect children's academic performance. However, there is a need for high-quality studies to support this. Therefore, the main objective of the Active Smarter Kids (ASK) study is to investigate the effect of daily physical activity on children's academic performance. Because of the complexity of the relation between physical activity and academic performance it is important to identify mediating and moderating variables such as cognitive function, fitness, adiposity, motor skills and quality of life (QoL). Further, there are global concerns regarding the high prevalence of lifestyle-related non-communicable diseases (NCDs). The best means to address this challenge could be through primary prevention. Physical activity is known to play a key role in preventing a host of NCDs. Therefore, we investigated as a secondary objective the effect of the intervention on risk factors related to NCDs. The purpose of this paper is to describe the design of the ASK study, the ASK intervention as well as the scope and details of the methods we adopted to evaluate the effect of the ASK intervention on 5 (th) grade children., Methods & Design: The ASK study is a cluster randomized controlled trial that includes 1145 fifth graders (aged 10 years) from 57 schools (28 intervention schools; 29 control schools) in Sogn and Fjordane County, Norway. This represents 95.3 % of total possible recruitment. Children in all 57 participating schools took part in a curriculum-prescribed physical activity intervention (90 min/week of physical education (PE) and 45 min/week physical activity, in total; 135 min/week). In addition, children from intervention schools also participated in the ASK intervention model (165 min/week), i.e. a total of 300 min/week of physical activity/PE. The ASK study was implemented over 7 months, from November 2014 to June 2015. We assessed academic performance in reading, numeracy and English using Norwegian National tests delivered by The Norwegian Directorate for Education and Training. We assessed physical activity objectively at baseline, midpoint and at the end of the intervention. All other variables were measured at baseline and post-intervention. In addition, we used qualitative methodologies to obtain an in-depth understanding of children's embodied experiences and pedagogical processes taking place during the intervention., Discussion: If successful, ASK could provide strong evidence of a relation between physical activity and academic performance that could potentially inform the process of learning in elementary schools. Schools might also be identified as effective settings for large scale public health initiatives for the prevention of NCDs., Trial Registration: Clinicaltrials.gov ID nr: NCT02132494 . Date of registration, 6(th) of May, 2014.

Background: High aerobic fitness is consistently associated with a favorable metabolic risk profile in children. Direct measurement of peak oxygen consumption (VO2peak) is often not feasible, thus indirect tests such as the Andersen test are required in many settings. The present study seeks to determine the reliability and validity of the Andersen test in 10-year-old children., Methods: A total of 118 10-year-old children (67 boys and 51 girls) were recruited from one school and performed four VO2peak tests over three weeks: three Andersen tests (indirect) and one continuous progressive treadmill test (direct). Of these, 104 children provided valid data on all Andersen tests and 103 children also provided valid data on the direct treadmill test. Reliability and validity were assessed using Bland Altman plots and linear regression analysis., Results: Bias (mean change) and random error (limits of agreement) were 26.7±125.2 m for test 2 vs. test 1 (p<.001 for mean difference) and 3.9±88.8 m for test 3 vs. test 2 (p = .514 for mean difference). The equation to estimate VO2peak suggested by Andersen et al. (2008) showed a poor fit in the present sample; thus, we suggest a new equation: VO2peak = 23.262+0.050*Andersen distance -3.858*gender -0.376*body weight (R2 = 0.61, standard error of the estimate = 5.69, p<.001, boys = 0, girls = 1)., Conclusions: The Andersen test provided reliable and valid data on a group level. However, a substantial degree of individual variability was found for estimates of VO2peak. Researchers should be aware of the amount of noise in indirect tests that estimate aerobic fitness.

Background: Geographical differences in cardiovascular diseases (CVD) have been observed among Norwegian counties. Better long-term health status and higher physical activity (PA) levels have been documented in the county of Sogn & Fjordane compared with other counties. However, recent trends in CVD risk factors have not been documented. The aim of this study was to investigate the secular trends in leisure time physical activity (LTPA) and other CVD risk factors over a 35-year period in a rural population of 40- to 42-year-olds in western Norway and to compare these trends with national trends., Methods: Data from eight cross-sectional studies from 1975-2010 (n = 375,682) were obtained from questionnaires and physical examinations and were analyzed using mixed model regression analyses., Results: Decreasing trends were observed for sedentary behavior (for women), moderate PA, smoking, systolic blood pressure (SBP), diastolic blood pressure (DBP), high-density lipoprotein (HDL-c) and total cholesterol (TC), whereas increasing trends were observed for body mass index (BMI), triglycerides (TG), light PA, vigorous PA and sedentary behavior for men. Compared to the national trends, the trends in the 40-42-year-olds from Sogn & Fjordane were more beneficial in terms of TG, HDL-c and BMI but less beneficial in terms of SBP and DBP., Conclusions: Over a 35-year-period, this study indicates that the LTPA level has been relatively stable in the county of Sogn & Fjordane. Upward trends were observed in light and vigorous PA, whereas a downward trend was observed in moderate PA. For sedentary behavior, an upward trend was observed in men, whereas a downward trend was observed in women. For smoking, BP and cholesterol decreasing trends were found, but increasing trends were observed in BMI and TG. Compared with the national data, the trends in Sogn & Fjordane were more beneficial for TG, HDL-c and BMI but less beneficial for BP.

Chronic living at altitudes of ∼2,500 m causes consistent hematological acclimatization in most, but not all, groups of athletes; however, responses of erythropoietin (EPO) and red cell mass to a given altitude show substantial individual variability. We hypothesized that athletes living at higher altitudes would experience greater improvements in sea level performance, secondary to greater hematological acclimatization, compared with athletes living at lower altitudes. After 4 wk of group sea level training and testing, 48 collegiate distance runners (32 men, 16 women) were randomly assigned to one of four living altitudes (1,780, 2,085, 2,454, or 2,800 m). All athletes trained together daily at a common altitude from 1,250-3,000 m following a modified live high-train low model. Subjects completed hematological, metabolic, and performance measures at sea level, before and after altitude training; EPO was assessed at various time points while at altitude. On return from altitude, 3,000-m time trial performance was significantly improved in groups living at the middle two altitudes (2,085 and 2,454 m), but not in groups living at 1,780 and 2,800 m. EPO was significantly higher in all groups at 24 and 48 h, but returned to sea level baseline after 72 h in the 1,780-m group. Erythrocyte volume was significantly higher within all groups after return from altitude and was not different between groups. These data suggest that, when completing a 4-wk altitude camp following the live high-train low model, there is a target altitude between 2,000 and 2,500 m that produces an optimal acclimatization response for sea level performance.

Purpose: To examine the performance of the MetaMax® I metabolic analyser of Cortex Biophysik, running a recent version of the software (MetaSoft v. 1.11.05), using the Douglas-bag method as reference., Experiments: First, 182 measurements of the maximal O(2) uptake on school children were analysed both by a former version of the software (MetaMax Analysis) and by a recent version (MetaSoft). In further experiments, seven grown-up subjects of different fitness levels cycled for 5 min at constant powers between 50 and 350 W while the O(2) uptake was measured simultaneously by the MetaMax I and the Douglas-bag method during the last minute of altogether 39 exercises., Results: The calculated maximal O(2) uptake of the 182 school children was on average 3% lower when the data were reanalysed by MetaSoft than when analysed by the former version of the software. There was in addition a 2% variation. In further experiments on grown-up subjects the O(2) uptake reported by the MetaMax I did not differ from that reported by the Douglas-bag system when data for all subjects were pooled, and the random error was 4%. However, the relationships differed slightly between the subjects (p = 0.005), and consequently the random error within each subject was 2-3%. The respiratory exchange ratio (R-value) reported by the MetaMax I differed systematically from that of the control method. However, a reliable R-value could be calculated from the instrument's raw data., Conclusions: Our data suggest that the MetaMax I running MetaSoft reports unbiased values of the O(2) uptake and with moderate random error.

The aim of this study was to investigate the effect of a 2-year school-based physical activity (PA) intervention in 9-year-old children on cardiovascular disease (CVD) risk factors. One intervention school (I-school) (n=125) and one control school (C-school) (n=131) were included. The children at the I-school carried out 60 min of PA daily. The PA lessons were planned, organized and led by expert physical education (PE) teachers. In the C-school, children were offered the normal 45 min of PE twice weekly. The intervention resulted in a greater beneficial development in systolic (P=0.003) and diastolic (P=0.002) blood pressure, total cholesterol-to-high-density lipoprotein cholesterol ratio (P=0.011), triglyceride (P=0.030) and peak oxygen uptake (P<0.001) in I-school children than in C-school children. No significant differences were observed in waist circumference, body mass index and the homeostasis model assessment for insulin resistance between the two groups. Furthermore, the intervention, primarily carried out at moderate intensity, had the strongest impact in children with the least favorable starting point. In conclusion, a daily school-based PA intervention can beneficially modify children's CVD risk profile if the intervention has sufficient duration and includes a substantial amount of daily PA, and if the PA is implemented by expert PE teachers., (© 2010 John Wiley & Sons A/S.)

The aim of this study was to describe changes in children's cardiorespiratory fitness (CRF) following a school-based physical activity (PA) intervention. In total, 259 children (age 9.3 ± 0.3 years) were invited to participate, of whom 256 participated. The children from the intervention school (63 boys, 62 girls) carried out 60-min PA over 2 school years. The children from the control school (62 boys, 69 girls) had the regular curriculum-defined amount of physical education in school, i.e. 45 min twice weekly. One hundred and eighty-eight children (73.4%) successfully completed both the baseline and the post-intervention peak oxygen uptake (VO₂ peak) test. VO₂ peak was measured directly during a continuous progressive treadmill protocol where the children ran until exhaustion. The children from the intervention school increased their mean VO₂ peak (95% confidence interval) 3.6 (2.5-4.6) mL/kg/min more than the children from the control school. This VO₂ peak value was adjusted for both sex and baseline VO₂ peak. Boys and girls demonstrated similar VO₂ peak responses. The intervention, primarily carried out at a moderate intensity, had the biggest impact in children with low initial CRF levels. In conclusion, a 2-year school-based 60-min daily PA intervention significantly improved CRF in children., (© 2009 John Wiley & Sons A/S.)

It is important to monitor changes over time in aerobic fitness and obesity in order to target interventions when health deteriorates. We analyzed data from three population studies of adolescents carried out in 1983, 1997, and 2003. Participants were 1050 adolescents from the whole country of Denmark in 1983, 410 in 1997, and 418 in 2003, the two latter cohorts from the City of Odense. VO(₂max) was estimated from maximal power output (MPO) in a cycle test with progressively increasing workload. Estimated VO(₂max) for boys and girls was 52 and 41 mL/min/kg, respectively, both in 1983, 1997, and 2003 with no difference between the three cohorts. However, body mass index (BMI) increased 10% in the upper decentile of the distribution since 1983. MPO decreased over time, but validation studies showed that this was not due to decreased VO(₂max) . The cohort from 1983 was tested twice by school teachers and experienced scientists, and the scientists found higher MPO than school teachers in the same subjects, which emphasize the importance of good validation studies., (© 2009 John Wiley & Sons A/S.)

This paper describes cardiovascular disease (CVD) risk factor levels in a population-representative sample of healthy, rural Norwegian children and examines the association between fitness and clustering of CVD risk factors. Final analyses included 111 boys and 116 girls (mean age 9.3+/-0.3). To determine the degree of clustering, six CVD risk factors were selected: homeostasis model assessment score, waist circumference, triglycerides, systolic blood pressure, total cholesterol to high-density lipoprotein ratio and fitness (VO2peak). Clustering was observed in 9.9% of the boys and 13.8% of the girls. In a different analysis, fitness was omitted as a CVD risk factor and analyzed against the five remaining CVD risk factors. Low fitness was a strong predictor for clustering of CVD risk factors, and children in the least-fit quartile had significantly poorer CVD risk factor values than all of those in the other quartiles. Finally, subjects were cross-tabulated into different fat-fit groups. For both sexes, the unfit and overweight/obese group had a significantly higher CVD risk factor score than the fit and normal weight group. Clustering of CVD risk factors was present in this group of rural children. Low fitness, and low fitness and high fatness combined, were highly associated with a clustered CVD risk.

Acute exposure to high altitude elicits respiratory alkalosis, and this is partially corrected by renal compensation. To determine the time course and magnitude of renal compensation during short-term moderate altitude exposure, we measured urine gas tensions and acid-base status in 48 healthy men and women at four levels of simulated altitude exposures. Each subject was exposed in pseudorandom order to simulated altitudes of 1780, 2085, 2455, and 2800 m in a decompression chamber for 24 h, separated by 1 week at sea level. Fresh urine was collected anaerobically at sea level and after 6 and 24 h of each altitude exposure. Urine pH increased significantly (p < 0.01) after 6 h at all altitudes and returned to baseline values by 24 h at the lowest altitudes. In contrast, urine pH remained elevated at the highest altitudes. The mean value of urine HCO at sea level was 1.67 +/- 0.25 mmol/L, increased significantly after 6 h at all altitudes, and then returned to near baseline after 24 h at three lower altitudes (1780, 2085, and 2455 m). However, it remained elevated at 2800 m. PCO2 in urine was significantly increased after 6 h and returned to baseline after 24 h at all altitudes. These results suggest that (1) short-term low to moderate altitude exposure results in a marked HCO diuresis, which may be caused by inhibition of the secretion of renal tubular H+, and (2) renal HCO compensation was completed by 24 h at low to moderate altitude, but still incomplete at higher altitude.

We measured blood erythropoietin (EPO) concentration, arterial O(2) saturation (Sa(O(2))), and urine PO(2) in 48 subjects (32 men and 16 women) at sea level and after 6 and 24 h at simulated altitudes of 1,780, 2,085, 2,454, and 2,800 m. Renal blood flow (Doppler) and Hb were determined at sea level and after 6 h at each altitude (n = 24) to calculate renal O(2) delivery. EPO increased significantly after 6 h at all altitudes and continued to increase after 24 h at 2,454 and 2,800 m, although not at 1,780 or 2,085 m. The increase in EPO varied markedly among individuals, ranging from -41 to 400% after 24 h at 2,800 m. Similar to EPO, urine PO(2) decreased after 6 h at all altitudes and returned to baseline by 24 h at the two lowest altitudes but remained decreased at the two highest altitudes. Urine PO(2) was closely related to EPO via a curvilinear relationship (r(2) = 0.99), although also with prominent individual variability. Renal blood flow remained unchanged at all altitudes. Sa(O(2)) decreased slightly after 6 h at the lowest altitudes but decreased more prominently at the highest altitudes. There were only modest, albeit statistically significant, relationships between EPO and Sa(O(2)) (r = 0.41, P < 0.05) and no significant relationship with renal O(2) delivery. These data suggest that 1) the altitude-induced increase in EPO is "dose" dependent: altitudes > or =2,100-2,500 m appear to be a threshold for stimulating sustained EPO release in most subjects; 2) short-term acclimatization may restore renal tissue oxygenation and restrain the rise in EPO at the lowest altitudes; and 3) there is marked individual variability in the erythropoietic response to altitude that is only partially explained by "upstream" physiological factors such as those reflecting O(2) delivery to EPO-producing tissues.