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Purpose: The Structured Days Hypothesis (SDH) posits that children’s behaviors associated with obesity – such as physical activity – are more favorable on days that contain more ‘structure’ (i.e., a pre-planned, segmented, and adult-supervised environment) such as school weekdays, compared to days with less structure, such as weekend days. The purpose of this study was to compare children’s moderate-to-vigorous physical activity (MVPA) levels on weekdays versus weekend days using a large, multi-country, accelerometer-measured physical activity dataset. Methods: Data were received from the International Children’s Accelerometer Database (ICAD) July 2019. The ICAD inclusion criteria for a valid day of wear, only non-intervention data (e.g., baseline intervention data), children with at least 1 weekday and 1 weekend day, and ICAD studies with data collected exclusively during school months, were included for analyses. Mixed effects models accounting for the nested nature of the data (i.e., days within children) assessed MVPA minutes per day (min/day MVPA) differences between weekdays and weekend days by region/country, adjusted for age, sex, and total wear time. Separate meta-analytical models explored differences by age and country/region for sex and child weight-status. Results/findings: Valid data from 15 studies representing 5794 children (61% female, 10.7 ± 2.1 yrs., 24% with overweight/obesity) and 35,263 days of valid accelerometer data from 5 distinct countries/regions were used. Boys and girls accumulated 12.6 min/day (95% CI: 9.0, 16.2) and 9.4 min/day (95% CI: 7.2, 11.6) more MVPA on weekdays versus weekend days, respectively. Children from mainland Europe had the largest differences (17.1 min/day more MVPA on weekdays versus weekend days, 95% CI: 15.3, 19.0) compared to the other countries/regions. Children who were classified as overweight/obese or normal weight/underweight accumulated 9.5 min/day (95% CI: 6.9, 12.2) and 10.9 min/day (95% CI: 8.3, 13.5) of additional MVPA on weekdays versus weekend days, respectively. Conclusions: Children from multiple countries/regions accumulated significantly more MVPA on weekdays versus weekend days during school months. This finding aligns with the SDH and warrants future intervention studies to prioritize less-structured days, such as weekend days, and to consider providing opportunities for all children to access additional opportunities to be active.

IntroductionAir pollution harms health across the life course. Children are at particular risk of adverse effects during development, which may impact on health in later life. Interventions that improve air quality are therefore urgently needed not only to improve public health now, but to prevent longer-term increased vulnerability to chronic disease. Low Emission Zones are a public health policy intervention aimed at reducing traffic-derived contributions to urban air pollution, but evidence that they deliver clear health benefits is lacking. We established a natural experiment design study (CHILL: Children’s Health in London and Luton) to evaluate the impacts of the introduction of London’s Ultra Low Emission Zone (ULEZ) on children’s health.Methods and analysisCHILL is a prospective two-arm parallel longitudinal cohort study of children aged 6-9 years, attending primary schools in Central London (the focus of the first phase of the ULEZ) and Luton (a comparator site). The primary goal of the study is to examine the impact of changes in annual air pollutant exposures as oxides of nitrogen, nitrogen dioxide, particulate matter less than 2.5microns and 10microns (NOx, NO2, PM2.5, PM10 respectively) across the two sites on lung growth, measured as forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), over four consecutive years. Secondary outcomes being investigated include a range of respiratory health indicators as well as inequality and health economic measures.Ethics and disseminationEthics approval has been given by Queen Mary University of London Research Ethics Committee (ref 2018/08). Dissemination will target audiences through a variety of channels, including research papers, conference and media presentations, web summaries and social media. CHILL is funded by National Institute for Health Research (NIHR) Public Health Research (Ref 16/139/09) with additional funding by Natural Environment Research Council, NIHR CLAHRC North Thames, NIHR ARC North Thames, and the Mayor of London. ClinicalTrials.gov: NCT04695093Strengths and limitations of this studyStrengthsCHILL uses a prospective parallel cohort design, allowing robust conclusions to be drawn on the impact of the ULEZ - a major city-wide air quality mitigation strategy - on air quality and children’s respiratory health.CHILL study cohorts include children from large and ethnically diverse populations living in urban areas characterised by poor air quality.LimitationsAttrition of study cohort population over time, although this has been accounted for in the original design of the study.Potential diminution of the ULEZ air pollution signal due to pre-compliance with ULEZ restrictions in the run up to the introduction of the scheme in Central London on the 8th April 2019, and minor impacts of other pollution mitigation measures.Added complexity of accounting for effects of COVID-19 and related lockdowns on traffic flows, air quality and children’s health.

Background: Evidence on the association between sitting for extended periods (i.e. prolonged sedentary time (PST)) and cardio-metabolic health is inconsistent in children. We aimed to estimate the differences in cardio-metabolic health associated with substituting PST with non-prolonged sedentary time (non-PST), light (LIPA) or moderate-to-vigorous physical activity (MVPA) in children. Methods: Cross-sectional data from 14 studies (7 countries) in the International Children’s Accelerometry Database (ICAD, 1998–2009) was included. Accelerometry in 19,502 participants aged 3–18 years, together with covariate and outcome data, was pooled and harmonized. Iso-temporal substitution in linear regression models provided beta coefficients (95%CI) for substitution of 1 h/day PST (sedentary time accumulated in bouts > 15 min) with non-PST, LIPA or MVPA, for each study, which were meta-analysed. Results: Modelling substitution of 1 h/day of PST with non-PST suggested reductions in standardized BMI, but estimates were > 7-fold greater for substitution with MVPA (− 0.44 (− 0.62; − 0.26) SD units). Only reallocation by MVPA was beneficial for waist circumference (− 3.07 (− 4.47; − 1.68) cm), systolic blood pressure (− 1.53 (− 2.42; − 0.65) mmHg) and clustered cardio-metabolic risk (− 0.18 (− 0.3; − 0.1) SD units). For HDL-cholesterol and diastolic blood pressure, substitution with LIPA was beneficial; however, substitution with MVPA showed 5-fold stronger effect estimates (HDL-cholesterol: 0.05 (0.01; 0.10) mmol/l); diastolic blood pressure: − 0.81 (− 1.38; − 0.24) mmHg). Conclusions: Replacement of PST with MVPA may be the preferred scenario for behaviour change, given beneficial associations with a wide range of cardio-metabolic risk factors (including adiposity, HDL-cholesterol, blood pressure and clustered cardio-metabolic risk). Effect estimates are clinically relevant (e.g. an estimated reduction in waist circumference of ≈1.5 cm for 30 min/day replacement). Replacement with LIPA could be beneficial for some of these risk factors, however with substantially lower effect estimates.

Funder: Ministero delle Politiche Agricole Alimentari e Forestali; doi: http://dx.doi.org/10.13039/501100005401, Funder: ZonMw; doi: http://dx.doi.org/10.13039/501100001826, Funder: The Research Council of Norway, Division for Society and Health., Background: Levels of physical activity and variation in physical activity and sedentary time by place and person in European children and adolescents are largely unknown. The objective of the study was to assess the variations in objectively measured physical activity and sedentary time in children and adolescents across Europe. Methods: Six databases were systematically searched to identify pan-European and national data sets on physical activity and sedentary time assessed by the same accelerometer in children (2 to 9.9 years) and adolescents (≥10 to 18 years). We harmonized individual-level data by reprocessing hip-worn raw accelerometer data files from 30 different studies conducted between 1997 and 2014, representing 47,497 individuals (2–18 years) from 18 different European countries. Results: Overall, a maximum of 29% (95% CI: 25, 33) of children and 29% (95% CI: 25, 32) of adolescents were categorized as sufficiently physically active. We observed substantial country- and region-specific differences in physical activity and sedentary time, with lower physical activity levels and prevalence estimates in Southern European countries. Boys were more active and less sedentary in all age-categories. The onset of age-related lowering or leveling-off of physical activity and increase in sedentary time seems to become apparent at around 6 to 7 years of age. Conclusions: Two third of European children and adolescents are not sufficiently active. Our findings suggest substantial gender-, country- and region-specific differences in physical activity. These results should encourage policymakers, governments, and local and national stakeholders to take action to facilitate an increase in the physical activity levels of young people across Europe.

Background Evidence on the association between sitting for extended periods (i.e. prolonged sedentary time (PST)) and cardio-metabolic health is inconsistent in children. We aimed to estimate the differences in cardio-metabolic health associated with substituting PST with non-prolonged sedentary time (non-PST), light (LIPA) or moderate-to-vigorous physical activity (MVPA) in children. Methods Cross-sectional data from 14 studies (7 countries) in the International Children’s Accelerometry Database (ICAD, 1998–2009) was included. Accelerometry in 19,502 participants aged 3–18 years, together with covariate and outcome data, was pooled and harmonized. Iso-temporal substitution in linear regression models provided beta coefficients (95%CI) for substitution of 1 h/day PST (sedentary time accumulated in bouts > 15 min) with non-PST, LIPA or MVPA, for each study, which were meta-analysed. Results Modelling substitution of 1 h/day of PST with non-PST suggested reductions in standardized BMI, but estimates were > 7-fold greater for substitution with MVPA (− 0.44 (− 0.62; − 0.26) SD units). Only reallocation by MVPA was beneficial for waist circumference (− 3.07 (− 4.47; − 1.68) cm), systolic blood pressure (− 1.53 (− 2.42; − 0.65) mmHg) and clustered cardio-metabolic risk (− 0.18 (− 0.3; − 0.1) SD units). For HDL-cholesterol and diastolic blood pressure, substitution with LIPA was beneficial; however, substitution with MVPA showed 5-fold stronger effect estimates (HDL-cholesterol: 0.05 (0.01; 0.10) mmol/l); diastolic blood pressure: − 0.81 (− 1.38; − 0.24) mmHg). Conclusions Replacement of PST with MVPA may be the preferred scenario for behaviour change, given beneficial associations with a wide range of cardio-metabolic risk factors (including adiposity, HDL-cholesterol, blood pressure and clustered cardio-metabolic risk). Effect estimates are clinically relevant (e.g. an estimated reduction in waist circumference of ≈1.5 cm for 30 min/day replacement). Replacement with LIPA could be beneficial for some of these risk factors, however with substantially lower effect estimates.

Despite a large and increasing evidence base on physical activity (PA) interventions, the high rates of physical inactivity and associated chronic diseases are continuing to increase globally. The purpose of this cumulative meta-analysis was to: investigate the evolution of randomized controlled trial evidence of individual-level PA interventions to asses if new trials are contributing novel evidence to the field. Through a two-staged search process, primary studies examining the effects of interventions targeted at increasing PA within healthy adult populations were pooled and selected from eligible systematic reviews. Cumulative meta-analyses were performed on effect sizes immediately post-intervention (n=62), and for long-term behavior change (≥12-months post-baseline; n=27). Sufficiency and stability of the evidence was assessed through application of pre-published indicators. Meta-analyses suggest overall positive intervention effects on PA. The evidence base for effectiveness immediately post-intervention reached levels of sufficiency and stability in 2007; and for long-term follow-up in 2011. In the time since, intervention effectiveness has not substantially changed, and further trials are unlikely to change the direction and magnitude of effect. Substantial evidence exists demonstrating that PA interventions can modify individual behavior in controlled settings. Researchers are urged to shift focus towards investigating the optimization, implementation, sustainability and cost-effectiveness of interventions., Funding for this study and the work of authors Jean Adams, Esther M F Van Sluijs and Rebecca Love was supported,wholly or in part, by the Centre for Diet and Activity Research(CEDAR), a UKCRC Public Health Research Centre of Excellence (RES-590-28-0002). Within this funding from the British Heart Foundation, Department of Health, Economic and Social Research Council, Medical Research Council and the Wellcome Trust, under the auspices of the UK Clinical Research Collaboration, is gratefully acknowledged.The work of Esther M F van Sluijs was supported by the Medical Research Council (MC_UU_12015/7).

Subsequent to the publication, several errors have been found in the paper and can be corrected as follows: The labelling on the studies in Figure 2 is incorrect. The referencing in Table 1 is inconsistent with the manuscript reference list. The correct Figure 2 and Table are shown here. 2 (Figure presented.) Effect on child physical activity from random effects meta-analysis of eligible studies. Overview of characteristics of 47 studies included in systematic review of family-based physical activity promotion (Table presented.) #Corresponds with a significant, positive change in outcome (see Supplementary Table 1 for full details) +Singapore, Mexico, Italy, New Zealand, Canada, Germany *Some studies employed both subjective and objective methods to measure physical activity †Some studies employed more than one intervention strategy.

Subsequent to the publication, several errors have been found in the paper and can be corrected as follows: The labelling on the studies in Figure 2 is incorrect. The referencing in Table 1 is inconsistent with the manuscript reference list. The correct Figure 2 and Table are shown here. 2 (Figure presented.) Effect on child physical activity from random effects meta-analysis of eligible studies. Overview of characteristics of 47 studies included in systematic review of family-based physical activity promotion (Table presented.) #Corresponds with a significant, positive change in outcome (see Supplementary Table 1 for full details) +Singapore, Mexico, Italy, New Zealand, Canada, Germany *Some studies employed both subjective and objective methods to measure physical activity †Some studies employed more than one intervention strategy.

BACKGROUND: Little is known about equity effects in primary care based physical activity interventions. This review explored whether differences in intervention effects are evident across indicators of social disadvantage, specified under the acronym PROGRESS-Plus (place of residence, race/ethnicity, occupation, gender, religion, education, social capital, socioeconomic status, plus age, disability and sexual orientation). METHODS: Six bibliographic databases were systematically searched for randomised controlled trials (RCTs) of physical activity interventions conducted in primary care. Harvest plots were used to synthesize findings from RCTs reporting subgroup or interaction analyses examining differences in intervention effects across levels of at least one PROGRESS-Plus factor. RESULTS: The search yielded 9052 articles, from which 173 eligible RCTs were identified. Despite PROGRESS-Plus factors being commonly measured (N = 171 RCTs), differential effect analyses were infrequently reported (N = 24 RCTs). Where reported, results of equity analyses suggest no differences in effect across levels or categories of place of residence (N = 1RCT), race (N = 4 RCTs), education (N = 3 RCTs), socioeconomic status (N = 3 RCTs), age (N = 16 RCTs) or disability (N = 2 RCTs). Mixed findings were observed for gender (N = 22 RCTs), with some interventions showing greater effect in men than women and others vice versa. Three RCTs examined indicators of social capital, with larger post-intervention differences in physical activity levels between trial arms found in those with higher baseline social support for exercise in one trial only. No RCTs examined differential effects by participant occupation, religion or sexual orientation. CONCLUSION: The majority of RCTs of physical activity interventions in primary care record sufficient information on PROGRESS-Plus factors to allow differential effects to be studied. However, very few actually report details of relevant analyses to determine which population subgroups may stand to benefit or be further disadvantaged by intervention efforts.

Physical activity and sedentary behaviour are associated with metabolic and mental health during childhood and adolescence. Understanding the inter-relationships between these behaviours will help to inform intervention design. This systematic review and meta-analysis synthesized evidence from observational studies describing the association between sedentary behaviour and physical activity in young people (