Longitudinal changes in objectively measured physical activity differ for weekdays and weekends among Chinese children in Hong Kong

Results from the Hong Kong's 2022 report card on physical activity for children and adolescents

Background/objective

This paper aimed to summarize the findings of the third (2022) Active Healthy Kids Hong Kong Report Card on Physical Activity for Children and Adolescents and evaluate the secular trends of physical activity related indicators.

Methods

Five behavioral indicators (Overall Physical Activity, Organized Sport and Physical Activity, Active Play, Active Transportation, and Sedentary Behavior), three outcome indicators (Physical Fitness, Sleep, and Obesity) and four sources of influence indicators (Family and Peers, School, Community and Environment, and Government) were assigned a letter grade (ranging from A+ to F or incomplete) based on the best available evidence following a harmonized approach developed by the Active Healthy Kids Global Alliance. Data sources included published journal articles, government reports, manual searches, and personal contacts; and consisted of both pre-COVID-19 and after-COVID-19 evidence.

Results

Grades for Overall Physical Activity (D−∗∗) and Sedentary Behavior (D) deteriorated compared to the 2018 Report Card. The other three behavioral indicators, Organized Sport and Physical Activity, Active Play, and Active Transportation, were assigned B−, D, and B+, respectively. Physical Fitness (D), Sleep (C−), and Obesity (D−) obtained the same grades as in the 2018 Report Card. School (B) and Government (C+) grades slightly improved, while Community and Environment grade (B) was stable. Family and Peers was not graded due to insufficient evidence.

Conclusions

Despite slight improvements in influence indicators, physical activity and sedentary behavior have changed unfavorably for children and adolescents in Hong Kong. Strategic investments are needed to improve adoption and implementation of effective interventions.

Movement guidelines for young children: Engaging stakeholders to design dissemination strategies in the Hong Kong early childhood education context

Background

Early childhood is a critical period during which patterns of movement behaviors are formed. The World Health Organization had endorsed guidelines for physical activity, sedentary behavior and sleep over a 24-h time period, which had been adopted by the Center for Health Protection of Hong Kong. This paper reports on stakeholder engagements that were conducted to inform the design of strategies to disseminate the guidelines in early childhood education (ECE) settings.

Methods

Using a mixed-methods study design, we sought to (a) assess the stakeholders' levels of awareness and knowledge of the Hong Kong movement guidelines for young children and (b) identify the factors that influence the uptake of the said guidelines. We conducted an online survey of early childhood education teachers (N =314), twelve focus groups involving teachers (N = 18) and parents (N = 18), and individual interviews of key informants (N = 7) and domestic workers who provide care for preschool-aged children (N = 7). Descriptive statistics were used for the quantitative data, and thematic analysis was performed on the qualitative data using an inductive and semantic approach following a realist framework.

Findings

Our findings show that teachers were aware of the movement guidelines for young children, but their knowledge of the specific guidelines was deficient; parents and domestic workers had limited awareness and knowledge of the guidelines. Uptake of the movement guidelines is enabled by parent engagement, activities in the ECE centers, home-school cooperation, and community activities for children. The challenges include the time poverty of parents, local curriculum requirements, limited physical spaces, social values, and pandemic-related restrictions.

Conclusion

We recommend that dissemination strategies in the ECE context should deliver knowledge content and support stakeholders in mitigating the challenges associated with time, space, and social conditions.

Physical activity correlates in children and adolescents with autism spectrum disorder: a systematic review

PURPOSE

This systematic review examined correlates of physical activity (PA) at all levels of the socio-ecological model (i.e., intrapersonal, interpersonal, environmental and policy level) in children and adolescents with autism spectrum disorder (ASD).

MATERIALS AND METHODS

Major electronic databases were searched from inception until March 23^rd, 2021. A summary coding was used to analyze the data for children (3-12 years) and adolescents (13-18 years) with ASD separately.

RESULTS

Out of the 79 potential PA correlates, retrieved from 32 studies (991 657 children; 3857 adolescents), only five correlates were consistently examined as a PA correlate (i.e., examined in four or more studies) in children and adolescents with ASD. Only age was inversely associated with PA in children and adolescents with ASD. Data on gender, body mass index, autism severity level and day of the week being physically active in children with ASD were mixed.

CONCLUSIONS

We only found consistent evidence for age being inversely related to PA. Our review indicates that more research is needed to explore intrapersonal, interpersonal, environmental and policy-related correlates of PA in children and adolescents with ASD.IMPLICATIONS FOR REHABILITATIONRehabilitation programs should take into account that in particular older children and adolescents with autism spectrum disorder are at risk for physical inactivity.Boys and girls with autism spectrum disorder need the same care when motivating them to be more physically active.

Differences in physical activity between weekdays and weekend days among U.S. children and adults: Cross-sectional analysis of NHANES 2011–2014 data

This study investigates differences in physical activity between weekdays and weekend days, and its associations with sociodemographic and anthropometric characteristics in the U.S population using the NHANES 2011–2014 data. Physical activity was measured using ActiGraph GT3X+. Raw acceleration data were converted to Monitor-Independent Movement Summary units (MIMS-units) that account for inter-device variability and eliminates non-human movement. The daily MIMS-units were averaged for weekdays and weekend days. Demographic characteristics were self-reported. Height and weight were objectively measured. The sample included 6611 adults aged ≥ 20 years and 3520 children aged between 6 and 19 years. The results show that more MIMS-units were registered on weekdays compared to weekend days for adults (652, 95%CI = 533, 770) and children (889, 95%CI = 702, 1076). Factors associated with physical activity in adults (gender, age, marital status, ethnicity, education level, and weight status) were similar for weekdays and weekend days. In children, physical activity was associated with ethnicity, weight status, and age. The level of differences in physical activity between weekdays and weekend days among adults was larger for men, Hispanic Americans, and those with lower education levels. Differences among children were similar across subgroups, except for those aged 16–19 years who had smaller level of difference compared to those aged 12–15 years. In conclusion, adults and children were more active on weekdays than weekend days. The effects of structured days (i.e., weekdays) on physical activity appeared to be similar across most child subgroups but more heterogeneous for adult subgroups. Interventions increasing physical activity opportunities during weekend days are warranted.

Weekday and Weekend Physical Activity of Preschool Children in Relation to Selected Socioeconomic Indicators

Physical activity (PA) is as vital for improving the health of young children as it is positively associated with a broad range of psychological, cognitive, and cardio-metabolic outcomes. The aims of this study were to: (1) to assess the level of PA and meeting the WHO recommendations: moderate-to-vigorous physical activity (MVPA) and the number of steps in Polish preschool boys and girls on weekdays and on weekends; (2) to investigate the relationship between selected socioeconomic indicators (self-reported by parents) and PA, including meeting the WHO recommendation for daily MVPA and the number of steps on weekdays and on weekends among Polish preschoolers. Data were collected in the 2017/2018 school year. The study included a total of 522 boys and girls both aged between 5 and 6 years. The ActiGraph GT3X-BT tri-axial accelerometer was used to measure PA. Selected socioeconomic indicators as well as parental body weight and body height were self-reported by parents/caregivers using a questionnaire. In most of the PA indicators analyzed for girls (moderate, vigorous, total MVPA, and steps/day), the averages were higher during the week than during the weekend. Moreover, significantly more boys met the criteria of MVPA, both on weekdays and over the weekend (32.3% boys and 19.2% girls on weekdays and 31.1% boys and 18.1% girls on weekends). Additionally, more boys met the step recommendations, but only on weekends (15.5% boys and 6.6% girls). It was found that if there were two people in a household, there was an almost a three-fold greater chance (adj. OR = 2.94, p = 0.032) of meeting the MVPA criterion with an even stronger association (over fivefold greater chance) in meeting the step recommendation (adj. OR = 5.56, p = 0.033). The differences in the day schedule may potentially contribute with the level of PA in girls. Among the analyzed selected socioeconomic indicators, only the number of people in a household had a significant association on PA.

Physical activity and fitness: The feasibility and preliminary effectiveness of wearable activity tracker technology incorporating altruistic motivation in youth

PURPOSE

The purpose of this study was to examine the feasibility and preliminary effectiveness of using wearable activity tracker technology, integrated with altruistic motivation in children to increase physical activity (PA), fitness, and prosocial behavior.

DESIGN AND METHODS

A quasiexperimental design was employed in two 4th grade classrooms in a rural southern state. The intervention was a wearable PA tracker and a web-based curriculum with activities to earn power points redeemable to provide life-saving food to undernourished kids internationally. Seventeen children in the intervention group participated in the 10-week PA program and 18 children were in the wait listed control group. Three measures were assessed in both groups at baseline and postintervention: (a) PA measured with accelerometers, (b) fitness levels measured with shuttle run, and (c) prosocial behavior measured with Strengths and Difficulties questionnaire.

RESULTS

Of the 35 children enrolled, the majority were nine years old (n = 28), black (n = 31) and female (n = 23). An overall enrollment rate of 88%, attrition rate of 9%, and an accelerometer noncompliance rate of 25% was determined to assess feasibility. There was no statistical significance between the control and intervention group outcome variables. The average minutes of PA in the control group decreased 8 min from baseline to postintervention (p = .05). In the intervention group, PA decreased by 10 min from baseline to postintervention (p = .12). In both the control and intervention groups, prosocial behavior scores decreased (p = .09 control; p = .62 intervention). The fitness scores, VO₂ max, did not significantly change (intervention p = .21; control p = .35).

PRACTICE IMPLICATIONS

Developing effective interventions that foster PA and dissuade sedentary behaviors are essential to enhancing PA and fitness levels. The recruitment, retention, and accelerometer wear adherence suggest this setting, with this population is feasible. The intervention is deliverable, however, the potential of wearable activity trackers and the effect of prosocial behavior that benefits others in increasing PA and improving cardiorespiratory fitness, should be further researched by building on the successful elements of this study.

Cross-validation of the Canadian Assessment of Physical Literacy second edition (CAPL-2): The case of a Chinese population

The present study aimed to culturally adapt the Canadian Assessment of Physical Literacy, Second Edition (CAPL-2) and examine its validity and reliability among Chinese children aged 8 to 12 years. The original manual of CAPL-2 was translated and culturally adapted from English into Chinese. A total of 327 children (153 boys, mean age = 10.0) completed CAPL-2 (Chinese) assessments. Internal consistency reliability and construct validity for subscales and total model was explored. Results reported a good fit after adjusting for covariation paths, chi-square (χ ² = 70.16, df = 43, p < 0.05), RMSEA = 0.04, 90% CI (0.024 - 0.062), CFI = 0.94, TLI = 0.90. Motivation and Confidence showed a good internal consistency (α = 0.82), compared to Knowledge and Understanding (α = 0.52). In general, there were few significant correlations between age and the subdomains as developmentally expected, and gender differences were observed with boys performing better than girls in total CAPL2 (Chinese) scores. This study was the first to cross-validate the CAPL-2 into the Chinese population. CAPL-2 (Chinese) offers the possibility of assessing physical literacy for researchers and practitioners and Chinese children's physical literacy development could be easily tracked in school settings.

Accelerometer-measured physical activity and sedentary behavior in Chinese children and adolescents: a systematic review and meta-analysis

OBJECTIVE

To synthesize evidence on accelerometer-measured moderate-to-vigorous physical activity (MVPA) and sedentary behavior (SB) levels of Chinese children and adolescents.

STUDY DESIGN

This is both a systematic review and meta-analysis study.

METHODS

Online databases were searched for studies published from January 2009 up to February 2019. These studies reported accelerometer-measured daily minutes of MVPA and/or SB among Chinese children and adolescents. Random-effects meta-analysis was used to separately pool the time spent in MVPA and SB.

RESULTS

Of 4754 records, 20 studies were included in the meta-analysis. Sample sizes ranged from 96 to 2163. The meta-analysis showed that Chinese children and adolescents spent 41.11 min/day in MVPA and 529.83 min/day in SB averagely. Boys spent more time in MVPA compared with girls (P = 0.01). Children accumulated more MVPA time than adolescents (P = 0.05), and children spent less time in SB than adolescents (P = 0.05). Unlike weekdays, SB was lower on weekends (P = 0.02). There were significant differences in children and adolescents' MVPA time in regions (P < 0.001).

CONCLUSIONS

MVPA level in Chinese children and adolescents is well below international recommendations, and their SB level is very high.

Associations of weather conditions with adolescents' daily physical activity, sedentary time, and sleep duration

Weather has been recognized as an environmental factor that affects daily activities. However, the effects of a humid subtropical climate on daily activity behavior are unclear. This study investigated the associations of weather conditions with physical activity (PA), sedentary time (ST), and sleep duration in a sample of 740 Hong Kong adolescents (mean age: 14.7 ± 1.6 years). The activPAL was used to assess the time spent during moderate to vigorous PA (MVPA), ST, and sleep. Weather data (e.g., temperature, relative humidity, rainfall amount, and sunlight duration) were obtained from the Hong Kong Observatory. Linear mixed models were constructed to examine the associations of weather conditions with the durations of MVPA, ST, and sleep on weekdays and weekend days, respectively. The analysis included valid data from 561 students (51.9% male). Among Hong Kong adolescents, a higher relative humidity was associated with reduced MVPA on weekdays and weekends, more ST on weekdays, and a longer sleep duration on weekends. A longer duration of sunlight induced less MVPA on weekends, but a longer sleep duration on weekdays. On weekends, higher temperatures correlated with increases in MVPA and ST but a decrease in sleep duration. Rainfall correlated inversely with sleep duration and positively with ST on weekdays. The associations of rainfall with MVPA exhibited opposite trends on weekdays and weekends. In summary, the relationships between weather conditions and daily activities exhibited day-type patterns. The findings suggest that environment-controlled indoor PA should be recommended during weather conditions of high relative humidity and higher temperatures.

Report Card Grades on the Physical Activity of Children and Youth Comparing 30 Very High Human Development Index Countries

BACKGROUND

To better understand the childhood physical inactivity crisis, Report Cards on physical activity of children and youth were prepared concurrently in 30 very high Human Development Index countries. The aim of this article was to present, describe, and compare the findings from these Report Cards.

METHODS

The Report Cards were developed using a harmonized process for data gathering, assessing, and assigning grades to 10 common physical activity indicators. Descriptive statistics were calculated after converting letter grades to interval variables, and correlational analyses between the 10 common indicators were performed using Spearman's rank correlation coefficients.

RESULTS

A matrix of 300 grades was obtained with substantial variations within and between countries. Low grades were observed for behavioral indicators, and higher grades were observed for sources of influence indicators, indicating a disconnect between supports and desired behaviors.

CONCLUSION

This analysis summarizes the level and context of the physical activity of children and youth among very high Human Development Index countries, and provides additional evidence that the situation regarding physical activity in children and youth is very concerning. Unless a major shift to a more active lifestyle happens soon, a high rate of noncommunicable diseases can be anticipated when this generation of children reaches adulthood.

Joint associations between weekday and weekend physical activity or sedentary time and childhood obesity

OBJECTIVE

To evaluate the single and joint associations of objectively measured moderate-to-vigorous physical activity (MVPA) and sedentary time on week and weekend days with obesity in children from 12 countries across all inhabited continents.

METHODS

A multinational, 12-country cross-sectional study of 5779 children aged 9-11 years was conducted. Time spent in MVPA and sedentary behaviors was assessed by waist-worn accelerometry. Logistic regression was used to examine the independent and joint associations of MVPA and sedentary time on weekdays and weekend with the odds of obesity.

RESULTS

After adjustment for all confounding factors, the odds ratios (ORs) of childhood obesity were the highest among children with a low level of MVPA on both weekdays and weekend (OR 4.67), high among children with a high level of MVPA on weekdays and a low level of MVPA on weekend (OR 1.99) and high among children with a low level of MVPA on weekdays and a high levels of MVPA on weekend (OR 2.20), compared to those with a high level of MVPA on both weekdays and weekend. Similarly, the ORs of childhood obesity were significantly higher among children with a high level of sedentary time on both weekdays and weekend (OR 1.87) compared with those with low levels of sedentary time on both weekdays and weekend.

CONCLUSIONS

Lower levels of MVPA or higher levels of sedentary time on either weekdays or weekend were associated with increased odds of obesity in 9-11 year old children in 12 countries.

Results from the Hong Kong's 2018 report card on physical activity for children and youth

BACKGROUND/OBJECTIVE

The Active Healthy Kids 2018 Hong Kong Report Card provides evidence-based assessment across 12 indicators of physical activity behaviors, sleep, and related community and government initiatives for children and youth.

METHODS

The systematic development process provided by the Active Healthy Kids Global Alliance was used. The best available data from the past 10 years were reviewed by a panel of experts. According to predefined benchmarks, letter grades were assigned to 12 indicators (Overall Physical Activity, Organized Sport Participation, Active Play, Active Transportation, Sedentary Behaviors, Physical Fitness, Sleep, Family, School, Community and Environment, Government, and Obesity).

RESULTS

Three of the five activity behaviors received C- or C grades: Overall Physical Activity (C-), Sedentary Behaviors (C-), and Organized Sport Participation (C). Active Transportation was graded B + . Same to the 2016 Hong Kong Report Card, Active Play could not be graded. School and Government were graded C. Family and Community and Environment was graded D- and B, respectively. Three new indicators were added after the 2016 Report Card and they were graded from C- (Sleep) to D (Physical Fitness) or D- (Obesity).

CONCLUSIONS

Children and youth in Hong Kong have low physical activity and physical fitness levels and high sedentary behaviors despite a generally favorable community environment. A high prevalence of obesity and low levels of family support warrant more public health action. Researchers should address the surveillance gap in active play and peer support.

Prospective Associations between Weekend Catch-Up Sleep, Physical Activity, and Childhood Obesity

BACKGROUND

Catch-up sleep and low physical activity on weekends have been commonly documented. Preliminary evidence on Chinese children, however, has shown a variety of weekly physical activity patterns. This study examined the prospective associations between weekend catch-up patterns of sleep and physical activity and obesity over a 2-year period in Chinese children.

METHODS

Prospective data from 599 children in the Understand Children's Activity and Nutrition (UCAN) cohort study were analyzed. Weekly patterns of obesogenic behaviors (physical activity and sleep duration) were assessed annually over a 2-year period. Moderate-to-vigorous physical activity (MVPA) and sedentary time were determined by ActiGraph accelerometry. Data on sleep durations and sociodemographic factors were obtained from parental-reported questionnaires. Weekend catch-up sleep and MVPA patterns were calculated and examined in relation to childhood obesity after controlling for sociodemographic variables and sedentary time.

RESULTS

Every additional hour of average weekly sleep duration was associated with a 16% decrease in the odds of obesity (OR: 0.841, 95%CI: 0.709 - 0.999). After adjustment of average sleep duration, weekend sleep catch-up categories showed no association with obesity risk. Over a 2-year period, half of the children demonstrated weekend catch-up MVPA. Weekend catch-up MVPA for less than 20 minutes (OR: 0.473, 95%CI: 0.258 - 0.867) or more than 20 minutes (OR: 0.505, 95%CI: 0.257 - 0.993) were both related to lower risk of obesity.

CONCLUSIONS

Weekend catch-up sleep did not ameliorate the risk of childhood obesity, whereas weekend catch-up MVPA did reduce that risk. More research is needed to explore the factors contributing to these obesogenic behavior patterns.

Promoting healthy home environments and lifestyles in families with preschool children: HomeStyles, a randomized controlled trial

The purpose of the HomeStyles randomized controlled trial was to determine the effect of participation in the HomeStyles intervention vs an attention control condition on the weight-related aspects of the home environment and lifestyle behavioral practices of families with preschool children. Parents of preschool children (n=489) were systematically randomized to experimental or attention control group after completing the baseline survey. Baseline and post surveys comprehensively assessed study outcomes using a socio-ecological approach incorporating valid, reliable intrapersonal (e.g., diet, activity), interpersonal (e.g., family meal frequency), and environmental measures (e.g., home media environment), and self-reported parent and child measured heights and weights. For all outcome measures, paired t-tests compared within group differences over time and ANCOVA, controlling for baseline scores and prognostic variables (e.g., parent sex), determined differences in post survey scores between groups. The final analytical sample (N=172; age 32.34±5.71SD; 58% White; 93% female) completed baseline and post surveys. The experimental group families had improved family meal and diet-related behaviors, and self-efficacy for food-related childhood obesity-protective practices. Household food supplies changed little, except for less availability of salty/fatty snacks. Within group effects indicated the control group also experienced some improvements, however these were few in number. ANCOVA revealed the experimental group parents had greater physical activity, reduced screentime, improved family mealtime behaviors, and increased self-efficacy for childhood obesity-protective behaviors and cognitions compared to the control group at post survey, though effect sizes were small. The HomeStyles program for families with preschool children promoted improvements in an array of obesity-preventive behaviors.

Effect and process evaluation of a kindergarten-based, family-involved cluster randomised controlled trial in six European countries on four- to six-year-old children's steps per day: the ToyBox-study

BACKGROUND

The ToyBox-intervention is a theory- and evidence-based intervention delivered in kindergartens to improve four- to six-year-old children's energy balance-related behaviours and prevent obesity. The current study aimed to (1) examine the effect of the ToyBox-intervention on increasing European four- to six-year-old children' steps per day, and (2) examine if a higher process evaluation score from teachers and parents was related to a more favourable effect on steps per day.

METHODS

A sample of 2438 four- to six-year-old children (51.9% boys, mean age 4.75 ± 0.43 years) from 6 European countries (Belgium, Bulgaria, Germany, Greece, Poland and Spain) wore a motion sensor (pedometer or accelerometer) for a minimum of two weekdays and one weekend day both at baseline and follow-up to objectively measure their steps per day. Kindergarten teachers implemented the physical activity component of the ToyBox-intervention for 6 weeks in total, with a focus on (1) environmental changes in the classroom, (2) the child performing the actual behaviour and (3) classroom activities. Children's parents received newsletters, tip cards and posters. To assess intervention effects, multilevel repeated measures analyses were conducted for the total sample and the six intervention countries separately. In addition, process evaluation questionnaires were used to calculate a total process evaluation score (with implementation and satisfaction as a part of the overall score) for teachers and parents which was then linked with the physical activity outcomes.

RESULTS

No significant intervention effects on four- to six-year-old children' steps per weekday, steps per weekend day and steps per average day were found, both in the total sample and in the country-specific samples (all p > 0.05). In general, the intervention effects on steps per day were least favourable in four- to six-year-old children with a low teachers process evaluation score and most favourable in four- to six-year-old children with a high teachers process evaluation score. No differences in intervention effects were found for a low, medium or high parents' process evaluation score.

CONCLUSION

The physical activity component of the ToyBox-intervention had no overall effect on four- to six-year-old children' steps per day. However, the process evaluation scores showed that kindergarten teachers that implemented the physical activity component of the ToyBox-intervention as planned and were satisfied with the physical activity component led to favourable effects on children's steps per day. Strategies to motivate, actively involve and engage the kindergarten teachers and parents/caregivers are needed to induce larger effects.

Isotemporal Substitution Analysis for Sedentary Behavior and Body Mass Index

PURPOSE

This study examined the prospective associations of reallocating time spent in different types of sedentary behavior, physical activity, and sleep with body mass index (BMI) in children using isotemporal substitution analysis.

METHODS

Chinese children in grades 1-3 were recruited to a cohort study in 2009 and were followed up over a 2-yr period. Reports were gathered from the parents on children's sedentary behavior, sleep duration, and sociodemographic variables. The reported sedentary behavior types were then grouped into three categories: screen time (e.g., watching TV), academic-related activities (e.g., doing homework), and other sedentary behaviors (e.g., sitting and talking). Moderate-to-vigorous physical activity (MVPA) and light-intensity physical activity were assessed by ActiGraph accelerometry (ActiGraph, Pensacola, FL). Isotemporal substitution models were performed to examine the effects of time allocation on BMI.

RESULTS

A total of 672 children (359 boys, mean age at recruitment = 7.6 yr) who had provided valid accelerometer data for at least one assessment time point were included in the analysis. Controlling for covariates and total behavior time, isotemporal substitution models indicated that the displacement of 30 min·d of other sedentary behaviors with equal amounts of screen time (B = 0.12; 95% confidence interval, 0.04-0.20) or academic-related activities (B = 0.13; 95% confidence interval, 0.04-0.21) was associated with higher BMI. Reallocating 30 min·d of MVPA with each of the sedentary behavior variables resulted in increased BMI.

CONCLUSIONS

The substitution of screen time or academic-related activities with other sedentary behaviors or MVPA was associated with lower BMI in Chinese children.

Understanding differences between summer vs. school obesogenic behaviors of children: the structured days hypothesis

BACKGROUND

Although the scientific community has acknowledged modest improvements can be made to weight status and obesogenic behaviors (i.e., physical activity, sedentary/screen time, diet, and sleep) during the school year, studies suggests improvements are erased as elementary-age children are released to summer vacation. Emerging evidence shows children return to school after summer vacation displaying accelerated weight gain compared to the weight gained occurring during the school year. Understanding how summer days differ from when children are in school is, therefore, essential.

DISCUSSION

There is limited evidence on the etiology of accelerated weight gain during summer, with few studies comparing obesogenic behaviors on the same children during school and summer. For many children, summer days may be analogous to weekend days throughout the school year. Weekend days are often limited in consistent and formal structure, and thus differ from school days where segmented, pre-planned, restrictive, and compulsory components exist that shape obesogenic behaviors. The authors hypothesize that obesogenic behaviors are beneficially regulated when children are exposed to a structured day (i.e., school weekday) compared to what commonly occurs during summer. This is referred to as the 'Structured Days Hypothesis' (SDH). To illustrate how the SDH operates, this study examines empirical data that compares weekend day (less-structured) versus weekday (structured) obesogenic behaviors in U.S. elementary school-aged children. From 190 studies, 155 (~80%) demonstrate elementary-aged children's obesogenic behaviors are more unfavorable during weekend days compared to weekdays.

CONCLUSION

In light of the SDH, consistent evidence demonstrates the structured environment of weekdays may help to protect children by regulating obesogenic behaviors, most likely through compulsory physical activity opportunities, restricting caloric intake, reducing screen time occasions, and regulating sleep schedules. Summer is emerging as the critical period where childhood obesity prevention efforts need to be focused. The SDH can help researchers understand the drivers of obesogenic behaviors during summer and lead to innovative intervention development.

Age, period and cohort effects and the predictors of physical activity and sedentary behaviour among Chinese children, from 2004 to 2011

BACKGROUND

Very few studies have explored the effects of age, time period, and cohort in association with biological, behavioral, economic, and environmental factors predictors on physical activity (PA) and sedentary behaviour (SB) among Chinese children.

METHODS

We used data from a cohort study of the China Health and Nutrition Survey (CHNS) between 2004 and 2011 (2004, 2006, 2009 and 2011). The outcomes of interest were metabolic equivalent of task (MET) hours per week from both active and sedentary activities. Age, gender, individual characteristics, household size, asset ownership, and urbanisation were included as covariates. Age, period and cohort effects analyses for PA and SB of children (6-17 y, n = 3528) was conducted to explicitly assess differences in PA and SB due to age vs. period effects, and implicitly assess differences by cohorts due to the period-specific experiences across individuals of varying ages.

RESULTS

The mean age of the sample in each time point fluctuated from 12.6 to 11.3 years and PA slightly decreased from 50.0 ± 63.2 MET hours per week (MET-hr./wk) in 2004 to 47.1 ± 54.9 MET-hr./wk. in 2011. However, SB increased from 31.8 ± 22.0 MET-hr./wk. to 37.6 ± 22.2 MET-hr./wk. Girls had lower PA and higher SB levels than boys. Controlling for age effects, marginal period effects on PA were observed in some survey years. Higher levels of urbanisation and number of household computers served as negative and positive predictors for PA and SB, respectively. Higher household income was a positive predictor of SB. Surprisingly, bigger household size was the only negative predictor of SB (P < 0.05).

CONCLUSIONS

This longitudinal study followed a large cohort of children over a significant period of their childhood. We observed potential age and secular trends in PA levels. Higher community urbanisation and number of home computers were associated with both PA and SB levels. Larger household size was the only factor that was negatively associated with SB. These findings shed light on health policy and preventative health strategies for China and other countries that are now facing similar public health challenges.

Factors of physical activity among Chinese children and adolescents: a systematic review

Background

Lack of physical activity is a growing problem in China, due to the fast economic development and changing living environment over the past two decades. The aim of this review is to summarize the factors related to physical activity in Chinese children and adolescents during this distinct period of development.

Methods

A systematic search was finished on Jan 10^th, 2017, and identified 2200 hits through PubMed and Web of Science. English-language published studies were included if they reported statistical associations between factors and physical activity. Adapted criteria from the Strengthening The Reporting of OBservational studies in Epidemiology (STROBE) statement and evaluation of the quality of prognosis studies in systematic reviews (QUIPS) were used to assess the risk of bias of the included studies. Related factors that were reported in at least three studies were summarized separately for children and adolescents using a semi-quantitative method.

Results

Forty two papers (published 2002–2016) were included. Most designs were cross-sectional (79%), and most studies used questionnaires to assess physical activity. Sample size was above 1000 in 18 papers (43%). Thirty seven studies (88%) showed acceptable quality by methodological quality assessment. Most studies reported a low level of physical activity. Boys were consistently more active than girls, the parental physical activity was positively associated with children and adolescents’ physical activity, children in suburban/rural regions showed less activity than in urban regions, and, specifically in adolescents, self-efficacy was positively associated with physical activity. Family socioeconomic status and parental education were not associated with physical activity in children and adolescents.

Conclusions

The studies included in this review were large but mostly of low quality in terms of study design (cross-sectional) and methods (questionnaires). Parental physical activity and self-efficacy are promising targets for future physical activity promotion programmes. The low level of physical activity raises concern, especially in suburban/rural regions. Future research is required to enhance our understanding of other influences, such as the physical environment, especially in early childhood.

Electronic supplementary material

The online version of this article (doi:10.1186/s12966-017-0486-y) contains supplementary material, which is available to authorized users.