Parent wellbeing, family screen time and socioeconomic status during early childhood predict physical activity of Aboriginal and Torres Strait Islander children at ages 8-13.

OBJECTIVES: Physical activity is holistically linked to culture and wellbeing among Aboriginal and Torres Strait Islander peoples, the First Nation Peoples of Australia. Socioecological correlates of high physical activity among Indigenous children include living in a remote area and low screen time but little is known about early life determinants of physical activity. This paper examines sociodemographic, family, community, cultural, parent social and emotional wellbeing determinants of physical activity among Aboriginal and Torres Strait Islander children. DESIGN: Longitudinal cohort study. METHODS: The Longitudinal Study of Indigenous Children, the largest First Nations child cohort study in the world, primarily collects data through parental report. Multiple logistic regression analyses examined Wave 1 (age 0-5 years) predictors of achieving ≥1 h/day of physical activity at Wave 9 (aged 8-13 years). RESULTS: Of the 1181 children, 596 (50.5 %) achieved ≥1 h of physical activity every day. Achieving ≥1 h/day of physical activity at Wave 9 was associated with the following Wave 1 determinants: high parent social and emotional wellbeing (resilience; adjusted odds ratio 1.87 (95 % confidence interval: 1.32-2.65)), living in remote (odds ratio 3.66 (2.42-5.54)), regional (odds ratio 2.98 (2.13-4.18)) or low socioeconomic areas (odds ratio 1.85 (1.08-3.17)), main source of family income not wages/salaries (odds ratio 0.66 (0.46-0.97)), and if families played electronic games (odds ratio 0.72 (0.55-0.94)). CONCLUSIONS: To achieve high physical activity levels among Aboriginal and Torres Strait Islander children, high parental culture specific social and emotional wellbeing and low family screen time in early life may compensate for apparently low socio-economic circumstances, including living in remote areas.

A Social Networking and Gamified App to Increase Physical Activity: Cluster RCT.

INTRODUCTION: Appealing approaches to increasing physical activity levels are needed. This study evaluated whether a social and gamified smartphone app (Active Team) could be one such approach. STUDY DESIGN: A 3-group cluster RCT compared the efficacy of Active Team with a basic self-monitoring app and waitlist control group. SETTING/PARTICIPANTS: Australian adults (N=444, mean age of 41 years, 74% female) were recruited in teams (n=121) and randomly assigned (1:1:1) to the Active Team (n=141, 39 teams), self-monitoring app (n=160, 42 teams), or waitlist group (n=143, 40 teams). Data were collected in 2016-2017, and analysis was conducted in 2018-2019. INTERVENTION: Active Team is a 100-day app-based, gamified, online social networking physical activity intervention. MAIN OUTCOME MEASURES: The primary outcome was change in objective physical activity from baseline to 3-month follow-up. Secondary outcomes included objective physical activity at 9 months and self-reported physical activity, quality of life, depression, anxiety and stress, well-being, and engagement. RESULTS: Mixed models indicated no significant differences in objective physical activity between groups at 3 (F=0.17, p=0.84; Cohen's d=0.03, 95% CI= -0.21, 0.26) or 9 months (F=0.23, p=0.92; d=0.06, 95% CI= -0.17, 0.29) and no significant differences for secondary outcomes of quality of life, depression, anxiety and stress, or well-being. Self-reported moderate-to-vigorous physical activity was significantly higher in the Active Team group at the 9-month follow-up (F=3.05, p=0.02; d=0.50, 95% CI=0.26, 0.73). Engagement was high; the Active Team group logged steps on an average of 72 (SD=35) days and used the social and gamified features an average of 89 (SD=118) times. CONCLUSIONS: A gamified, online social networking physical activity intervention did not change objective moderate-to-vigorous physical activity, though it did increase self-reported moderate-to-vigorous physical activity and achieve high levels of engagement. Future work is needed to understand if gamification, online social networks, and app-based approaches can be leveraged to achieve positive behavior change. TRIAL REGISTRATION: This study is registered at Australian and New Zealand Clinical Trial Registry (protocol: ANZCTR12617000113358).

Life on holidays: differences in activity composition between school and holiday periods in Australian children.

BACKGROUND: Recently, a small number of studies have suggested that gains in fitness and reductions in body fat achieved during the school term are reversed or stagnate during the holiday period. This may be associated with changed activity patterns. The aim of this study was to compare 24-h activity compositions between school and holiday periods in Australian children. METHODS: The participants in this study were 366 children (53% female, 13.4 ± 2.3 years) who were a subgroup of the 2007 Australian National Children's Nutrition and Physical Activity Survey. Each child recalled use of time on at least one school day, one weekend day and one holiday using the Multimedia Activity Recall for Children and Adults. Composite "in-term" and "holiday" use-of-time profiles were generated by weighting school days by 5, and weekends by 2 where data were available. Difference between holiday and in-term time use was assessed using a compositional multivariate linear model for repeated measures. Subsequent models tested for interaction between time of measurement and socio-economic status or body mass index. RESULTS: Time use was significantly different between holidays and in-term days (F = 103, p < 0.0001). On holidays, children accumulated 140 min less School-related time, compensated by sleeping 40 min longer, 58 min more Screen Time, and 35 min more Domestic/Social time. Children spent 10 min less in vigorous physical activity, and although sitting time was 33 min/day less during holidays, estimated total daily energy expenditure (TDEE) was 5.4% lower. Differences between holiday and in-term activity compositions did not vary by parental education (F = 1.2, p = 0.25), postcode-level socio-economic status (F = 0.9, p = 0.56) or weight status (F = 1.7, p = 0.07). CONCLUSIONS: In this subsample of a nationally representative survey of Australian children, holidays were characterised by longer sleep and higher TV and videogame time, lower vigorous activity and lower TDEE. Uncompensated by dietary adjustments, these differences would result in an accumulation of about 650 g of fat over a six-week holiday period. Holiday activity patterns may be a promising focus for obesity prevention efforts.

Association between breakfast frequency and physical activity and sedentary time: a cross-sectional study in children from 12 countries.

BACKGROUND: Existing research has documented inconsistent findings for the associations among breakfast frequency, physical activity (PA), and sedentary time in children. The primary aim of this study was to examine the associations among breakfast frequency and objectively-measured PA and sedentary time in a sample of children from 12 countries representing a wide range of human development, economic development and inequality. The secondary aim was to examine interactions of these associations between study sites. METHODS: This multinational, cross-sectional study included 6228 children aged 9-11 years from the 12 International Study of Childhood Obesity, Lifestyle and the Environment sites. Multilevel statistical models were used to examine associations between self-reported habitual breakfast frequency defined using three categories (breakfast consumed 0 to 2 days/week [rare], 3 to 5 days/week [occasional] or 6 to 7 days/week [frequent]) or two categories (breakfast consumed less than daily or daily) and accelerometry-derived PA and sedentary time during the morning (wake time to 1200 h) and afternoon (1200 h to bed time) with study site included as an interaction term. Model covariates included age, sex, highest parental education, body mass index z-score, and accelerometer waking wear time. RESULTS: Participants averaged 60 (s.d. 25) min/day in moderate-to-vigorous PA (MVPA), 315 (s.d. 53) min/day in light PA and 513 (s.d. 69) min/day sedentary. Controlling for covariates, breakfast frequency was not significantly associated with total daily or afternoon PA and sedentary time. For the morning, frequent breakfast consumption was associated with a higher proportion of time in MVPA (0.3%), higher proportion of time in light PA (1.0%) and lower min/day and proportion of time sedentary (3.4 min/day and 1.3%) than rare breakfast consumption (all p ≤ 0.05). No significant associations were found when comparing occasional with rare or frequent breakfast consumption, or daily with less than daily breakfast consumption. Very few significant interactions with study site were found. CONCLUSIONS: In this multinational sample of children, frequent breakfast consumption was associated with higher MVPA and light PA time and lower sedentary time in the morning when compared with rare breakfast consumption, although the small magnitude of the associations may lack clinical relevance. TRIAL REGISTRATION: The International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE) is registered at (Identifier NCT01722500 ).

Physical activity among indigenous Australian children and youth in remote and non-remote areas.

Sport and physical activity (PA) hold particular significance in Australian Indigenous communities, and have the potential to address many of the health and education challenges faced by Indigenous communities. Optimal levels of PA are an important foundation in efforts to build healthy communities and reduce social disadvantage experienced to date. Yet little evidence relating to the current levels of PA within these communities, or the relationship between PA and outcomes, has been available. Drawing on national survey data from the Australian Bureau of Statistics, we examine levels of PA in the Australian Aboriginal and Torres Strait Islander Health Survey 2012-13. These data describe PA levels among Indigenous Australians, aged 5-17 years, in remote and non-remote communities. We also examine the relationship between PA and participation in education and self-reported health among 15-17 year olds. Overall, participation rates appear to be high, with 64-84% of youth reporting at least 60 min of PA on the previous day. A gender gap was also evident, with lower levels of activity among girls. PA decreased with age, particularly at or around the age of puberty. There were no significant associations between PA and either self-reported health or engagement in study. There was a relationship between high PA and low area-level socio-economic status in remote areas, but no association in non-remote areas. The differences between remote and non-remote areas highlight the importance of disaggregated analysis of Indigenous populations and are consistent with qualitative studies identifying locally contextualised factors influential in promoting PA.

International variability in 20†m shuttle run performance in children and youth: who are the fittest from a 50-country comparison? A systematic literature review with pooling of aggregate results.

OBJECTIVES: To describe and compare 20 m shuttle run test (20mSRT) performance among children and youth across 50 countries; to explore broad socioeconomic indicators that correlate with 20mSRT performance in children and youth across countries and to evaluate the utility of the 20mSRT as an international population health indicator for children and youth. METHODS: A systematic review was undertaken to identify papers that explicitly reported descriptive 20mSRT (with 1-min stages) data on apparently healthy 9-17 year-olds. Descriptive data were standardised to running speed (km/h) at the last completed stage. Country-specific 20mSRT performance indices were calculated as population-weighted mean z-scores relative to all children of the same age and sex from all countries. Countries were categorised into developed and developing groups based on the Human Development Index, and a correlational analysis was performed to describe the association between country-specific performance indices and broad socioeconomic indicators using Spearman's rank correlation coefficient. RESULTS: Performance indices were calculated for 50 countries using collated data on 1 142 026 children and youth aged 9-17 years. The best performing countries were from Africa and Central-Northern Europe. Countries from South America were consistently among the worst performing countries. Country-specific income inequality (Gini index) was a strong negative correlate of the performance index across all 50 countries. CONCLUSIONS: The pattern of variability in the performance index broadly supports the theory of a physical activity transition and income inequality as the strongest structural determinant of health in children and youth. This simple and cost-effective assessment would be a powerful tool for international population health surveillance.

Associations of neighborhood social environment attributes and physical activity among 9-11 year old children from 12 countries.

We investigated whether associations of neighborhood social environment attributes and physical activity differed among 12 countries and levels of economic development using World Bank classification (low/lower-middle-, upper-middle- and high- income countries) among 9-11 year old children (N=6161) from the International Study of Childhood Obesity, Lifestyle, and the Environment (ISCOLE). Collective efficacy and perceived crime were obtained via parental/guardian report. Moderate-to-vigorous physical activity (MVPA) was assessed with waist-worn Actigraph accelerometers. Neighborhood environment by country interactions were tested using multi-level statistical models, adjusted for covariates. Effect estimates were reported by country and pooled estimates calculated across World Bank classifications for economic development using meta-analyses and forest plots. Associations between social environment attributes and MVPA varied among countries and levels of economic development. Associations were more consistent and in the hypothesized directions among countries with higher levels economic development, but less so among countries with lower levels of economic development.

The Canadian Assessment of Physical Literacy: Development of a Model of Children's Capacity for a Healthy, Active Lifestyle Through a Delphi Process.

BACKGROUND: The Canadian Assessment of Physical Literacy (CAPL) was conceptualized as a tool to monitor children's physical literacy. The original model (fitness, activity behavior, knowledge, motor skill) required revision and relative weights for calculating/interpreting scores were required. METHODS: Nineteen childhood physical activity/fitness experts completed a 3-round Delphi process. Round 1 was open-ended questions. Subsequent rounds rated statements using a 5-point Likert scale. Recommendations were sought regarding protocol inclusion, relative importance within composite scores and score interpretation. RESULTS: Delphi participant consensus was achieved for 64% (47/73) of statement topics, including a revised conceptual model, specific assessment protocols, the importance of longitudinal tracking, and the relative importance of individual protocols and composite scores. Divergent opinions remained regarding the inclusion of sleep time, assessment/ scoring of the obstacle course assessment of motor skill, and the need for an overall physical literacy classification. CONCLUSIONS: The revised CAPL model (overlapping domains of physical competence, motivation, and knowledge, encompassed by daily behavior) is appropriate for monitoring the physical literacy of children aged 8 to 12 years. Objectively measured domains (daily behavior, physical competence) have higher relative importance. The interpretation of CAPL results should be reevaluated as more data become available.

Use of time in people with chronic obstructive pulmonary disease--a systematic review.

"Physical inactivity" and "sedentary lifestyles" are phrases often used when describing lifestyles of people with chronic obstructive pulmonary disease (COPD). Evidence suggests activity types, independent of energy expenditure, influence health outcomes, so understanding patterns of time use is important, particularly in chronic disease. We aimed to identify reports of time use in people with COPD. Predefined search strategies were used with six electronic databases to identify individual activity reports (including frequencies and/or durations) in which community-dwelling people with COPD engaged. Eligible studies were assessed independently against predefined criteria and data were extracted by two reviewers. Data synthesis was achieved by aggregating activity reports into activity domains (sports/exercise, screen time, transport, quiet time, self-care, sociocultural, work/study, chores, and sleep). Twenty-six publications reported 37 specific daily activities. People with COPD were found to spend extended periods in sedentary behaviors (eg, standing [194 min/day]; sitting [359 min/day]; lying [88 min/day]), have limited engagement in physical activity (eg, walking [51 min/day]; exercising [1.2 episodes per week {ep/w}, 13 min/day]), have high health care needs (medical appointments [1.0 ep/w]), and experience difficulties associated with activities of daily living (eg, showering [2.5 ep/w, 60 minutes per episode]; preparing meals [4.7 ep/w]). Little data could be found describing how people with COPD use their time, and data synthesis was problematic because of variations in methodologies, population differences, and research emphases. Identified data largely referred to posture and were skewed according to country, assessment methods, and disease severity. Comparisons with age-matched population data showed people with COPD spent less time engaged in personal-care activities (self-care and sleeping) and chores than people in similar age groups. The incorporation of time-use outcomes in future research designs should be encouraged. Ideally, these tools should use consistent frameworks and comparable outcome measures in order to provide clearer descriptions of time use in chronic disease.

More than just physical activity: time use clusters and profiles of Australian youth.

OBJECTIVE: To describe time use clusters and correlate-cluster profiles of Australian youth. DESIGN: Secondary analysis of cross-sectional national survey. METHODS: Data were from the National Children's Nutrition and Physical Activity Survey, a random sample (n=1853) of 9-16 years old Australians (February-August 2007). Time use data were collected using the Multimedia Activity Recall for Children and Adults, and collapsed into 17 age-adjusted variables for sex-specific cluster analysis. Cluster associations with socio-demographic, anthropometric, health and dietary variables were analysed. RESULTS: For boys (n=930), the Social tasker cluster was characterised by social interaction and chores & work, the Techno-active cluster by team sport and TV and the Techno-studious cluster by video games and study. Average daily pedometer steps, age and remoteness were significant cluster correlates. For the girls (n=923), the Social screenie cluster was characterised by TV and social interaction, the Quiet actives cluster by quiet time and non-team sport and the Techno-studious cluster by video games and study. Pedometer steps, age, parental income and education, parent-child age difference, "extra foods", fat and fruit intakes were significant correlates. CONCLUSIONS: Distinct sex-specific time use clusters and profiles exist among Australian youth. These findings may assist the development of targeted time use interventions to improve health and well-being.

The place of physical activity in the time budgets of 10- to 13-year-old Australian children.

BACKGROUND: Low physical activity has been associated with increased fatness and deceased fitness. This observational study aimed to describe the magnitude, composition, and time-distribution of moderate-to-vigorous physical activity (MVPA) in Australian children. METHODS: A total of 1132 10 to 13 year old schoolchildren completed a 24-h activity recall diary on 2 to 4 occasions. MVPA was defined as any activity requiring ≥3METs, including sport, play, active transport, chores, and other activities. RESULTS: MVPA was higher in boys than girls (173 vs 140 min/day; P<.0001), higher on nonschool days than school days (166 vs 143 min/day; P<.0001), and decreased with age (9 min/day per year of age). MVPA consisted of structured sport (37%), active transport (26%), unstructured play (24%), and chores/miscellaneous activities (13%). Every hour of MVPA was associated with a reduction in screen time (26.5 min), non-screen-based sedentary pastimes (8 min), and sleep (5.5 min). The least active quartile of children were more likely to be girls (OR=3.4), have higher screen time, and sleep more. From 4:00-6:30 PM on school days there were large differences in participation between high-active and low-active children. CONCLUSION: Findings suggest MVPA interventions should target girls, screen time and focus on the after-school period.

Development and evaluation of an adult use-of-time instrument with an energy expenditure focus.

Measurement in behavioural epidemiology depends on high resolution and precise and accurate measures of the behaviour of interest. Few questionnaires in the adult population are able to simultaneously collect the multidimensional information that is emerging as being important in the relationship between behaviour and health. This project had two objectives: (1) to develop an adult version of the computer-delivered Multimedia Activity Recall for Children and Adolescents (MARCA), a 24-h activity recall instrument that can measure use-of-time and estimate energy expenditure and (2) to determine the test-retest reliability and convergent validity of the developed adult MARCA. Thirty-eight healthy subjects (mean±SD, 31.7±12.1 yr) completed two recalls of the adult MARCA within 24-h and accelerometer counts were measured on 30 of the subjects. Bland-Altman analysis and intraclass correlation coefficients (ICC) were used to quantify the test-retest reliability of the adult MARCA. Spearman rank correlation coefficients (rho) were used to quantify convergent validity of the adult MARCA compared to accelerometer counts. The test-retest reliability coefficients of the adult MARCA were high with intra-class coefficients ranging from 0.99 to 1.00. Moderate to strong validity was observed for physical activity level (PAL) (MET.min score of accelerometer wear time) and accelerometer counts per minute (rho=0.72). The adult MARCA is a valid and reliable self-report measure of use-of-time and energy expenditure, capable of a wide variety of flexible use-of-time analyses related to a wide range of behaviours.

How do school-day activity patterns differ with age and gender across adolescence?

PURPOSE: A knowledge of how young people use their time could be instrumental in informing health interventions, modeling consumer behaviors, and planning service delivery. The aim of the present study was to describe age- and gender-related patterns in the self-reported use of time on school days in a large sample of Australian children and adolescents aged between 10 and 18 years. METHODS: A single, detailed use-of-time diary for a school day was collected from 6024 Australians aged 10-18 from several state and regional surveys conducted in the states of South Australia (SA) and Victoria between 2001 and 2006. Time-use profiles were analyzed for a range of active and sedentary state behaviors. RESULTS: Boys reported higher physical activity levels (PALs), moderate-to-vigorous physical activity (MVPA), and sports than girls. There were no differences in free play, and girls used more active transport. All activity-related variables decreased with age, except active transport, which peaked at 14-15 years. Boys exhibited higher levels of screen time, whereas girls had higher levels of passive transport. Screen time and its components (television, videogames, and computer use) peaked in the peripubertal years. CONCLUSION: Age- and gender-related patterns of time use vary greatly within adolescence. This may reflect a mix of biological and social factors.

Development of a compendium of energy expenditures for youth.

BACKGROUND: This paper presents a Compendium of Energy Expenditures for use in scoring physical activity questionnaires and estimating energy expenditure levels in youth. METHOD/RESULTS: Modeled after the adult Compendium of Physical Activities, the Compendium of Energy Expenditures for Youth contains a list of over 200 activities commonly performed by youth and their associated MET intensity levels. A review of existing data collected on the energy cost of youth performing activities was undertaken and incorporated into the compendium. About 35% of the activity MET levels were derived from energy cost data measured in youth and the remaining MET levels estimated from the adult compendium. CONCLUSION: The Compendium of Energy Expenditures for Youth is useful to researchers and practitioners interested in identifying physical activity and energy expenditure values in children and adolescents in a variety of settings.

Assigning energy costs to activities in children: a review and synthesis.

PURPOSE: Compendia of energy costs are often used to assign energy expenditures (EE) to self-reported and observed activity. As there is a lack of data on the energy cost of children's everyday activities, adult values are often used as surrogates. However, the best way to adjust adult values for use with children remains unclear. Various strategies have been used to estimate rates of EE in children. METHODS: To evaluate these existing methods for assigning EE to children, a literature search reviewed all English-language studies that measured energy costs in healthy 6.0-17.9 yr olds using criterion EE measures. Data were combined using the Monte Carlo simulation procedure, with walking and running forming separate data sets. RESULTS: The resultant data set (excluding walking and running) contained 5592 data points encompassing 51 activities. Analyses revealed using adults METs, combined with child resting metabolic rates, as the best existing technique to assign EE to children when measured values are not available. Prediction equations for the energy cost of walking and running were calculated using multiple regression. CONCLUSION: This study has provided a literature base and analytical support for a compendium of energy costs for use with children with energy costs expressed as METs.

Worldwide variation in the performance of children and adolescents: an analysis of 109 studies of the 20-m shuttle run test in 37 countries.

This study is a meta-analysis of 109 reports of the performance of children and adolescents on the 20-m shuttle run test (20-mSRT). The studies were performed in 37 countries and included data on 418,026 children, tested between 1981 and 2003. Results were expressed as running speed (km x h(-1)) at the final completed stage of the 20-mSRT. Raw data were combined with pseudodata using Monte Carlo simulation. The 20-mSRT performances were expressed as z-scores relative to all children of the same age and sex from all countries. An overall "performance index" was derived for each country as the average of the age- and sex-specific z-scores for all children from that country. Factorial analysis of variance was used to compare scores among countries and regions, and between boys and girls of the same age. There was wide and significant (P < 0.0001) global variability in the performance of children. The best performing children were from the Northern European countries Estonia, Iceland, Lithuania, and Finland (0.6 - 0.9 standard deviations above the global average). The worst performing children were from Singapore, Brazil, USA, Italy, Portugal, and Greece (0.4 - 0.9 standard deviations below the global average). There is evidence that performance was negatively related to being overweight, as well as to a country's average temperature.

Screenieboppers and extreme screenies: the place of screen time in the time budgets of 10-13 year-old Australian children.

OBJECTIVES: Excessive 'screen time' has been associated with a range of psychosocial disturbances and increasing pediatric obesity. This study describes the magnitude, distribution, composition and time-distribution of children's screen use; examines correlates of screen use; and characterises 'extreme' screen users (top quartile). METHODS: 1,039 South Australian children aged 10-13 years old completed a multimedia 24-hour activity recall diary on 2-4 occasions in 2002, including at least one school day and one non-school day. RESULTS: The median screen time was 229 minutes.d(-1). This was higher in boys (264 vs. 196 minutes; p<0.001) and on non-school days (260 vs. 190 minutes; p<0.001), increased with age (p=0.003), and decreased with socio-economic status (SES; p=0.003). Television consumed 73% of all screen time, video games 19%, non-game computer use 6%, and cinema 2%. The top quartile of screen users were more likely to be boys (OR=3.8), have low physical activity (OR=4.3), spend >25% of screen time playing video games (OR=1.8), sleep less, and be of lower SES. CONCLUSIONS AND IMPLICATIONS: Interventions to reduce screen time should target inactive, low-SES boys, encourage earlier bedtimes, and limit video game use.

Secular trends in the performance of children and adolescents (1980-2000): an analysis of 55 studies of the 20m shuttle run test in 11 countries.

It is widely believed that the performance of children and adolescents on aerobic fitness tests is declining. To test this hypothesis, this meta-analysis compared the results of 55 reports of the performance of children and adolescents aged 6-19 years who have used the 20m shuttle run test (20mSRT). All data were collected in the period 1981-2000. Following corrections for methodological variation, the results of all studies were expressed using the common metric of running speed (km/h) at the last completed stage. Raw data were combined with pseudodata generated from reported means and standard deviations using Monte Carlo simulation. Where data were available on children and adolescents from the same country of the same age and sex, but tested at different times, linear regression was used to calculate rates of change. This was possible for 11 (mainly developed) countries, representing a total of 129,882 children and adolescents in 151 age x sex x country slices. There has been a significant decline in performance in the 11 countries where data were available, and in most age x sex groups, with a sample-weighted mean decline of 0.43% of mean values per year. The decline was most marked in older age groups and the rate of decline was similar for boys and girls. There has been a very rapid secular decline in the 20mSRT performance of children and adolescents over the last 20 years, at least in developed countries. The rate of decline is not related to the change in the country's relative wealth, as quantified by per capita gross domestic product (GDP).