Physical activity intervention improves executive function and language development during early childhood: The active early learning cluster randomized controlled trial.

This study aimed to determine the effects of the Active Early Learning (AEL) childcare center-based physical activity intervention on early childhood executive function and expressive vocabulary via a randomized controlled trial. Three-hundred-and-fourteen preschool children (134 girls) aged 3-5 years from 15 childcare centers were randomly assigned to the intervention (8 centers; n = 170 children) or control group (7 centers, n = 144 children) in May 2019. Participants were mostly Australian (85%) and from slightly higher areas of socio-economic status than the Australian average. There was an AEL intervention effect on inhibition (ß = 0.5, p = .033, d = 0.29) and expressive vocabulary (ß = 1.97, p = .001, d = 0.24). Integration of the AEL physical activity intervention into the daily childcare routine was effective in enhancing children's executive function and expressive language development.

The effect of height on estimates of the change in BMI-based prevalence of childhood obesity.

BACKGROUND/OBJECTIVES: Body mass index (BMI, body mass/height2) is biased toward height in children. Here we investigate how change in population height affected change in BMI-based estimates of the prevalence of overweight and obesity in Australian children. SUBJECTS/METHODS: Height, weight, and percent body fat (%BF) were measured at ages 8, 10, and 12 years (1855 sets of measures). Age-specific relationships between BMI and height were derived, adjusting for %BF, to estimate the degree of height bias inherent in BMI. Then, from cross-sectional measurements recorded in 1985 (N = 2388) and 1995 (N = 2148) in 8, 10, and 12 year olds, changes in overweight/obesity prevalences were calculated before and after accounting for the BMI-height bias. RESULTS: Estimates of the effect of height on BMI following adjustment for %BF were similar across age groups and all were significant at p < 0.001. Referring to 12 year olds, at the same %BF for a 1% increase in height there was 0.77% (95% CI 0.55, 0.99) increase in BMI in boys, and 0.74% (0.28, 1.02) increase in girls. Between 1985 and 1995, mean height of 12-year-old boys and girls increased 3.9 and 3.2 cm, respectively. In 1985 unadjusted prevalences of combined overweight/obesity in boys and girls were 13.5% and 13.0%, respectively, and in 1995 were 24% and 24.5%. The latter values were reduced to 21.6% and 22.6% after adjusting for increased height. CONCLUSIONS: Previously reported increases in childhood overweight/obesity in Australia between 1985 and 1995 were likely to be moderately overestimated as a result of increased population height; suggesting that population height be taken into account in any pediatric investigation of changes in overweight/obesity prevalence over time.

Impact of cultural background on fundamental movement skill and its correlates.

Children's fundamental movement skill levels (FMS) predict moderate-to-vigorous physical activity (MVPA). Asian children have been reported as less active than English-Europeans, possibly due to poorer skills. This study compared the FMS of children from Culturally and Linguistically Diverse (CALD) backgrounds and examined FMS correlates. A total of 261 children (122 males) aged 9-to-11 years were divided based on language spoken at home: English-European (n = 105) and Asian (n = 156). Height, mass, FMS (Test of Gross Motor Development-2), MVPA (accelerometer) and cardio-respiratory fitness (20m multistage shuttle run) were directly measured. Sex, age, language and perceived sport competence (CY-PSPP) were self-reported. Independent sample t-tests assessed age, BMI, FMS and perception by CALD group. Linear mixed models examined FMS correlates. Asian-speaking children had lower object control skill (35.5 v 37.2; CI [0.17, 3.18]; p < 0.03) compared to English-European- children, but no between-group differences in locomotor skills were observed. Fitness, physical activity and sport competence perception were positively associated with object control, yet adjusting for these variables (and age and BMI) did not remove the CALD effect (B = -2.02, SE = 0.69, p = 0.004). Cultural factors may affect object control competence in Asian-Australian children.

Effects of Habitual Physical Activity and Fitness on Tibial Cortical Bone Mass, Structure and Mass Distribution in Pre-pubertal Boys and Girls: The Look Study.

Targeted weight-bearing activities during the pre-pubertal years can improve cortical bone mass, structure and distribution, but less is known about the influence of habitual physical activity (PA) and fitness. This study examined the effects of contrasting habitual PA and fitness levels on cortical bone density, geometry and mass distribution in pre-pubertal children. Boys (n = 241) and girls (n = 245) aged 7-9 years had a pQCT scan to measure tibial mid-shaft total, cortical and medullary area, cortical thickness, density, polar strength strain index (SSIpolar) and the mass/density distribution through the bone cortex (radial distribution divided into endo-, mid- and pericortical regions) and around the centre of mass (polar distribution). Four contrasting PA and fitness groups (inactive-unfit, inactive-fit, active-unfit, active-fit) were generated based on daily step counts (pedometer, 7-days) and fitness levels (20-m shuttle test and vertical jump) for boys and girls separately. Active-fit boys had 7.3-7.7 % greater cortical area and thickness compared to inactive-unfit boys (P < 0.05), which was largely due to a 6.4-7.8 % (P < 0.05) greater cortical mass in the posterior-lateral, medial and posterior-medial 66 % tibial regions. Cortical area was not significantly different across PA-fitness categories in girls, but active-fit girls had 6.1 % (P < 0.05) greater SSIpolar compared to inactive-fit girls, which was likely due to their 6.7 % (P < 0.05) greater total bone area. There was also a small region-specific cortical mass benefit in the posterior-medial 66 % tibia cortex in active-fit girls. Higher levels of habitual PA-fitness were associated with small regional-specific gains in 66 % tibial cortical bone mass in pre-pubertal children, particularly boys.

Outcomes of a four-year specialist-taught physical education program on physical activity: a cluster randomized controlled trial, the LOOK study.

BACKGROUND: The objective of this study was to investigate the effect of a 4-year specialist-taught Physical Education (PE) program on physical activity (PA) among primary school children. METHODS: A 4-year cluster randomised controlled trial was conducted in children (initially aged 8 years) from 29 primary schools (13 Intervention, 16 Control). Intervention students (N = 457) received 2 × 45 min PE lessons per week from specialist-trained PE teachers (68 lessons per year, 272 lessons over 4 years). Control group students (N = 396) received usual practice PE from generalist classroom teachers. PA during PE lessons was examined using the System for Observing Fitness Instruction Time (SOFIT). Pedometers (steps/day) were worn for 7 days each year, and accelerometers were worn concurrently in the final two years to assess moderate to vigorous (MVPA) and sedentary activity. Linear and generalized mixed models were used to determine differences in Intervention and Control student PA and the proportion of students meeting PA guidelines. RESULTS: The intervention increased SOFIT-observed student MVPA during PE lessons by 6.5 mins (16.7 v 10.2, p < 0.001). Within intervention schools, participants increased their whole-day step counts (boys = 449 [CI,140 to 756]; girls = 424 [CI,222 to 626]) and minutes of MVPA (boys = 8.0 [CI,6.8 to 9.2]; girls = 3.5 [CI,1.7 to 5.4]) on PE days. However, compared to the Control group the Intervention did not: increase habitual steps/day or MVPA when averaged over 7 days; elicit greater improvements in these measures over time; or increase the odds of meeting step/day or MVPA recommendations. At age 11 years Intervention group boys were 20 mins less sedentary per day (380 [CI,369 to 391] vs 360 [CI,350 to 369]) and this effect was sustained at age 12 years. CONCLUSIONS: Well-designed specialist-taught PE can improve student PA during PE lessons. However for PE to be a significant contributor to improving habitual PA in pre-adolescent children, daily classes are likely to be required, and even this would need to be supplemented with a wider multicomponent strategy. Our finding of a reduction in sedentary time among Intervention boys warrants further investigation into the potential role PE could play in influencing sedentary behaviour.

Longitudinal patterns of physical activity in children aged 8 to 12 years: the LOOK study.

BACKGROUND: Data on longitudinal monitoring of daily physical activity (PA) patterns in youth over successive years is scarce but may provide valuable information for intervention strategies aiming to promote PA. METHODS: Participants were 853 children (starting age ~8 years) recruited from 29 Australian elementary schools. Pedometers were worn for a 7-day period each year over 5 consecutive years to assess PA volume (steps per day) and accelerometers were worn concurrently in the final 2 years to assess PA volume (accelerometer counts (AC) per day), moderate and vigorous PA (MVPA), light PA (LPA) and sedentary time (SED). A general linear mixed model was used to examine daily and yearly patterns. RESULTS: A consistent daily pattern of pedometer step counts, AC, MVPA and LPA emerged during each year, characterised by increases on school days from Monday to Friday followed by a decrease on the weekend. Friday was the most active and Sunday the least active day. The percentage of girls and boys meeting international recommendations of 11,000 and 13,000 steps/day respectively on a Monday, Friday and Sunday were 36%, 50%, 21% for boys and 35%, 45%, 18% for girls. The equivalent percentages meeting the recommended MVPA of >60 min/day on these days were 29%, 39%, 16% for boys and 15%, 21%, 10% for girls. Over the 5 years, boys were more active than girls (mean steps/day of 10,506 vs 8,750; p<0.001) and spent more time in MVPA (mean of 42.8 vs 31.1 min/day; p<0.001). Although there was little evidence of any upward or downward trend in steps/day from age 8 to 12 years, there was a trend toward lower MVPA, LPA and a corresponding increase in SED from age 11 to 12 years. CONCLUSION: A weekly pattern of PA occurred in children as young as age 8 on a day by day basis; these patterns persisting through to age 12. In addition to supporting previous evidence of insufficient PA in children, our data, in identifying the level and incidence of insufficiency on each day of the week, may assist in the development of more specific strategies to increase PA in community based children.

Physical education, obesity, and academic achievement: a 2-year longitudinal investigation of Australian elementary school children.

OBJECTIVES: We determined whether physical education (PE) taught by specialists contributed to academic development and prevention of obesity in elementary school children. METHODS: Our 2-year longitudinal study involved 620 boys and girls initially in grade 3 in Australia, all receiving 150 minutes per week of PE. One group (specialist-taught PE; n = 312) included 90 minutes per week of PE from visiting specialists; the other (common-practice PE; n = 308) received all PE from generalist classroom teachers. Measurements included percentage of body fat (measured by dual-emission x-ray absorptiometry) and writing, numeracy, and reading proficiency (by government tests). RESULTS: Compared with common-practice PE, specialist-taught PE was associated with a smaller increase in age-related percentage of body fat (P = .02). Specialist-taught PE was also associated with greater improvements in numeracy (P < .03) and writing (P = .13) scores. There was no evidence of a reading effect. CONCLUSIONS: The attenuated age-related increases in percentage of body fat and enhanced numeracy development among elementary school children receiving PE from specialists provides support for the role of PE in both preventive medicine and academic development.

Schools with fitter children achieve better literacy and numeracy results: evidence of a school cultural effect.

Relationships of academic achievement (government tests) with physical fitness (multistage run), physical activity (pedometers) and percent body fat (dual emission X-ray absorptiometry) were examined at both the aggregate school level and the individual child level using data collected from 757 children in 29 elementary schools. Statistical adjustments included gender, grade and socioeconomic status. Between-school relationships of the academic scores with fitness and physical activity were strong and positive, with some evidence of (negative) relationships with percent body fat. The between-child relationships were weaker, and nonexistent with percent body fat. Stronger between-school than between-child relationships favor the argument that variation in school cultures, characterized by concurrent attention to fitness and academic achievement, might play a more dominant role in explaining these relationships than any direct effect of fitness on academic achievement.

The effect of a 6-month physical literacy intervention on preschool children's gross and fine motor skill: The Active Early Learning randomised controlled trial.

OBJECTIVES: The Active Early Learning intervention was designed to support childcare educators to imbed physical literacy promoting activities into the daily childcare curriculum. The objective of this study was to determine whether this physical literacy intervention had any influence on motor skill development. DESIGN: 22-week stratified cluster randomised controlled trial. METHODS: Fifteen childcare centres (8 intervention, 7 control centres; 314 children, 180 boys, 4.3y ±â€¯0.4) participated in the study. Six motor skills were assessed: object control (ball drop/catch and bean bag throw accuracy), locomotor control (10 m shuttle run), stability (one-leg balance and tiptoe walking on a line), and fine motor control (coin manipulation). Intervention effects were evaluated using linear mixed models adjusted for age, sex, socio-economic status, and centre clustering. RESULTS: There was evidence for an intervention effect on fine motor control (-0.47 s, CI [-0.93 to -0.02], p = .041) and the ball drop/catch task (0.68, CI [0.01-1.35], p = .046), but not for locomotor control, stability, or throw accuracy. CONCLUSIONS: Improvements in children's gross and fine motor skills can be achieved with a physical literacy intervention delivered by childcare educators. However, broad enhancement of motor skills cannot be assumed by simply introducing more physical literacy promoting activities into the daily routine, and specific motor skill instruction seems warranted in childcare settings.

Using compositional data analysis to explore accumulation of sedentary behavior, physical activity and youth health.

PURPOSE: The study aimed to describe youth time-use compositions, focusing on time spent in shorter and longer bouts of sedentary behavior and physical activity (PA), and to examine associations of these time-use compositions with cardiometabolic biomarkers. METHODS: Accelerometer and cardiometabolic biomarker data from 2 Australian studies involving youths 7-13 years old were pooled (complete cases with accelerometry and adiposity marker data, n = 782). A 9-component time-use composition was formed using compositional data analysis: time in shorter and longer bouts of sedentary behavior; time in shorter and longer bouts of light-, moderate-, or vigorous-intensity PA; and "other time" (i.e., non-wear/sleep). Shorter and longer bouts of sedentary time were defined as <5 min and ≥5 min, respectively. Shorter bouts of light-, moderate-, and vigorous-intensity PA were defined as <1 min; longer bouts were defined as ≥1 min. Regression models examined associations between overall time-use composition and cardiometabolic biomarkers. Then, associations were derived between ratios of longer activity patterns relative to shorter activity patterns, and of each intensity level relative to the other intensity levels and "other time", and cardiometabolic biomarkers. RESULTS: Confounder-adjusted models showed that the overall time-use composition was associated with adiposity, blood pressure, lipids, and the summary score. Specifically, more time in longer bouts of light-intensity PA relative to shorter bouts of light-intensity PA was significantly associated with greater body mass index z-score (zBMI) (ß = 1.79; SE = 0.68) and waist circumference (ß = 18.35, SE = 4.78). When each activity intensity was considered relative to all higher intensities and "other time", more time in light- and vigorous-intensity PA, and less time in sedentary behavior and moderate-intensity PA, were associated with lower waist circumference. CONCLUSION: Accumulating PA, particularly light-intensity PA, in frequent short bursts may be more beneficial for limiting adiposity compared to accumulating the same amount of PA at these intensities in longer bouts.

Heart rate variability improves in 3-5-year-old children following a 6-month physical activity-based intervention: the Active Early Learning (AEL) cluster randomised controlled trial.

Heart rate variability (HRV) measurement provides non-invasive assessment of autonomic stability and cardiometabolic disease risk. Insufficient physical activity in early childhood may contribute to negative cardiometabolic health. The Active Early Learning (AEL) study was a 6-month randomised controlled trial investigating the effects of a physical activity-based program incorporating movement within the daily curriculum of preschool children. The current study assessed the effects of the AEL intervention on HRV as a measure of cardiac vagal control. Children aged between 3-5 years and enrolled in a preschool with an attendance of ≥15 children were eligible. Physical activity was recorded using an Actigraph wGT3x accelerometer worn at the waist of participants over 3 consecutive days. A Polar H10 chest strap measured HRV with the HF-band and RMSSD representing cardiac vagal control. After 6 months of the AEL trial, linear mixed model analyses revealed a significant intervention effect for increased HF (p = 0.044). The control group did not demonstrate changes in cardiac vagal control after the intervention ceased. Independent of age, sex, physical activity and BMI, the AEL study elicited significant improvements in the cardiac vagal control of participants who received the intervention. Findings highlight the importance of investigating HRV for assessing the cardiometabolic health in young children. ANZCTR trial registration number: ACTRN12619000638134. Novelty: The AEL curriculum improved child HRV independent of age, sex, physical activity and BMI. Heart rate and RR intervals did not demonstrate changes for the intervention and control groups. Multivariate programs for developing physical competence, confidence, knowledge and motivation may improve child health.

Relationship between heart rate variability and body mass index: A cross-sectional study of preschool children.

Reduced heart rate variability (HRV) is associated with overweight and obesity in adults. However, little is known about this relationship in early childhood. We investigated the relationship between resting vagally-mediated HRV and body mass index (BMI) in Australian preschool children. Children were recruited from 13 non-government early learning centres located in Queensland and New South Wales, Australia. From this population-based sample, data from 146 healthy children (58 females) between 3 and 5 years of age (mean age 4.35 ± 0.44 years) were analysed. BMI was calculated from child body weight and height. Physical activity was recorded using an Actigraph wGT3x accelerometer worn at the waist of participants over 3 consecutive days. A Polar H10 chest strap measured seated, resting RR intervals for the calculation of HRV with the root mean square of successive differences (RMSSD) reflecting vagally-mediated activity. The relationship between HRV and BMI was analysed using a linear mixed model adjusted for age, sex and physical activity. Analysis revealed that RMSSD (ln) demonstrated a significant inverse relationship with BMI (ß = -0.06; 95% CI = -0.12 - -0.01; p = 0.032), and the model accounted for 23% of the variance in RMSSD (ln). Notably, a one unit increase in BMI resulted in a reduction in RMSDD (ln) of 0.06. This investigation demonstrated evidence for a significant inverse linear relationship between vagally-mediated HRV and BMI in 3 - 5-year-old Australian children, similar to that of adults. Furthermore, this relationship was independent of age, sex and physical activity levels. Results may indicate that the cardiometabolic health of preschool children is, in part, influenced by the relationship between vagally-mediated HRV and weight status.

Child and Parent Physical Activity, Sleep, and Screen Time During COVID-19 and Associations With Mental Health: Implications for Future Psycho-Cardiological Disease?

The COVID-19 pandemic has afforded the opportunity for some to improve lifestyle behaviours, while for others it has presented key challenges. Adverse changes in global lifestyle behaviours, including physical activity, sleep, and screen time can affect proximal mental health and in turn distal cardiovascular outcomes. We investigated differences in physical activity, sleep, and screen time in parents and children during early stages of the COVID-19 pandemic in Australia compared to pre-COVID-19 national data; and estimated associations between these movement behaviours with parent and child mental health. Cross-sectional baseline data from the COVID-19 Pandemic Adjustment Study (CPAS; N = 2,365) were compared to nationally representative pre-pandemic data from the Longitudinal Study of Australian Children (LSAC; N = 9,438). Participants were parents of children aged ≤ 18 years, residing in Australia. Parents provided self-report measures of mental health, physical activity and sleep quality, and reported on child mental health, physical activity and screen time. Children in CPAS had significantly more sleep problems and more weekend screen time. Their parents had significantly poorer sleep quality, despite increased weekly physical activity. Children's sleep problems were significantly associated with increased mental health problems, after accounting for socioeconomic status, physical activity, and screen time. Poorer parent sleep quality and lower levels of physical activity were significantly associated with poorer mental health. Monitoring this cohort over time will be important to examine whether changes in movement behaviour are enduring or naturally improve with the easing of restrictions; and whether these changes have lasting effects on either parent or child mental health, and in turn, future risk for CVD.

Depression, stress and vascular function from childhood to adolescence: A longitudinal investigation.

BACKGROUND: Psychological distress is associated with risk markers for cardiovascular disease, including increased arterial stiffness and high blood pressure, but it's unclear when these first manifest. This study aims to investigate the effect of psychosocial stress and depression on arterial stiffness and blood pressure in a cohort study of Australian children followed through to adolescence. METHOD: Depression and psychosocial stress in 520 young people (265 boys; M age = 11.6 y) were assessed via the Children's Depression Inventory and Children's Stress Questionnaire respectively. Carotid-femoral pulse wave velocity was assessed using applanation tonometry, with further assessments of supine brachial blood pressure and percent body fat (dual x-ray absorptiometry). All measures were repeated four years later at age 16-years. RESULTS: We found no cross-sectional or longitudinal evidence that children self-reporting higher levels of psychosocial stress or depressive symptoms had greater arterial stiffness. Children reporting an increase in depressive symptoms had an increase in diastolic blood pressure and mean arterial pressure over time. An effect was also evident for pulse pressure, where higher pulse pressure was found in children with lower psychosocial stress at baseline and in children self-reporting a decrease in stress between baseline and follow-up. CONCLUSIONS: Findings from the current study contribute to the scant paediatric literature but only provide limited support for any influence of psychological factors on blood pressure. Depressive symptoms in apparently healthy adolescents may exert some influence on later risk for cardiovascular disease via increases in diastolic blood pressure and mean arterial pressure, but these effects were small.

Cross-Sectional Associations of Total Daily Volume and Activity Patterns across the Activity Spectrum with Cardiometabolic Risk Factors in Children and Adolescents.

Sedentary and physical activity patterns (bouts/breaks) may be important for cardiometabolic health in early life. This study aimed to examine cross-sectional associations of total daily volume and patterns across the activity spectrum with cardiometabolic risk factors in youth aged 7-13 years. Objectively measured accelerometer and cardiometabolic risk factor data were pooled from two studies (n = 1219; 69% valid accelerometry). Total daily volume of sedentary time and light-, moderate-, and vigorous-intensity physical activity was determined. Time in sustained bouts and median bout lengths of all intensities and breaks in sedentary time were also calculated. Outcomes included body mass index, waist circumference, blood pressure, blood lipids, and a cardiometabolic summary score. Regression models revealed beneficial associations between total daily volumes of moderate- and vigorous-intensity physical activity and cardiometabolic risk. Time spent in ≥1 min vigorous-intensity physical activity bouts was beneficially associated with cardiometabolic risk, yet this disappeared after adjusting for total vigorous-intensity physical activity and confounders. Time accumulated in light- (≥1 min; ≥5 min) and moderate-intensity (≥1 min) physical activity bouts was detrimentally associated with cardiometabolic risk. Total daily volume and activity patterns may have implications for cardiometabolic risk early in life. Sporadic physical activity may be more beneficial for health than sustained physical activity.

Activity Accumulation and Cardiometabolic Risk in Youth: A Latent Profile Approach.

INTRODUCTION: This cross-sectional study aimed to i) identify and characterize youth according to distinct physical activity (PA) and sedentary (SED) accumulation patterns, and ii) investigate associations of these derived patterns with cardiometabolic risk factors. METHODS: ActiGraph accelerometer data from 7- to 13-yr-olds from two studies were pooled (n = 1219; 843 (69%) with valid accelerometry included in analysis). Time accumulated in ≥5- and ≥10-min SED bouts, ≥1- and ≥5-min bouts of light, and ≥1-min bouts of moderate and vigorous PA was calculated. Frequency of breaks in SED was also obtained. Latent profile analysis was used to identify groups of participants based on their distinct accumulation patterns. Linear and logistic regression models were used to test associations of group accumulation patterns with cardiometabolic risk factors, including adiposity indicators, blood pressure, and lipids. Total PA and SED time were also compared between groups. RESULTS: Three distinct groups were identified: "prolonged sitters" had the most time in sustained SED bouts and the least time in vigorous PA bouts; "breakers" had the highest frequency of SED breaks and lowest engagement in sustained bouts across most PA intensities; and "prolonged movers" had the least time accumulated in SED bouts and the most in PA bouts across most intensities. Although breakers engaged in less time in PA bouts compared with other groups, they had the healthiest adiposity indicators. No associations with the remaining cardiometabolic risk factors were found. CONCLUSION: Youth accumulate their daily activity in three distinct patterns (prolonged sitters, breakers, and prolonger movers), with those breaking up sitting and least time in prolonged PA bouts across the day having a lower adiposity risk. No relationships with other cardiometabolic risk factors were identified.

Contrasting longitudinal and cross-sectional relationships between insulin resistance and percentage of body fat, fitness, and physical activity in children-the LOOK study.

BACKGROUND: Knowledge of individual changes in insulin resistance (IR) and longitudinal relationships of IR with lifestyle-associated factors are of important practical significance, but little longitudinal data exist in asymptomatic children. We aimed to determine (a) changes in the homeostatic model of insulin resistance (HOMA-IR) over a 2-yr period and (b) comparisons of longitudinal and cross-sectional relationships between HOMA-IR and lifestyle-related risk factors. METHODS: Our subjects, 241 boys and 257 girls, were assessed at age 8.1 yr (SD 0.35) and again 2 yr later for fasting blood glucose and insulin, dual X-ray absorptiometry-assessed percentage of body fat (%BF), pedometer-assessed physical activity (PA), and cardio-respiratory fitness (CRF) by multistage running test. RESULTS: HOMA-IR was initially 9% greater in girls than boys and 27% greater 2 yr later. There was no evidence of longitudinal relationships between HOMA-IR and %BF in boys or girls, despite significant cross-sectional relationships (p < 0.001). In boys, there was evidence of a longitudinal relationship between HOMA-IR and both PA (p < 0.001) and CRF (p = 0.05). In girls, we found a cross-sectional relationship between HOMA-IR and CRF (p < 0.001). CONCLUSIONS: HOMA-IR increases between 8 and 10 yr of age and to a greater extent in girls. Longitudinal, unlike cross-sectional, relationships do not support the premise that body fat has any impact on HOMA-IR during this period or that PA or CRF changes affect HOMA-IR in girls. These data draw attention to difficulties in interpreting observational studies in young children.

The lifestyle of our kids (LOOK) project: outline of methods.

This methods paper outlines the overall design of a community-based multidisciplinary longitudinal study with the intent to stimulate interest and communication from scientists and practitioners studying the role of physical activity in preventive medicine. In adults, lack of regular exercise is a major risk factor in the development of chronic degenerative diseases and is a major contributor to obesity, and now we have evidence that many of our children are not sufficiently active to prevent early symptoms of chronic disease. The lifestyle of our kids (LOOK) study investigates how early physical activity contributes to health and development, utilizing a longitudinal design and a cohort of eight hundred and thirty 7-8-year-old (grade 2) school children followed to age 11-12 years (grade 6), their average family income being very close to that of Australia. We will test two hypotheses, that (a) the quantity and quality of physical activity undertaken by primary school children will influence their psychological and physical health and development; (b) compared with existing practices in primary schools, a physical education program administered by visiting specialists will enhance health and development, and lead to a more positive perception of physical activity. To test the first hypothesis we will monitor all children longitudinally over the 4 years. To test the second we will involve an intervention group of 430 children who receive two 50min physical education classes every week from visiting specialists and a control group of 400 who continue with their usual primary school physical education with their class-room teachers. At the end of grades 2, 4, and 6 we will measure several areas of health and development including blood risk factors for chronic disease, cardiovascular structure and function, physical fitness, psychological characteristics and perceptions of physical activity, bone structure and strength, motor control, body composition, nutritional intake, influence of teachers and family, and academic performance.

Day-dependent step-count patterns and their persistence over 3 years in 8-10-year-old children: the LOOK project.

BACKGROUND: Physical activity in children is known to be generally lower at weekends but whether systematic day-to-day differences exist throughout the week is unclear. AIM: To determine if weekly patterns of pedometer-assessed physical activity (PPA) exist in elementary school-aged Australian boys and girls and whether they persist over 3 years. SUBJECTS AND METHODS: Seven-day pedometer measurements were recorded from 389 boys and 387 girls of initial age 8.0 (SD 0.3) in three successive years during spring. General linear mixed modelling was used to investigate patterns and the persistence of PPA. RESULTS: A pattern did emerge, significant differences in PPA occurring between certain days of the week (p<0.001). This pattern was similar in each year, PPA increasing from Monday through to Friday, decreasing on Saturday and again on Sunday. PPA was greater in boys (p<0.001), but less so on weekends. Significant day-to-day and year-to-year intra-class correlations of PPA (0.14 and 0.29, respectively, both p<0.001)) within individuals provided evidence of tracking on a daily basis, and to a lesser extent yearly. CONCLUSIONS: A well-defined week-long pattern of steps/day emerged in these 8-10-year-old children, the pattern being similar in three consecutive years.

BMI is a misleading proxy for adiposity in longitudinal studies with adolescent males: The Australian LOOK study.

OBJECTIVES: Despite evidence suggesting caution, employment of body mass index (BMI, kgm-2) as a proxy for percentage of body fat (PFat) in longitudinal studies of children and adolescents remains commonplace. Our objective was to test the validity of change in BMI as a proxy for change in PFat measured by dual-energy X-ray absorptiometry (DXA) during adolescence. DESIGN: Longitudinal study. METHODS: Healthy, predominantly Australian youth of mainly Caucasian background (131 females and 115 males) underwent repeated measures at 12.0 (SD 0.3) and 16.0 (SD 0.3) years for height, weight and PFat (DXA). RESULTS: There was no significant difference in the percentage changes in BMI and PFat for the females (ß=2.45, standard error (SE)=1.39, 95% confidence interval (CI)=[-0.27; 5.17]) with their mean BMI increasing 15% as their mean PFat increased 18%. However, for the males, while their mean BMI also increased 15%, their mean PFat was reduced 25%; this change being highly significant (ß=-42.25, SE=2.23, 95% CI=[-46.22, -38.27]). CONCLUSIONS: While change in BMI is likely to be a rough proxy for change in PFat measured by DXA in longitudinal studies of adolescent females, this is not the case for adolescent males, where increased BMI is likely to correspond with decreased PFat. Consequently, inferences from longitudinal studies of adolescents which have assumed that an increase in BMI (or BMI Z-scores or percentiles) represents an increase in adiposity require reconsideration.