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 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.

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.

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.

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.

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.

Drivers of adolescent adiposity: Evidence from the Australian LOOK study.

OBJECTIVES: To contribute to our understanding of the drivers of body composition during adolescence we sought to employ valid and reliable measures to investigate cross-sectional and longitudinal relationships between percentage body fat (%BF) and physical activity (PA), moderate and vigorous PA (MVPA), sedentary time (ST), total energy, sugar and fat intake. DESIGN: Longitudinal cohort study. METHODS: We measured 556 (289 male) participants at age 12.4 (SD 0.4) years, and 269 (123 males) at 16.3 (SD 0.4) years, for %BF (dual energy X-ray absorptiometry); habitual PA, MVPA, ST (accelerometry); and dietary intake ('multi-pass' weekday and weekend 24-h recall). Accounting for likely under-reporting of energy intake (Goldberg cut-off), general linear mixed modelling was used to generate relationships with %BF. RESULTS: Cross-sectional analyses indicated that 10min more MVPA per day was associated with 0.6 lower %BF (95%CI 0.4-0.9, p<0.001), and 10min less ST/day with 0.07 lower %BF (95%CI 0.00-0.15, p<0.001), independently of PA. In contrast, %BF was unrelated to total energy (p=0.4), sugar intake (p=0.2) or fat intake (p=0.9). Longitudinal analysis showed that if PA was increased by 3% (10,000 counts/day) over the 4 years, then %BF was reduced by 0.08 (95%CI 0.05-0.12, p=0.06). CONCLUSIONS: The independent relationships of %BF with PA and ST, but absence of relationships with energy, sugar or fat intake, suggest that general community campaigns in a developed country directed at reducing adolescent obesity through modifications to energy intake and output would benefit from a more concerted focus on the latter.

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.

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.

Symptoms of stress and depression effect percentage of body fat and insulin resistance in healthy youth: LOOK longitudinal study.

OBJECTIVE: This study examined the longitudinal and cross-sectional effects of both psychosocial stress and depressive symptoms on insulin resistance and percentage body fat in a cohort of healthy Australian children, following them from childhood into adolescence. METHOD: Participants were 791 healthy, initially Grade 2 children (7-8 years; 394 girls), selected from the general community. Psychosocial stress was assessed using the Children's Stress Questionnaire, while depressive symptoms were assessed using the Children's Depression Inventory. Fasting blood samples for serum insulin and plasma glucose were collected to calculate the homeostasis model assessment-insulin resistance (HOMA-IR). Other measurements were height, weight, percentage body fat (dual energy x-ray absorptiometry), physical activity (pedometers), and pubertal maturation (Tanner score). RESULTS: Boys who reported more symptoms of depression had higher insulin resistance, irrespective of adiposity (p = .016); and longitudinally, we found a trend for boys who developed more depressive symptoms to develop higher insulin resistance (p = .073). These findings did not extend to girls. Furthermore, boys and girls with higher depressive symptoms had a higher percentage of body fat (p = .011 and .020, respectively); and longitudinally, boys whose depressive symptoms increased became fatter (p = .046). CONCLUSION: Our data provide evidence that early symptoms of depression increase insulin resistance, independent of adiposity. Our evidence that early symptoms of depression may lead to overweight, and obesity provides further reason to suggest that early attention to children with depression, even in preclinical stages, may reduce risk of chronic disease in later life. (PsycINFO Database Record

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.

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.

Why Are Girls Less Physically Active than Boys? Findings from the LOOK Longitudinal Study.

BACKGROUND: A gender-based disparity in physical activity (PA) among youth, whereby girls are less active than boys is a persistent finding in the literature. A greater understanding of the mechanisms underlying this difference has potential to guide PA intervention strategies. METHODS: Data were collected at age 8 and 12 years (276 boys, 279 girls) from 29 schools as part of the LOOK study. Multilevel linear models were fitted separately for boys and girls to examine effects of individual, family and environmental level correlates on pedometer measured PA. Cardio-respiratory fitness (multi-stage run), percent fat (DEXA), eye-hand coordination (throw and catch test) and perceived competence in physical education (questionnaire) were used as individual level correlates. At the family level, parent's support and education (questionnaire) were used. School attended and extracurricular sport participation were included as environmental level correlates. RESULTS: Girls were 19% less active than boys (9420 vs 11360 steps/day, p<0.001, 95%CI [1844, 2626]). Lower PA among girls was associated with weaker influences at the school and family levels and through lower participation in extracurricular sport. School attended explained some of the variation in boys PA (8.4%) but not girls. Girls compared to boys had less favourable individual attributes associated with PA at age 8 years, including 18% lower cardio-respiratory fitness (3.5 vs 4.2, p<0.001, CI [0.5,0.9]), 44% lower eye-hand coordination (11.0 vs 17.3, p<0.001, CI [5.1,9.0]), higher percent body fat (28% vs 23%, p<0.001, CI [3.5,5.7]) and 9% lower perceived competence in physical education (7.7 vs 8.4, p<0.001, CI [0.2,0.9]). Participation in extracurricular sport at either age 8 or 12 years was protective against declines in PA over time among boys but not girls. CONCLUSION: Girls PA was less favourably influenced by socio-ecological factors at the individual, family, school and environmental levels. These factors are potentially modifiable suggesting the gap in PA between boys and girls can be reduced. Strategies aiming to increase PA should be multicomponent and take into consideration that pathways to increasing PA are likely to differ among boys and girls.

The influence of sport club participation on physical activity, fitness and body fat during childhood and adolescence: The LOOK Longitudinal Study.

OBJECTIVES: To investigate the longitudinal effect of sport participation in physical activity, fitness and body fat changes during childhood and adolescence. DESIGN: Longitudinal study (134 boys, 155 girls) of Australian youth aged 8-16 years. METHODS: Physical activity was assessed by pedometers and accelerometers, fitness by the 20m shuttle-run, body fat by DEXA and club sport participation by questionnaire. Linear mixed models were used to determine the effects of sport participation and gender differences. RESULTS: Sports club participants were more physically active at all age groups than non-participants; boys took an extra 1800 steps (p<0.001) and girls 590 steps per day (p<0.01) and boys engaged in an extra 9min and girls 6min more moderate to vigorous PA per day (both p<0.05). Fitness was higher among sports participants (boys 27% and girls 20% higher, both p<0.001) and sport participant girls had 2.9% less body fat (p<0.05). Higher fitness scores were maintained over time by sports participants but their greater PA diminished during adolescence, this being more evident among girls. Only 20% of sports club participants met the recommended daily average of 60min MVPA. CONCLUSIONS: Sport participants were more active, fitter and had less body fat (girls only) than non-sports participants. However, the associated benefits of sport with PA diminished during adolescence and the majority of sports participants did not meet recommended levels of PA. Strategies aiming to maximise the benefits of sports participation may be enhanced by providing special attention to the early adolescent period particularly among girls.

Effects of a Specialist-Led, School Physical Education Program on Bone Mass, Structure, and Strength in Primary School Children: A 4-Year Cluster Randomized Controlled Trial.

This 4-year cluster randomized controlled trial of 365 boys and 362 girls (mean age 8.1 ± 0.3 years) from grade 2 in 29 primary schools investigated the effects of a specialist-taught physical education (PE) program on bone strength and body composition. All children received 150 min/week of common practice (CP) PE from general classroom teachers but in 13 schools 100 min/week of CP PE was replaced by specialized-led PE (SPE) by teachers who emphasized more vigorous exercise/games combined with static and dynamic postural activities involving muscle strength. Outcome measures assessed in grades 2, 4, and 6 included: total body bone mineral content (BMC), lean mass (LM), and fat mass (FM) by DXA, and radius and tibia (4% and 66% sites) bone structure, volumetric density and strength, and muscle cross-sectional area (CSA) by pQCT. After 4-years, gains in total body BMC, FM, and muscle CSA were similar between the groups in both sexes, but girls in the SPE group experienced a greater gain in total body LM (mean 1.0 kg; 95% CI, 0.2 to 1.9 kg). Compared to CP, girls in the SPE group also had greater gains in cortical area (CoA) and cortical thickness (CoTh) at the mid-tibia (CoA, 5.0% [95% CI, 0.2% to 1.9%]; CoTh, 7.5% [95% CI, 2.4% to 12.6%]) and mid-radius (CoA, 9.3% [95% CI, 3.5% to 15.1%]; CoTh, 14.4% [95% CI, 6.1% to 22.7%]), whereas SPE boys had a 5.2% (95% CI, 0.4% to 10.0%) greater gain in mid-tibia CoTh. These benefits were due to reduced endocortical expansion. There were no significant benefits of SPE on total bone area, cortical density or bone strength at the mid-shaft sites, nor any appreciable effects at the distal skeletal sites. This study indicates that a specialist-led school-based PE program improves cortical bone structure, due to reduced endocortical expansion. This finding challenges the notion that periosteal apposition is the predominant response of bone to loading during the prepubertal and early-pubertal period.