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ABSTRACT 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. © 2015 American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

Runners are prone to delayed onset muscle soreness (DOMS) during long distance training. This especially holds for unaccustomed training volumes at moderate to high intensities. We investigated the effects of a marine oil complex, PCSO-524®, derived from the New Zealand green-lipped mussel (formulated as Lyprinol® and Omega XL®) on DOMS after a 30 km training run. Methods: Initially, peak oxygen uptake of 32 distance runners (4 female, 28 male; median age 45 years, range 28-53) was measured on a treadmill with a 1.5 km hour-1 increase every 4 minutes starting from 8.5 km hour-1. At least 1-week after this initial test, they participated in a 30 km road run at a speed corresponding to about 70% of their individual peak oxygen uptake on a flat terrain. Before and after (0, 24, and 48 hours) the run, blood concentration of creatine kinase (CK) were measured and pain sensation was determined (pain scale from 0 = no pain to 10 = extremely painful). Runners were then matched in pairs based on maximal CK and peak oxygen uptake, and allocated randomly into two different groups. One group was supplemented with 400 mg per day of PCSO-524® for 11 weeks, the other group with an olive oil placebo. After that period, CK and pain sensations were remeasured following a second 30 km run at the same speed and on the same terrain. Results: The general pattern of soreness in the PCSO-524® supplemented group was reduced by 1.1 units (standard error 0.41) compared to the placebo (P < 0.05), the effects being greater in lesser trained runners (P < 0.05). CK levels were positively associated with pain sensation (P < 0.05), but trends toward lower CK in the PCSO-524® group, which were also more pronounced in the lesser trained runners, were not statistically significant. Conclusion: Pain sensations experienced by distance runners following a 30 km run were reduced by supplementation with the marine oil complex PCSO-524®, an effect which was greater in lesser trained runners. [ABSTRACT FROM AUTHOR]

This study aimed to investigate seasonal heat acclimatization in active adolescents following summer. Fifteen (5 females) active adolescents (14.6 ± 1.0 y) completed a 45-min heat response test (HRT) walking at 60% $\dot {\rm V}$ V ˙ O2peak in 40°C and 30% relative humidity before and after summer (i.e. November 2022 and March 2023). During the HRT, gastro-intestinal temperature (Tgi), skin temperature (Tsk), heart rate, local sweat rate (LSR) and whole-body sweat loss (WBSL) were recorded. Carbon monoxide rebreathing and dual-energy X-ray absorptiometry scans determined resting hematological measures and body composition. Participants completed physical activity (PA) diaries and wore an accelerometer for two one-week periods (pre- and post-summer). Daytime wet-bulb globe temperature (WBGT) was calculated for each summer day. Data are presented as posterior mean and 90% credible intervals. Participants reported 7 ± 4 h·wk−1 of outdoor PA, and daytime WBGT was 21.2 ± 4.6°C. Following summer, resting Tgi and heart rate were reduced by 0.2°C [−0.3, −0.1; probability of direction = 99%] and 7 beats·min−1 [−10, −3; 100%], respectively. During the HRT, there was an earlier onset of sweating (−0.2°C [−0.3, −0.0; 98%]), an attenuated rise of Tgi (0.2°C [−0.5, 0.0; 92%]) and mean Tsk changed by −0.2°C [−0.5, 0.1; 86%]. There was minimal evidence for heat adaptations in LSR or WBSL, hematological parameters or perceptual measures. This is the first study to demonstrate seasonal heat adaptations in active adolescents. Reductions in resting Tgi and exercising Tsk and a lower Tgi at the onset of sweating were associated with a smaller rise in Tgi during the HRT following summer. [ABSTRACT FROM AUTHOR]

Background: Athletes and military personnel are often expected to compete and work in hot and/or humid environments, where decrements in performance and an increased risk of exertional heat illness are prevalent. A physiological strategy for reducing the adverse effects of heat stress is to acclimatise to the heat. Objective: The aim of this systematic review was to quantify the effects of relocating to a hotter climate to undergo heat acclimatisation in athletes and military personnel. Eligibility Criteria: Studies investigating the effects of heat acclimatisation in non-acclimatised athletes and military personnel via relocation to a hot climate for < 6 weeks were included. Data Sources: MEDLINE, SPORTDiscus, CINAHL Plus with Full Text and Scopus were searched from inception to June 2022. Risk of Bias: A modified version of the McMaster critical review form was utilised independently by two authors to assess the risk of bias. Data Synthesis: A Bayesian multi-level meta-analysis was conducted on five outcome measures, including resting core temperature and heart rate, the change in core temperature and heart rate during a heat response test and sweat rate. Wet-bulb globe temperature (WBGT), daily training duration and protocol length were used as predictor variables. Along with posterior means and 90% credible intervals (CrI), the probability of direction (Pd) was calculated. Results: Eighteen articles from twelve independent studies were included. Fourteen articles (nine studies) provided data for the meta-analyses. Whilst accounting for WBGT, daily training duration and protocol length, population estimates indicated a reduction in resting core temperature and heart rate of − 0.19 °C [90% CrI: − 0.41 to 0.05, Pd = 91%] and − 6 beats·min−1 [90% CrI: − 16 to 5, Pd = 83%], respectively. Furthermore, the rise in core temperature and heart rate during a heat response test were attenuated by − 0.24 °C [90% CrI: − 0.67 to 0.20, Pd = 85%] and − 7 beats·min−1 [90% CrI: − 18 to 4, Pd = 87%]. Changes in sweat rate were conflicting (0.01 L·h−1 [90% CrI: − 0.38 to 0.40, Pd = 53%]), primarily due to two studies demonstrating a reduction in sweat rate following heat acclimatisation. Conclusions: Data from athletes and military personnel relocating to a hotter climate were consistent with a reduction in resting core temperature and heart rate, in addition to an attenuated rise in core temperature and heart rate during an exercise-based heat response test. An increase in sweat rate is also attainable, with the extent of these adaptations dependent on WBGT, daily training duration and protocol length. PROSPERO Registration: CRD42022337761. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Cardiorespiratory fitness and adiposity as mortality predictors in older adults," by X. Sui and colleagues in the 2007 issue of the "Journal of American Medical Association."

Background: Physiological heat adaptations can be induced following various protocols that use either artificially controlled (i.e. acclimation) or naturally occurring (i.e. acclimatisation) environments. During the summer months in seasonal climates, adequate exposure to outdoor environmental heat stress should lead to transient seasonal heat acclimatisation. Objectives: The aim of the systematic review was to assess the available literature and characterise seasonal heat acclimatisation during the summer months and identify key factors that influence the magnitude of adaptation. Eligibility Criteria: English language, full-text articles that assessed seasonal heat acclimatisation on the same sample of healthy adults a minimum of 3 months apart were included. Data Sources: Studies were identified using first- and second-order search terms in the databases MEDLINE, SPORTDiscus, CINAHL Plus with Full Text, Scopus and Cochrane, with the last search taking place on 15 July 2021. Risk of Bias: Studies were independently assessed by two authors for the risk of bias using a modified version of the McMaster critical review form. Data Extraction: Data for the following outcome variables were extracted: participant age, sex, body mass, height, body fat percentage, maximal oxygen uptake, time spent exercising outdoors (i.e. intensity, duration, environmental conditions), heat response test (i.e. protocol, time between tests), core temperature, skin temperature, heart rate, whole-body sweat loss, whole-body and local sweat rate, sweat sodium concentration, skin blood flow and plasma volume changes. Results: Twenty-nine studies were included in this systematic review, including 561 participants across eight countries with a mean summer daytime wet-bulb globe temperature (WBGT) of 24.9 °C (range: 19.5–29.8 °C). Two studies reported a reduction in resting core temperature (0.16 °C; p < 0.05), 11 reported an increased sweat rate (range: 0.03–0.53 L·h−1; p < 0.05), two observed a reduced heart rate during a heat response test (range: 3–8 beats·min−1; p < 0.05), and six noted a reduced sweat sodium concentration (range: − 22 to − 59%; p < 0.05) following summer. The adaptations were associated with a mean summer WBGT of 25.2 °C (range: 19.6–28.7 °C). Limitations: The available studies primarily focussed on healthy male adults and demonstrated large differences in the reporting of factors that influence the development of seasonal heat acclimatisation, namely, exposure time and duration, exercise task and environmental conditions. Conclusions: Seasonal heat acclimatisation is induced across various climates in healthy adults. The magnitude of adaptation is dependent on a combination of environmental and physical activity characteristics. Providing environmental conditions are conducive to adaptation, the duration and intensity of outdoor physical activity, along with the timing of exposures, can influence seasonal heat acclimatisation. Future research should ensure the documentation of these factors to allow for a better characterisation of seasonal heat acclimatisation. PROSPERO Registration: CRD42020201883. [ABSTRACT FROM AUTHOR]

Background: Health organisations such as the United Nations continue to place an expectation on school physical education (PE) programmes and wider school strategies to ensure students develop physical literacy and receive the well-established benefits of meeting physical activity guidelines. Barriers to meet this expectation such as lack of trained PE teachers, lack of time and greater emphasis on academic achievement are ongoing challenges to schools. The purpose of this study was to evaluate the impact of the multi-component Physical Education Physical Literacy (PEPL) intervention, designed to improve students' fundamental movement skill, perceived physical abilities and level of physical activity. Method: A qualified PE teacher implemented the PEPL intervention across seven schools, and another seven schools formed a control group as part of a randomised cluster-based trial. Grade 5 students (N = 318, age 10.4 years ± SD 0.4) completed assessments of physical activity, fundamental movement skill, attitudes towards PE, and self-perceptions of physical abilities before and after a 33-week intervention. Intervention effects were examined using general linear mixed models. Post-intervention focus groups with students were used to develop insights into experiences and outcomes. Results: With no significant gender interactions, the PEPL approach led to enhanced object control skills (β = 1.62; SE = 0.61; p = 0.008), with little evidence of any other fundamental movement skill improvements in excess of those in the control group. There was also modest evidence for an effect on accelerometer measured moderate-to-vigorous physical activity (MVPA) during school time (β = 4.50; SE = 2.39; p = 0.058), but this was not accompanied by any significant intervention effect over the entire week. Questionnaires indicated students in the PEPL programme became less satisfied with their own sporting ability (β = −0.20; SE = 0.08; p = 0.013) but qualitative data analyses suggested that they enjoyed the PEPL approach experience, becoming more motivated and confident in their physical abilities. Conclusions: Evidence of enhanced object control skill, increased confidence and motivation to be physically active, and moderate evidence of more MVPA during school time, indicate that the introduction of the PEPL approach contributed to the development of student physical literacy. A decrease in perceived sporting competence warrants greater attention on student's self-perceptions in future iterations of the intervention. Trial registration: Australian New Zealand Clinical Trials Registry identifier: ACTRN12615000066583. [ABSTRACT FROM AUTHOR]

Background: Physical education (PE) can be considered the centrepiece of school physical literacy (PL) programs, but ineffective lessons or an absence of PE across the public primary school system has raised concern. This study aimed to evaluate the implementation, acceptability and impact of teacher delivery of PE as part of a multicomponent Physical Education Physical Literacy (PEPL) approach, designed to improve classroom teachers' provision of PE and PL opportunities within a cluster of suburban primary schools. Method: Within a pragmatic randomised cluster-based trial with mixed methods, a PEPL coach was appointed to seven schools for one school year, with another seven schools continuing their usual practice as the control group. The coach's role was to support and professionally develop classroom teachers to teach PE and to create opportunities that develop PL inside and outside the school environment. Focusing on Grade 5 teachers, the implementation, acceptability and teacher impact were assessed using direct observations of PE teaching style, a daily log kept by the coach and interviews with principals and teachers. Results: The PEPL coach visited each school on average once a week for the 33 available weeks of the school year. There were several positive effects for teachers and schools. With no classroom teacher initially taking PE or classroom physical activity breaks, all seven teachers regularly introduced a PE lesson and activity breaks into their weekly schedule. PE class instructional time increased (intervention; +4.8 vs. control; −3.5 min/lesson; β = 1.69; SE = 0.76; p =.05), with lessons of greater duration (intervention; +8.6 vs. control +1.9 min/lesson; β = 1.14, SE = 0.58, p =.05) and moderate and vigorous physical activity increased 5.7 min in intervention classes (p <.05). The PEPL coach introduced regular physical activities before and after school and linked the schools with a national sports coaching scheme. Interviews indicated that the PEPL approach was both valued and well-accepted by staff, that classroom teacher confidence to teach PE increased and that principals perceived a shift toward a school 'culture' of physical activity. Conclusions: Well-received by classroom teachers and principals, the PEPL approach resulted in classroom teachers introducing both PE and activity breaks into their weekly teaching program and schools were linked to external sport coaching programs. These effects suggest that the PEPL approach enhanced opportunities for the development of physical literacy in this suburban primary school setting. Trial registration: Australian New Zealand Clinical Trials Registry identifier: ACTRN12615000066583. [ABSTRACT FROM AUTHOR]

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. 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. 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. 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. [ABSTRACT FROM AUTHOR]

Physical activity may benefit mental health, yet the potentially protective role of elementary school physical education (PE) on childhood mental health is unknown. The aim of the current study was to determine the effect of a specialist-taught PE program on indicators of childhood mental health. In this cluster-randomized controlled trial, participants were initially 821 healthy children (8 years, 406 girls) from 29 schools. Thirteen schools were allocated to the 4-year intervention program of specialist-taught PE, with the remaining schools forming the control group. Mental health indicators of depression, body image, and stress were measured at ages 7, 8, and 12 years. Assessments of covariates included percent body fat (DEXA), physical activity (pedometers), puberty (Tanner stages), and socioeconomic status. After receiving 1 year of specialist-taught PE, children of the intervention group reported a −0.71-unit decrease in body dissatisfaction compared to a 3.01-unit increase in control group children (p =.042); and a mean decrease in depressive symptoms (ineffectiveness), which was −0.27 units more than the control group (p =.005). Mixed-model analyses investigating longer-term effects revealed that the early positive effect of the intervention on body dissatisfaction and depression was not sustained over time. In fact, there was evidence of an intervention effect of an overall increase in depressive symptoms over the 4 years of the study for girls only. While our specialist-taught PE intervention had a positive influence on girls' body dissatisfaction and boys' depressive symptoms in the first year, this was not sustained over the 4-year duration of the study. Physical activity may benefit mental health, yet the potentially protective role of elementary school physical education (PE) on mental health is unknown. The aim of the current study was to determine how PE taught by specialist-trained PE teachers influences children's levels of stress, depression. and body image. In this investigation, spanning 4 years, our specialist-taught PE intervention had a positive influence on girls' body dissatisfaction and boys' depressive symptoms in the first year. However, this was not sustained over the 4-year duration of the intervention. In fact, there was evidence that girls receiving the intervention, and therefore having greater exposure to PE, had an overall increase in depressive symptoms. These findings demonstrate that PE can influence childhood mental health, for the better or worse, and suggest that PE could provide a useful vehicle through which to deliver well-being programs, in which case, teachers tasked with the delivery of PE might benefit from additional training to minimize any potential negative impact of PE on children's mental health. These findings have important implications for educational policymakers and emphasize the need to acknowledge the psychological and physiological differences between boys and girls when developing PE curricula. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to investigate the associations of biological sex and aerobic fitness (i.e., V̇O 2peak ) on the change in gastrointestinal temperature (∆ Tgi ) and whole-body sweat rate (WBSR) of children exercising in warm conditions., Methods: Thirty-eight children (17 boys, mean ± SD = 13.7 ± 1.2 yr; 21 girls, 13.6 ± 1.8 yr) walked for 45 min at a fixed rate of metabolic heat production (8 W·kg -1 ) in 30°C and 40% relative humidity. Biological sex and relative V̇O 2peak were entered as predictors into a Bayesian hierarchical generalized additive model for Tgi . For a subsample of 13 girls with measured body composition, body fat percent was entered into a separate hierarchical generalized additive model for Tgi . Sex, V̇O 2peak , and the evaporative requirement for heat balance ( Ereq ) were entered into a Bayesian hierarchical linear regression for WBSR., Results: The mean ∆ Tgi for boys was 0.71°C (90% credible interval = 0.60-0.82) and for girls 0.78°C (0.68-0.88). A predicted 20 mL·kg -1 ·min -1 higher V̇O 2peak resulted in a 0.19°C (-0.03 to 0.43) and 0.24°C (0.07-0.40) lower ∆ Tgi in boys and girls, respectively. A predicted ~13% lower body fat in the subsample of girls resulted in a 0.15°C (-0.12 to 0.45) lower ∆ Tgi . When Ereq was standardized to the grand mean, the difference in WBSR between boys and girls was -0.00 L·h -1 (-0.06 to 0.06), and a 20-mL·kg -1 ·min -1 higher predicted V̇O 2peak resulted in a mean difference in WBSR of -0.07 L·h -1 (-0.15 to 0.00)., Conclusions: Biological sex did not independently influence ∆ Tgi and WBSR in children. However, a higher predicted V̇O 2peak resulted in a lower ∆ Tgi of children, which was not associated with a greater WBSR, but may be related to differences in body fat percent between high and low fitness individuals., (Copyright © 2023 by the American College of Sports Medicine.)

Objectives: To assess the magnitude of seasonal heat acclimatisation in recreationally active adults and contextualise the process by documenting the factors that influence adaptations., Design: Longitudinal, repeated measures design., Methods: Seventeen (7 females) recreationally active adults (28 ± 8 yr, V̇O 2peak 54 ± 8 mL·kg -1 ·min -1 ) exercising outdoors a minimum of 5 h·wk -1 completed a 45-min heat response test running at 60 % V̇O 2peak in 40 °C and 30 % relative humidity prior to, midway through, and following summer. Self-reported physical activity diaries were completed at the beginning and end of summer. Daytime wet-bulb globe temperature was calculated for each day of summer. Data were analysed using Bayesian ordinal regressions., Results: Daytime wet-bulb globe temperature was 22.0 ± 4.4 °C, with the most common hour for recreational exercise being 17:00 to 18:00. Following summer, the rise in oesophageal temperature and mean skin temperature during the heat response test was lower by 0.12 °C [90 % credible interval: -0.30, 0.06; probability of direction = 87 %] and 0.43 °C [-0.74, -0.10; 98 %], respectively. Moreover, forearm local sweat rate increased by 0.26 mg·cm -2 ·min -1 [0.15, 0.36; 100 %]. There was minimal evidence of a change in the increase in heart rate (1 beat·min -1 [-3, 5; 62 %]), or whole-body sweat rate (0.03 L·h -1 [-0.11, 0.15; 68 %]) during the heat response test., Conclusions: Although there was evidence of partial heat adaptation in recreationally active adults following summer, a combination of exercising later in the day and the prevailing environmental conditions (La Niña in South-Eastern Australia) may have blunted the development of further adaptations., Competing Interests: Declaration of interest statement None., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

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 ± 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., (Copyright © 2022 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

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) (β = 1.79; SE = 0.68) and waist circumference (β = 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., (Copyright © 2021. Production and hosting by Elsevier B.V.)

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 H 10 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 (β = -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., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2021 The Authors.)

Background/objectives: Body mass index (BMI, body mass/height 2 ) 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., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)