Pilot randomized controlled trial of a game-based intervention for teaching basketball in Chinese primary school physical education.

This study aimed to examine the preliminary efficacy and feasibility of implementing a tailored version of the MASTER coach education programme in Chinese primary schools to support physical education (PE) teachers' basketball lesson design and delivery. A total of 20 primary schools in Beijing, China were recruited, with one PE teacher and their class (N = 715 students aged 10-13 yrs) from each school included in the study and randomly allocated to the MASTER intervention (n = 10) or control group (n = 10). Compared to the control group, a significant difference was observed in the MASTER group for the proportion of playing-form activities delivered during PE (27.65, 95% CI [20.27, 35.03]) and for teachers' perceptions of confidence (23.92, 95% CI [15.87, 31.92]) and competence (24.12, 95% CI [10.28, 24.71]) to teach. Significant differences between groups were observed for students' perceived athletic competence (3.56%; 95% CI [3.15, 3.96]), enjoyment (11.83%; 95% CI [10.98, 12.69]), well-being (8.51%; 95% CI [7.02, 10.00]), intrinsic motivation (+0.74%; 95% CI [0.30, 1.17]), introjected motivation (-2.24%; 95% CI [-2.77, -1.70]), and external motivation (-0.49%; 95% CI [-0.90, -0.08]). The MASTER programme was effective in improving teaching practices in Chinese primary schools, and in facilitating improvements in teacher and student outcomes.

Mediating effects of sleep on mental health in older adolescents: Findings from the Burn 2 Learn randomized controlled trial.

PURPOSE: Our study explored the mediating effect of sleep-related variables on older adolescents' mental health in the context of a school-based physical activity intervention. METHODS: We evaluated the Burn 2 Learn (B2L) intervention using a cluster randomized controlled trial, which included two cohorts. Participants for this sub-study were from the second cohort, which included 292 older adolescents (16.0 ± 0.5 years) from 10 secondary schools in New South Wales, Australia. Teachers at intervention schools delivered two high-intensity activity breaks (approximately 10 mins) per week to students during academic lessons. Participants completed measures of mental health (i.e., perceived stress and internalizing problems) and hypothesized mediators (i.e., sleep duration, sleep latency, awakenings, and daytime sleepiness) at baseline (February-April 2019) and post-intervention (August-September 2019). Single mediation analyses were conducted to explore the potential mediating effects of sleep variables on mental health outcomes using a product-of-coefficient test. RESULTS: We observed a small statistically significant effect for perceived stress (ß = -0.11, SE = 0.034, p = 0.002), but not for internalizing problems (ß = 0.02, SE = 0.051, p = 0.760). There were no significant intervention effects for sleep-related variables. Several sleep-related variables were associated with mental health outcomes but no mediated effects were found. CONCLUSION: The B2L intervention had a small beneficial effect on perceived stress, however our mediation analyses suggest this was not explained by changes in sleep-related variables. Markers of sleep were associated with mental health constructs, highlighting the importance of sleep for good psychological health. However, in the context of a physical activity intervention, effects on mental health may be driven by other behavioral, neurobiological, or psychosocial mechanisms.

Scaling-Up Adolescent High-Intensity Interval Training Programs for Population Health.

High-intensity interval training (HIIT) has become a polarizing form of exercise. In this article, we argue that adolescent HIIT programs can have population health impact if they are (i) integrated into existing opportunities, (ii) designed to develop physical literacy, (iii) delivered in an engaging manner, and (iv) guided and supported by an implementation framework that addresses relevant barriers and facilitators.

The epidemiology of muscle-strengthening activity among adolescents from 28 European countries.

AIMS: This study aimed to describe the prevalence and socio-demographic and lifestyle-related correlates of muscle-strengthening activity (MSA; strength/resistance training, sit-ups/push-ups, etc.) among a large sample of European adolescents. METHODS: Data were drawn from the European Health Interview Survey Wave 2 (2013-2014), including 8818 adolescents (15-17 years) from 28 European countries. Self-reported MSA was assessed using a previously validated survey item. Population-weighted prevalence ratios were calculated for (a) 'none' (0 days/week), (b) 'insufficient MSA' (1-2 days/week) or (c) 'sufficient MSA' (⩾3 days/week). Generalised linear models using Poisson regression with robust error variance were used to calculate the prevalence ratios for adolescents reporting sufficient MSA by socio-demographic/lifestyle characteristics and by European region. RESULTS: Overall, 19.4% (95% confidence interval (CI) 18.3-20.7) reported sufficient (⩾3 days/week) MSA and 57.9% (95% CI 56.4-59.6) reported none. Females, adolescents from Southern and Eastern European regions, those not meeting the aerobic guideline and adolescents classified as overweight were significantly associated with a lower likelihood of reporting sufficient MSA, independent of other characteristics. CONCLUSIONS: The majority of European adolescents do not meet the MSA guidelines. Future large-scale MSA public-health interventions should target female and currently inactive adolescents, as well as those from Southern and Eastern European regions.

Evaluating the reach, effectiveness, adoption, implementation and maintenance of the Resistance Training for Teens program.

BACKGROUND: Physical activity guidelines recommend young people engage in regular muscle-strengthening activities (e.g., resistance training [RT]). However, few school-based physical activity interventions have been delivered at-scale or promoted RT. The aim of this study was to evaluate the reach, effectiveness, adoption, implementation and maintenance of the Resistance Training for Teens (RT for Teens) program. METHODS: Data were collected between August 2015 and October 2020. RE-AIM was operationalized as: (i) Reach: number and characteristics of students estimated to be exposed to the program; (ii) Effectiveness: impact of the program on student-level outcomes measured in a subsample of 750 students from 17 schools; (iii) Adoption: number and representativeness of schools with one or more teachers trained to deliver the program; (iv) Implementation: extent to which the program was delivered as intended; and (v) Maintenance: extent to which the program was sustained in schools. RESULTS: The estimated program reach was ~ 10,000 students, out of a total student population of ~ 200,000 (~ 5%). Students were from diverse socioeconomic and ethnic backgrounds. Improvements in muscular fitness, RT self-efficacy, perceived cardiorespiratory fitness and flexibility, and participation in muscle-strengthening physical activities were documented. A total of 30 workshops were delivered, involving 468 teachers from 249 schools from diverse geographical regions. Implementation varied considerably, with teachers adapting the program to suit the context of their school and student cohorts. However, RT skill development and the promotion of muscular fitness were the session components delivered most during sessions. Teachers' adherence to the SAAFE (Supportive, Active, Autonomous, Fair and Enjoyable) teaching principles was high. Approximately 30% of teachers (144/476) registered to use the RT for Teens app. At the school-level, 37% (93/249) of schools had at least one registered user (teacher and/or student). A total of 2,336 workouts and 3,116 fitness tests were completed by registered users. Of the 249 schools represented, 51 (20.5%) sent an additional (previously untrained) teacher to a second workshop. CONCLUSIONS: The RT for Teens program had broad reach and adoption. However, intervention delivery varied considerably across schools and additional support strategies are required to optimize intervention implementation and maintain program delivery over time. Future studies will benefit from the utilization of accepted frameworks, recommendations and guidelines for implementation research. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry (ACTRN12621000352808), retrospectively registered 1st February 2021.

Cardiorespiratory fitness, muscular fitness and mental health in older adolescents: A multi-level cross-sectional analysis.

Physical activity interventions that promote cardiorespiratory (CRF) and muscular fitness (MF) may improve mental health in young adolescents. However, less is known about the links between fitness and mental health in older adolescents, as they are an understudied population. In addition, the association between MF and adolescents' mental health is less clear than it is for CRF. Our primary aim was to investigate whether MF is independently associated with mental health in a sample of older adolescents. Our secondary aim was to determine if the association between fitness and mental health was moderated by sex, socio-economic status (SES) or weight status. Participants were 670 students (16.0 [0.4] years, 44.6% female) from 20 secondary schools in New South Wales, Australia. Mental health (well-being and internalizing problems) was self-reported using the Short Warwick-Edinburgh Mental Wellbeing Scale and the Strengths and Difficulties Questionnaire. We assessed CRF using the Progressive Aerobic Cardiovascular Endurance Run and MF using the push-up and standing long jump tests. After controlling for CRF, MF was not associated with mental health. CRF was associated with well-being (ß = 0.20, p < .001) and internalizing problems (ß = -0.27, p < .001). The strength of association between CRF and mental health was stronger in girls, than boys. No interaction effects were observed for SES or weight status. Although cross-sectional, our findings provide further evidence of the potential benefits of CRF for adolescents' mental health (i.e., well-being and internalizing problems), particularly girls. However, MF may be less relevant for mental health among this population.

Time-efficient intervention to improve older adolescents' cardiorespiratory fitness: findings from the 'Burn 2 Learn' cluster randomised controlled trial.

BACKGROUND: Cardiorespiratory fitness (CRF) is an important marker of current and future health status. The primary aim of our study was to evaluate the impact of a time-efficient school-based intervention on older adolescents' CRF. METHODS: Two-arm cluster randomised controlled trial conducted in two cohorts (February 2018 to February 2019 and February 2019 to February 2020) in New South Wales, Australia. Participants (N=670, 44.6% women, 16.0±0.43 years) from 20 secondary schools: 10 schools (337 participants) were randomised to the Burn 2 Learn (B2L) intervention and 10 schools (333 participants) to the control. Teachers in schools allocated to the B2L intervention were provided with training, resources, and support to facilitate the delivery of high-intensity interval training (HIIT) activity breaks during curriculum time. Teachers and students in the control group continued their usual practice. The primary outcome was CRF (20 m multi-stage fitness test). Secondary outcomes were muscular fitness, physical activity, hair cortisol concentrations, mental health and cognitive function. Outcomes were assessed at baseline, 6 months (primary end-point) and 12 months. Effects were estimated using mixed models accounting for clustering. RESULTS: We observed a group-by-time effect for CRF (difference=4.1 laps, 95% CI 1.8 to 6.4) at the primary end-point (6 months), but not at 12 months. At 6 months, group-by-time effects were found for muscular fitness, steps during school hours and cortisol. CONCLUSIONS: Implementing HIIT during curricular time improved adolescents' CRF and several secondary outcomes. Our findings suggest B2L is unlikely to be an effective approach unless teachers embed sessions within the school day. TRIAL REGISTRATION NUMBER: Australian New Zealand Clinical Trials Registry (ACTRN12618000293268).

Feasibility of test administration and preliminary findings for cognitive control in the Burn 2 learn pilot randomised controlled trial.

The feasibility requirements of administering field-based cognitive assessments are rarely reported. We examined the feasibility of administering a group-based cognitive test battery in a school setting with older adolescents. Several types of reliability were also assessed in the control group. Preliminary efficacy and the relationship between changes in fitness and changes in cognitive control were also explored following a 14-week HIIT intervention (3 sessions/week). Participants completed a cognitive test battery measuring inhibition (flanker), and working memory (n-back) at baseline and post-test. Health-related fitness assessments were also conducted. Test administration took approximately 30.8 ± 1.5 minutes to complete with up to six participants simultaneously. The test battery demonstrated acceptable reliability (ICC = 0.5-0.81), with significant changes observed for flanker incongruent accuracy, and 2-back non-target accuracy from baseline to post-test. Regarding efficacy, small-to-moderate effects were observed for accuracy outcomes, while several small associations were found between changes in fitness and changes in cognition. Findings from the current study suggest a cognitive test battery can be administered with older adolescents in a school setting. However, there remains a lack of adequate reporting of administration requirements for field-based cognitive assessments. Efficacy findings should be confirmed with a larger and more representative sample of older adolescents.

Temporal trends in the sit-ups performance of 9,939,289 children and adolescents between 1964 and 2017.

We estimated international/national temporal trends in sit-ups performance for children and adolescents, and examined relationships between national trends in sit-ups performance and national trends in health-related/sociodemographic indicators. Data were obtained by systematically searching studies reporting on temporal trends in sit-ups performance for apparently healthy 9-17 year-olds, and by examining nationally representative fitness datasets. Trends at the country-sex-age level were estimated by sample-weighted regression models relating the testing year to mean sit-ups performance. International/national trends were estimated by a post-stratified population-weighting procedure. Pearson's correlations quantified relationships between national trends in sit-ups performance and national trends in health-related/sociodemographic indicators. A total of 9,939,289 children and adolescents from 31 countries/special administrative regions between 1964 and 2017 collectively showed a large improvement of 38.4% (95% CI: 36.8 to 40.0) or 7.1% per decade (95% CI: 6.8 to 7.4). Large international improvements were experienced by all age and sex groups, with the rate of improvement slowing from 1964 to 2000, stabilizing near zero until 2010, before declining. Trends differed between countries, with national trends in vigorous physical activity a strong, positive correlate of national trends in sit-ups performance. More sit-ups data are needed from low- and middle-income countries to better monitor trends in muscular fitness. PROSPERO REGISTRATION NUMBER: CRD42013003657.

Development and Evaluation of the High-Intensity Interval Training Self-Efficacy Questionnaire.

This study involved the design and evaluation of the High-Intensity Interval Training Self-Efficacy Questionnaire (HIIT-SQ). Phase 1: Questionnaire items were developed. Phase 2: Australian adolescents (N = 389, 16.0 ± 0.4 years, 41.10% female) completed the HIIT-SQ, and factorial validity of the measurement model was explored. Phase 3: Adolescents (N = 100, age 12-14 years, 44% female) completed the HIIT-SQ twice (1 week apart) to evaluate test-retest reliability. Confirmatory factor analysis of the final six items (mean = 3.43-6.73, SD = 0.99-25.30) revealed adequate fit, χ2(21) = 21, p = .01, comparative fit index = .99, Tucker-Lewis index = .99, root mean square of approximation = .07, 90% confidence interval [.04, .11]. Factor loading estimates showed that all items were highly related to the factor (estimates range: 0.81-0.90). Intraclass coefficients and typical error values were .99 (95% confidence interval [.99, 1.00]) and .22, respectively. This study provides preliminary evidence for the validity and reliability of scores derived from the HIIT-SQ in adolescents.

Feasibility and Preliminary Efficacy of a Teacher-Facilitated High-Intensity Interval Training Intervention for Older Adolescents.

PURPOSE: This study was designed to assess the feasibility and preliminary efficacy of a teacher-facilitated high-intensity interval training intervention for older adolescents (ie, 16-18 y). METHODS: Two secondary schools from New South Wales, Australia were recruited, and participants (ie, grade 11 students; 16.2 [0.4] y) were randomized at the school level to the Burn 2 Learn intervention (n = 38), or a wait-list control group (n = 30). Teachers were trained to facilitate the delivery of the novel high-intensity interval training program, which involved 3 sessions per week (∼12-20 min) for 14 weeks. A range of process measures were used to assess intervention feasibility (ie, recruitment, retention, attendance, and program satisfaction). Primary (cardiorespiratory fitness, determined using the progressive aerobic cardiovascular endurance run shuttle run test) and secondary outcomes were assessed at baseline and posttest (14-wk). RESULTS: Sixty-eight grade 11 students were recruited at baseline (85% of target sample), 61 participants completed posttest assessments (90% retention) and on average, participants performed 1.9 sessions per week. Overall, teachers (4.0/5) and students (4.0/5) were satisfied with the Burn 2 Learn program. Group by time effects were observed for cardiorespiratory fitness (8.9 laps; 95% confidence intervals, 1.7-16.2) and a selection of secondary outcomes. CONCLUSION: This study provides evidence for the feasibility and preliminary efficacy of a teacher-facilitated high-intensity interval training intervention for older adolescents.

Prevalence and correlates of resistance training skill competence in adolescents.

The aim of this study is to examine the prevalence and correlates of adolescents' resistance training (RT) skill competence. Participants were 548 adolescents (14.1 ± 0.5 years) from 16 schools in New South Wales, Australia. RT skills were assessed using the Resistance Training Skills Battery. Demographics, BMI, muscular fitness, perceived strength, RT self-efficacy, and motivation for RT were also assessed. The proportion demonstrating "competence" and "near competence" in each of the six RT skills were calculated and sex differences explored. Associations between the combined RT skill score and potential correlates were examined using multi-level linear mixed models. Overall, the prevalence of competence was low (range = 3.3% to 27.9%). Females outperformed males on the squat, lunge and overhead press, whereas males performed better on the push-up (p < .05). Significant associations were seen for a number of correlates, which largely differed by sex. Muscular fitness was moderately and positively associated with RT skills among both males (ß = 0.34, 95%CIs = 0.23 to 0.46) and females (ß = 0.36, 95%CIs = 0.23 to 0.48). Our findings support a link between RT skills and muscular fitness. Other associations were statistically significant but small in magnitude, and should therefore be interpreted cautiously.

Framework for the design and delivery of organized physical activity sessions for children and adolescents: rationale and description of the 'SAAFE' teaching principles.

The economic burden of inactivity is substantial, with conservative estimates suggesting the global cost to health care systems is more than US$50 billion. School-based programs, including physical education and school sport, have been recommended as important components of a multi-sector, multi-system approach to address physical inactivity. Additionally, community sporting clubs and after-school programs (ASPs) offer further opportunities for young people to be physically active outside of school. Despite demonstrating promise, current evidence suggests school-based physical activity programs, community sporting clubs and ASPs are not achieving their full potential. For example, physical activity levels in physical education (PE) and ASP sessions are typically much lower than recommended. For these sessions to have the strongest effects on young people's physical activity levels and their on-going physical literacy, they need to improve in quality and should be highly active and engaging. This paper presents the Supportive, Active, Autonomous, Fair, Enjoyable (SAAFE) principles, which represent an evidence-based framework designed to guide the planning, delivery and evaluation of organized physical activity sessions in school, community sport and ASPs. In this paper we provide a narrative and integrative review of the conceptual and empirical bases that underpin this framework and highlight implications for knowledge translation and application.

Integrating smartphone technology, social support and the outdoor physical environment to improve fitness among adults at risk of, or diagnosed with, Type 2 Diabetes: Findings from the 'eCoFit' randomized controlled trial.

The risk and prevalence of Type 2 Diabetes (T2D) has dramatically increased over the past decade. The aim of this study was to develop, implement and evaluate a physical activity intervention to improve aerobic and muscular fitness among adults at risk of, or diagnosed with T2D. A 20-week, assessor blinded, parallel-group randomized controlled trial (RCT) was conducted at the University of Newcastle (June-December 2015). Adults were randomized to the intervention (n=42) or wait-list control group (n=42). The theory-based intervention included: Phase 1 (weeks 1-10) integrated group sessions (outdoor physical activity and cognitive mentoring), and the eCoFit smartphone application (app). Phase 2 (weeks 11-20) only included the eCoFit app. Participants were assessed at baseline, 10weeks and 20weeks. Linear mixed models (intention-to-treat) were used to determine group-by-time interactions at 10weeks (primary time-point) and 20weeks for the primary outcomes. Several secondary outcomes were also assessed. After 10weeks, significant group-by-time effects were observed for aerobic fitness (4.5mL/kg/min; 95% CI [1.3, 7.7], d=0.68) and muscular fitness (lower body) (3.4 reps, 95% CI [2.7, 4.2], d=1.45). Intervention effects for secondary outcomes included significant increased physical activity (1330steps/week), improved upper body muscular fitness (5 reps; arm-curl test), improved functionality (-1.8s; timed-up and go test) reduced waist circumference (2.8cm) and systolic blood pressure (-10.4mmHg). After 20weeks, significant effects were observed for lower body muscular fitness and health outcomes. eCoFit is an innovative lifestyle intervention which integrates smartphone technology, social support, and the outdoor environment to improve aerobic and muscular fitness.

Global participation in sport and leisure-time physical activities: A systematic review and meta-analysis.

This review aimed to determine the most popular physical activities performed by children, adolescents, and adults globally. Statistic bureau websites and article databases Scopus, ProQuest, SPORTDiscus, and Science Direct were searched between November 17th, 2014 and April 31st, 2015. Eligible studies were published in the last 10years with participation rates for specific physical activities among individuals five years or older. Data extraction for included articles (n=64) was assessed independently and agreed upon by two authors. A random-effects model was used to calculate participation rates in specific activities for each age group and region. In total 73,304 articles were retrieved and 64 articles representing 47 countries were included in the final meta-analysis. Among adults, walking was the most popular activity in the Americas (18.9%; 95% CI 10.2 to 32.5), Eastern Mediterranean (15.0%; 95% CI 5.8 to 33.6), Southeast Asia (39.3%; 95% CI 0.9 to 98.0) and Western Pacific (41.8%; 95% CI 25.2 to 60.6). In Europe and Africa, soccer (10.0%; 95% CI 6.5 to 15.1) and running (9.3%; 95% CI 0.9 to 53.9), respectively, were top activities. Child and adolescent participation results were highly dependent upon region. American youth team sport participation was high, while youth from the Eastern Mediterranean and Western Pacific were more likely to report participation in lifelong physical activities. Global data for adults reflects a consistent pattern of participation in running and walking. Among all age groups and regions soccer was popular. In children and adolescents, preferences were variable between regions.

Mediators of change in screen-time in a school-based intervention for adolescent boys: findings from the ATLAS cluster randomized controlled trial.

The mechanisms of behavior change in youth screen-time interventions are poorly understood. Participants were 361 adolescent boys (12-14 years) participating in the ATLAS obesity prevention trial, evaluated in 14 schools in low-income areas of New South Wales, Australia. Recreational screen-time was assessed at baseline, 8- and 18-months, whereas potential mediators (i.e., motivation to limit screen-time and parental rules) were assessed at baseline, 4- and 18-months. Multi-level mediation analyses followed the intention-to-treat principle and were conducted using a product-of-coefficients test. The intervention had a significant impact on screen-time at both time-points, and on autonomous motivation at 18-months. Changes in autonomous motivation partially mediated the effect on screen-time at 18-months in single and multi-mediator models [AB (95% CI) = -5.49 (-12.13, -.70)]. Enhancing autonomous motivation may be effective for limiting screen-time among adolescent males. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry No: ACTRN12612000978864.

Targeted Health Behavior Interventions Promoting Physical Activity: A Conceptual Model.

This article presents a conceptual model illustrating a targeted approach to the design and delivery of health behavior interventions that focus on physical activity promotion. We hypothesize that researchers who i) enhance the sociocultural relevance of their core intervention components and ii) recognize the unique contributions of both intervention design and delivery will experience greater intervention engagement and improved outcomes.

Assessing the sustained impact of a school-based obesity prevention program for adolescent boys: the ATLAS cluster randomized controlled trial.

BACKGROUND: Obesity prevention interventions targeting 'at-risk' adolescents are urgently needed. The aim of this study is to evaluate the sustained impact of the 'Active Teen Leaders Avoiding Screen-time' (ATLAS) obesity prevention program. METHODS: Cluster RCT in 14 secondary schools in low-income communities of New South Wales, Australia. Participants were 361 adolescent boys (aged 12-14 years) 'at risk' of obesity. The intervention was based on Self-Determination Theory and Social Cognitive Theory and involved: professional development, fitness equipment for schools, teacher-delivered physical activity sessions, lunch-time activity sessions, researcher-led seminars, a smartphone application, and parental strategies. Assessments for the primary (body mass index [BMI], waist circumference) and secondary outcomes were conducted at baseline, 8- (post-intervention) and 18-months (follow-up). Analyses followed the intention-to-treat principle using linear mixed models. RESULTS: After 18-months, there were no intervention effects for BMI or waist circumference. Sustained effects were found for screen-time, resistance training skill competency, and motivational regulations for school sport. CONCLUSIONS: There were no clinically meaningful intervention effects for the adiposity outcomes. However, the intervention resulted in sustained effects for secondary outcomes. Interventions that more intensively target the home environment, as well as other socio-ecological determinants of obesity may be needed to prevent unhealthy weight gain in adolescents from low-income communities. TRIAL REGISTRATION: Australian Clinical Trial Registry ACTRN12612000978864.

Intervention to reduce recreational screen-time in adolescents: Outcomes and mediators from the 'Switch-Off 4 Healthy Minds' (S4HM) cluster randomized controlled trial.

INTRODUCTION: The primary objective was to evaluate the impact of the 'Switch-off 4 Healthy Minds' (S4HM) intervention on recreational screen-time in adolescents. METHODS: Cluster randomized controlled trial with study measures at baseline and 6-months (post-intervention). Eligible participants reported exceeding recreational screen-time recommendations (i.e., >2h/day). In total, 322 adolescents (mean age=14.4±0.6years) from eight secondary schools in New South Wales, Australia were recruited. The S4HM intervention was guided by Self-Determination Theory and included: an interactive seminar, eHealth messaging, a behavioral contract and parental newsletters. The primary outcome was recreational screen-time. Secondary outcomes included mental health (i.e., well-being, psychological distress, self-perceptions), objectively measured physical activity, and body mass index (BMI). Outcome analyses were conducted using linear mixed models and mediation was examined using a product-of-coefficients test. RESULTS: At post-intervention, significant reductions in screen-time were observed in both groups, with a greater reduction observed in the intervention group (-50min/day versus -29min, p<0.05 for both). However, the adjusted difference in change between groups was not statistically significant (mean=-21.3min/day, p=0.255). There were no significant intervention effects for mental health outcomes, physical activity or BMI. Significant mediation effects for autonomous motivation were found. CONCLUSIONS: Participants in both the S4HM intervention and control groups significantly reduced their screen-time, with no group-by-time effects. Enhancing autonomous motivation might be a useful intervention target for trials aimed at reducing adolescents' recreational screen-time. TRIAL REGISTRATION: ACTRN12614000163606.