Discussion: HIIE and CMIE both improved glycaemic control in the 24h period following exercise. The HIIE was however ≈38% more time-efficient, consisted of ≈23% less total work (Watts), and increased the time spent with lowered glucose levels over a 24h period. HIIE therefore may be a convenient and physiologically beneficial exercise model to be included in exercise programs for overweight and inactive populations who are at risk of developing chronic lifestyle disease. 167 Improving Muscular Fitness Enhances Psychological Well-being in Low-income Adolescent Boys: Findings from the ATLAS Cluster RCT AWARD FINALIST Friday 23 October D. Lubans 1 * • J. Smith 1 • P. Morgan 1 • M. Beauchamp 2 • A. Miller 1 • C. Lonsdale 3 • P. Parker 3 • K. Dally 1 1 University of Newcastle, PRC in Physical Activity and Nutrition • 2 University of British Columbia, School of Kinesiology • 3 Australian Catholic University, Institute for Positive Psychology and Education Background: Physical inactivity, poor fitness and excessive recreational screen-time may have a detrimental impact on adolescents’ psychological well-being, but there is a lack of causal evidence, as the majority of studies have been cross-sectional. Carefully designed experimental studies combined with statistical mediation tests are needed to determine the influence of changes in behaviors and fitness on well-being in young people. The aim of this study was to explore the effect of the Active Teen Leaders Avoiding Screen-time (ATLAS) intervention on psychological well-being in adolescent boys and to examine potential mediating mechanisms. Methods: The intervention was evaluated using a cluster randomized controlled trial in 14 secondary schools located in low-income communities (N=361 adolescent boys, mean age=12.7± 0.5 years). ATLAS was a school-based obesity prevention intervention targeting the health behaviors [i.e., physical activity, screen-time and sugar-sweetened beverage (SSB) consumption] of adolescent boys considered ‘at-risk’ of obesity. The intervention was delivered over 20 weeks and consisted of teacher professional development, researcher-led seminars, enhanced school sport sessions, lunch-time physical activity mentoring sessions, provision of fitness equipment to schools, a smartphone application and website, pedometers for self-monitoring, and parental strategies to reduce screen-time. Assessments were conducted at baseline and post-intervention (8-months). The primary outcome was psychological well-being, determined using Diener and colleagues’ Flourishing Scale. Changes in muscular fitness (timed push-up test), resistance training skill competency (Resistance Training Skills Battery), recreational screen-time (Adolescent Sedentary Activity Questionnaire), and SSB consumption (NSW Schools Physical Activity and Nutrition Survey) were examined as potential mediating mechanisms. Intervention effects and mediation analyses were tested using multi-level linear regression analysis in MPlus. Results: The intervention effect on psychological well-being was small, but statistically significant [unstandardised regression coefficient, C =1.40, standard error (SE) =0.63, p =0.027]. In the multiple mediator model that included all of the hypothesized mediators, changes in muscular fitness were significantly associated with changes in well-being (p =0.001). Muscular fitness satisfied the criteria for mediation and accounted for 44.0% of the intervention effect on well-being. Discussion: The results of this study provide causal evidence for the beneficial effects of improving muscular fitness in relation to psychological well-being in a sample of adolescent boys from low-income backgrounds. While the primary aim of the intervention was obesity prevention, the results of this study suggest that the ATLAS program had ‘spillover effects’ in supporting boys’ psychological well-being, and that these effects occurred as a result of improvements in muscular fitness. 168 Work-matched high-intensity interval and traditional continuous endurance training similarly attenuate maximal strength gain during concurrent training AWARD FINALIST J. Fyfe 1 2 * • D. Bishop 1 2 • J. Bartlett 1 4 • E. Hanson 1 3 • N. Stepto 1 2 1 Institute of Sport, Exercise and Active Living, Victoria University, Australia • 2 College of Sport and Exercise Science, Victoria University, Australia • 3 Department of Exercise and Sport Science, University of North Carolina, USA • 4 Western Bulldogs Football Club, Melbourne, Australia Introduction: Simultaneously undertaking resistance and endurance exercise is termed concurrent training, and can attenuate muscle hypertrophy and strength gains compared to performing resistance training (RT) alone. However, the role of individual training variables in this ‘interference effect’ is unclear. High-intensity interval training (HIT) is a potent stimulus for improving performance and metabolic health markers compared with traditional continuous (CONT) endurance training. However, whether HIT and CONT differentially affect strength and hypertrophy outcomes during concurrent training is unknown. Methods: Twenty-three recreationally-active males were ranked by baseline 1RM leg press strength and randomly assigned to one of three training groups: 1) HIT+RT (n=8), 2) CONT+RT (n=7) and 3) RT (n=8). Participants completed 8 weeks of group-specific training and were assessed for maximal lower- and upper-body strength (1RM leg press and bench press, respectively), maximal lower-body counter-movement jump [CMJ] force/ power, and body composition (DXA) before (PRE) and following completion of the training program (POST). Results: Maximal lower-body strength improved from PRE-POST for RT (mean change ±90% confidence interval; 37.4 ±9.9%; effect size [ES] ±90% confidence interval; 1.31 ±0.3; P
(-6.4 ±16.6%; ES, -0.41 ±1.09). Lower body lean mass similarly increased between PRE-POST for RT (3.7 ±2.1%; ES; 0.27 ±0.15; P
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