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Keith Tolfrey

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Julia Zakrzewski and Keith Tolfrey

Consensus on the exercise protocol used to measure Fatmax (exercise intensity corresponding to maximum fat oxidation (MFO)) in children has not been reached. The present study compared Fatmax estimated using the 3 min incremental cycling protocol (3-INC) and a protocol consisting of several 10 min constant work rate exercise bouts (10-CWR) in 26 prepubertal children. Group Fatmax values were the same for 3-INC and 10-CWR (55% VO2peak) and 95% limits of agreement (LoA) were ± 7% VO2peak. Group MFO values were similar between protocols, although 95% LoA were -94 to 113 mg·min−1. While 3-INC provides a valid estimation of Fatmax compared with 10-CWR, caution should be exercised when estimating MFO in prepubertal children.

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Joey C. Eisenmann and Keith Tolfrey

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Rachel Massie, James Smallcombe, and Keith Tolfrey

Purpose: Chronic exercise programs can induce adaptive compensatory behavioral responses through increased energy intake (EI) and/or decreased free-living physical activity in adults. These responses can negate the benefits of an exercise-induced energy deficit; however, it is unclear whether young people experience similar responses. This study examined whether exercise-induced compensation occurs in adolescent girls. Methods: Twenty-three adolescent girls, heterogeneous for weight status, completed the study. Eleven adolescent girls aged 13 years completed a 12-week supervised exercise intervention (EX). Twelve body size–matched girls comprised the nonexercise control group (CON). Body composition, EI, free-living energy expenditure (EE), and peak oxygen uptake ( V ˙ O 2 ) were measured repeatedly over the intervention. Results: Laboratory EI (EX: 9027, 9610, and 9243 kJ·d−1 and CON: 9953, 9770, and 10,052 kJ·d−1 at 0, 12, and 18 wk, respectively; effect size [ES] = 0.26, P = .46) and free-living EI (EX: 7288, 6412, and 5273, 4916 kJ·d−1 and CON: 7227, 7128, and 6470, 6337 kJ·d−1 at 0, 6, 12, and 18 wk, respectively; ES ≤ 0.26, P = .90) did not change significantly over time and were similar between groups across the duration of the study. Free-living EE was higher in EX than CON (13,295 vs 12,115 kJ·d−1, ES ≥ 0.88, P ≥ .16), but no significant condition by time interactions were observed (P ≥ .17). Conclusion: The current findings indicate that compensatory changes in EI and EE behaviors did not occur at a group level within a small cohort of adolescent girls. However, analysis at the individual level highlights large interindividual variability in behaviors, which suggests a larger study may be prudent to extend this initial exploratory research.

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Alice Emily Thackray, Laura Ann Barrett, and Keith Tolfrey

Eleven healthy girls (mean ± SD: age 12.1 ± 0.6 years) completed three 2-day conditions in a counterbalanced, crossover design. On day 1, participants either walked at 60 (2)% peak oxygen uptake (energy deficit 1.55[0.20] MJ), restricted food energy intake (energy deficit 1.51[0.25] MJ) or rested. On day 2, capillary blood samples were taken at predetermined intervals throughout the 6.5 hr postprandial period before, and following, the ingestion of standardized breakfast and lunch meals. Fasting plasma triacylglycerol concentrations (TAG) was 29% and 13% lower than rest control in moderate-intensity exercise (effect size [ES] = 1.39, p = .01) and energy-intake restriction (ES = 0.57, p = .02) respectively; moderate-intensity exercise was 19% lower than energy-intake restriction (ES = 0.82, p = .06). The moderate-intensity exercise total area under the TAG versus time curve was 21% and 13% lower than rest control (ES = 0.71, p = .004) and energy-intake restriction (ES = 0.39, p = .06) respectively; energy-intake restriction was marginally lower than rest control (-10%; ES = 0.32, p = .12). An exercise-induced energy deficit elicited a greater reduction in fasting plasma TAG with a trend for a larger attenuation in postprandial plasma TAG than an isoenergetic diet-induced energy deficit in healthy girls.

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Keith Tolfrey, Alice Emily Thackray, and Laura Ann Barrett

Exaggerated postprandial triacylglycerol concentrations (TAG) independently predict future cardiovascular events. Acute exercise and diet interventions attenuate postprandial TAG in adults. This paper aims to examine the exercise postprandial lipemia studies published to date in young people. Nine studies satisfied the inclusion criteria adopted for this summary. The majority of studies are in boys (22% girls) and have shown a single ~60-min session of moderate-intensity exercise, performed 12-18 hours before a standardized meal, reduces postprandial TAG. Manipulations of exercise duration and intensity suggest an exercise energy expenditure dose-dependent response is not supported directly in healthy young people. Studies investigating alternative exercise bouts have reported lower postprandial TAG after simulated intermittent games activity, high-intensity interval running and cumulative 10-min blocks over several hours, which may appeal to the spontaneous physical activity habits of young people. Although extension of these initial findings is warranted, exercise may be an effective strategy to promote regular benefits in TAG metabolism in children and adolescents; this may contribute to an improved cardiovascular disease risk profile early in life.

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Keith Tolfrey, Ian Gordon Campbell, and Alan Mark Batterham

This study examined the effect of exercise training on peak VO2 of 26 (12 boys and 14 girls) prepubertal children. Exercise training involved 12 weeks of stationary cycling for 30 min, 3 times · week−1 at 79.3 ± 1.2% (M ± SD) peak heart rate. Nineteen maturity matched controls (10 boys and 9 girls) completed all tests excluding the training. When alterations in habitual physical activity and percent body fat were included as covariates in the analyses, the exercise training did not have a significant effect on peak VO2 for boys or girls. These data may either indicate a maturity related, blunted training response or that prepubertal children require a more intense exercise stimulus.

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Keith Tolfrey, Julia Kirstey Zakrzewski-Fruer, and Alice Emily Thackray

Two publications were selected because they are excellent representations of studies examining different ends of the exercise-sedentary behavior continuum in young people. The first study is an acute response study with 13 mixed-sex, mid to late adolescents presenting complete data from 4 different randomized experimental crossover conditions for analyses. Continuous glucose monitoring showed that interrupting prolonged continuous sitting with body-weight resistance exercises reduced the postprandial glucose concentration compared with a time-matched uninterrupted period of sitting. Furthermore, the effects of the breaks in sitting time were independent of the energy content of the standardized meals, but variations in the area under the glucose time curves expression were important. The second study adopted a chronic 12-week exercise training intervention design with a large sample of obese children and adolescents who were allocated randomly to high-intensity interval training (HIIT), moderate-intensity continuous training, or nutritional advice groups. HIIT was the most efficacious for improving cardiorespiratory fitness compared with the other interventions; however, cardiometabolic biomarkers and visceral/subcutaneous adipose tissue did not change meaningfully in any group over the 12 weeks. Attrition rates from both HIIT and moderate-intensity continuous training groups reduce the validity of the exercise training comparison, yet this still provides a solid platform for future research comparisons using HIIT in young people.

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Keith Tolfrey, Julia K. Zakrzewski-Fruer, and James Smallcombe

Three publications were selected based on the strength of the research questions, but also because they represent different research designs that are used with varying degrees of frequency in the pediatric literature. The first, a prospective, longitudinal cohort observation study from 7 to 16 years with girls and boys reports an intrinsic reduction in absolute resting energy expenditure after adjustment for lean mass, fat mass, and biological maturity. The authors suggest this could be related to evolutionary energy conservation, but may be problematic now that food energy availability is so abundant. The second focuses on the effect of acute exercise on neutrophil reactive oxygen species production and inflammatory markers in independent groups of healthy boys and men. The authors suggested the boys experienced a “sensitized” neutrophil response stimulated by the exercise bout compared with the men; moreover, the findings provided information necessary to design future trials in this important field. In the final study, a dose-response design was used to examine titrated doses of high intensity interval training on cardiometabolic outcomes in adolescent boys. While the authors were unable to identify a recognizable dose-response relationship, there are several design strengths in this study, which was probably underpowered.