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Girls’ acute responses to group-based high-intensity interval exercise (HIIE) are not well characterized. Purpose: To compare acute responses to treadmill-based HIIE (TM) and body-weight resistance exercise circuit (CIRC) and to CIRC performed in a small-group setting (group CIRC). Method: Nineteen girls (9.1 [1.1] y) completed exercise testing on a TM to determine peak oxygen uptake, peak heart rate (HR_peak), and maximal aerobic speed. The TM involved eight 30-second sprints at 100% maximal aerobic speed. The CIRC consisted of 8 exercises of maximal repetitions performed for 30 seconds. Each exercise bout was followed by 30 seconds of active recovery. The blood lactate concentration was assessed preexercise and postexercise. The ratings of perceived exertion, affective valence, and enjoyment were recorded at preexercise, Intervals 3 and 6, and postexercise. Results: The mean heart rate was higher during group CIRC (92% [7%] HR_peak) than CIRC (86% [7%] HR_peak) and TM (85% [4%] HR_peak) ( ${\eta }_{\mathrm{p}}^2$  = .49). The mean oxygen uptake equaled 76% (11%) of the peak oxygen uptake for CIRC and did not differ from TM (d = 0.02). The CIRC elicited a greater postexercise blood lactate concentration versus TM (5.8 [1.7] vs 1.4 [0.4] mM, d = 3.61). The perceptual responses were similar among conditions (P > .05), and only the rating of perceived exertion increased during exercise ( ${\eta }_{\mathrm{p}}^2$  = .78). Conclusion: Whether performed individually or in a small group, CIRC represents HIIE and may be a feasible alternative to running-based HIIE.

Purpose: To assess children’s physical activity, sedentary behavior, liking, and motivation during 3 separate simulated recess conditions: playing alone, with their parent participating, and with their peer participating. Methods: Children participated in the 3 separate conditions. During each condition, the children had access to an outdoor playground and sedentary activity options for 30 minutes. Accelerometry recorded the physical activity. Time allocated to sedentary options was monitored via a stopwatch. A visual analog scale was used to assess liking, and motivation was assessed as the children’s willingness to participate in an additional 10 minutes of each condition. Results: The children sat 88% less and were 33% more physically active with their peer versus playing alone. The children also sat 65% less during the parent condition than alone. Lastly, the children reported ≥34% liking and were ≥2-fold more likely to participate in the additional 10-minute activity bout during the parent and peer conditions than alone. The differences were significant (P ≤ .05) except for the children’s decision to participate in the additional 10 minutes in the parent versus the alone condition (P = .058). Conclusions: Relative to the alone condition, the presence of a peer or parent reduced sedentary behavior and increased liking and the motivation to participate in that condition. However, only the presence of a peer increased physical activity versus alone.

This study compared the effects of self-selected exercise intensity (SEI) versus predetermined exercise intensity (PEI) on blood pressure (BP) and arterial stiffness in adolescents with obesity. A total of 37 adolescents, 14.7 (1.6) years old, body mass index ≥95th percentile were randomly allocated into SEI (n = 18; 12 boys) or PEI (n = 19; 13 boys). Both groups exercised for 35 minutes on a treadmill, 3 times per week, for 12 weeks. The SEI could set the speed at the beginning of the sessions and make changes every 5 minutes. The PEI adolescents were trained at an intensity set at 60% to 70% of heart rate reserve. Brachial and central BP, pulse pressure, augmentation index, and carotid–femoral pulse wave were determined at baseline and after 12 weeks. Both groups reduced brachial systolic BP (SEI, Δ = −9 mm Hg; PEI, Δ = −4 mm Hg; P < .01), central systolic BP (SEI, Δ = −4 mm Hg; PEI, Δ = −4 mm Hg; P = .01), and central pulse pressure (SEI, Δ = −4 mm Hg; PEI, Δ = −3 mm Hg; P = .02) without differences between groups. No changes in the augmentation index and carotid–femoral pulse wave were observed in either group. The SEI induced similar changes in various cardiovascular outcomes compared with PEI in adolescents with obesity.

Purpose: To investigate the association between the heart rate (HR) at maximal fat oxidation (MFO) and the HR at the aerobic threshold (AerT) in adolescent boys and girls, and to identify sex differences in the intensity that elicits MFO (Fat_max) as a percentage of HR peak (HR_peak). Methods: Fifty-eight healthy adolescents participated in this study (29 boys and 29 girls). Participants performed a cardiopulmonary exercise test on a cycle ergometer. MFO was calculated using a stoichiometric equation, and the AerT was identified using gas exchange parameters. Results: A strong correlation between HR at Fat_max and HR at AerT was found in both boys and girls (r = .96 and .94, respectively). Fat_max as a percentage of HR_peak occurred at 61.0% (4.9%) of HR_peak and 66.8% (6.9%) of HR_peak in adolescent boys and girls (P = .001, F = 13.6), respectively. MFO was higher in boys compared with girls (324 [150] and 240 [95] mg/min, respectively), and no sex differences were observed in the relative contribution of fat to energy expenditure at Fat_max. Conclusions: HR at Fat_max and HR at AerT were highly correlated in adolescent boys and girls. Girls obtained Fat_max at a higher percentage of HR_peak than boys.

Purpose: To assess the effect of 1 week of consuming a placebo “energy drink” compared with a week of drinking regular water on daily physical activity in obese children participating in a weight reduction multidisciplinary program. Methods: Seventeen prepubertal (age = 128.7 [26.6] m) overweight and obese children (7 females and 10 males) participated in the study. Participants received 7 bottles of mineral water per week for 2 weeks. Different types of information were randomly provided regarding the drink consumed in each week: standard (water) versus deliberate positive information (presumed energy drink and placebo). Daily step count was measured using pedometers and compared using paired t test. Results: After consuming the placebo drink, children demonstrated a significantly higher average daily step number (10,452 [4107]) compared with the days they drank water (8168 [2928], P < .005). This difference was attributed mainly to male participants. Conclusion: The use of placebo in the form of deliberate positive information was associated with a significant increase in real-life physical activity in overweight and obese children, especially in boys. Positive information may be used to encourage children with obesity to enhance daily physical activity and energy expenditure.

Given the high prevalence of overweight/obesity and the low prevalence of engaging in physical activity in children, it is important to identify barriers that impede child physical activity. One potential barrier is parental stress. The current study examined the association between parental stress levels and girls’ and boys’ moderate to vigorous physical activity. Children aged 5–7 years and their families (n = 150) from 6 racial/ethnic groups (n = 25 each Black, Hispanic, Hmong, Native American, Somali, and White families) were recruited for the Family Matters mixed-methods study in 2015 through primary care clinics in Minneapolis and St Paul, MN. Two in-home visits were carried out with families 10 days apart for data collection, with an 8-day observational period in between when children wore accelerometers. Higher parental stress levels were associated with fewer minutes of moderate to vigorous physical activity in girls (P < .05) compared with boys. On average, girls with a parent reporting a stress rating of 10 engaged in 24 minutes less of physical activity per day than girls with a parent with a stress rating of 1. The results suggest that parental stress may reduce girls’ engagement in physical activity. The implications of these results include targeting parental stress and coping skills in future physical activity interventions. In addition, when addressing child physical activity in health care visits with parents and daughters, providers may want to focus their anticipatory guidance on parental stress and coping skills in addition to providing resources to help parents manage stress.

Purpose: To characterize the acute effects of a long-duration adventure race on knee extensor (KE) fatigue and the knee functional ratio in adolescent athletes. Methods: Twenty trained male adolescents (aged 14–17 y) performed an adventure race of 68.5 km. Maximal voluntary isometric contraction (MVIC) KE and knee flexor torques were measured before and immediately after the race. Central and peripheral components of neuromuscular fatigue were quantified from the maximal voluntary activation level and the doublet peak torque (Tw₁₀₀), respectively. The peak eccentric knee flexor torque to concentric KE torque ratio was also measured to determine functional ratio. Results: The race completion time was 05:38 (00:20) hours. Significant reductions in MVIC_KE (−14.7%, P < .001) and MVIC_KF (−17.0%, P < .01) were observed after the race. Voluntary activation level decreased by 8.3% (P < .001) while Tw₁₀₀ remained unchanged. Peak eccentric knee flexor torque decreased 16.0% (P < .001) while peak concentric KE torque did not change. This resulted in a significant reduction in functional ratio (−12.0%, P < .01). Conclusion: The adventure race induced a moderate fatigue, which was mainly explained by central factors without significant peripheral fatigue. However, particular attention should be paid to the knee muscular imbalance incurred by the race, which could increase the risk of ligament injury in adolescent athletes.