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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.

Purpose: In girls and women, the authors studied the effects of an acute bout of low-impact, moderate-intensity exercise serum on myoblast and osteoblast proliferation in vitro. Methods: A total of 12 pre/early pubertal girls (8–10 y old) and 12 women (20–30 y old) cycled at 60% VO₂max for 1 hour followed by 1-hour recovery. Blood samples were collected at rest, mid-exercise, end of exercise, mid-recovery, and end of recovery. C2C12 myoblasts and MC3T3E1 osteoblasts were incubated with serum from each time point for 1 hour, then monitored for 24 hours (myoblasts) or 36 hours (osteoblasts) to examine proliferation. Cells were also monitored for 6 days (myoblasts) to examine myotube formation and 21 days (osteoblasts) to examine mineralization. Results: Exercise did not affect myoblast or osteoblast proliferation. Girls exhibited lower cell proliferation relative to women at end of exercise (osteoblasts, P = .041; myoblasts, P = .029) and mid-recovery (osteoblasts, P = .010). Mineralization was lower at end of recovery relative to rest (P = .014) in both girls and women. Myotube formation was not affected by exercise or group. Conclusion: The systemic environment following one acute bout of low-impact moderate-intensity exercise in girls and women does not elicit osteoblast or myoblast activity in vitro. Differences in myoblast and osteoblast proliferation between girls and women may be influenced by maturation.

Purpose: To verify the reciprocal longitudinal relationships between cardiorespiratory fitness (CRF), percentage body fat (%body fat), and metabolic syndrome in Brazilian primary school students. Method: This longitudinal study involved 420 children and adolescents followed for 3 years (2011–2014). The continuous Metabolic Syndrome (cMetSyn) score was calculated by summing adjusted z scores of glucose, systolic blood pressure, total cholesterol/high-density lipoprotein cholesterol ratio, triglycerides, and waist circumference. The CRF was assessed using running/walking tests, and %body fat was assessed through sex-specific 2-site skinfold thickness. Cross-lagged panel models were used to analyze longitudinal reciprocal relationships between CRF and %body fat with cMetSyn. Results: Results indicated that 2011 %body fat significantly predicted both 2014 CRF scores and 2014 cMetSyn scores (P < .001); however, 2011 CRF only predicted 2014 %body fat (P < .001) but not 2014 cMetSyn (P = .103). Furthermore, 2011 cMetSyn predicted 2014 %body fat (P = .002). The model explained 36%, 48%, and 37% of the variance in 2014 CRF, %body fat, and cMetSyn, respectively. Conclusion: The results suggest a reciprocal inverse relationship between %body fat and metabolic syndrome risk and that %body fat may play a more important role in the risk of developing metabolic syndrome compared with CRF.

Purpose: To examine the effect of growth hormone (GH) treatment on physical performance in children with idiopathic short stature and normal GH secretion. Materials and Methods : A total of 24 children participated in the study (13 GH-treated, 11 non-treated, aged 8–13 y, 11 males and 13 females, Tanner stage 1–2). Participants performed a battery of motor skill performance tests (Eurofit), as well as the Wingate anaerobic test. Results: No statistically significant differences in any of the Eurofit physical fitness test results (eg, 20-m shuttle run 33.0 [15.1] vs 25.1 [21.0] laps in treated and nontreated participants, respectively, P = .25) or the Wingate anaerobic test were found between the groups (eg, peak power 5.0 [2.9] vs 3.9 [2.6] watts/kg in treated and nontreated participants, respectively, P = .2). Conclusions: Therapeutic usage of exogenous GH for pre and early pubertal children with idiopathic short stature and normal GH secretion was not associated with beneficial effects on physical performance indices. This suggests that the use of GH as a potential performance enhancing agent, in this age group, at least at commonly used doses, is not advantageous.

Purpose: The authors examined the relationship between mother and child activity. Methods: The authors compared moderate–vigorous physical activity (MVPA) and sedentary time of low-income mothers with obesity and their 6- to 12-year-old children on week (WD) and weekend (WE) days. A total of 196 mother–child pairs wore accelerometers simultaneously for a week. Mothers completed questionnaires. Spearman correlation and multivariate regression were used. Results: WE MVPA (accelerometry) was significantly correlated between mothers with children aged 6–7 (r _s = .35) and daughters (r _s = .27). Self-reported maternal PA time spent with one of their children was significantly correlated with the WE MVPA of all children (r _s = .21) and children aged 8–10 (r _s = .22) and with the WD MVPA of all children (r _s = .15), children aged 8–10 (r _s = .23), aged 11–12 (r _s = .52), and daughters (r _s = .37), and inversely correlated to the WD sedentary time of all children (r _s = −.21), children aged 8–10 (r _s = −.30), aged 11–12 (r _s = −.34), daughters (r _s = −.26), and sons (r _s = −.22). In multivariate regression, significant associations were identified between reported child–mother PA time together and child MVPA and sedentary time (accelerometry). Conclusions: Mothers may influence the PA levels of their children with the strongest associations found in children aged 6–7 and daughters. Mother–child coparticipation in PA may lead to increased child MVPA and decreased sedentary behavior.

Purpose: The purpose of this study was to examine the impact of the Coronavirus disease 2019 on male and female anthropometric variables and physical performance. Methods: This study utilized a mixed (time [PRE vs POST], gender [male vs female]) methods design to examine changes in the body mass index and physical fitness performance measures prior to and following closures. Data were collected from 264 third through eighth graders. This sample consisted of 131 males and 133 females. The data was collected through anthropometric (body mass index) and physical performance measures and was analyzed with separate 2 × 2 mixed-factorial analyses of variance (time [PRE, POST] × gender [male, female]). Results: The findings indicated both males and females exhibited mean increases in the body mass index (+10.6%; 18.8–20.8 kg·m⁻², P < .001, partial η ² = .627) and decreases in push-ups (−35.6%; 7.3–4.7 repetitions, P < .001, partial η ² = .371), sit-ups (−19.4%; 22.7–18.3 repetitions, P < .001, partial η ² = .420), and the Progressive Aerobic Cardiovascular Endurance Run test (−26.7%; 31.4–22.4 laps, P < .001, partial η ² = .644) scores from PRE to POST. Conclusion: The results of this study demonstrate that both males and females exhibited significant anthropometric and physical performance losses during the Coronavirus disease 2019 shutdown.