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Purpose: The development of sprint running during youth has received renewed interest, but questions remain regarding the development of speed in youth, especially the influences of sex, training, and maturity status. Methods: One hundred and forty-seven team sport trained (69 girls; 14.3 [2.1] y) and 113 untrained (64 girls; 13.8 [2.7] y) youth completed two 30-m sprints separated by 2-minute active rest. Velocity was measured using a radar gun at >46 Hz, with power and force variables derived from a force–velocity–power profile. Results: Boys produced a significantly higher absolute peak power (741 [272] vs 645 [229] W; P < .01) and force (431 [124] vs 398 [125] N; P < .01) than girls, irrespective of maturity and training status. However, there was a greater sex difference in relative mean power and peak velocity in circa peak height velocity adolescents (46.9% and 19.8%, respectively) compared with prepeak height velocity (5.4% and 3.2%) or postpeak height velocity youth (11.6% and 5.6%). Conclusions: Sprint development in youth is sexually dimorphic which needs considering when devising long-term training plans. Further research is needed to explore the independent, and combined, effects of sex, training, and maturity status on sprint performance kinetics in youth.

Purpose: The aim of this systematic review is to reveal the social, personal, and contextual factors that influence physical activity (PA) in children and adolescents during and after cancer treatment. Method: SPORTDiscus, Cochrane, Web of Science, PubMed, and FIS Education electronic database were systematically searched. Results: The 13 included studies show that social support (parents, siblings, and friends) in particular is rated as important by cancer survivors; for example, doing PA together. Depending on the treatment status and state of health, particularities arise. During the acute treatment phase, parents issued more prohibitions regarding PA than after treatment. The state of health and concern about infections are described as inhibiting factors. Not all hospitals generally offer special exercise programs for cancer patients, and in some cases, only sporadic exercise sessions were conducted by specialized staff. In addition, the hospital atmosphere, such as cramped rooms, tends to be associated with demotivating effects. Conclusions: Both inhibiting and promoting factors in the area of social, personal, and contextual factors could be identified. The most fundamental factor for PA is the physical condition. Social factors, such as parents or friends, often have a motivating effect and can promote PA. Inhibiting factors are mainly context-related, such as an environment unsuitable for PA. Although the review highlights interesting aspects, further treatment-related and longitudinal studies could provide deeper insights.

Purpose: To assess the association between the amount of recess provision and children’s accelerometer-measured physical activity (PA) levels. Methods: Parents/guardians of 6- to 11-year-olds (n = 451) in the 2012 National Youth Fitness Survey reported recess provision, categorized as low (10–15 min; 31.9%), medium (16–30 min; 48.0%), or high (>30 min; 20.1%). Children wore a wrist-worn accelerometer for 7 days to estimate time spent sedentary, in light PA, and in moderate to vigorous PA using 2 different cut points for either activity counts or raw acceleration. Outcomes were compared between levels of recess provision while adjusting for covariates and the survey’s multistage, probability sampling design. Results: Children with high recess provision spent less time sedentary, irrespective of type of day (week vs weekend) and engaged in more light or moderate to vigorous PA on weekdays than those with low recess provision. The magnitude and statistical significance of effects differed based on the cut points used to classify PA (eg, 4.7 vs 11.9 additional min·d⁻¹ of moderate to vigorous PA). Conclusions: Providing children with >30 minutes of daily recess, which exceeds current recommendations of ≥20 minutes, is associated with more favorable PA levels and not just on school days. Identifying the optimal method for analyzing wrist-worn accelerometer data could clarify the magnitude of this effect.

Purpose: Studying physical activity in toddlers using accelerometers is challenging due to noncompliance with wear time (WT) and activity log (AL) instructions. The aims of this study are to examine relationships between WT and AL completion and (1) demographic and socioeconomic variables, (2) parenting style, and (3) whether sedentary time differs by AL completion. Methods: Secondary analysis was performed using baseline data from a community wellness program randomized controlled trial for parents with toddlers (12–35 mo). Parents had toddlers wear ActiGraph wGT3x accelerometers and completed ALs. Valid days included ≥600-minute WT. Analysis of variance and chi-square analyses were used. Results: The sample (n = 50) comprised racial and ethnically diverse toddlers (mean age = 27 mo, 58% male) and parents (mean age = 31.7 y, 84% female). Twenty-eight families (56%) returned valid accelerometer data with ALs. Participants in relationships were more likely to complete ALs (P < .05). Toddler sedentary time did not differ between those with ALs and those without. Conclusions: We found varied compliance with WT instructions and AL completion. Returned AL quality was poor, presenting challenges in correctly characterizing low-activity counts to improve internal validity of WT and physical activity measures. Support from marital partners may be important for adherence to study protocols.

Purpose: We examined fluid intake, the relation between body mass (BM) loss and performance, and core temperature in young triathletes during a competition in tropical climate. Methods: Fluid intake and pre and post BM were measured in 35 adolescent athletes, and core temperature was measured in one female and one male. Results: Mean urine specific gravity (1.024 [0.007]) indicated that athletes were in suboptimal state of hydration upon waking. Race time was 73.2 (8.0) minutes. BM decreased by 0.6 (0.3) kg (P < .05). Fluid intake (528.5 [221.6] mL) replaced 47% of the fluid loss (1184.9 [256.4] mL) and was higher during run (11.5 [6.6] mL·min⁻¹) compared to bike (7.3 [3.1] mL·min⁻¹), P < .01. Loss in BM was ≥1.0% in 66% and ≥1.5% in 29% of the athletes. Males showed a moderate association between percentage loss in BM and finishing time (r = −.52), higher sweat rates (1.0 [0.3] L·h⁻¹), and faster times (69.4 [7.5] min; P < .05). Core temperature rose to 40.1 °C in the female and 39.6 °C in the male. Conclusion: Young triathletes competing in a hot/humid climate became mildly to moderately dehydrated and hyperthermic even when water and sports drinks were available but did not show symptoms of heat illness.

Purpose: Previous literature has demonstrated the mediating role of adiposity in the association between cardiorespiratory fitness (CRF) and cardiometabolic risk as well as the potential role of CRF in attenuating the adverse consequences associated with excess weight. This study aimed to evaluate the mediating role of CRF and adiposity in the possible association with cardiometabolic risk. Method: Observational 3-year longitudinal study that included 420 children and adolescents (10.50 [2.05] y of age at baseline; 56.2% girls). Body mass index (BMI) was calculated, and CRF was evaluated using field assessments. A clustered cardiometabolic risk score (cMetS) was calculated from glucose, systolic blood pressure, total cholesterol/high-density lipoprotein cholesterol ratio, and triglycerides z scores. Analyses evaluated the mediating role of BMI in the association between CRF and cMetS as well as whether CRF mediated the association between BMI and cMetS. Results: BMI at baseline was directly associated with the cMetS at follow-up (0.102; 95% confidence interval, 0.020 to 0.181), independently of CRF, whereas CRF was only indirectly associated with cMetS at follow-up through BMI (−0.036; 95% confidence interval, −0.070 to −0.009), meaning that the association between CRF and cMetS was explained via the mediation role of BMI. Conclusions: BMI presented direct association with cMetS, whereas CRF exhibited indirect association with cMetS mediated via BMI.