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Purpose: This study examined longitudinal associations between average physical activity (PA) levels in children and their sleep duration, and whether changes in PA levels are associated with their sleep duration. Methods: Data were collected on 108 children at 4 time points: when children were 6, 12, 18, and 24 months of age (44% female, 50% Non-Hispanic White). PA was assessed using accelerometry. Children’s daytime, nighttime, and 24-hour sleep duration were measured with actigraphy. Linear mixed model analyses estimated the associations between average PA levels over time and changes in PA over time, treating each sleep duration variable as an outcome in separate linear mixed model analyses. Results: Children with higher total PA levels slept less during the day compared with children with lower total PA levels over the 2-year period. The strength of the relationship between a child’s PA levels and their 24-hour sleep duration decreased as they approached 24 months of age. Conclusions: The results suggest that while PA may be developmentally beneficial overall, it appears that its relationship with sleep duration is not clinically relevant in very young children.

Purpose: To determine the acute response of lactate supplementation on athletic performance. Method: Fifteen athletes under the age of 15 performed the following 4 sessions in a nonrandomized order: (1) familiarization, (2) control, (3)  participants ingested calcium lactate (21.5 mg·kg⁻¹ body mass), and (4) participants ingested a placebo (PLA, calcium carbonate, 21.5 mg·kg⁻¹ body mass). The capsules were randomly offered and consumed 60 minutes before the physical tests. To assess the physical performance, the athletes executed squat jump, countermovement squat jump, 20-m linear sprint, change of direction test, and running anaerobic sprint test. Results: There were no significant differences between conditions for squat jump, countermovement jump, change of direction, and minimum power obtained in the running anaerobic sprint test (P > .05). Conversely, we observed a worse performance (P < .05) in the 20-m linear sprint test in the PLA and lactate conditions compared with control (P < .05). The lactate condition worsened performance during running anaerobic sprint test for peak power, mean power, and fatigue index compared with control and PLA (P < .05). Conclusions: Calcium lactate supplementation worsened repetitive running sprint ability and 20-m sprint performance. However, lactate supplementation does not affect jump or agility capacity. Therefore, calcium lactate supplementation seems to be an ineffective strategy to improve anaerobic and neuromuscular performance in soccer players 15 years of age or less.

Purpose: Rigorous evidence concerning the reliability of physical tests among young athletes is lacking. Therefore, this study aimed to comprehensively determine the retest reliability of the most commonly used tests to assess physical qualities in adolescent rugby league players, and to provide the standard error of measurement and minimal detectable change for each test to support objective athlete monitoring. Method: A repeated-measures design was employed with 50 adolescent, schoolboy rugby league players (16.2 [1.3] y) completing the same testing battery across 2 consecutive weeks. Within each week, stature, body mass, and ∑4 skinfold thickness assessments, as well as countermovement jump, medicine ball throw, and 1-repetition maximum bench press, back squat, and prone row tests were conducted on the first testing day. Forty-eight hours later, a second testing day contained the 10- and 20-m linear sprints, 505-Agility Test, L-run Test, and Multistage Fitness Test. Results: Nonsignificant (P > .05), trivial differences (d _av = 0.00–0.16) were evident between trials in all tests. The coefficient of variation ranged from 0.05% to 4.02% across tests. The intraclass correlation ranged from .704 to .999. All tests presented relatively low standard error of measurement, with accompanying minimal detectable change provided. Conclusion: These data can help inform decision making among end-users when implementing tests in a repeated manner and interpreting testing data.

Background: Exercise optimizes peak bone mass accrual, particularly if the loading is high magnitude and distributed in abnormal directions. Little is known about the influence of early intense training in sport during peak bone mass accrual, especially in boys. Methods: Ninety-eight males aged 6–24 years (gymnasts, swimmers, and controls) completed the bone-specific physical activity questionnaire and a 7-day exercise diary. Dual-energy X-ray absorptiometry determined bone mineral properties of the total body (less head) and lumbar spine (LS, L1–L4) and total lean mass. Subgroup analyses were conducted for juniors (prepubescent), adolescents (11–16 y), and seniors (17–24 y). Results: Lean mass was positively associated with total body less head and LS bone outcomes in all 3 age groups (R ² = .632–.770, P < .05), and bone-specific physical activity questionnaire scores were associated with LS bone mineral density in adolescents and seniors (R ² = .440 and .591, P < .05). Senior gymnasts had significantly higher LS bone mineral density (in grams per square centimeter) and Z-scores than swimmers (P = .004) and controls (P = .012). Conclusions: Elite gymnastics is associated with superior peak bone mass accrual in young males. The benefits appear more pronounced during young adulthood compared with prepuberty, potentially reflecting an extended time course for bone adaptation.

Traditionally, sports participation has been based on the chronological age of the individual with year of birth determining participation grouping. However, grouping by chronological age can result in individuals who are nearly a full year different in age competing within the same age group. Moreover, during the pubertal years, age grouping may provide physical (size) advantage to early maturers and disadvantage to late maturers. These advantages/disadvantages could impact talent selection, psychosocial aspects of sport participation, technical and tactical skill development, competitiveness, and injury risk. Biobanding is an alternative method for determining sport participation categorization and uses factors of growth and/or maturation, rather than traditional chronological age, for grouping athletes. Implementation of biobanding in sports may be advantageous to both early and late-maturing athlete development.

Humans are fascinated by the bipedal locomotor capacities at both ends of the athletic spectrum—sprinting speed and endurance. Some of the more popular field (eg, soccer, rugby, and lacrosse) and court (eg, basketball, tennis, and netball) sports utilize mixed energy systems requiring an interplay of both maximal sprinting speed (MSS) and maximal aerobic speed (MAS) to meet the high-intensity running demands of varying frequency, duration, intensity, and recovery. Recently, these locomotor capacities have been considered in combination to produce what is called the anaerobic speed reserve (ASR) as part of the locomotor profile concept (MSS, MAS, and ASR). The purpose of this narrative review is to (1) provide an overview of the locomotor profile concept; (2) review the assessment methods for estimating MSS, MAS, and ASR; (3) examine the age-, sex-, and maturity-associated variations in MSS, MAS, and ASR; (4) examine the trainability of MSS, MAS, and ASR in youth athletes; and (5) conclude with the practical applications using principles of long-term athlete development for training the locomotor profile in youth field and court sport athletes. Based on the available data in young male athletes, MSS, MAS, and ASR generally increase with age and across maturity groups and are trainable. Overall, decisions on training need to consider the sport demands, current fitness and maturity status, and targeted training adaptation sought.

Purpose: This study examined the impact of an 8-week corrective dance intervention on thoracic hyperkyphosis, scapular position, breathing, and happiness in girls aged 10–12 years. Methods: Sixty participants were randomly assigned to either an experimental (EX) or control (CO) group. The intervention involved rhythmic and corrective movements conducted 3 times a week. Measurements were taken before and after the intervention for thoracic hyperkyphosis angle, scapular position, lung function, and happiness levels. Results: EX showed greater improvements (P = .001) than CO for the decrement of thoracic hyperkyphosis angle (48.20–42.80°) than in CO (47.66°–46.59°), and scapular position improved more (P = .003) in EX (1.48°–1.20°) than in CO (1.44°–1.42°). Forced vital capacity (P = .001) and forced expiratory volume in 1 second (P = .001) significantly increased in EX (FVC: 2.65–3.40 L; FEV1: 2.32–2.74 L), while they remained stable in CO. Happiness levels significantly improved (P = .001) in EX (42.20–49.79) and slightly decreased in CO (41.80–40.15). Conclusions: The 8-week dance program improved posture, scapular position, breathing, and happiness in girls aged 10–12 years. It enhances physical health, emotional well-being, and social skills in children and adolescents.

Purpose: This systematic review and meta-analysis aimed to systematically examine and summarize recent evidence on the effects of soccer-based training (SBT) on anthropometric measures in children and adolescents with overweight/obesity. Methods: Adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis 2020 guidelines, a thorough literature search across 7 electronic databases was conducted on October 11, 2023. The studies’ methodological quality was evaluated using the QualSyst tool, followed by conducting a meta-analysis with a random-effects model, and the certainty of evidence was assessed. Results: Six studies were included, with 4 studies of strong methodological quality and 2 studies of moderate methodological quality. The results of the meta-analysis revealed SBT decreases fat mass percentage (effect size [ES] = 0.47 [small]; P = .002), with no significant effect of SBT on body mass index (ES = 0.180 [small]; P = .275), body mass (ES = 0.183 [trivial]; P = .212), fat-free mass (ES = 0.074 [trivial]; P = .635), or waist circumference (ES = 0.358 [small]; P = .053). The certainty of evidence was moderate for all outcomes. Conclusions: SBT appears to decrease fat mass percentage, without affecting body mass, body mass index, fat-free mass, or waist circumference in obese/overweight children and adolescents. These findings require further investigation given the moderate certainty of evidence. Registration: The protocol of this review was registered in the Open Science Framework database (https://doi.org/10.17605/OSF.IO/8P4V2).

Purpose: This study examined the effectiveness of an early childhood educator (ECE)-focused physical activity e-Learning course on children’s physical activity and sedentary time in childcare. Methods: A cluster randomized controlled trial was conducted in 12 childcare centers in London, Ontario, Canada. A total of 145 preschoolers and 42 ECEs participated in this study. ECEs in the intervention condition completed a 5-hour e-Learning course related to physical activity. Outcomes were preschoolers’ minutes of moderate- to vigorous-intensity physical activity, light-intensity physical activity, and sedentary time assessed using accelerometers. Results: The intervention did not have a significant effect on moderate- to vigorous-intensity physical activity (d < 0.01, P = .984), light-intensity physical activity (d = −0.17, P = .386), or sedentary time (d = 0.07, P = .717) from baseline to postintervention. There was also no significant intervention effect on moderate- to vigorous-intensity physical activity (d = 0.27, P = .260), light-intensity physical activity (d = −0.08, P = .740), or sedentary time (d = −0.15, P = .520) from baseline to follow-up. Conclusions: Providing ECEs with online training in physical activity through an e-Learning course may not be sufficient to increase physical activity levels among young children in their care. It may be essential to deliver multicomponent interventions to increase preschoolers’ engagement in physical activity in childcare.

This study critically examines the suitability of using a single drop height to assess the reaction strength index in trained and active participants, a key component of athletic performance. Using a cross-sectional design, 377 trained (n = 163) and active (n = 214) participants aged 14–18 years performing drop jumps from 4 different heights (24, 32, 40, and 48 cm) were studied. The primary aim was to explore the individual differences in reaction strength index at these heights and to assess whether a single height can reliably represent stretch-shortening cycle capabilities. While the repeated measures analysis of variance did not reveal any significant differences, the Bland–Altmann analysis revealed significant individual discrepancies between the performance of the drop heights, resulting in a mean absolute error of 32.1 and a mean absolute percentage error of 20.6%. These results strongly suggest that a single drop height is not sufficient to determine performance in the stretch-shortening cycle. This has important practical implications as it can lead to underestimates of performance trends. The study advocates the inclusion of a range of drop heights in routine testing to accurately measure reactive power and thus improve the effectiveness of individualized training programs for young athletes/active youth.