Sébastien Ratel

Purpose : It is well described that adolescents with obesity show a higher cost of walking (Cw) compared with their lean counterparts, but it remains unknown how the degree of obesity and adiposity impact this Cw in this population. The present study, a secondary analysis of the EBOY cohort (Energy Balance and Obesity in Youth), explores the influence of the degree of obesity and adiposity on the Cw in adolescents with obesity. Method : The Cw was assessed using indirect calorimetry, and body composition was measured by dual-energy X-ray absorptiometry. Participants were divided into tertiles based on their anthropometrics and body composition outcomes. Results : The present study shows a tertile effect for body weight, z -score of body mass index, fat-free mass, and fat mass (FM; in kilograms) on gross and net absolute Cw ( P < .001), while there was only a FM (in percenatage) tertile effect on net absolute Cw ( P = .045). Conclusion : Cw in weight stable adolescents suffering from obesity seems to be mainly under the influence of the mechanical load imposed by the increase of body weight, z -score of body mass index, fat-free mass, and FM in kilograms, while the effects of the percentage of FM appears to be less clear and remains to be further explored.

Purpose : The aim of this study was to investigate the extent to which relative age effect (RAE) impacts the development of perceptual-cognitive skills and how training background may potentially offset RAE from childhood into adolescence. Method : One hundred sixty-five 10- to 16-year-old male participants were divided into 8 groups based on their birth quartiles (BQ ₁ [January–March], BQ ₂ [April–June], BQ ₃ [July–September], and BQ ₄ [October–December]) and training background (moderately trained: 1–2 sessions/wk and well-trained: 4–5 sessions/wk). Their perceptual-cognitive skills were evaluated using a 3D multiple-object tracking task (ie, the NeuroTracker [NT]) with (3D) and without (2D) stereopsis. Results : In moderately trained children, NT scores progressively decreased from BQ ₁ to BQ ₄ , with a significant difference between the first 3 birth quartiles and BQ ₄ ( P < .01), independent of stereopsis. In well-trained children, however, no significant differences were detected in NT scores between quartiles, and well-trained children in BQ ₄ exhibited NT scores comparable to moderately trained children in the first 3 quartiles. Conclusion : RAE showed a significant disadvantage on the perceptual-cognitive scores in moderately trained children born in BQ ₄ . However, well-trained children born in BQ ₄ performed similarly to other well-trained children and to moderately trained children born in the first 3 birth quartiles, meaning that training background may offset the disadvantage associated with RAE from childhood into adolescence.

Purpose : Lower-limb strength assessment is essential for talent identification, training program design, and return-to-play decisions. However, the influence of biological maturity on test reliability remains unclear, particularly in prepubertal players whose motor coordination is still developing. This study examined the test–retest reliability of dominant-limb abduction, adduction, and anterior and posterior chain tests in elite youth football players, and compared reliability across maturity stages and movement types. Methods : Seventy academy players were divided into 3 groups: 24 prepubertal, 18 pubertal, and 28 postpubertal. Following at least 2 familiarization sessions, players performed 5 maximal isometric strength tests on 2 occasions 1 week apart. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) were calculated for each test, and statistical comparisons between maturity groups were performed using the Modified Signed-Likelihood Ratio Test (for CVs) and Fisher Z transformation (for ICCs). Results : Most tests demonstrated good to excellent reliability across all maturity levels (CV < 10%, ICC > .90). However, postpubertal players exhibited significantly lower CVs and higher ICCs than prepubertal players in several tests, particularly for polyarticular standing posterior chain movements ( P < .05). No significant differences were observed between prepubertal and pubertal players. Conclusions : These results indicate that test reliability improves with biological maturity, likely due to enhanced motor coordination and movement control. Consequently, the reliability of lower-limb strength assessments is not interchangeable between maturity categories, and results should be interpreted with caution when used for talent identification or long-term player monitoring in elite youth football players.

Background: A significant decline in physical activity levels of children and adolescents has been reported over the last decades, and it appears that the magnitude of decrease in physical activity levels was accentuated during and after the COVID-19 pandemic. This has resulted in children having health problems that were traditionally seen mainly in older adults, such as sarcopenic obesity, osteopenia, neuromuscular disorders, cardiometabolic complications, and dynapenia (reduced levels of muscle force). Objectives: To explore the latest reports, which show that modern-day youth are at greater risk of pediatric dynapenia related to muscle disuse, and discuss training strategies to reverse this condition according to the specific physiological characteristics of children and adolescents. Methodology: The terms “pediatric dynapenia”, “physical activity levels in youth/children/adolescents” and “resistance training for youth/children/adolescents” were used for selecting studies on PubMed and Google Scholar databases. Results and Discussion: Pediatric dynapenia is closely associated with the development of co-morbidities along the lifespan. Effective resistance training methods according to the appropriate maturity level, such as eccentric-based resistance exercises, are necessary for increases in muscle strength in children and adolescents. Conclusion: Public initiatives that support effective exercise training strategies such as resistance training programs in schools and community centers in Brazil and around the world are necessary to monitor and reduce the sedentarism and risk of pediatric dynapenia in children and adolescents, accentuated by the COVID-19 pandemic.

Objective: This study aimed to investigate the effect of relative age on gross motor coordination (GMC) development, taking into account biological maturity and sex. Methods: 729 participants aged 10 to 16 years completed three GMC tests newly designed to minimize the potentially confounding effects of physical fitness. The tests included a Hand-Foot coordination test, Dribbling-Targeting test (DT test), and a T balance and agility test (T test). Relative age was determined using birth quartiles: BQ₁ (January–March); BQ₂ (April–June); BQ₃ (July–September); and BQ₄ (October–December). Regarding biological maturity, the participants were categorized according to their estimated peak height velocity (pre- and post-PHV). Results: Relative age did not significantly impact the overall GMC score. In contrast, biological maturity emerged as a significant determinant of GMC, with post-PHV participants outperforming their pre-PHV counterparts in the three tests (p < 0.001). The results also showed a significant main effect of sex in the DT and T tests, i.e., in tasks involving dynamic coordination and agility, with boys consistently outperforming girls (p < 0.001). Significant biological maturity × sex interactions in the DT and T tests also indicated an advantage of boys over girls with advancing biological maturity (p < 0.05). Conclusions: these findings highlight the importance of considering biological maturity and sex rather than relative age in GMC development from childhood through adolescence.