Background: Early-maturing players tend to have physical advantages during formative stages, but it remains unclear whether these advantages translate into long-term professional success. This study examines how biological maturation influences participation and career trajectories in youth football. Methods: Anthropometric and competitive data were collected from 47 players (13.53 ± 1.08 years) in a top-tier academy during the 2010–2011 season. The maturation status was assessed using the Tanner–Whitehouse II RUS method, and the career outcomes were tracked in 2024–2025. Results: Early-maturing players showed higher anthropometric values and greater participation. However, late maturers were more likely to reach professional football (p = 0.003), with all players competing in the top five European leagues belonging to the late-maturing group. Conclusions: Early maturation does not guarantee professional success. Strategies such as bio-banding and personalized training can reduce biases and support talent development, highlighting the need for a more holistic approach to player evaluation.

Background: Health-related quality of life is a key indicator of well-being that integrates physical, emotional, and social dimensions. Identifying its determinants during childhood and adolescence is essential to guide effective health promotion strategies. Objective: To analyze the association between health-related quality of life and demographic, anthropometric, biochemical, lifestyle, and environmental variables in school-aged children and adolescents. Methods: A cross-sectional study was conducted during the 2023–2024 academic year in northeastern Spain. A total of 571 children and adolescents participated in the study (mean age = 11.64 ± 1.64 years), of whom 254 were girls (44.48%). Health-related quality of life was assessed using the Revised Children’s Quality of Life Questionnaire (KINDL-R), a validated instrument for assessing perceived well-being in pediatric populations. Independent variables included waist-to-height ratio, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, adherence to the Mediterranean diet, weekly physical activity, sleep quality, and residential context (i.e., large urban areas, small urban areas, and municipalities). Multiple linear regression analysis was performed to explore the associations. Results: Older age was associated with lower health-related quality of life (β = −1.07; 95% CI: −1.61 to −0.53; p < 0.001). In contrast, better adherence to the Mediterranean diet (β = 0.72; 95% CI: 0.09 to 1.37; p = 0.023), better sleep quality (b = −2.48; p < 0.001), and participants living in cities and large urban areas reported compared to those in municipalities were associated with higher HRQoL (p < 0.05), with moderate effect sizes. No significant associations were found for sex, waist-to-height ratio, cholesterol levels, or physical activity. Conclusions: This study highlights the importance of adopting a multidimensional approach to promote health-related quality of life in young populations, addressing dietary habits, sleep quality, and environmental factors within health promotion strategies.

Background/Objectives: Cardiorespiratory fitness (CRF) is a key indicator of current and future health in children and adolescents, and is influenced by both physiological and behavioral factors. This study examined the associations between CRF, body composition, and health-related habits in 685 children and adolescents (aged 8–16 years) who regularly participated in extracurricular sports programs in northeastern Spain. Methods: Participants underwent anthropometric assessments, completed a 20 m shuttle run test to evaluate CRF, and filled out validated questionnaires on physical activity levels, sleep quality, and adherence to the Mediterranean diet. Results: Significant sex differences were observed, with boys achieving higher CRF performance (p < 0.001), primarily associated with greater muscle mass (p < 0.001) and lower body fat percentage (p < 0.001). Age positively correlated with improved CRF (p < 0.001), whereas higher body mass index (p = 0.003) and fat mass (p = 0.020) negatively impacted fitness outcomes. Conclusions: These findings underscore the critical role of physical activity and optimal body composition in promoting cardiorespiratory fitness among youth, emphasizing the importance of targeted interventions to foster healthy behaviors from early childhood. Future research should adopt longitudinal designs to better elucidate the dynamic interactions between lifestyle factors, body composition, and physical fitness throughout childhood and adolescence.

Organized sports are assumed to boost overall physical activity, but evidence suggests structured training does not always increase general activity outside formal sessions. This study explores the link between physical activity levels and weekly training hours in adolescent athletes across sports and competition levels. A total of 10,196 participants aged 11 to 19 were included in the analyses. Participants were classified into seven groups: inactive, somewhat active, non-competitive athletes, and athletes competing at the local, regional, national, or international level. They completed the Spanish version of the Physical Activity Questionnaire and answered questions regarding their performance level, training volume, and socioeconomic status. Girls exhibited lower physical activity levels than boys, even at higher competition levels where both sexes had comparable training hours. Competitive athletes reported the highest physical activity levels. In competitive athletes, physical activity levels decreased with age despite a substantial increase in weekly training hours. They were similar across athletes competing in different sports and at different levels, despite significant differences in training hours. Many athletes, including those at the national and international levels, displayed low physical activity levels, and no clear relationship was found between physical activity level and weekly training hours. The current study provides valuable insights into adolescent physical activity patterns by sex, age, sport, and competition level. Girls showed lower physical activity than boys, even with similar training hours. Physical activity levels declined with age despite increasing training volumes, and no strong association was observed between physical activity and weekly training hours. These results reveal a discrepancy between structured training and overall activity levels, challenging assumptions about the impact of sports participation on daily physical activity.

Objective: This study analyzed the relationship between self-perceived physical fitness and anthropometric and biochemical variables in young athletes from extracurricular sports programs in northeastern Spain. Methods: A cross-sectional design was used with a sample of 673 young athletes. Data collection included self-reported physical fitness and objective anthropometric and biochemical measurements. The analysis explored associations between perceived fitness dimensions and physical/biochemical variables, with attention to sex differences. Results: Fat mass showed significant inverse associations with all perceived fitness dimensions: general fitness (OR = 0.62, 95% CI [0.41, 0.94]), cardiorespiratory fitness (OR = 0.56, 95% CI [0.37, 0.83]), muscular strength (OR = 0.61, 95% CI [0.41, 0.91]), speed/agility (OR = 0.59, 95% CI [0.39, 0.88]), and flexibility (OR = 0.57, 95% CI [0.39, 0.84]). Higher fat mass was consistently linked to lower perceived fitness. HDL levels were positively associated with general (OR = 1.40, 95% CI [1.13, 1.74]) and cardiorespiratory fitness (OR = 1.32, 95% CI [1.07, 1.62]), while LDL levels showed no significant effect (p > 0.05). Sex differences emerged for general fitness (OR = 0.52, 95% CI [0.33, 0.82]) and flexibility (OR = 0.51, 95% CI [0.33, 0.78]), favoring boys, but no differences were found for cardiorespiratory fitness, muscular strength, or speed/agility (p > 0.05). This suggests that shared athletic environments may reduce typical sex-based disparities. Conclusions: Our findings emphasize the importance of considering both anthropometric and biochemical variables when evaluating perceived fitness in youth athletes. Regular athletic engagement may buffer sex-based differences in fitness perception.

In an era where childhood health is increasingly at risk, understanding the role of physical activity in promoting well-being is critical. The COR-School project investigates the impact of physical activity on cardiometabolic health in over 700 Spanish children and adolescents aged 8 to 16 years. Over three years, the study will conduct three assessments (baseline and two follow-ups) to evaluate peak post-exercise levels of high-sensitivity cardiac troponin T (hs-cTnT), a biomarker for cardiac stress, following a submaximal 20 m shuttle run test. Secondary objectives include examining the influence of maturational status, physical activity, and cardiorespiratory fitness on hs-cTnT. Participants will complete fitness tests, questionnaires on health habits, sleep, and diet, as well as anthropometric and body composition measurements. Blood samples collected at baseline and three hours post-exercise will measure cardiac biomarkers and lipid profiles. Cardiovascular responses will be tracked using heart rate monitors. Normal ranges of hs-cTnT will be determined using data distribution (percentiles or mean ± SD), stratified by age, sex, and maturational stage. Statistical analyses, including repeated measures ANOVA and Pearson correlation, will explore trends across time, sex, developmental stages, and other health-related outcomes. Beyond providing clinical insights by establishing reference values for hs-cTnT in healthy youth after exercise, findings will inform educational policies to promote physical activity in schools, emphasizing its role in improving fitness, health behaviors, and overall development.