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PURPOSE: To estimate the biological maturity status of youth football players 9-14 yr old using a noninvasive method and to compare the body size of players of contrasting status. METHODS: Subjects were members of youth football teams in two central Michigan communities. Height and weight were measured on 653 boys 8.7-14.6 yr. Heights of biological parents of 582 boys were reported and subsequently adjusted for overestimation. Decimal age, height, and weight of the player and midparent height were used to predict mature (adult) height for the boy. Current height of each player was expressed as a percentage of his predicted mature height to provide an estimate of biological maturity status. Percentage of predicted mature height of each boy was expressed as a z-score to classify players into maturity groups. ANCOVA, controlling for age, was used to compare body size in contrasting maturity groups. RESULTS: Mean percentages of predicted mature height of the players matched those of longitudinal reference samples, but there was a trend for higher percentages among older players, suggesting advanced maturation. Overall, 405 boys were classified as on time/average in maturity status (69.6% [95%CI 65.7-73.3]), 154 were classified as early/advanced (25.5% [95%CI 23.0-30.3]), and only 23 were classified as late/delayed (3.9% [95%CI 2.6-6.0]). The gradient for height, weight, and BMI was as follows: early > on time > late, and differences were greater for weight and the BMI than for height. CONCLUSION: Percentage of predicted mature height attained at a given age appears to be a reasonable indicator of maturity status. The method needs to be validated with other more direct indicators (skeletal age, sexual maturation) and applied to other samples. [ABSTRACT FROM AUTHOR]

The assessment of biological maturation is a central topic in pediatric exercise sciences. Skeletal age (SA) reflects changes in each bone of the hand and wrist from initial ossification to the adult state. This study examined intra-observer and inter-examiner agreement is Greulich-Pyle (GP) assessments of SA in 97 male tennis players 8.6-16.8 years of age. Two observers independently examined all films on two occasions using the GP method. The SA of each bone was evaluated. The mean and median of SAs assigned for each bone was the individual SA for each participant. The calculation was exclusively based on the bones that were not skeletally mature. Intra-observer mean differences were significant for several bones with better results by the experienced examiner (observer B). Comparisons between SA values of the two independent observers indicated significant differences for the ulna, metacarpals II and III, and distal phalanx V. Nevertheless, the magnitude of the bone-specific differences was small, perhaps trivial. Differences in individual SA values of the tennis players based on the non-mature bones of the hand-wrist were negligible based on the mean (0.04±0.39, t = 0.321, p = 0.749) or the median (0.05±0.58, t = 0.007, p = 0.994). Nevertheless, the current study confirmed examiners as a source of error in the estimation of SA using the Greulich-Pyle method and highlighted the importance of calculating SAs based on non-mature bones among adolescent players., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2025 Celis-Moreno et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

This study examined the validity of two automated methods (BAUSport, BoneXpert software using Fels, Greulich-Pyle, Tanner-Whithouse III protocols) for estimating skeletal age (SA) in young athletes in comparison to a reference standard (Fels). 85 male and female athletes, nine to seventeen years of age, from multiple sports were assessed for SA as part of an annual medical and health screening programme. Intra-class correlations demonstrated high degrees of association between the automatic methods for estimating SA (BAUSport r = .98; BoneXpert r = .96-.99) and the discrepancy between SA and chronological age (SA-CA) (BAUSport r = .93; BoneXpert r = .88-.97), with the reference standard. Concordance analyses for the categorisation of participants as early, on-time and late maturing also demonstrated substantial levels of agreement for both methods (BAUSport Kappa = .71; BoneXpert Fels Kappa = .63) with the reference standard. Bland-Altman plots comparing the automatic methods with the reference standard identified statistically significant fixed biases, ranging in magnitude from small to large. Collectively, these results suggest that BoneXpert and BAUSport can provide comparable estimates of SA and SA-CA in young athletes relative to the Fels method. Biases in the estimation of SA should, however, be considered and the automatic methods should be implemented as part of a comprehensive growth and maturity screening protocol. The non-invasive nature of the BAUSport method affords particular advantages (no radiation exposure, portability) in contexts where the regular estimation of SA is recommended., Competing Interests: The authors declared no conflict of interest., (Copyright © Biology of Sport 2024.)

Estimated ages at take-off (TO) and at peak height velocity (PHV) based on two models and maturity status based upon age at PHV and skeletal age (SA) were compared in a longitudinal sample of male soccer players. In addition, estimated ages at PHV in 13 longitudinal samples of soccer players were compared. The longitudinal height records of 58 players of European ancestry, measured annually on four or five occasions between 11 and 16 years, were modeled with Superimposition by Translation and Rotation (SITAR) and Functional Principal Component Analysis (FPCA) to estimate ages at TO and PHV. SAs were assessed with the Fels method. Ages at PHV in 13 longitudinal samples of soccer players (Europe 7, Japan 6) were evaluated with meta-analysis. Estimated ages at TO, 11.2 ± 0.8 (SITAR) and 11.0 ± 0.8 (FCPA) years, and at PHV, 13.6 ± 0.9 (SITAR) and 13.7 ± 0.0 (FCPA) years, were similar. An earlier age at PHV was associated with advanced skeletal maturity status (rho = -0.77 at ~14 years). Ages at PHV among European players indicated a north (later) - south (earlier) gradient, and were later than ages at PHV among Japanese players. In summary, ages at TO and PHV were similar with SITAR and FPCA, and ages at PHV were most strongly correlated with SA at ~14 years. Mean ages at PHV showed a north-south gradient among European samples, and were later compared to Japanese samples., Competing Interests: The authors declare no conflict of interest., (Copyright © Biology of Sport 2024.)

This study aimed to explore the interaction between growth rate on specific injury incidence and burden on pre-, circa- and post-peak height velocity (PHV) periods. Injury and stature data collected during the 2000-2020 seasons in an elite football academy were retrospectively analysed. Only players with height measurements from childhood until the attainment of adult height were included in the study (N = 84). Growth data were smoothed using a cubic spline to calculate daily growth rate and height. Growth rate was categorised into three groups: fast (> 7.2 cm/year), moderate (3.5-7.2 cm/year) and slow (< 3.5 cm/year). Percentage of observed adult height was used to classify players as pre-PHV (< 88%), circa-PHV (88-95%) or post-PHV (> 95%). Overall and specific injury incidence and burden and rate ratios for comparisons between growth rate groups were calculated on pre-, circa- and post-PHV periods, separately. Overall injury incidence and burden were greater in pre-PHV players with quicker growth rates compared to players growing moderately and slowly. All in all, players with more rapid growth-rates were at higher risk for growth-related injuries in all pre-, circa- and post-PHV periods. Post-PHV, the incidence and burden of joint/ligament injuries were 2.4 and 2.6-times greater in players growing slowly compared to players growing moderately. Practitioners should monitor growth rate and maturity status and consider their interaction to facilitate the design of targeted injury risk reduction strategies., Competing Interests: The authors report there are no competing interests to declare., (Copyright © Biology of Sport 2024.)

This study investigated the extent to which biological maturation selection biases existed according to playing position in national-level youth soccer. A total of 159 players from the U13 to U16 age groups in the Football Association of Ireland's national talent pathway and international representative squads had their relative biological maturity status assessed using the Khamis-Roche method for the percentage of predicted adult height at the time of observation. Players were categorised as goalkeeper (GK), central defender (CD), full-back (FB), centre defensive midfielder (CDM), centre midfielder (CM), centre attacking midfielder (CAM), wide midfielder (WM) or centre forward (CF). A series of one-sampled means t-tests were used to examine the degree to which biological maturation selection biases existed across playing positions. A non-parametric Kruskal-Wallis test was used to evaluate inter-positional differences. A small to very large selection bias in favour of early maturing players existed for GK (D = 0.7), CD (D = 1.65), FB (D = 0.49), CM (D = 0.62), WM (D = 0.78), and CF (D = 0.76) (p < 0.05). Maturational selection biases did not exist for CDM or CAM. Moreover, CD were significantly more advanced in maturation compared to FB, CDM and CAM (p < 0.05). This study supports the contention that maturation selection biases exist in youth soccer, but the magnitude of this bias is highly dependent upon playing position. The very strong maturity selection biases at the national level evidenced in this investigation highlight the need for Football Associations to explore strategies, such as futures programmes, to help to retain talented, yet late maturing athletes., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © Biology of Sport 2023.)

Background: Skeletal age (SA) is an estimate of biological maturity status that is commonly used in sport-related medical examinations. This study considered intra-observer reproducibility and inter-observer agreement of SA assessments among male tennis players., Methods: SA was assessed with the Fels method in 97 male tennis players with chronological ages (CA) spanning 8.7-16.8 years. Radiographs were evaluated by two independent trained observers. Based on the difference between SA and CA, players were classified as late, average or early maturing; if a player was skeletally mature, he was noted as such as an SA is not assigned., Results: The magnitude of intra-individual differences between repeated SA assessments were d = 0.008 year (observer A) and d = 0.001 year (observer B); the respective coefficients of variation were 1.11% and 1.75%. Inter-observer mean differences were negligible (t = 1.252, p = 0.210) and the intra-class correlation coefficient was nearly perfect (ICC = 0.995). Concordance of classifications of players by maturity status between observers was 90%., Conclusion: Fels SA assessments were highly reproducible and showed an acceptable level of inter-observer agreement between trained examiners. Classifications of players by skeletal maturity status based on assessments of the two observers were highly concordant, though not 100%. The results highlight the importance of experienced observers in skeletal maturity assessments., (© 2023. The Author(s).)

Background: The adolescent growth spurt is associated with an increased risk of injury in young athletes. Aim: This study aimed to use an interdisciplinary collaboration between technical coaches, sports scientists, and medical staff to mitigate this risk. Subjects and methods: 77 male academy footballers were followed across two seasons. At-risk players were identified using somatic maturity status and growth rate in stature and the lower limbs, using thresholds of 88% to 92.8% of predicted adult stature, ≥7.2 cm/year, and ≥3.6 cm/year, respectively. During the 2019-20 season, players with symptoms of a growth-related injury or two of three risk factors were included in an intervention strategy that included modified training load, football-specific skills, balance, coordination and landing drills, and an individualised strength program. Results: For players with the three risk factors, there was a significant reduction in the incidence (rate ratio [RR] = 0.14 (5.2 per 1000h → 0.8 per 1000h, p  = 0.05) and burden (RR = 0.08 (216 per 1000h → 17 per 1000h, p  = 0.02) between the seasons. For players with ≤2 risk factors, there were no significant differences in injury risk between the baseline and intervention seasons. Conclusion: Overall, it may be possible to mitigate injury incidence and burden during the adolescent growth spurt in high-risk athletes.

The purpose of this study was to determine intra- and inter-observer agreement for the three skeletal ages derived from the TW2 method among male pubertal soccer players. The sample included 142 participants aged 11.0-15.3 years. Films of the left hand-wrist were evaluated twice by each of two observers. Twenty bones were rated and three scoring systems used to determine SA adopting the TW2 version: 20-bone, CARPAL and RUS. Overall agreement rates were 95.1% and 93.8% for, respectively, Observer A and Observer B. Although, agreement rates between observers differed for 13 bones (5 carpals, metacarpal-I, metacarpal-III, metacarpal-V, proximal phalanges-I, III and V, distal phalanx-III), intra-class correlationa were as follows: 0.990 (20-bone), 0.969 (CARPAL), and 0.988 (RUS). For the three SA protocols, BIAS was negligible: 0.02 years (20-bone), 0.04 years (CARPAL), and 0.03 years (RUS). Observer-associated error was not significant for 20-bone SA (TEM = 0.25 years, %CV = 1.86) neither RUS SA (TEM = 0.31 years, %CV = 2.22). Although the mean difference for CARPAL SAs between observers (observer A: 12.48±1.18 years; observer B: 12.29±1.24 years; t = 4.662, p<0.01), the inter-observer disagreement had little impact (TEM: 0.34 years: %CV: 2.78). The concordance between bone-specific developmental stages seemed was somewhat more problematic for the carpals than for the long bones. Finally, when error due to the observer is not greater than one stage and the replicated assignments had equal probability for being lower or higher compared to initial assignments, the effect on SAs was trivial or small., Competing Interests: The authors have declared that no competing interests exist.

Context: Most available data on athletic development training models focus on adult or professional athletes, where increasing workload capacity and performance is a primary goal. Development pathways in youth athletes generally emphasize multisport participation rather than sport specialization to optimize motor skill acquisition and to minimize injury risk. Other models emphasize the need for accumulation of sport- and skill-specific hours to develop elite-level status. Despite recommendations against sport specialization, many youth athletes still specialize and need guidance on training and competition. Medical and sport professionals also recommend progressive, gradual increases in workloads to enhance resilience to the demands of high-level competition. There is no accepted model of risk stratification and return to play for training a specialized youth athlete through periods of injury and maturation. In this review, we present individualized training models for specialized youth athletes that (1) prioritize performance for healthy, resilient youth athletes and (2) are adaptable through vulnerable maturational periods and injury., Evidence Acquisition: Nonsystematic review with critical appraisal of existing literature., Study Design: Clinical review., Level of Evidence: Level 4., Results: A number of factors must be considered when developing training programs for young athletes: (1) the effect of sport specialization on athlete development and injury, (2) biological maturation, (3) motor and coordination deficits in specialized youth athletes, and (4) workload progressions and response to load., Conclusion: Load-sensitive athletes with multiple risk factors may need medical evaluation, frequent monitoring, and a program designed to restore local tissue and sport-specific capacity. Load-naive athletes, who are often skeletally immature, will likely benefit from serial monitoring and should train and compete with caution, while load-tolerant athletes may only need occasional monitoring and progress to optimum loads., Strength of Recommendation Taxonomy (sort): B.

This study aimed to: (1) examine differences in physical performance across birth-quartiles and maturity-status, and (2) determine the relationships among relative age, maturation and physical performance in young male soccer players. The sample included 199 males aged between 8.1 and 18.9 years, from two professional soccer academies in the English Football League. Data were collected for height, weight, self-reported biological parent heights, 30 m sprint time and countermovement jump (CMJ) height. Relative age was conveyed as a decimal, while maturity status was determined as the percentage of predicted adult height (PAH). There were no significant differences in any measure between birth quartiles, however early maturers outperformed on-time and later maturers in most performance measures. Pearson-product-moment correlations revealed that maturation was inversely associated with 30 m sprint time in U12 to U16 ( r = -0.370-0.738; p < 0.05), but only positively associated with CMJ performance in U12 ( r = 0.497; p < 0.05). In contrast, relative age was unrelated to sprint performance and only significantly associated with superior CMJ performance in U16. This study indicates that maturity has a greater association with sprint performance than relative age in English male academy soccer players. Practitioners should monitor and assess biological maturation in young soccer players to attempt to control for the influence on physical performance, and avoid biasing selection on absolute performance rather than identifying the most talented player.

Background: The aim of this study was to assess whether adjusting the weight categorisation of children for their biological maturity status could improve the accuracy of predicting weight status and cardiometabolic risk at age 17., Methods: Data from 1525 participants (787 female) from the ALSPAC study were analysed. Participants' weight status at age 11 was estimated using first standard chronological age and sex adjusted BMI cut-offs, and again using maturity adjusted BMI cut-offs. Each BMI category at age 11 was regressed against cardiometabolic risk score and BMI category at age 17, controlling for sex, ethnicity and socio-economic status., Results: At age 11 years, 22% of boys and 46% of girls who were categorised as overweight or having obesity based on chronological age were re-categorised into a lower BMI category after adjusting for biological maturity. Biologically adjusted BMI categories better predicted BMI category at age 17 compared with non-adjusted BMI categories (∆BIC = - 21.69); the odds of having obesity at age 17 were 18.28 times greater with each increase in BMI category at age 11. Adjusted and non-adjusted BMI status at 11 years showed equivalent accuracy in predicting cardiometabolic risk at age 17; the odds ratio of high cardiometabolic risk was 1.85, with heightened risk in boys, particularly early maturers., Conclusion: The traditional method of categorising adolescents into a BMI category may over-predict overweight and obesity, particularly in girls. Adjusting for biological maturity when estimating weight status through calculating adolescents' BMI classification was equivalent to standard approaches in predicting other cardiovascular risk at age 17., (© 2021. The Author(s).)

Baseline characteristics of 31 healthy male U15 soccer players who were classified as select or non-select at the end of the season were compared. Players were 14.4 ± 0.54 years (13.6-15.3 years) at baseline; characteristics included body size, proportions and composition, estimated maturity status, several functional capacities, and coach classifications of potential in the sport. Decisions regarding selection or non-selection were made about two months after baseline. Select and non-select U15 soccer players differed significantly in estimated maturity status, body size, proportions and estimated muscle mass, functional tests related to speed, power and strength, and coach evaluation of potential, specifically tactical skills on offense and skills associated with creativity and decision making. When age and biological maturity status were statistically controlled, select and non-select players differed significantly only on the vertical jump, grip strength, and coach ratings of tactical skills on offense and of creativity and decision making. Results of stepwise discriminant analysis highlighted the importance of coach evaluation of tactical skills associated with offense, and of power and strength in distinguishing select from non-select players. The results highlight the advantages of advanced biological maturity status among adolescent male soccer players and also the importance of coach perceptions of talent. The latter implies a need for further study of the basis of coach perceptions, specifically how they are influenced by and perhaps interact with player characteristics at different ages, and how the perceptions influence playing time and player behaviors and interactions., Competing Interests: The authors declared no conflicts of interests regarding the publication of the manuscript., (Copyright © Biology of Sport 2021.)

The purpose of the study was to evaluate predicted maturity offset (time before age at PHV) and age at PHV (chronological age [CA] minus maturity offset) in a longitudinal sample of 58 under-13 club level soccer players in central Portugal for whom ages at PHV were estimated with the SITAR model. Two maturity offset prediction equations were applied: the original equation which requires CA sitting height, estimated leg length, height and weight, and a modified equation which requires CA and height. Predicted maturity offset increased, on average, with CA at prediction throughout the age range considered, while variation in predicted maturity offset and ages at PHV within CA groups was considerably reduced compared to variation in observed ages at offset and at PHV. Predicted maturity offset and ages at PHV were consistently later than observed maturity offset and age at PHV among early maturing players, and earlier than observed in late maturing players. Both predicted offset and ages at PHV with the two equations were, on average, later than observed among players maturing on time. Intra-individual variation in predicted ages at PHV with each equation was considerable. The results for soccer players were consistent with similar studies in the general population and two recent longitudinal studies of soccer players. The results question the utility of predicted maturity offset and age at PHV as valid indicators of maturity timing and status., Competing Interests: The authors have declared that no competing interests exist.

Background: The aim of the study was to examine the contribution of chronological age (CA), skeletal maturation, training experience and concurrent body size descriptors, to inter-individual variance in left ventricular mass (LVM) among female adolescent soccer players., Methods: The sample included 228 female soccer players 11.8-17.1 years. Training experience defined as years of participation in competitive soccer (range 2-9 years), was obtained by interview. Stature, body mass and skinfolds (triceps, medial calf) were measured. Fat mass was estimated; Fat-free mass was derived. LVM was assessed by echocardiography. Skeletal maturity status was as the difference of skeletal age (SA, Fels method) minus CA., Results: Fat-free mass was the most prominent single predictor of LVM (R 2  = 36.6%). It was associated with an allometric coefficient close to linearity (k = 0.924, 95%CI: 0.737 to 1.112). A significant multiplicative allometric model including body mass, fat-free mass, CA, training experience and skeletal maturity status was also obtained (R = 0.684; R 2  = 46.2%)., Conclusion: Stature has limitations as a valid size descriptor of LVM. Body mass, fat-free mass, training experience, CA, body mass and skeletal maturity status were relevant factors contributing to inter-individual variability in LVM.

Background: To evaluate the concordance of skeletal age (SA) with two predicted estimates of biological maturity status in elite British youth tennis players., Method: Participants were 71 male and female elite youth tennis players aged 8 to 16 years. Weight, height, and sitting height were measured. SA (Fels method) was the criterion indicator of maturity status. Maturity status was predicted with two methods: predicted age at peak height velocity and percentage of predicted adult height at the time of observation. Players were classified as late, average (on time), or early maturing with each method. Concordance of classifications was evaluated with kappa coefficients and Spearman's rank order correlations., Results: Kappa coefficients between maturity status classifications were low in both sexes, - 0.11 to 0.22, while Spearman's rank order correlations between maturity status classifications based on SA and the percentage of predicted mature height were moderate in males (0.35) and females (0.25), but the corresponding correlations based on predicted age at peak height velocity (PHV) varied, moderate and negative in boys (- 0.37) and low and positive in girls (0.11). Concordance of maturity status classifications based on the prediction methods and SA among tennis players was thus limited., Conclusions: Maturity status based on the percentage of predicted mature height at the time of observation correlated better with maturity status based on SA in contrast to status based on predicted age at PHV in this sample of elite youth tennis players.

Motor coordination and physical fitness are multidimensional concepts which cannot be reduced to a single variable. This study evaluated multivariate relationships among morphology, physical fitness and motor coordination in 74 pre-pubertal girls 8.0-8.9 years of age. Data included body dimensions, eight fitness items and four motor coordination tasks (KTK battery). Maturity status was estimated as percentage of predicted mature stature attained at the time of observation. Canonical correlation analysis was used to examine the relationships between multivariate domains. Significant pairs of linear functions between indicators of morphology and fitness (r c = 0.778, Wilks' Lambda = 0.175), and between fitness and motor coordination (r c = 0.765, Wilks' Lambda = 0.289) were identified. Girls who were lighter and had a lower waist-to-stature ratio and % fat mass attained better scores in the endurance run, sit-ups and standing long jump tests, but poorer performances in hand grip strength and 2-kg ball throw. Better fitness test scores were also associated with better motor coordination scores. Relationships between body size and estimated fatness with motor fitness suggested an inverse relationship that was particularly evident in performance items that required the displacement of the body through space, while motor coordination was more closely related with fitness than with somatic variables.

Background: Time spent outdoors is associated with higher physical activity levels among children, yet it may be threatened by parental safety concerns and the attraction of indoor sedentary pursuits. The purpose of this study was to explore the relationships between these factors and outdoor time during children's discretionary periods (i.e., after school and over the weekend)., Methods: Data from 462 children aged 9-11 years old were analysed using generalised linear mixed models. The odds of spending > 1 h outdoors after school, and > 2 h outdoors on a weekend were computed, according to demographic variables, screen-based behaviours, media access, and parental safety concerns. Interactions with sex and socioeconomic status (SES) were explored., Results: Boys, low SES participants, and children who played on their computer for < 2 h on a school day had higher odds of spending > 1 h outside after school than girls, high SES children and those playing on a computer for ≥2 h, respectively. Counterintuitive results were found for access to media devices and crime-related safety concerns as both of these were positively associated with time spent outdoors after school. A significant interaction for traffic-related concerns*sex was found; higher road safety concerns were associated with lower odds of outdoor time after school in boys only. Age was associated with weekend outdoor time, which interacted with sex and SES; older children were more likely to spend > 2 h outside on weekends but this was only significant among girls and high SES participants., Conclusions: Our results suggest that specific groups of children are less likely to spend their free time outside, and it would seem that only prolonged recreational computer use has a negative association with children's outdoor time after school. Further research is needed to explore potential underlying mechanisms, and parental safety concerns in more detail.

Objectives: Physical activity (PA) can provide numerous physical and psychological health gains, yet a low proportion of children in England are sufficiently active to accrue benefit. Analysing the correlates of PA from a socioecological perspective may help to identify factors that promote versus discourage PA. The purpose of the present study was to: (1) assess the relationships between a wide range of potential correlates and intensity-specific PA and (2) explore which correlates are associated with meeting government PA guidelines., Design, Setting and Participants: Cross-sectional study on children aged 9-11 years from the South West of England (n=425; 183 males)., Outcome Measures: A mixture of self-reported and objective measures (eg, body mass index (BMI), accelerometer-derived PA, self-reported sport participation, etc) were collected from child participants, parents and school teachers. After adjusting for covariates (ie, age, sex and accelerometer wear time), multilevel modelling techniques were employed to examine the relationships between potential correlates and light-intensity, moderate-intensity and vigorous-intensity PA, as measured with an ActiGraph GT3X+ accelerometer. Generalised linear mixed modelling was used to analyse the correlates associated with government-recommended levels of PA., Results: Computer use shared a negative association whereas parent support for PA showed a positive relationship with light-intensity PA. In terms of moderate-intensity PA, computer use and BMI z-score shared a negative association whereas positive relationships were found for sport participation, active transport and for outdoor time after school. Children at schools with 25%-49% of pupils attending school sport/PA clubs did more moderate-intensity PA than those attending schools with lower participation rates. For vigorous-intensity PA, a negative relationship was observed for BMI z-score, and positive associations for self-efficacy, active transport, parent support and the presence of crossing guards on routes to school. Correlates associated with meeting the PA guidelines were BMI z-score (negative), sport participation, active transport and outdoor time after school (all positive)., Conclusion: Results demonstrate that factors pertaining to the individual, home and school environment may play an important role in understanding the correlates of differing PA intensities in children., Trial Registration Number: NCT01722500., Competing Interests: Competing interests: None declared., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

The intermittent nature of match performance in youth soccer supports relevance of ability to repeatedly produce high-intensity actions with short recovery periods. This study was aimed to examine the reproducibility of a repeated dribbling ability protocol and, additionally, to estimate the contribution of concurrent tests to explain inter-individual variability in repeated dribbling output. The total sample comprised 98 players who were assessed as two independent samples: 31 players were assessed twice to examine reliability of the protocol; and 67 juveniles aged 16.1 ± 0.6 years were compared by the competitive level (local, n = 34; national, n = 33) to examine construct validity. All single measurements appeared to be reasonably reliable: total (ICC = 0.924; 95%CI: 0.841 to 0.963); ideal (ICC = 0.913; 95%CI: 0.820 to 0.958); worst (ICC = 0.813; 95%CI: 0.611 to 0.910). In addition, the percentage of the coefficient of variation was below the critical value of 5% for total (%CV = 3.84; TEM = 2.51 s); ideal (%CV = 3.90, TEM = 2.48 s). Comparisons between local and national players suggested magnitude effects as follows: moderate (d-value ranged from 0.63 to 0.89) for all repeated sprint ability scores; large for total (d = 1.87), ideal (d = 1.72), worst (d = 1.28) and moderate for composite scores: the fatigue index (d = 0.69) and the decrement score (d = 0.67). In summary, the dribbling protocol presented reasonable reproducibility properties and output extracted from the protocol seemed to be independent from biological maturation.

Objectives: The purpose of this study was to explore the independent associations between multiple lifestyle behaviours (physical activity, sleep, screen time (ST) and diet) and overweight and obesity in UK children. The second objective was to compare body mass index (BMI) z-score between children who meet health guidelines for each lifestyle behaviour and those who do not and to explore the impact of interactions between lifestyle behaviours on BMI z-score., Design, Setting and Participants: Cross-sectional study on children aged 9-11 years in the UK (n=374)., Outcome Measures: Participants were classified as overweight or obese using the WHO BMI cut-points. Moderate-to-vigorous intensity physical activity (MVPA) and sleep duration were measured using an ActiGraph GT3X+ accelerometer, whereas ST and dietary habits were assessed using questionnaires. Multilevel multiple logistic regression was employed to analyse associations between lifestyle behaviours and overweight/obesity. Participants were then categorised according to whether or not they met specific health criteria for MVPA, ST, sleep and diet. Multilevel multiple linear regression was used to compare these groupings on the outcome of BMI z-score and interactions were explored., Results: MVPA and longer sleep duration were associated with lower odds of overweight or obesity, whereas ST and a healthy diet score were associated with increased odds of overweight/obesity. No association was found for an unhealthy diet score. Meeting MVPA guidelines was significantly associated with a lower BMI z-score in all models, and significant two-way interactions were observed for physical activity and sleep, ST and sleep, and physical activity and diet., Conclusions: MVPA, sleep and ST are important lifestyle behaviours associated with overweight/obesity among children. More research is required to confirm the role of diet on adiposity and such work would benefit from objective assessment. Overall, this work suggests that strategies aimed at improving compliance with health guidelines are needed., Trial Registration Number: NCT01722500., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)

Objectives: To describe the degree of disability, anthropometric variables, quality of life (QoL), and school backpack weight in boys and girls aged 11-17 years. The differences in QoL between those who did or did not report low back pain (LBP) were also analyzed., Methods: Eighty-six girls (13.9 ± 1.9 years of age) and 63 boys (13.7 ± 1.7 years of age) participated. LBP was assessed by questionnaire, and disability using the Roland-Morris Disability Questionnaire. QoL was assessed by the Pediatric Quality of Life Inventory (PedsQL). Multivariate analyses of variance and covariance were used to assess differences between groups., Results: Girls reported higher disability than boys (p = 0.01), and lower QoL in the domains of physical (p < 0.001) and emotional functioning (p < 0.01), psychosocial health (p = 0.02) and physical health summary score (p < 0.001), and on the total PedsQL score (p < 0.01). School backpack weight was similar in both genders (p = 0.61) and in participants with and without LBP (p = 0.15). After adjustments, participants with LBP reported lower physical functioning (p < 0.01), influencing lower physical health summary score (p < 0.01)., Conclusions: Girls had higher disability and lower QoL than boys in the domains of physical and emotional functioning, psychosocial health, and physical health summary scores, and on the total PedsQL score; however, similar school backpack weight was reported. Participants with LBP revealed lower physical functioning and physical health summary score, yet had similar school backpack weight to those without LBP., (Copyright © 2015 Sociedade Brasileira de Pediatria. Published by Elsevier Editora Ltda. All rights reserved.)

Background: The 'Be the Best You Can Be' (BtBYCB) program is a school-based intervention designed to foster positive physical, psychological, and social development via empowering young people to take ownership over their own personal development. The aim of this work is to determine the effectiveness of the BtBYCB program on (i) pupils' well-being, self-perceptions, self-esteem, aspirations, and learning strategies; and (ii) changes in modifiable health-risk behaviors (i.e., physical activity, diet, smoking, and alcohol consumption)., Methods/design: A two-arm cluster randomized controlled trial employing a wait-list control plus qualitative and mixed-method evaluations was used. Participants were school pupils from Years 7 and 8 (aged 11-13 years). Ten schools located in southwest England were randomly allocated to receive the BtBYCB intervention (n = 5 schools; 711 pupils) or a control condition (i.e., usual Personal, Social, and Health Education classes) (n = 5 schools; 622 pupils). Participants in the intervention condition received a program consisting of (i) a talk from an Olympian/Paralympian; (ii) 11 one-hour teacher-led PSHE classroom sessions in which pupils identified their aspirations, values, and interests and explored and acted on these via activities such as personal development planning, goal-setting, and peer-mentoring; and (iii) participated in a celebration event (e.g., second visit from Olympian/Paralympian and short individual presentations). Data were collected at baseline, post-intervention, and at 3-month follow-up.Focus groups (pupils and teachers) and individual interviews (headteachers) were conducted in the 5 intervention schools to (i) gain an in-depth understanding of mechanisms of change; (ii) explore ways in which the participants' motivation and engagement could be enhanced, and (iii) elicit user-feedback pertaining to how the program, content, and appeal could be improved.A mixed-method approach was used to describe and explain the differing experiences of particular groupings within and across the intervention schools; i.e., those for whom the program was effective, those that experienced little, if any change, and those for whom the program led to an inverse effect., Discussion: The findings of this work will provide insight into the effectiveness of an innovative and child-centered program. The research will inform improvements to the BtBYCB program as well as other interventions targeting child/youth health and wellness., Trial Registration: The trial is registered as Current Controlled Trials ISRCTN99443695.

The purpose of the study was to evaluate the developmental changes in performance in a repeated-sprint ability (RSA) test in young soccer players of contrasting maturity status. A total of 83 regional level Portuguese youth soccer players, aged 11-13 years at baseline was assessed annually. Stature, body mass, 7x34.2-m sprint protocol (25-s active recovery), 20-m multi-stage continuous shuttle endurance run and counter-movement jump (CMJ) without the use of the arms were measured. Fat-free mass (FFM) was determined by age and gender-specific formulas. Developmental changes in total sprint time across ages were predicted using multilevel modeling. Corresponding measurements were performed on an independent cross-sectional subsample of 52 youth soccer players 11-17 years to evaluate the predictive model. CA, CA(2), maturational status (SA-CA), body size (mass and stature), FFM, aerobic endurance, lower limb explosive strength and annual volume training significantly improved the statistical fit of the RSA multilevel model. In 'late' maturing athletes, the best model for predicting change in RSA was expressed by the following equation: 86.54 - 2.87 x CA + 0.05 x CA(2) - 0.25 x FFM + 0.15 x body mass + 0.05 x stature - 0.05 x aerobic endurance - 0.09 x lower limb explosive strength - 0.01 x annual volume training. The best fitting models for players who were 'on time' and 'early' maturing were identical to the best model for late maturing players, less 0.64 seconds and 1.74 seconds, respectively. Multilevel modeling provided performance curves that permitted the prediction of individual RSA performance across adolescent years in regional level soccer players. Key pointsRepeated-sprint ability tests are a valuable sport-specific field test of sprint performance in youth soccer players. Here, the test had reasonable reliability and can be useful to trainers and coaches in the assessment of young athletes and in monitoring changes over time.The total sprint time of youth soccer players advanced in biological maturation improves more, on average, than that of players who are on time (average) and late in maturation. The performance difference between early and late maturing players is consistent after about 13 years of age.Multilevel modeling is a promising statistical technique for analyzing the development of functional capacity in a sport. It has the potential to provide useful information to assist trainers and coaches in evaluating and facilitating the development of individual players.

Background: The aim of this study is to investigate the relationships between HbA1c and other risk factors like obesity, functional fitness, lipid profile, and inflammatory status in older adults. Epidemiological evidence suggests that HbA1c is associated with cardiovascular and ischemic heart disease risk. Excess of body weight and obesity are considered to play a central role in the development of these conditions. Age is associated with several risk factors as increased body fat and abdominal fat, deterioration of the lipid profile, diabetes, raising in inflammatory activity, or decreased functional fitness., Methods: Data were available from 118 participants aged 65-95 years, including 72 women and 46 men. Anthropometric variables were taken, as was functional fitness, blood pressure and heart rate. Blood samples were collected after 12 h fasting, and HbA1c, hs-CRP, TG, TC, HDL-C, LDL-C, and glycaemia were calculated. Bivariate and partial correlations were performed to explore associations amongst the variables of interest. Differences between groups were explored by performing factorial analysis of variance., Results: HbA1c levels ranged from 4.6%-9.4% with 93% of the cases below 6.5%. Women had higher HbA1c, glycaemia, TC, BMI, and lower and upper flexibility than men. Men had higher BW, WC, 6-min walking distance, and VO2peak than women. Age, SBP, DBP, HRrest, HRpeak, HDL-C, LDL-C, TG, TG/HDL-C ratio, Log10 hs-CRP, upper and lower strength, and agility and dynamic balance were similar in men and women. HbA1c had positive associations with glycaemia, HDL-C, TG/HDL-C, BW, WC, BMI, but not with functional fitness, TC, LDL-C, Log10 hs-CRP, PAD, or PAS. Obese participants had higher HbA1c than non-obese only when IDF and not USDHHS criteria were applied., Conclusions: Older women had higher HbA1c than men, even after controlling for BMI. HbA1c associates equally with BW, BMI or WC. Population-based criteria are recommended to classify obesity and to identify higher levels of HbA1c in obese older adults. HbA1c associates with atherogenic dyslipidemia particularly with TG and TG/HDL-C ratio, but not with TC, HDL-C, or LDL-C. HbA1c is not associated with hs-CRP, and with functional fitness and aerobic endurance.

Purpose: To examine the potential confounding effect of biological maturation on the relations between chronological age and health-related quality of life in adolescent British females., Methods: Biological maturation, chronological age, and health-related quality of life were assessed in 366 British female students in years 7-10 (M = 13.0 years, SD = 0.8). The Kid-Screen 10 was used to assess health-related quality of life. Percentage of predicted adult height attained at measurement was used as an estimate of biological maturation., Results: Pearson product moment correlation demonstrated a statistically significant inverse relation between chronological age and health-related quality of life. This relation was, however, attenuated and non-significant once biological maturation was controlled for., Conclusions: Researchers studying health-related quality of life in youth should consider and/or control for the potential confounding effect of biological maturation.

Background: The weakening of the cardiovascular system associated with aging could be countered by increasing levels of physical activity and functional fitness. However, inconsistent findings have been found, and the variety of characteristics of exercise used in previous studies may partly explain that inconsistent results., Objective: To investigate the training effect of sixteen weeks of moderate intensity, progressive aerobic and strength-based training on metabolic health of older women and men., Methods: Sixty three sedentary individuals (mean (SD) age 76 (8) years) were randomly assigned to control (n = 31) or exercising (n = 32) groups. The training group was separated to aerobic (n = 18) or strength-based (n = 14). Training took place three times a week. Subjects agreed not to change their diet or lifestyle over the experimental period., Results: Exercising group attained after treatment significant differences on body weight, waist circumference, body mass index, diastolic blood pressure, triglycerides, total cholesterol, HDL-cholesterol, LDL-cholesterol, total cholesterol/HDL-cholesterol relationship, high sensitivity C-reactive protein, and 6-minute walk distance. The control group only had significant differences on waist circumference., Conclusion: The training programs produced significant benefits on metabolic health indicators of sedentary older women and men.

Objective: To evaluate the growth, maturity status and functional capacity of youth soccer players grouped by level of skill., Subjects: The sample included 69 male players aged 13.2-15.1 years from clubs that competed in the highest division for their age group., Methods: Height and body mass of players were measured and stage of pubic hair (PH) was assessed at clinical examination. Years of experience in football were obtained at interview. Three tests of functional capacity were administered: dash, vertical jump and endurance shuttle run. Performances on six soccer-specific tests were converted to a composite score which was used to classify players into quintiles of skill. Multiple analysis of covariance, controlling for age, was used to test differences among skill groups in experience, growth status and functional capacity, whereas multiple linear regression analysis was used to estimate the relative contributions of age, years of training in soccer, stage of PH, height, body mass, the height x weight interaction and functional capacities to the composite skill score., Results: The skill groups differed significantly in the intermittent endurance run (p<0.05) but not in the other variables. Only the difference between the highest and lowest skill groups in the endurance shuttle run was significant. Most players in the highest (12 of 14) and high (11 of 14) skill groups were in stages PH 4 and PH 5. Pubertal status and height accounted for 21% of the variance in the skill score; adding aerobic resistance to the regression increased the variance in skill accounted for to 29%. In both regressions, the coefficient for height was negative., Conclusion: Adolescent soccer players aged 13-15 years classified by skill do not differ in age, experience, body size, speed and power, but differ in aerobic endurance, specifically at the extremes of skill. Stage of puberty and aerobic resistance (positive coefficients) and height (negative coefficient) are significant predictors of soccer skill (29% of the total explained variance), highlighting the inter-relationship of growth, maturity and functional characteristics of youth soccer players.