Age at peak height velocity in Polish adolescents: Effect of socioeconomic factors

Age at peak height velocity (APHV) is an indicator of maturity timing which is applicable to both sexes, and which is influenced by environmental factors. The objective of this study was to assess variation in APHV associated with several indicators of socioeconomic status (SES) in a longitudinal sample of Polish adolescents. The sample included 739 boys born in 1983 and followed annually from 12 to 16 years, and 597 girls born in 1985 and followed annually from 9 to 13 years. The height records were fitted with the SITAR model to estimate APHV. SES was estimated using principal component analysis of indicators of familial status based on parental education, family size, living conditions and household possessions. Statistical analyses included analysis of variance (one-way for general SES and three-way for parental education and family size) and Tukey post-hoc tests for unequal samples. General SES (p <.001) and family size (p < .05) significantly influenced APHV among boys, while only maternal education (p < .05) significantly influenced APHV among girls. Among youth from families of higher SES, as defined by the respective indicators, APHV was attained significantly earlier, on average, than in peers from families of lower SES. Overall, the results showed a sex-dependent effect of SES on APHV, and highlighted the influence of favorable socioeconomic conditions for optimal growth and maturation during adolescence.

Secular change in heights of rural adults in west-central poland between 1986 and 2016: The transition from pre- to post-communism

Secular change in the heights of adult men and women resident in ten rural communities in west-central Poland in four decennial surveys between 1986 and 2016 is considered. The adults were parents of children attending schools in rural communities in the province of Poznań. During each survey, parents of school children were asked to complete a questionnaire which requested their ages, heights and completed levels of education. Ages were reported in whole years. The self-reported heights were adjusted for the tendency of individuals to overestimate height. Height loss among of individuals 35+ years was estimated with sex-specific equations and was added to the adjusted heights. Secular gains in heights of adult males across the 30 year interval, and across the 1986-1996 and 2006-2016 surveys were, on average, larger than corresponding gains in heights of adult females; the sex difference between 1996 and 2006 surveys was negligible. When heights were regressed on year of birth, heights of males and females born before 1950 (prior to World War II and shortly after) showed minimal and non-significant secular changes, while heights of those born post-1950 showed larger and significant secular gains, more so in males than in females. The results highlight significant secular trends in the heights of rural adults over a 30-year interval. Consistent with other studies in Poland, the positive trends likely reflected political, educational and socio-economic changes and by inference improved nutritional and health conditions across generations.

Regional variation in body size and estimated secular change among adult Indian males born in the 1890s-1950s

Regional variation in the body size of Indian men 18-84 years of age (birth years 1891-1957) was considered. Heights, weights, and BMIs of Indian males from four regions of the country - North, East-Northeast, Central, and West were compared. Heights of men 35+ years of age were adjusted for estimated height loss with age; the estimate was added to observed height to provide an estimate of maximum height. Linear regressions of measured height and estimated maximum height on year of birth were used to evaluate secular change by region. Differences in measured and estimated maximum heights and weight among regions were significant in all age groups, while differences in the BMI were significant in all age groups except 55+ years. Men from the North region were tallest and those from the East-Northeast region were shortest, while body weight and the BMI varied among regions. Regression analyses of year of birth on measured and estimated maximum heights indicated small differences in estimates of secular change among regions but suggested a decline in estimated maximum heights with age among men in the four regions born in 1891 through the 1930s, and small but variable estimates of secular change in heights among men born in the 1930s through 1957. The variation likely reflected socio-economic disparities and ecological differences among regions, and by inference nutritional status though data are limited.

Nutritional status of infants and young children in India across three decades: Analysis of five national family health surveys

BACKGROUND

Three indicators of early childhood undernutrition and associated factors are evaluated among under-5 children in five National Family Health Surveys in India spanning 1992 to 2021.

METHODS

Data for 533,495 children under 5 years of age (U-5) were analysed in the context of three commonly used indicators of early childhood undernutrition - wasting, stunting and underweight. In addition to descriptive and inferential statistics, binary logistic regression was used to estimate the effects of specific explanatory factors on the three indicators using adjusted odds ratios.

RESULTS

Over the three-decade interval, stunting was reduced by 22.1% in boys and 20.9% in girls, followed by underweight, 19.3% in boys and 17.4% in girls; wasting, in contrast, was reduced to a considerably lesser extent, 2.8% in boys and 0.9% in girls. Demographic, maternal and socioeconomic factors were associated with the incidence of early childhood undernutrition, specifically among young mothers and those with less education in low-income families, and among children from Scheduled Tribes or Scheduled Castes. Stunting and underweight declined significantly over the past three decades while wasting changed negligibly. The disparity in the occurrence of early childhood undernutrition was apparent throughout socioeconomic categories and regions of India.

CONCLUSIONS

The results highlight the need for special programs aimed at reducing waste among children and also the need for customized initiatives focused on the improvement of maternal education and wealth in addition to other ancillary factors related to regional variation.

Influence of body size and skeletal maturity status on strength and motor performances of soccer players 9-16 years

The contributions of height, weight and skeletal age (SA) to strength and motor performances of male soccer players 9-12 (n = 60) and 13-16 (n = 52) years were estimated. SA was assessed with the Fels method, and was expressed as the standardized residual of the regression of SA on chronological age CA (SAsr). Static strength (right + left grip), speed (5 m, 20 m sprints), acceleration (10 to 20 m), agility (figure-of-eight run), explosive strength (vertical jump) and endurance (yo-yo intermittent shuttle run, 13-16 years only) were measured. Hierarchical multiple regression was used. The interaction of SAsr with body size (height and height x weight interaction) explained most of the variance in strength in both age groups, 9-12 years (51.6%) and 13-16 years (56.7%), and in speed (31.4%, 38.7%), acceleration (39.6%), and explosive strength (32.6%) among players 13-16 years. In contrast, SAsr alone explained limited amounts of variance in strength, speed, acceleration and vertical jump among players 9-12 years (1.4-4.5%) and 13-16 years (0-0.5%). Results for agility varied with CA group, while SAsr per se was the primary contributor to endurance among players 13-16 years (18.5% of the variance). Although the influence of body size and skeletal maturity status on performances was significant, the explained variance differed among tasks and between CA groups, and suggested a role for other factors affecting performances of the soccer players.

Variation in body size and weight status among Hindu and Muslim Indian males born in the 1890s through the 1950s

Hindus and Muslims represent the two largest religions in India, and also differ in nutritional status, health-related habits and standard of living associated with economic disparities. In this context, the present study considered estimated secular changes in body size, proportions, and weight status among Hindu and Muslim Indian men. The data are from anthropological surveys in the 1970s which included measurements of height, weight and sitting height of 43,950 males 18-84 years (birth years 1891-1957). Leg length was estimated; the BMI and sitting height/height ratio were calculated. Heights of men 35 + years were adjusted for estimated height loss with age. Weight status was also classified relative to WHO criteria for the BMI. Anthropometric characteristics of the two groups were compared with MANCOVA with age and geographic region as covariates. Linear regression of height on year of birth was also used to estimate secular change in each group. Heights, weights, and BMIs tended to be, on average, greater among Muslim than Hindu men at most ages, while distributions by weight status between groups were negligible. Sitting height was greater among Muslim men but estimated leg length did not differ between groups; the sitting height/height ratio thus suggested proportionally shorter legs among Muslim men. Results of the regression analyses indicated negligible differences in secular change between groups across the total span of birth years but indicated a decline in adjusted heights of men in both groups born between 1891 through 1930s and little secular change among those born in the 1930s through 1957. The variation in heights, weights and BMIs between Muslim and Hindu men at most ages suggested variation in socio-economic status and dietary habits between the groups, whereas the negligible estimated secular changes in height between groups likely reflected economic, social, and nutritional conditions during the interval of British rule and the transition to independence.

Estimating Maturity Status in Elite Youth Soccer Players: Evaluation of Methods

PURPOSE

To evaluate the concordance of predicted maturity status classifications (pre-, circa- or post-peak height velocity) relative to observed age at PHV in youth soccer players.

METHODS

Longitudinal height records for 124 male soccer players were extracted from academy records spanning the 2000-2022 seasons. Age at PHV for each player was estimated with the Super-Imposition by Translation and Rotation (SITAR) model. Players were classified as pre-, circa- or post-PHV using both ±1 year and ± 0.5 year criteria to define the circa-PHV interval. Maturity status was estimated with several prediction protocols: maturity offset (Mirwald, Moore-1, Moore-2), maturity ratio (Fransen), percentage of predicted adult height (PAH%) using the Khamis-Roche (KR) and Tanner-Whitehouse-2 (TW2-RUS) equations using several bands: 85%-96%, 88%-96%, 88%-93%, and 90%-93% for the circa-PHV interval, and visual evaluation of individual growth-curves alone or with PAH% based on KR and TW2-RUS. Concordance of maturity status classifications based on complete growth curves and predicted estimates of maturity status was addressed with percentage agreement and Cohen's kappa.

RESULTS

Visual evaluation of the growth curves had the highest concordance (≈ 80%) with maturity status classifications (pre-, circa-, post-PHV) based on longitudinal data for individual players. Predicted maturity offset with the Mirwald, Moore-1 and Fransen equations misclassified about one- third to one-half of the players, while concordance based on PAH% varied with the band used, but not with the method of height prediction.

CONCLUSIONS

Visual assessment of the individual growth curves by an experienced assessor provides an accurate estimate of maturity status relative to PHV. Maturity offset prediction equations misclassifies the majority of players, while PAH% provides a reasonably valid alternative.

Interrelationships among skeletal age, growth status and motor performances in female athletes 10-15 years

BACKGROUND

Motor performances of youth are related to growth and maturity status, among other factors.

AIM

To estimate the contribution of skeletal maturity status per se to the motor performances of female athletes aged 10-15 years and the mediation effects of growth status on the relationships.

SUBJECTS AND METHODS

Skeletal age (TW3 RUS SA), body size, proportions, estimated fat-free mass (FFM), motor performances, training history and participation motivation were assessed in 80 non-skeletally mature female participants in several sports. Hierarchical and regression-based statistical mediation analyses were used.

RESULTS

SA per se explained a maximum of 1.8% and 5.8% of the variance in motor performances of athletes aged 10-12 and 13-15 years, respectively, over and above that explained by covariates. Body size, proportions, and hours per week of training and participation motivation explained, respectively, a maximum of 40.7%, 18.8%, and 22.6% of the variance in performances. Mediation analysis indicated specific indirect effects of SA through stature and body mass, alone or in conjunction with FFM on performances.

CONCLUSION

SA per se accounted for small and non-significant amounts of variance in several motor performances of female youth athletes; rather, SA influenced performances indirectly through effects on stature, body mass and estimated FFM.

Ages at peak height velocity in male soccer players 11-16 years: relationships with skeletal age and comparisons among longitudinal studies

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.

Body size and weight status of adult Indian males born in the 1890s-1950s: Age and secular change in the context of demographic, economic, and political transformation

OBJECTIVES

To evaluate secular change in body size and weight status of adult Indian males born in 1891-1957 and surveyed in the 1970s.

METHODS

Data are from Anthropological Surveys. Only men were included in the surveys due to high female illiteracy and lack of female researchers. Indian society was also strongly conservative at the time, especially in rural areas, and the measurement of women by men was not permitted. Heights and weights of 43 950 males 18-84 years (born 1891-1957) were measured. The BMI was calculated; weight status of individuals was classified relative to WHO criteria and suggested criteria for the Asia-Pacific region. Heights of men 35+ years were also adjusted for age-related stature loss. Trends in measured and adjusted heights, body weight and the BMI, and in weight status were evaluated by age groups. Linear regression of measured height and adjusted height on year of birth was used to estimate secular effects.

RESULTS

Mean heights declined slightly with age to 50 years and declined sharply through 60+ years, while mean weights increased into the 40s and then declined. Mean BMIs were relatively stable from 30 to 60 years. The prevalence of thinness and normal weight was high, while that of overweight and obesity was low. Regression analyses indicated limited secular change across the total range of birth years but suggested a decline in adjusted heights among men born in 1891 through the 1930s, and little change among men born subsequently.

CONCLUSIONS

Age-related trends and results of the regression analyses by year of birth indicated negligible secular change in heights of Indian men 18-84 years born between 1891 and 1957. BMIs indicated a high prevalence of thinness and normal weight and low prevalence of overweight and obesity.

Body Size, Fatness and Skeletal Age in Female Youth Soccer Players

Growth and maturation are central concerns in the organization of training and competitions in youth sports. This study examined maturity-associated variation in body size and adiposity among adolescent girls participating in competitive age group youth soccer. The sample included 441 players 10.08-16.73 years of age. Stature and body mass were measured and body composition was predicted. The Fels method was used to estimate skeletal age. Skeletally maturity status (late, average or early maturing) was based on the difference between chronological and skeletal age for each player. Mean stature approximated the 50th percentiles of the general population in all competitive age groups, while mean weight fluctuated between 50th and 75th percentiles. Age- and maturity-specific means for estimated fat mass ranged between 18.0% and 28.2%. The number of players classified as skeletally mature increased with competitive age groups (under-13: 0%; under-15: 8%; under-17: 49%). In general, early maturing girls tended to be heavier than their age group peers and especially when compared to late maturing players.

Fine and gross motor skills in 7-10 years old Indian children exposed to a natural disaster during early development

Fetal life and infancy are extremely sensitive to adverse environmental conditions. This study aimed to assess the effect of exposure to a natural disaster (cyclone Aila) in utero or during infancy on fine and gross motor functions in preadolescent Indian children. The study was conducted in West Bengal, India, and included approximately 700 children (7-10 years old) who were prenatally or postnatally exposed to cyclone Aila and a nonaffected group. Anthropometric measures included height, weight, and birthweight. Socioeconomic status was based on parental education, family size, and income. Motor functions were assessed using the short form of Bruininks-Oseretsky Test of Motor Proficiency (BOT-2). Statistical analyses included, for example, generalized linear models. There were no differences in motor functions relative to the timing of the exposure (trimester) during pregnancy. Compared to the controls, prenatal Aila exposure resulted in poorer performance in all BOT-2 subtests, except for fine motor precision, strength, and balance (the last in boys), while postnatal Aila exposure, compared to the controls, resulted in poorer performance in manual dexterity, bilateral coordination, balance (girls only), and speed and agility. Early life exposure to a natural disaster has long-term adverse effect on motor proficiency in children. By inference, the welfare of pregnant women and infants should be of particular concern for emergency and health services during an environmental cataclysm.

Intra-observer reproducibility and inter-observer agreement of Fels skeletal age assessments among male tennis players 8-16 years

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.

Characteristics of external loads of Hockey5s associated with the new version of U16 youth field hockey competition

External workloads associated Hockey 5 s, the new version of youth field hockey, were evaluated in 31 elite U16 male field players (15.4 ± 0.7 years) from three national teams. Mixed-longitudinal observations for the 31 players provided complete data for 33 forwards and 43 defenders. Activities of the players during games were monitored with the GPSports SPI Elite System with a sampling frequency of 10 Hz and were analysed with GPSports Team AMS (version R1 2015.14, Australia). Observed variables did not differ between forwards and defenders, and the three periods of play were differentiated only by maximal speed in the second and third periods. The greatest distances covered were in speed zone 3 (10.0-15.9 km h^-1; 35.5-38.2%) and the smallest in speed zones 4 (16.0-22.9 km h^-1; 14.8-15.6%) and 5 (> 23 km h^-1; 0.4-1.4%). The trends indicated high intensity levels for the entire match and by position and periods. Active time of forwards and defenders accounted for about one-half of a game's duration (~ 15.7 of 30 min). Overall, the Hockey 5s format was highly demanding of players and included relatively short intervals for recovery. The results emphasize the need for preparation that includes specific mixed anaerobic and aerobic training and also the importance of recovery during breaks.

Age at menarche, environmental stress, and social inequality: Evidence from Poland in the 1930s-1950s

OBJECTIVE

To address the relationship between socioeconomic factors and age of menarche among Polish women born and reared in periods that varied considerably in environmental stresses: the Great Depression of the 1930s, the interval of World War II, and the interval of communist rule following World War II through the 1950s.

METHODS

The data set included information on age at menarche and socioeconomic status (SES) of 718 women born during the Great Depression (n = 182), WWII (n = 189), and post-WWII through the 1950s (n = 347). A structured semi-parametric statistical model (generalized additive model [GAM] class) was used for analysis. An ANOVA-like linear model was used to test for marginal effects of SES-related factors and their interactions together with nonparametric seasonal effect.

RESULTS

The influence of period of birth, month of birth, region of early childhood, and father's education, and the interaction between period of birth and father's education on age at menarche were statistically significant. During the economic crisis and the interval of WWII, differences in ages at menarche between the extreme categories of father's education were marked. The differences in ages at menarche between women from the lowest and highest social groups were markedly reduced among women born during the post-war interval. In addition, women born in February-March attained menarche earlier than women born in September-October.

CONCLUSIONS

Unpredictable conditions associated with the economic crisis and war conditions had a stronger impact on age at menarche among women from families of lower SES compared to women from better economic circumstances. Individuals born and reared in low SES conditions likely suffered more severe deterioration across the spectrum of the standard of living and quality of life compared to those with a higher SES.

Blood Lead Level and Handgrip Strength in Preadolescent Polish Schoolchildren

Environmental pollutions, particularly toxic elements such as lead, are among the most significant factors affecting the growth and functional development of children. The aim of this study was to evaluate the effect of blood lead levels on handgrip strength (HGS) in urban children resident in the Copper Basin of Lower Silesia, Poland, controlling for the effects of chronological age, body size and socioeconomic status. The study included 165 boys (9−11 years of age) and 79 girls (9−10 years of age) from Polkowice town. Anthropometric measurements involved height, body mass and grip strength of the left and right hands. Maternal education was a proxy for socioeconomic status. Based on the median value of blood lead level (3.10 µg/dL), the two groups-below and above/equal median value-were defined. Analysis of covariance revealed that age (all p < 0.001), sex (at least p < 0.01), BMI (all p < 0.001), and blood lead level (at least p < 0.05) had a significant effect on the three indicators of HGS (right hand, left hand, average), while the level of maternal education did not significantly affect HGS (p > 0.05). The results of this study indicate a potentially negative effect of elevated blood lead level on grip strength in preadolescent children, irrespective of sex.

Skeletal age assessed by TW2 using 20-bone, carpal and RUS score systems: Intra-observer and inter-observer agreement among male pubertal soccer players

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.

Age of Early Specialization, Competitive Volume, Injury, and Sleep Habits in Youth Sport: A Preliminary Study of US Youth Basketball

BACKGROUND

Concerns for youth sports in the United States often focus on early sport specialization, overemphasis on competition, injuries, and burnout. Little research has addressed relationships among the preceding and other concerns, including time away from organized sport, sleep, and perceptions of physical and psychological well-being.

HYPOTHESIS

There is an association between reported competitive gameplay volume and specialization, injury, and fatigue among elite youth basketball players.

STUDY DESIGN

Cross-sectional study; convenience sample.

LEVEL OF EVIDENCE

Level 4.

METHODS

An anonymous questionnaire was administered to a convenience sample of youth basketball players between 13 and 18 years of age from across the United States. Participants were queried about multiple factors, including the extent of their participation in organized basketball and other sports, time away from organized basketball, injury, sleep, and feelings of exhaustion related to basketball participation.

RESULTS

A total of 772 participants (145 girls, 627 boys) completed a survey. All participants played for a select or elite club basketball team and/or a high school basketball team. Overall, 49% played more than 50 games within the past year. A total of 73% were specialized in basketball, 58% prior to age 14 years, and 35% prior to age 11 years. In all, 70% reported less than 1 month away from organized basketball within the past year, and 28% reported no time away. A total of 54% reported sleeping less than the recommended 8 hours each night during the school year. Within the prior year, 55% reported feeling physically exhausted and 45% reported feeling mentally exhausted from basketball. Regression analysis did not find any significant relationships between early specialization prior to age 14 years and basketball-related injury or feelings of mental or physical exhaustion.

CONCLUSION

In this select group of youth basketball players, the majority specialized in basketball prior to age 14 years and reported a large number of competitive events with little time away from organized basketball.

CLINICAL RELEVANCE

The results from a sample of highly competitive youth basketball players indicate issues that warrant further attention and research regarding the potential impact of specialization, frequent competitions, lack of time away from organized sport, and perceptions of well-being in young athletes.

Weight status of rural school youth in Poland: secular change 1986-2016

The objective of this study was to evaluate secular changes in the Body Mass Index (BMI) and weight status of rural children and adolescents in west-central Poland across decennial surveys spanning 1986 and 2016. Participants were 8,677 boys and girls 7-15 years attending schools in 10 rural communities in 1986, 1996, 2006, and 2016. Heights and weights were measured; BMIs were calculated. Weight status was classified using International Obesity Task Force (IOTF) criteria. The sample was partitioned into three age groups (7-9, 10-12, 13-15 years) for analysis of secular change in the BMI using sex-specific analysis of covariance (ANCOVA) with age and age² as covariates, and for comparison of the prevalence of mild, moderate and severe thinness and of overweight and obesity. BMIs increased, on average, across the four surveys, but differences between adjacent surveys varied. Prevalence of severe and moderate thinness was low in both sexes, while mild thinness tended to decline over time, more so among girls. Overweight and obesity increased over time, especially in 2006 and 2016 compared to 1986 and 1996. In conclusion, secular changes in the BMI between 1986 and 2016 were significant. Age-adjusted mean BMIs suggested a gradient, 2016 > 2006 > 1996 > 1986, except in girls 13-15 years. However, changes across the decennial surveys varied. The observed changes in overweight and obesity between 1986 and 2016 were consistent with studies in Poland spanning the past two generations.

Observed and predicted ages at peak height velocity in soccer players

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.

Assessment of skeletal age in youth female soccer players: Agreement between Greulich-Pyle and Fels protocols

OBJECTIVE

The purpose of the study was to evaluate the agreement between the Fels and Greulich-Pyle methods for the assessment of skeletal age (SA) in female youth soccer players.

METHODS

The sample included 441 Portuguese players 10.08-16.73 years of age who regularly participated in organized and competitive soccer. Standardized radiographs of the left hand-wrist were obtained and analyzed by an experienced examiner. SA was estimated with the Fels and Greulich-Pyle (GP) methods. Differences between SA and chronological age (CA) were used to define skeletal maturity groups: late, average and early maturing. In addition to descriptive statistics, Cohen's kappa and Lin concordance correlation coefficients were used to evaluate agreement between methods.

RESULTS

Intraindividual differences in SA based on the two methods varied between 0.10 to 1.47 years among age groups with larger mean differences at older ages. Agreement of maturity classifications between methods was 74% at younger ages (under-13: kappa = 0.48; under-14: kappa = 0.39; Lin CCC = 0.68) and declined with increasing CA (under-17: 19% agreement; kappa = 0.001; Lin CCC = 0.11). About 19% of the total sample was skeletally mature with the Fels method and an SA was not assigned; in contrast, no players were skeletally mature with the GP method.

CONCLUSIONS

GP SAs were systematically lower than Fels SAs among female soccer players. Intraindividual variability in SAs between methods was considerable. The findings highlight the impact of method on estimates of maturity status.

Growth and maturity status of young male table tennis players

A maturity-associated gradient among adolescent athletes in many sports tends to favour early maturing participants. This study was aimed to describe inter-individual variance in growth and skeletal maturation among male youth table tennis. The sample included 99 players registered in competitive clubs for at least 2 years. Chronological age (CA) ranged 10.00-14.63 years. Stature and body mass were plotted relative to US references. Skeletal age (SA) was estimated with the Fels method. Maturity status was given as SA minus CA. Somatic maturation was derived from predicted age at peak height velocity. Mean values for stature and weight were above the reference medians from 10 to 13 years and at the median in the oldest group. In general, SA was in advance to CA (CA: 12.45 ± 1.28 years; SA: 13.44 ± 2.37 years). The majority of the players were early maturing according to SA (52%) and average maturing based on the somatic indicator (80%). The results suggested that table tennis tends to retain taller and heavier participants who are somewhat advanced in skeletal maturity. Participation in youth table tennis and opportunities to win need to consider age- and maturity-associated variations, particularly regarding bands for competitions.

Growth and Maturity Status of Female Soccer Players: A Narrative Review

Reported mean ages, heights and weights of female soccer players aged <19 years in 161 studies spanning the years 1992-2020 were extracted from the literature or calculated from data available to the authors; 35 studies spanning the years 1981-2020 also included an indicator of biological maturation. Heights and weights were plotted relative to U.S. reference data. Preece-Baines Model 1 was fitted to moving averages to estimate ages at peak velocity. Maturity indicators included skeletal age, pubertal status, age at menarche, percentage of predicted adult height and predicted maturity offset. Heights and weights showed negligible secular variation across the time interval. Heights were slightly above or approximated the reference medians through 14 years old and then varied between the medians and 75th percentiles through 18 years old. Weights were above the reference medians from 9 to 18 years old. Mean ages at menarche ranged from 12.7 to 13.0 years. The trend in heights and weights suggested the persistence and/or selection of taller and heavier players during adolescence, while estimated age at peak height velocity (PHV) and ages at menarche were within the range of mean ages in European and North American samples. Data for skeletal and sexual maturity status were limited; predicted maturity offset increased linearly with mean ages and heights at prediction.

Developmental fitness curves: assessing sprint acceleration relative to age and maturity status in elite junior tennis players

BACKGROUND

The influence of maturity-status on athletic performance is reasonably well-documented. Methodological and practical issues of assessment and lack of longitudinal data have impacted the success of various models.

AIM

To develop age- and sex-specific developmental curves for sprint acceleration in elite youth tennis players and to address variation in performance relative to chronological and biological age.

SUBJECTS AND METHODS

Measures of acceleration were available for 3120 elite youth tennis players aged 8-15 years attending National and Regional Talent Identification days. Variation in acceleration by chronological and estimated biological ages was evaluated in corresponding data for an independent sample of elite youth players 8.9 to 15.1 years of age.

RESULTS

Acceleration varied as a function of chronological and biological age relative to developmental curves. Early maturing males and females had significantly poorer performances when acceleration was considered relative to biological age. Significant discrepancy in percentiles relative to biological versus chronological ages was also evident between early and late maturing players of each sex.

CONCLUSION

Evaluating performance relative to developmental curves and maturity status may be a practical means of monitoring long-term athlete development in tennis.

Predicting the timing of the peak of the pubertal growth spurt in elite male youth soccer players: evaluation of methods

BACKGROUND

Three commonly used non-invasive protocols are implemented to estimate the timing at which PHV most likely occurs. Accurate estimation of circumpubertal years can aid in managing training load of adolescent athletes.

AIM

Three protocols were compared against observed age at PHV: an estimate of 13.8 ± 1.0 years - generic age at PHV (from longitudinal measures); an estimate based on the maturity offset equation, predicted age at PHV ±1.0 year; a window of PHV based on 85-96% of predicted adult height at time of observation.

SUBJECTS AND METHODS

A final sample of 23 (from 28) adolescent male participants were selected from the academy of an English Premier League club. Anthropometric measures were collected across five playing seasons; age at PHV was estimated with Super-Imposition by Translation and Rotation (SITAR). The three protocols were compared based on measures at 13.0 years. Results and Conclusions: An age window based on predicted maturity offset did not improve estimation of PHV compared to generic age method; however, the percentage of predicted adult height window showed improvement in performance shown by the following results. Predicted age at PHV correctly assigned 15 participants (65%) as experiencing PHV, while the percentage height correctly assigned 17 participants (74%). Generic age and predicted age at PHV correctly predicted observed age at PHV for 14 participants (61%), percentage of adult height window correctly predicted 22 participants (96%).

Accuracy of maturity prediction equations in individual elite male football players

BACKGROUND

Equations predicting age at peak height velocity (APHV) are often used to assess somatic maturity and to adjust training load accordingly. However, information on the intra-individual accuracy of APHV in youth athletes is not available.

AIM

The purpose of this study is to assess the accuracy of predication equations for the estimation of APHV in individual youth male football players.

SUBJECTS AND METHODS

Body dimensions were measured at least every three months in 17 elite youth male football players (11.9 ± 0.8 years at baseline) from the 2008-2009 through the 2011-2012 seasons. APHV was predicted at each observation with four suggested equations. Predicted APHV was compared to the player's observed APHV using one-sample-t-tests and equivalence-tests. Longitudinal stability was assessed by comparing the linear coefficient of the deviation to zero.

RESULTS

Predicted APHV was equivalent to the observed APHV in none of the players. A difference with a large effect size (Cohen's d > 0.8) was noted in 87% of the predictions. Moreover, predictions were not stable over time in 71% of the cases.

CONCLUSIONS

None of the evaluated prediction equations is accurate for estimating APHV in individual players nor are predictions stable over time, which limits their utility for adjusting training programmes.

Prediction of maturity offset and age at peak height velocity in a longitudinal series of boys and girls

BACKGROUND

Predicted maturity offset, defined as time before peak height velocity (PHV) is increasingly used as an indicator of maturity status in studies of physical activity, fitness, and sport.

OBJECTIVE

To validate maturity offset prediction equations in longitudinal samples of boys and girls.

METHODS

The original and modified maturity offset prediction equations were applied to serial data for 266 boys (8-17 years) and 147 girls (8-16 years) from the Cracow Growth Study. Actual age at PHV for each youngster was estimated with the SITAR protocol. In addition to maturity offset, the difference between CA at prediction and maturity offset provided an estimate of predicted age at PHV.

RESULTS

Predicted maturity offset and age at PHV increased, on average, with CA at prediction. Variation in predictions was reduced compared to that in observed ages at offset and at PHV, and was more apparent with the modified equations. Relatively few predicted ages at PHV approximated observed age at PHV in early and late maturing youth of both sexes; predictions were later than observed among the former, and earlier than observed among the latter.

CONCLUSION

Predicted maturity offset and ages at PHV with the original and modified equations increase with CA at prediction, have reduced variation, and have major limitations with early and late maturing boys and girls.

Sex Differences in Body Composition Changes after Preseason Training in Elite Handball Players

The purpose of this study was to evaluate changes in the estimated body composition of elite female and male Polish handball players during a five-week preseason training camp. Height and weight were measured, while body composition was estimated with bioelectrical impedance in 18 male and 17 female handball players before and after the five-week training protocol. Components of body composition included total body water (TBW), fat-free mass (FFM), muscle mass (MM), and absolute and relative fat mass (FM). Weight and body mass index (BMI) did not change in males, but declined in females after five weeks of training. FM and %FM declined, while estimated TBW, FFM, and MM increased significantly after training in both males and females. In contrast, comparisons of log transformed ratios for changes in weight, the BMI and body composition in males and females, respectively, suggested that estimated TBW, FFM, and MM increased relatively more in females than in males, while FM and %FM decline relatively more in males than females. Overall, the five-week preseason training program modified the body composition of male and female handball players. FM and %FM decreased, while estimated TBW, FFM, and MM increased, in both males and females after the preseason training program. Comparisons of log transformed ratios for changes in body composition in males and females suggested sexual dimorphism in response to intensive preseason training.

Bio-Banding in Youth Sports: Background, Concept, and Application

Inter-individual differences in size, maturity status, function, and behavior among youth of the same chronological age (CA) have long been a concern in grouping for sport. Bio-banding is a recent attempt to accommodate maturity-associated variation among youth in sport. The historical basis of the concept of maturity-matching and its relevance to youth sport, and bio-banding as currently applied are reviewed. Maturity matching in sport has often been noted but has not been systematically applied. Bio-banding is a recent iteration of maturity matching for grouping youth athletes into 'bands' or groups based on characteristic(s) other than CA. The percentage of predicted young adult height at the time of observation is the estimate of maturity status of choice. Several applications of bio-banding in youth soccer have indicated positive responses from players and coaches. Bio-banding reduces, but does not eliminate, maturity-associated variation. The potential utility of bio-banding for appropriate training loads, injury prevention, and fitness assessment merits closer attention, specifically during the interval of pubertal growth. The currently used height prediction equation requires further evaluation.

Do mating preferences remain the same when phenotypes change? Assortative mating for physical characteristics in an indigenous community in the valley of Oaxaca, southern Mexico

Objective. To test the hypothesis that assortative mating for physical characteristics differs before and after major secular increases in height in an indigenous community in the Valley of Oaxaca, Mexico. Methods. Spouse pairs were identified in household and anthropometric surveys of a Zapotec-speaking community in 1978 (n = 68-70 pairs) and 2000 (n = 99-100 pairs). Height, weight, arm circumference, triceps skinfold and grip strength were measured. Assortative mating was calculated as Pearson correlations. Results. Husband-wife correlations for age were high in both years (r = 0.96, 0.95). Assortative mating for height was significant in 1978 (r = 0.35, p < 0.001) and in 2000 (r = 0.21, p < 0.01), but decreased when ages were controlled (1978, 0.21, p < 0.05; 2000, 0.11). Correlations (zero and second order, respectively) were low for the BMI (1978, 0.02, 0.02; 2000, 0.04, 0.05). Spouse correlations for grip strength were significant in both surveys (r = 0.25 to 0.45), but were reduced (p > 0.05) when ages of spouses were controlled (r = -0.02 to 0.16). Conclusion. Assortative mating for physical characteristics did not differ between surveys conducted before (1978) and after (2000) major secular increases in height in the community, and any possible genetic effect of the secular trend on assortative was likely negligible.

Scaling left ventricular mass in adolescent female soccer players

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 (R2 = 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; R2 = 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.

Thinness, overweight, and obesity in indigenous school children and youth in Mexico

Background: The prevalence of overweight (OWT) and obesity (OB), defined by the body mass index (BMI, kg/m²) among children and youth has increased worldwide in the last 30-40 years.Aim: To evaluate the weight status, defined by the BMI, of indigenous school children and youth resident in different regions of MexicoSubjects and methods: Students 6-18 years (31,448 boys, 27,306 girls) were enrolled in bilingual schools for indigenous children and youth in Mexico in 2012. Height and weight were measured; the BMI was calculated. The BMI of each student was classified relative to International Obesity Task Force (IOTF) age- and sex-specific criteria as thin (three grades), normal, overweight (OWT) or obese (OB). The sample was divided into five geographic regions for analysis: North, Central, South-Gulf, South-Pacific, and South-Southeast. Age- and sex-specific prevalence, 95% confidence intervals, and Chi-square tests were calculated.Results: Prevalence of OWT + OB was highest in the South-Gulf, South-Pacific and South-Southeast regions and lowest in the North and Central regions, while thinness was most prevalent in the North and Central regions.Conclusion: Prevalence of severe and moderate thinness was relatively low, while the combined prevalence of OWT + OB was generally more prevalent in indigenous boys than girls. However, the prevalence of thinness, OWT + OB among indigenous children and youth was lower than in the general population of children and youth in Mexico.

Bio-banding in academy football: player's perceptions of a maturity matched tournament

Background: Individual differences in biological maturation impact player selection and development in youth football.Aim: To evaluate players perceptions of competing in a football tournament where they were matched by maturity rather than chronological age.Subjects: Participants included male junior footballers from three professional academies (n = 115).Methods: The study employed multiple methods of analysis, including one sample mean t-tests, equivalence tests, ANOVAs, and thematic analysis of qualitative data derived from open-ended questions.Results and conclusions: Player's perceived the bio-banding format as providing two main benefits. Early maturing players perceived greater physical and technical challenge, and in turn new opportunities and challenges. Late maturing players perceived less physical and technical challenge, yet greater opportunity to demonstrate technical and tactical abilities. The players reported that they enjoyed and understood the purpose of the bio-banded format, and perceived less risk for injury. Players in all three maturity groups reported more opportunity to engage in leadership behaviours, influence game-play, and express themselves on the ball in the bio-banded format. Bio-banding may facilitate development for both early and late maturing academy players by presenting new learning environments and challenges.

Relative age and maturation selection biases in academy football

This study examined the simultaneous effects of relative age and biological maturity status upon player selection in an English professional soccer academy. A total of 202 players from the U9 to U16 age groups, over an eight-year period (total of 566 observations), had their relative age (birth quarter) and biological maturity (categorised as late, on-time or early maturing based upon the Khamis-Roche method of percentage of predicted adult height at time of observation) recorded. Players born in the first birth quarter of the year (54.8%) were over-represented across all age groups. A selection bias towards players advanced in maturity status for chronological age emerged in U12 players and increased with age; 0% of players in the U15 and U16 age group were categorised as late maturing. A clear maturity selection bias for early maturing players was, however, only apparent when the least conservative criterion for estimating maturity status was applied (53.8% early and 1.9% late maturing in the U16 age group). Professional football academies need to recognise relative age and maturation as independent constructs that exist and operate independently. Thus, separate strategies should perhaps be designed to address the respective selection biases, to better identify, retain and develop players.

Internal and External Loads During Hockey 5's Competitions Among U16 Players

Konarski, JM, Konarska, A, Strzelczyk, R, Skrzypczak, M, and Malina, RM. Internal and external loads during Hockey 5's competitions among U16 players. J Strength Cond Res XX(X): 000-000, 2019-The purpose of the study was to characterize the external and internal loads associated with Hockey 5's, the modified small-sided format of competition for U16 field hockey introduced in 2014. Subjects were 10 males, 15.2-16.3 years, who were field players on the U16 Polish National Team. A GPSports Athlete Tracking System was used to estimate external loads (sprints, total distance), and a Polar Team2 unit was used to monitor internal loads (heart rate [HR] and energy expenditure [EE]) during active time of play for 8 field players in 2 international matches. Players covered, on average, a distance of 2,217 ± 178 m during a match including 614 ± 12 m sprinting at 8.1 ± 0.8 km·h with a speedmax of 23.1 ± 1.1 km·h. HRmean was 170.5 ± 6.6 b·min, whereas HRmax was 184.9 ± 6.4 b·min. Speed, sprinting, and distance covered did not differ among periods, whereas HR was greater during the second and third periods. HRmax, %HRmax, and EE varied between forwards and defenders, and among periods. Effort expended by field players during Hockey 5's games can be characterized as heavy. The results highlight the need for preparation in both aerobic and anaerobic activities, which include a major speed component and adequate time for rapid recovery to facilitate the adaptation of youth players to the demands of the modified game. Although not directly comparable, comparison of internal loads during Hockey 5's and 11-a-side matches suggests more intensive activity of field players in the former.

Cross-Sectional Analysis Investigating the Concordance of Maturity Status Classifications in Elite Caucasian Youth Tennis Players

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.

Repeated Sprint Ability in Youth Soccer Players: Independent and Combined Effects of Relative Age and Biological Maturity

The objective of the study was to examine the effects of the relative age effect (RAE) and predicted maturity status on body size and repeated sprint ability (RSA: 7 x 34.2 m / 25 s interval) in youth soccer. The sample was composed of 197 male players aged 13-14 years. Body mass, stature, and sitting height were measured, RSA was assessed in the field, and age at peak height velocity (APHV) was predicted. Factorial ANOVA tested the independent and combined effects of RAE given by birth quarters (BQs) and maturity status on dependent variables. Players born in the second birth quarter (BQ2) were significantly taller (F = 4.28, p < 0.01) than their peers born in BQ1 and BQ3. Additionally, players born in BQ2 performed better than players born in BQ4 in RSA total time and ideal time (F ranged between 4.81 and 4.90, p < 0.01), while players born in BQ1 exhibited a lower RSA fatigue index compared to those born in BQ4 (F = 2.90, p < 0.05). The interaction of the BQ and maturity status was a significant source of inter-individual variation for body size (F ranged between 64.92 and 105.57; p < 0.01) and RSA output (F ranged between 4.082 and 6.76; p < 0.05). In summary, being relatively older and, simultaneously, advanced in maturity status corresponds to a substantial advantage in characteristics that are related to soccer-specific fitness.

Body mass index and physical fitness in Brazilian adolescents

OBJECTIVE

Evaluate the relationship between body mass index and physical fitness in a cross-sectional sample of Brazilian youth.

METHODS

Participants were 3849 adolescents (2027 girls) aged 10-17 years. Weight and height were measured; body mass index was calculated. Physical fitness was evaluated with a multistage 20m shuttle run (cardiovascular endurance), standing long jump (power), and push-ups (upper body strength). Participants were grouped by sex into four age groups: 10-11, 12-13, 14-15, and 16-17 years. Sex-specific ANOVA was used to evaluate differences in each physical fitness item among weight status categories by age group. Relationships between body mass index and each physical fitness item were evaluated with quadratic regression models by age group within each sex.

RESULTS

The physical fitness of thin and normal youth was, with few exceptions, significantly better than the physical fitness of overweight and obese youth in each age group by sex. On the other hand, physical fitness performances did not consistently differ, on average, between thin and normal weight and between overweight and obese youths. Results of the quadratic regressions indicated a curvilinear (parabolic) relationship between body mass index and each physical fitness item in most age groups. Better performances were attained by adolescents in the mid-range of the body mass index distribution, while performances of youth at the low and high ends of the body mass index distribution were lower.

CONCLUSION

Relationships between the body mass index and physical fitness were generally nonlinear (parabolic) in youth 10-17 years.

Adolescent characteristics of youth soccer players: do they vary with playing status in young adulthood?

Adolescent characteristics of young adult soccer players (n = 35) were compared with those of youth teammates (n = 124) no longer involved in soccer. Former U-13 players active in soccer as young adults were slightly later in maturation and performed better in several functional and soccer skills than youth teammates. Former U-15 players active in soccer as young adults did not differ in maturity status from youth teammates but were chronologically older and performed better in agility and ball control. Young adult regional and national players in both age groups were rated significantly higher on the potential for success by their youth coaches, and national players were rated significantly higher than regional players. The results highlight the need for study of interactions among coaches, youth training and playing environments and the growth, maturity, functional, skill and behavioural characteristics of youth players, and how these interactions may influence persistence in soccer and later playing status.

Sex-dependent effect of post-migration adaptation on height and relative lower leg length in Polish youth

BACKGROUND

Growth in tibia length is considered to be particularly sensitive to environmental stress.

AIM

To estimate the effect of parental migration status on the relative length of the tibia in their school-age children.

SUBJECTS AND METHODS

Data included a nationwide random sample of 17,155 schoolchildren, 7-18 years of age, examined between 1966 and 1969 in Poland who provided information on anthropometric measurements and demographic and social characteristics. Parental migration status was based on paternal migration history. After standardisation by LMS method, z-scores of relative tibia length and z-scores of height were used for analysis. Three-way ANOVA was used to evaluate the influence of migration on tibia length-to-height ratio.

RESULTS

Sons of migrants have a significantly higher tibia length-to-height ratio compared to sons of non-migrants. Children of non-migrants were taller than children of migrants among boys in medium SES and among girls in high and low SES. Relative tibia length indicated significant effects of migration among boys in all age categories and in late adolescent girls: sons of migrants had a higher ratio and daughters of migrants had a lower tibia length-to-height ratio.

CONCLUSION

It is possible that migration experiences of the parents may have influenced the growth of their offspring. The results emphasise the potential importance of research addressing the impact of different types of migration on growth of children.

Multilevel modelling of longitudinal changes in isokinetic knee extensor and flexor strength in adolescent soccer players

The purpose of the study was to model the longitudinal development of knee extension (KE) and flexion (KF) strength in adolescent soccer players. A mixed-longitudinal sample composed of 67 soccer players aged 11.0-13.9 years at baseline was followed on three-to-five occasions over 5 years. Stature, body mass and several skinfold thicknesses were measured. Fat mass was estimated from skinfolds and fat-free mass (FFM) derived. Skeletal age was estimated with the TW2-RUS protocol. An isokinetic dynamometer was used to obtain peak torque of KE and KF from concentric assessments at an angular velocity of 180°/s. Multilevel random effects regression analyses were performed. Among youth soccer players aged 11-16 years, isokinetic strength of the knee muscle groups was reasonably predicted from chronological age (CA), stature and FFM: KE = -66.170 + 5.353 × (CA) + 0.594 × (CA²) + 0.552 × (stature) + 1.414 × (FFM), and KF = -9.356 + 2.708 × (CA) + 1.552 × (FFM). In conclusion, CA per se accounted for annual increments of 5.4 Nm in KE and 2.7 Nm in KF.

Skeletal maturity and oxygen uptake in youth soccer controlling for concurrent size descriptors

Interrelationships among skeletal maturity status, body size, ventilator thresholds (VT) and peak oxygen uptake (VO2peak) were considered in 47 adolescent male soccer players aged 12.5-15.4 years. Body mass, stature, and the triceps and subscapular skinfolds were measured. The latter were used to estimate fat mass and fat-free mass. Skeletal age was assessed with the Fels method. VO2peak and VO2 at the first (VT1) and second (VT2) ventilatory thresholds were determined during an incremental maximal exercise test on a motorized treadmill. Ratio standards and allometric models were used in the analysis. Scaling exponents suggested linearity for all combinations between size descriptors and physiological variables, except between log-transformed values of VT1 and body mass (mL·kg-0.801·min, 95%CI: 0.649 to 0.952). Early maturing players attained greater values than players classified as "on-time" in skeletal maturity for the three ventilatory parameters expressed in absolute terms (d ranged from 0.65 to 0.71). The differences were attenuated after normalizing for mass descriptors using ratio standards and scaled variables (d ranged from 0.00 to 0.31). The results suggested significant variability between maturity groups when moving from VT1 to maximal metabolic conditions expressed by unit of stature (VT1: t = -2.413, p = 0.02, d = 0.60; VT2: t = -2.488, p = 0.02, d = 0.65; VO2peak: t = -2.475, p = 0.02, d = 0.65). Skeletal maturity status and associated variation in overall body size affects VT1, VT2 and VO2peak. The observed scaling of ventilatory outputs for body size may be related to the better running economy and smaller body size of average maturing athletes.

Geographic variation in the growth status of indigenous school children and youth in Mexico

OBJECTIVE

To analyze variation in the growth status of indigenous children and youth attending bilingual schools, escuelas albergues, for the indigenous population in México.

MATERIALS AND METHODS

The children and youth attended escuelas albergues in 1,009 localities in 21 Mexican states in 2012. Heights and weights of 31,448 boys and 27,306 girls 6-18 years of age were measured by trained staff at each school; the BMI was calculated. The students were divided into five geographic regions for analysis: North, Central, South-Gulf, South-Pacific, and South-Southeast. Growth status was compared to United States reference percentiles (P).

RESULTS

Mean heights of children and youth from the five regions varied between P10 and P5 of the reference until about 13 years (girls) and 14 years (boys); subsequently, heights were ≤P5. Mean weights in both sexes were at P25 of the reference between 6 and 12 years, and then varied between P25 and P10 in boys and were ≥P25 in girls. Given the elevated weights relative to heights compared to the reference, mean BMIs of indigenous boys and girls were at or above the reference medians. Children and youth in the North and Central regions were, on average, taller than those in the South-Pacific and South-Southeast regions, while heights of those in the South-Gulf region were generally intermediate. In contrast, mean weights and BMIs differed negligibly among the regions.

CONCLUSIONS

The geographic gradient in heights of indigenous children and youth was consistent with a north-to-south pattern noted among indigenous adults in studies spanning 1898 through 2013. Variation in height among children and youth likely reflected ethnic-specific and geographic variation interacting with economic and nutritional factors.