Physical activity and fitness in an international growth standard for preadolescent and adolescent children

Concepts related to energy expenditure, physical activity and physical fitness, and methods of assessment are briefly considered. Variation in energy expenditure, physical activity, and physical fitness associated with age and sex during childhood and adolescence and relationships between physical activity and physical fitness in children and adolescents are reviewed. Implications of undernutrition and obesity for physical activity and physical fitness, and secular changes in physical activity and physical fitness, are briefly highlighted. The review concludes with specific recommendations for and limitations of inclusion of indicators of physical activity and fitness in the construction of an International Growth Standard for Preadolescent and Adolescent Children.

Lead and growth status of school children living in the copper basin of south-western Poland: differential effects on bone growth

OBJECTIVE

The study analyzed the relationship between blood lead (BPb) levels and growth status of upper and lower body segments among schoolchildren living in the copper basin of south-western Poland.

MATERIALS AND METHODS

Schoolchildren 7-15 years of age (463 males, 436 females) living in the vicinity of copper smelters and refineries were tested for blood lead. Weight, height, symphyseal height (leg, lower segment length), and arm length were measured. Trunk (upper segment including head and neck) length was estimated as height minus symphyseal height. The BMI was calculated using weight/height2 (kg m-2).

RESULTS

Mean blood lead in the total sample was 7.7 +/- 3.5 micro g dL-1 (2.0-33.9 micro g dL-1). Blood lead level was significantly and linearly related to reduced weight, height, trunk, leg, and arm lengths. The estimated reduction in height was 5 mm per 1 micro g dL-1 increase in blood lead (5.0 cm per 10 micro g dL-1). The reduction occurred in leg length (males, 64%; females 72%) compared to trunk length (males, 36%; females, 28%). Estimated reductions in arm length were 2.0 cm (males) and 2.5 cm (females) per 10 micro g dL-1 increase in blood lead. Hence, limb (leg and arm) lengths were markedly reduced.

CONCLUSIONS

Linear skeletal growth was reduced with increased blood lead, even at levels below that considered for action by US CDC standards. The reduction in height occurred primarily in leg length. Arm length was also reduced, suggesting limb lengths in general were affected by blood lead. Results are consistent with lead-associated interruption of (1) major epiphyseal growth plate chondrocyte hyperplasia, hypertrophy, and interrupted matrix calcification as a primary cause of stunted long bone growth, and reduced stature; and (2) attenuated osteoblast activity (proliferation and migration) as a secondary cause of stunted growth in the study population.

Characteristics of youth soccer players aged 13-15 years classified by skill level

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.

Physical fitness of children and adolescents in the United States: status and secular change

The physical fitness of school-age children in the United States is considered from two perspectives--status and secular change. This chapter principally examines health-related fitness, including the BMI, though performance-related fitness is briefly considered. Concepts of reference data and standards and factors that may influence secular change are initially discussed. National data on the physical fitness status of school children in the continental United States are limited to the 1980s. Ethnic variation in physical fitness is not considered except for the prevalence of overweight and obesity. More recent physical fitness data, including examination of ethnic variation, are based on several statewide and more local surveys. Although results vary by test, the majority of American school children meet or exceed criterion-referenced standards, although sex differences are not consistent. Poor morphological fitness manifest in obesity is an exception. The prevalence of overweight and obesity has increased since the early 1980s. Secular data for specific fitness items are less extensive. Regression analyses suggest a recent decline in maximal aerobic power in girls, but fairly stable levels between the 1930s and today in boys. However, the highest values for boys occur in the 1960s and 1970s and more recent values are somewhat lower. The general trend may be consistent with the decline since the 1980s in aerobic performance assessed with the 20 m shuttle run. These trends highlight the need for updated national physical fitness data for American youth.

Maturity offset in gymnasts: application of a prediction equation

PURPOSE

To verify the applicability of the prediction equation for maturity offset in a sample of female gymnasts followed longitudinally through adolescence.

METHODS

Fifteen gymnasts were followed longitudinally for 6-7 yr across adolescence. Weight, height, and sitting height were measured at annual intervals. The Preece-Baines Model I was fitted to longitudinal height data for individual gymnasts to derive age at peak height velocity (PHV). The curve-fitting protocol was successfully fit to the height records of 13 of the 15 gymnasts with standard errors of estimate between 0.02 and 0.28 cm. Maturity offset was calculated from measurements taken at each observation for the 13 gymnasts and also added to chronological age at each observation point to provide an estimated age at PHV. Age at PHV derived with the Preece-Baines model was used as the criterion. Differences between the criterion age at PHV and predicted age at PHV were calculated.

RESULTS

Maturity offset overestimates age at PHV in gymnasts. Mean predicted ages at PHV deviate linearly from the criterion age at PHV, but the difference is significant only at 9 yr. Correlations between maturity offset predicted ages at PHV and criterion age at PHV range from -0.13 to +0.76. The Bland-Altman plot of criterion and predicted ages at PHV suggest a systematic bias in the predictions.

CONCLUSION

Maturity offset appears to have limitations when applied to female gymnasts. Care is warranted in utilizing maturity offset per se and predicted age at PHV based on maturity offset as an indicator of maturity timing in female gymnasts and perhaps other short females.

Adiposity and cardiac dimensions among 9- to 18-year-old youth: the Québec Family Study

The relationship between adiposity and cardiac dimensions were considered in healthy 9- to 18-year-old boys (n=198) and girls (n=154). Indicators of adiposity included the body mass index (BMI), sum of skinfolds (SSF) and trunk-to-extremity ratio (TER). The following left ventricular (LV) dimensions were measured by echocardiography: internal diameter (LVIDd); posterior wall thickness (PWT) and intraventricular septal wall thickness. LV mass (LVM) was estimated. In boys, 11 of 45 correlations were significant. The magnitude of the correlations increased across age groups and most of the correlations were significant in the oldest age group. In girls, 18 of 45 correlations were significant, but there were inconsistent patterns in the magnitude of the correlations across age groups. Correlations between BMI and LVIDd and LVM were highest in youth 13-15 years, whereas other correlations involving the BMI were rather constant across age groups. Correlations involving SSF were significant only in 9-12 and 13-15 year olds. There were no significant correlations involving TER in female subjects. In the total sample of boys, only correlations between the BMI and LV parameters were significant (r=0.14-0.38), except for the relationship between SSF and PWT (r=0.21). The TER was weakly associated with LV parameters. In the total sample of girls, correlations for LV parameters were significant for both the BMI (r=0.20-0.43) and SSF (r=0.18-0.28; except for LVIDd). TER was not significantly related to LV parameters except LVIDd (r=0.16). The findings indicate that the BMI is an important determinant of LV structure.

Weight training in youth-growth, maturation, and safety: an evidence-based review

OBJECTIVE

To review the effects of resistance training programs on pre- and early-pubertal youth in the context of response, potential influence on growth and maturation, and occurrence of injury.

DESIGN

Evidence-based review.

METHODS

Twenty-two reports dealing with experimental resistance training protocols, excluding isometric programs, in pre- and early-pubertal youth, were reviewed in the context of subject characteristics, training protocol, responses, and occurrence of injury.

RESULTS

Experimental programs most often used isotonic machines and free weights, 2- and 3-day protocols, and 8- and 12-week durations, with significant improvements in muscular strength during childhood and early adolescence. Strength gains were lost during detraining. Experimental resistance training programs did not influence growth in height and weight of pre- and early-adolescent youth, and changes in estimates of body composition were variable and quite small. Only 10 studies systematically monitored injuries, and only three injuries were reported. Estimated injury rates were 0.176, 0.053, and 0.055 per 100 participant-hours in the respective programs.

CONCLUSION

Experimental training protocols with weights and resistance machines and with supervision and low instructor/participant ratios are relatively safe and do not negatively impact growth and maturation of pre- and early-pubertal youth.

Estimated maturity status and perceptions of adult autonomy support in youth soccer players

In this study, we examined the relations between biological maturity status, body mass index, age, and perceptions of adult autonomy support in the context of youth soccer. A total of 70 female and 43 male soccer players, aged 9 - 15 years, completed three adult-specific versions (i.e. mother, father, coach) of the perceived autonomy support subscale from the Interpersonal Style Scale. The participants' percent predicted adult stature was used as an estimate of biological maturity status. Multiple linear regression analyses revealed that advanced maturity status in male players predicted lower perceptions of autonomy support from the coach. Maturity status was unrelated to perceptions of autonomy support from the coach in female soccer players, and paternal and maternal autonomy support in male and female players. Age and body mass index were unrelated to perceptions of adult (i.e. coach, mother, father) autonomy support in male and female players.

A multidisciplinary selection model for youth soccer: the Ghent Youth Soccer Project

OBJECTIVES

To determine the relationships between physical and performance characteristics and level of skill in youth soccer players aged 12-16 years.

METHODS

Anthropometry, maturity status, functional and sport-specific parameters were assessed in elite, sub-elite, and non-elite youth players in four age groups: U13 (n = 117), U14 (n = 136), U15 (n = 138) and U16 (n = 99).

RESULTS

Multivariate analyses of covariance by age group with maturity status as the covariate showed that elite players scored better than the non-elite players on strength, flexibility, speed, aerobic endurance, anaerobic capacity and several technical skills (p<0.05). Stepwise discriminant analyses showed that running speed and technical skills were the most important characteristics in U13 and U14 players, while cardiorespiratory endurance was more important in U15 and U16 players. The results suggest that discriminating characteristics change with competitive age levels.

CONCLUSIONS

Characteristics that discriminate youth soccer players vary by age group. Talent identification models should thus be dynamic and provide opportunities for changing parameters in a long-term developmental context.

Effect of Physical Education and Activity Levels on Academic Achievement in Children

PURPOSE

This study was conducted to determine the effect of physical education class enrollment and physical activity on academic achievement in middle school children.

METHODS

Participants were 214 sixth-grade students randomly assigned to physical education during either first or second semesters. Moderate and vigorous physical activity (MVPA) (number of 30-min time blocks) outside of school was assessed using the 3-d physical activity recall (3DPAR). The 3DPAR time blocks were converted to ordinal data with scores of 1 (no activity), 2 (some activity), or 3 (activity meeting Healthy People 2010 guidelines). Academic achievement was assessed using grades from four core academic classes and standardized test scores (Terra Nova percentiles).

RESULTS

Grades were similar regardless of whether students were enrolled in physical education during first or second semesters. Physical education classes averaged only 19 min of MVPA. Students who either performed some or met Healthy People 2010 guidelines for vigorous activity had significantly higher grades (P < 0.05) than students who performed no vigorous activity in both semesters. Moderate physical activity did not affect grades. Standardized test scores were not significantly related to physical education class enrollment or physical activity levels.

CONCLUSION

Although academic achievement was not significantly related to physical education enrollment, higher grades were associated with vigorous physical activity, particularly activity meeting recommended Healthy People 2010 levels.

Puberty and physical self-perceptions of competitive female figure skaters: an interdisciplinary approach

This study considered the interrelationships among biological maturation and its physical correlates, social physique anxiety, and appearance-related physical self-perceptions in 113 adolescent female figure skaters participating in solo (n = 73) or partner contexts (n = 40). Participants were interviewed about their menarcheal status, underwent a battery of anthropometric measurements, and completed the Physical Self Description Questionnaire and the Social Physique Anxiety Scale. Menarcheal status was a stronger correlate of physical self-perceptions than age. A combination of biological and psychological characteristics accounted for 25% of the variance in appearance-related physical self-perceptions. Younger, premenarcheal, ectomorphic skaters reporting lower social physique anxiety were more satisfied with their body fat and sport competence but reported lower self-esteem, global physical self-concept, and appearance scores. Skating context did not predict physical self-perceptions.

Incidence and player risk factors for injury in youth football

OBJECTIVE

To estimate the incidence of injuries in youth football and to assess the relationship between player-related risk factors (age, body size, biological maturity status) and the occurrence of injury in youth football.

DESIGN

Prospective over two seasons.

SETTING

Two communities in central Michigan.

PARTICIPANTS

Subjects were 678 youth, 9-14 years of age, who were members of 33 youth football teams in two central Michigan communities in the 2000 and 2001 seasons.

METHODS

Certified athletic trainers (ATCs) were on site to record the number of players at all practices and home games (exposures) and injuries as they occurred. A reportable injury (RI) was defined by the criteria used in the National Athletic Trainers' Association (NATA) survey of several high school sports. Estimated injury rates (95% confidence intervals) per athlete exposures (AE) and per number of athletes were calculated for practices and games by grade. Player risk factors included age, height, weight, BMI and estimated maturity status.

MAIN OUTCOME MEASURE

Estimated injury rates and relative risks of injury during practices and games by grade; logistic regression to evaluate relationships between player-related risk factors and risk of injury.

RESULTS

A total of 259 RIs, 178 in practice and 81 in games, were recorded during the two seasons. Practice injury rates increased with grade level, while game injury rates were similar among fourth through fifth grade and sixth grade players and about twice as high among seventh and eighth grade players. The majority of RIs during the two seasons was minor (64%); the remainder was moderate (18%) and major (13%). Injured fourth through fifth grade players were significantly lighter in weight and had a lower BMI; otherwise, injured and non-injured players within each grade did not differ in age, body size and estimated biological maturity status. Logistic regressions within grade revealed no significant associations between injury and age, height, BMI, and maturity status.

CONCLUSION

Game injury rates are higher than practice injury rates, and the incidence of injury tends to increase with grade level. Age, height, BMI and maturity status were not related to the risk of injury in youth football players.

Wrist pain, distal radial physeal injury, and ulnar variance in the young gymnast

In gymnastics, the wrist joint is subjected to repetitive loading in a weightbearing fashion. In this setting, chronic wrist pain is quite common. Because gymnasts ordinarily enter the sport at very young ages and train for several years before skeletal maturity is attained, the growth plates of the wrist are at risk for injury. In addition, imaging studies have identified evidence of injury to the distal radial physis and the development of positive ulnar variance. Recent studies provide more information on the relationships between these findings, as well as factors that may predispose some gymnasts to wrist pain. This article provides a comprehensive review of these issues and offers suggestions for management, preventive measures, and future research.

Changes in the BMI of Polish conscripts between 1965 and 2001: secular and socio-occupational variation

OBJECTIVE

To describe changes in the body mass index (BMI) of nationally representative samples of young adult Polish males between 1965 and 2001, and to investigate variation in the incidence of underweight, overweight and obesity between 1965 and 2001 in the young adult males in the context of the socio-political transformation that occurred in Poland since 1989.

SUBJECTS

Four 10% nationwide random samples of 29-year-old Polish conscripts examined in 1965, 1986, 1995 and 2001. The conscripts were divided into four socio-occupational groups based on paternal education, occupation and degree of urbanization.

MEASUREMENTS

Height, weight and BMI (weight (kg)/height (m2)).

RESULTS

The proportion of overweight and underweight young adult males in the population increased between 1965 and 2001. The fraction of underweight decreased only among sons of farmers and entrepreneurs between 1986 and 1995 and then increased in all socio-occupational groups between 1995 and 2001. On the other hand, the proportion of overweight young adults gradually increased in all groups between 1965 and 2001.

CONCLUSION

Socio-occupational position of the family is an important factor influencing underweight and overweight in young adult males. This factor apparently operates through a differential distribution of income, which influences components of lifestyle most likely associated with level of habitual physical activity and/or diet.

Maturity-associated variation in the body size and proportions of elite female gymnasts 14-17 years of age

The aim of this study was to evaluate variations in the size and body proportions of elite female gymnasts associated with individual differences in maturity status. The subjects were 150 gymnasts, 14.0-17.9 years of age, who had participated in the 24th World Championship in Artistic Gymnastics, Rotterdam. Height, body mass, sitting height and biacromial and bicristal breadths were measured. Leg length was estimated as the height minus sitting height, and the ratio of sitting height to height was calculated. Information on menarcheal status was obtained by means of a questionnaire, and hand-wrist radiographs were taken to assess skeletal maturity status. For the purpose of data analysis the gymnasts were divided into three maturity groups within each single-year chronological age (CA) group from 14 to 17 years: pre-menarcheal (n=65); post-menarcheal but not skeletally mature (SA<16.0 years, n=37); post-menarcheal, skeletally mature (n=48). Differences among the groups were tested with analysis of variance and post hoc Tukey tests. The results showed that pre-menarcheal gymnasts are smaller in all dimensions compared to post-menarcheal gymnasts in all age groups but that the significance of differences varies. Post-menarcheal, skeletally mature gymnasts are heavier than pre-menarcheal gymnasts, but weight does not differ between gymnasts in the two post-menarcheal groups (with one exception, 16 years). Post-menarcheal, skeletally mature gymnasts have proportionally shorter legs than gymnasts in the other two maturity categories. Elite gymnasts of contrasting maturity status show similar trends in body size and proportions similar to those of non-athlete adolescent girls of contrasting maturity status. The results highlight the need to consider maturity-associated variation in the body dimensions of gymnasts before attributing their characteristics to the demands of regular training.

The relationship between peak height velocity and physical performance in youth soccer players

Longitudinal changes in height, weight and physical performance were studied in 33 Flemish male youth soccer players from the Ghent Youth Soccer Project. The players' ages at the start of the study ranged from 10.4 to 13.7 years, with a mean age of 12.2 +/- 0.7 years. Longitudinal changes were studied over a 5 year period. Peak height velocity and peak weight velocity were determined using non-smoothed polynomials. The estimations of peak height velocity, peak weight velocity and age at peak height velocity were 9.7 +/- 1.5 cm x year-1, 8.4 +/- 3.0 kg x year-1 and 13.8 +/- 0.8 years, respectively. Peak weight velocity occurred, on average, at the same age as peak height velocity. Balance, speed of limb movement, trunk strength, upper-body muscular endurance, explosive strength, running speed and agility, cardiorespiratory endurance and anaerobic capacity showed peak development at peak height velocity. A plateau in the velocity curves was observed after peak height velocity for upper-body muscular endurance, explosive strength and running speed. Flexibility exhibited peak development during the tear after peak height velocity. Trainers and coaches should be aware of the individual characteristics of the adolescent growth spurt and the training load should also be individualized at this time.

Familial similarity in body size in an isolated Zapotec-speaking community in the valley of Oaxaca, southern Mexico: estimated genetic and environmental effects

OBJECTIVE

The study used path analysis to estimate genetic and environmental determinants of familial similarity in anthropometric characteristics among children from a rural subsistence agrarian community in the Valley of Oaxaca in southern Mexico.

METHODS

Anthropometric dimensions included height, weight, arm circumference and triceps skinfold; the BMI was calculated. Parent-offspring pairs (n = 34) were constructed from pedigrees and prior studies using listwise case deletion for parent-male child and parent-female child, respectively. Path coefficients for genetic and environmental effects were computed using linear regression. Age effects were held constant by computing residuals after parameter regression on age and age2. Environmental effects were analysed using a previously published factor analysis of village ecology.

RESULTS

By path analysis, the paternal effect was low-to-moderately strong on males (0.21-0.57) but low on females (0.13-0.23). Maternal effects were low, inconsistent and negligible on males (-0.16-0.09), but high on females (0.57-0.81), except for height (0.19). Estimated environmental effects on sibling similarity were low (0.12-0.27).

CONCLUSION

The environment exerts a relatively consistent effect on growth status, and probably accounts for the low path coefficients (i.e. sibling correlations, parent-offspring regressions). Sex-specific effects are apparent in a strong paternal influence on male offspring height and moderate influences on weight, triceps skinfold, and arm circumference. Maternal influences are small on the anthropometric characteristics of males, but are exceptionally large on female weight, triceps skinfold and arm circumference. Estimated environmental effects on sibling similarity are low-to-moderately high.

Opportunity for Natural Selection and Gene Flow in an Isolated Zapotec-Speaking Community in Southern Mexico in the Throes of a Secular Increase in Size

Our object in this paper is to analyze the opportunity for natural selection and gene flow in an isolated Zapotec-speaking community in the valley of Oaxaca, southern Mexico, that is undergoing a secular increase in body size. Surveys were conducted in the community in 1968, 1978, and 2000, including anthropometric and census data. No secular change was found in the growth status of schoolchildren and adult height between 1968 and 1978; subsequently, major secular gains in height occurred among children and adolescents between 1978 and 2000. The 1978 household data were used to compute gene flow (3.3%) and opportunity for selection intensity (I = 1.312). Migration and other demographic information was obtained from household census data for 1978 and 2000, and mortality information was extracted from community records and archives. These data were used to compute gene flow and opportunity for natural selection. Gene flow increased from 3.3% to 4.7% and intensity of natural selection decreased from 1.312 to 0.272 from 1978 to 2000. Variance in fertility increased slightly over time (12.25 to 13.69). Opportunity for selection was dominant during the prereproductive period in 1978, but approached 0 for the mortality component in 2000, resulting in a marked decrease in the mortality component (Im) of selection (0.626 and 0.019, respectively) and total opportunity for selection (I = 1.312 and 0.272, respectively). Secular increase in height and markedly decreased opportunity for natural selection (1) were associated with better health and nutritional conditions. Genotype-environment interaction and environmental influences are apparently the predominant causes of the secular trend. If natural selection plays a role in causing the secular trend, it is a small one.

Craniofacial dimensions in children in rural Oaxaca, Southern Mexico: Secular change, 1968–2000

The objective of this investigation was to analyze the underlying cause(s) of secular changes in craniofacial dimensions among indigenous children in an isolated community in Oaxaca, southern Mexico, between 1968-2000. Subjects were schoolchildren resident in a rural, agrarian, Zapotec-speaking community in the Valley of Oaxaca, previously characterized as mildly-to-moderately undernourished with growth-stunting in 1968 and 1978. In 2000, children had experienced a secular increase in height compared with two prior growth surveys. Four craniofacial dimensions (head length, head breadth, and bizygomatic and bigonial breadths) were measured during anthropometric surveys of schoolchildren aged 6-13 years in 1968, 1978, and 2000. Cephalic and zygomandibular indices were calculated. Samples by survey were: 1968, 151 males and 157 females; 1978, 179 males and 184 females; and 2000, 180 males and 186 females. The analysis was based on a total of 1,037 children. Multivariate analysis of covariance was used to assess secular trend effects, with height, age, and age2 as covariates by sex. Over the interval of 32 years, significant secular changes occurred in craniofacial dimensions and one index: 1) head length was shorter in boys and girls; 2) bizygomatic breadth was narrower in boys and girls; 3) head breadth increased over time only among girls; 4) brachycephalization increased significantly in a linear manner among both sexes; and 5) the zygomandibular index decreased significantly only in boys. Thus, the cranial complex remodeled to a shorter head length, both relatively (brachycephalization) and absolutely. Remodeling over time also resulted in a narrower face, with the midface changing at about the same rate as the lower face (i.e., mandible). Secular changes are generally recognized as multifactorial. Changes in the cephalic index and cranium over time in schoolchildren in an isolated rural agrarian Zapotec-speaking community in the Valley of Oaxaca suggest that the underlying forces for the secular change are associated: 1) decreased food (maize) coarseness or grit content (masticatory stress), and 2) relaxed natural selection, resulting in 3) a greater role for developmental plasticity.

Anthropometry and somatotype of competitive female figure skaters 11-22 years. Variation by competitive level and discipline

AIM

Variation in anthropometric characteristics and somatotype of female figure skaters by level of competition and discipline was examined.

METHODS

EXPERIMENTAL DESIGN

ANCOVA with age as the covariate was used to compare the anthropometry of skaters by level (test stream, pre-elite, elite) and discipline (free, dance, pair), while MANCOVA was used to compare somatotype.

SETTING

purposive sampling reflecting the skating population by level and discipline was used to recruit skaters in 4 American, and 7 Canadian figure skating clubs.

PARTICIPANTS

a total of 161 competitive female figure skaters 11-22 years of age (15.7+/-2.4 years) comprised the sample.

MEASURES

a battery of 15 anthropometric dimensions was taken on each skater. Several dimensions, ratios and Heath-Carter somatotypes were derived.

RESULTS

Test skaters are heavier and generally larger than pre-elite skaters. Test stream skaters also have larger limb circumferences, estimated calf and arm musculature, and a thicker sum of skinfolds, and are more endomorphic than pre-elite skaters. Elite skaters are more mesomorphic than pre-elite skaters. The sitting height/stature (SH/ST) ratio is significantly lower in pre-elite skaters, while elite and test stream skaters do not differ in this indicator of proportions. Free skaters are taller and heavier; have a higher body mass index (BMI), limb circumferences and sum of skinfolds; and proportionally shorter legs than dancers and pair skaters. Free skaters, dancers and pair skaters, however, do not differ in somatotype.

CONCLUSIONS

The results suggest that figure skating favors lightness, leanness, higher mesomorphy and lower endomorphy at more elite levels. Shortness, leanness and linearity of physique appear to be selective factors associated with specialization in dance and pair skating.

The relative age effect in soccer: a match-related perspective

Asymmetries in the distributions of birth dates in senior professional and youth soccer players have been interpreted as evidence for systematic discrimination against individuals born shortly before the cut-off date in assigning youth to specific age groups. This concept is known as the "relative age effect". The results of a longitudinal study of birth date distritubions of 2757 semi-professional and amateur senior soccer players in Belgium are presented. Records for competitive games were available in official statistics provided by the Royal Belgian Football Association. The chi-square statistic was used to examine differences between observed and expected birth date distributions. Regression analyses indicated a shift of bias when two different start dates were compared. Players born in the early part of the new age band (January to March) were over-represented compared with players born late in the new selection period (October to December). However, players with birthdays at the start of the old selection year (August) were still represented. In a retrospective analysis of 2138 players, variables indicative of match involvement, number of selections for matches, and time played were examined in relation to the relative age effect. The group of semi-professional and amateur senior soccer players born in the first quarter of the selected age band received more playing opportunities. Comparisons of birth date distributions (traditional approach to relative age effect) with match-related variables gave similar, though not entirely consistent, results. However, there were no differences for the mean number of selections and for playing minutes between players born at the start or the end of the selection year. Our findings suggest that match-based variables may provide a more reliable indication of the relative age effect in soccer.

Secular change in age at menarche in rural Oaxaca, southern Mexico: 1968--2000

OBJECTIVE

To evaluate secular change in the age at menarche between 1978 and 2000 in residents of a rural Zapotec-speaking community in Oaxaca, southern Mexico, using status quo and retrospective methods.

MATERIALS AND METHODS

Status quo menarcheal status of girls 9-18 years of age in 1978 (n= 101) and 2000 (n=238) and retrospective ages at menarche of adult women 19+ years of age in 1978 (n = 228) and 2000 (n = 246) were obtained via interview. Probit analysis was used to estimate median ages at menarche and 95% confidence intervals (CI) for the status quo data. Analysis of variance and linear regression was used to compare the retrospective data across surveys.

RESULTS

The median ages at menarche of adolescents are 14.8+/-1.2 years (0.24 year, 95% CI 14.2-15.4 years) in 1978 and 13.0+/-1.0 years (0.10 year, 95% CI 12.7-13.3 years) in 2000. Age at menarche has declined by 1.8 years over about 23 years, 0.78 year/decade (95% CI = 0.65-0.91 year/decade). Recalled ages at menarche do not differ by age group in the 1978 survey, but differ significantly by age group in the 2000 survey (p <0.001). Within the 2000 survey, the two youngest age groups (< 29, 30-39 years) do not differ, but attain menarche earlier than women in the four older age groups (p < 0.05), who do not differ from each other in age at menarche. The estimated rates of secular decline in age at menarche in adult women vary between 0.38 and 0.42 years/decade (0.26-0.56 year/decade).

CONCLUSIONS

There is a major secular decline in the age at menarche of adolescent girls and young adult women between 1978 and 2000. The estimated rate of decline in adult women is about one-half of that in adolescent girls. The secular decline in age at menarche is consistent with corresponding secular gains height, sitting height and estimated leg length of children and adolescents in the community; corresponding secular gains are smaller in young adults 19-29 years.

Evidence based physical activity for school-age youth

OBJECTIVES

To review the effects of physical activity on health and behavior outcomes and develop evidence-based recommendations for physical activity in youth.

STUDY DESIGN

A systematic literature review identified 850 articles; additional papers were identified by the expert panelists. Articles in the identified outcome areas were reviewed, evaluated and summarized by an expert panelist. The strength of the evidence, conclusions, key issues, and gaps in the evidence were abstracted in a standardized format and presented and discussed by panelists and organizational representatives.

RESULTS

Most intervention studies used supervised programs of moderate to vigorous physical activity of 30 to 45 minutes duration 3 to 5 days per week. The panel believed that a greater amount of physical activity would be necessary to achieve similar beneficial effects on health and behavioral outcomes in ordinary daily circumstances (typically intermittent and unsupervised activity).

CONCLUSION

School-age youth should participate daily in 60 minutes or more of moderate to vigorous physical activity that is developmentally appropriate, enjoyable, and involves a variety of activities.

Maturity status of youth football players: a noninvasive estimate

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.

Inbreeding avoidance in an isolated indigenous Zapotec community in the valley of Oaxaca, southern Mexico

We analyzed inbreeding using surname isonymy in an indigenous genetic isolate. The subjects were residents of a rural Zapotec-speaking community in the valley of Oaxaca, southern Mexico. The community can be classified as a genetic isolate with an average gene flow of < or = 3% per generation. Surnames were collected for individuals in each household in pedigree form using the culturally traditional patronym-matronym naming. Estimation of inbreeding from surname isonymy is facilitated by the traditional patronym-matronym name assignment among indigenous Mexican populations. A total of 2,149 individuals had valid surname patronym-matronym pairings, including 484 deceased ancestors. Surname isonymy analysis methods were used to estimate total inbreeding and to segregate it into random and nonrandom components. The surname isonymy coefficient computed from 119 isonymous surname pairings (119/2,149) was 0.0554. The estimated inbreeding coefficient from surname isonymy was 0.0138 (0.0554/4). The random and nonrandom components of inbreeding were F(r) = 0.0221 and F(n) = -0.0091, respectively. The results suggest that consanguinity is culturally avoided. Nonrandom inbreeding decreased total inbreeding by about 41%. Total estimated inbreeding by surname isonymy was 0.0138, which is similar to inbreeding estimated from a sample of pedigrees, 0.01. Socially prescribed inbreeding avoidance substantially lowered total F through negative nonrandom inbreeding. Even in the situation of genetic isolation and small effective population size (N(e)), estimated inbreeding is lower than may have otherwise occurred if inbreeding were only random. However, among the poorest individuals, socially prescribed jural rules for inbreeding avoidance failed to operate. Thus the preponderance of inbreeding appears to occur among the poor, economically disadvantaged in the community.

Combined influence of body mass index and waist circumference on coronary artery disease risk factors among children and adolescents

OBJECTIVES

In adult populations, it is recognized widely that waist circumference (WC) predicts health risk beyond that predicted by BMI alone; current recommendations for adults are that a combination of BMI and WC be used to classify obesity-related health risk. For children and adolescents, however, little is known about the combined influence of BMI and WC on health outcomes. The objectives of this study were to determine whether BMI and WC predict coronary artery disease (CAD) risk factors independently for children and adolescents and to assess the clinical utility of using WC in combination with BMI to identify CAD risk.

METHODS

Subjects included 2597 black and white, 5- to 18-year-old, male and female youths. Outcome measures included 7 CAD risk factors. In the first analysis step, BMI and WC were used as continuous variables to predict CAD risk factors. In the second analysis step, participants were placed into normal-weight, overweight, and obese BMI categories and, within each BMI category, CAD risk factors were compared for groups with low and high WC values.

RESULTS

When BMI and WC were included in the same regression model to predict CAD risk factors, the added variance above that predicted by BMI or WC alone was minimal, which indicated that BMI and WC did not have independent effects on the risk factors. For example, for systolic blood pressure, BMI alone explained 7.3% of the variance, WC alone explained 7.7% of the variance, and the combination of BMI and WC explained 8.1% of the variance. When BMI and WC values were categorized with a threshold approach, WC provided information on CAD risk beyond that provided by BMI alone, particularly when the categories were used to predict elevated CAD risk factor levels. For instance, in the overweight BMI category, the high-WC group was approximately 2 times more likely to have high triglyceride levels, high insulin levels, and the metabolic syndrome, compared with the low-WC group.

CONCLUSION

These findings provide some evidence that a combination of BMI and WC should be used in clinical settings to evaluate the presence of elevated health risk among children and adolescents.

Maturity-associated variation in sport-specific skills of youth soccer players aged 13 – 15 years

The aim of this study was to estimate the contribution of experience, body size and maturity status to variation in sport-specific skills of adolescent soccer players. The participants were 69 players aged 13.2-15.1 years from three clubs that competed in the highest division for their age group. Height and body mass were measured and stage of pubic hair development was assessed at clinical examination. Years of experience in football was obtained at interview. Six football skill tests were administered: ball control with the body, ball control with the head, dribbling with a pass, dribbling speed, shooting accuracy and passing accuracy. Multiple linear regression analysis was used to estimate the relative contributions of age, stage of sexual maturity, height, body mass and years of formal training in soccer to the six skill tests. Age, experience, body size and stage of puberty contributed significantly but in different combinations to the variance in four of the six skill tests: dribbling with a pass (21%; age, stage of maturity), ball control with the head (14%; stage of maturity, height, body height x body mass interaction), ball control with the body (13%; stage of maturity, years of training) and shooting accuracy (8%; stage of maturity, height; borderline significance, P = 0.06). There were no significant predictors for the tests of dribbling speed and passing accuracy. In conclusion, age, experience, body size and stage of puberty contributed relatively little to variation in performance in four of the six soccer-specific skill tests in adolescent footballers aged 13-15 years.

Growth status and estimated growth rate of youth football players: a community-based study

OBJECTIVE

To characterize the growth status of participants in community-sponsored youth football programs and to estimate rates of growth in height and weight.

DESIGN

Mixed-longitudinal over 2 seasons.

SETTING

Two communities in central Michigan.

PARTICIPANTS

Members of 33 youth football teams in 2 central Michigan communities in the 2000 and 2001 seasons (Mid-Michigan PONY Football League).

METHODS

Height and weight of all participants were measured prior to each season, 327 in 2000 and 326 in 2001 (n = 653). The body mass index (kg/m) was calculated. Heights and weights did not differ from season to season and between the communities; the data were pooled and treated cross-sectionally. Increments of growth in height and weight were estimated for 166 boys with 2 measurements approximately 1 year apart to provide an estimate of growth rate.

MAIN OUTCOME MEASURE

Growth status (size-attained) of youth football players relative to reference data (CDC) for American boys and estimated growth rate relative to reference values from 2 longitudinal studies of American boys.

RESULTS

Median heights of youth football players approximate the 75th percentiles, while median weights approximate the 75th percentiles through 11 years and then drift toward the 90th percentiles of the reference. Median body mass indexes of youth football players fluctuate about the 85th percentiles of the reference. Estimated growth rates in height approximate the reference and may suggest earlier maturation, while estimated growth rates in weight exceed the reference.

CONCLUSION

Youth football players are taller and especially heavier than reference values for American boys. Estimated rates of growth in height approximate medians for American boys and suggest earlier maturation. Estimated rates of growth in weight exceed those of the reference and may place many youth football players at risk for overweight/obesity, which in turn may be a risk factor for injury.

Adolescent growth spurts in female gymnasts

OBJECTIVES

Three questions were addressed: (1) Do female gymnasts have adolescent growth spurts in height, sitting height, and leg length? (2) Are the sequence and magnitude of spurts comparable with female adolescent non-athletes? (3) How do the data compare with other female gymnasts and with short girls?

STUDY DESIGN

Height and sitting height were measured annually on 15 Belgian gymnasts from 8.7 +/- 1.5 to 15.5 +/- 1.5 years. The gymnasts trained, on average, approximately 15 h/wk. Leg length was estimated as height minus sitting height. The Preece-Baines Model I was fitted to individual growth records to estimate ages at peak velocity and peak velocities for the three dimensions. Age at menarche and skeletal age were also assessed.

RESULTS

Gymnasts have clearly defined adolescent spurts in height, estimated leg length, and sitting height that occur approximately 1 year later and are slightly less intense than in nonathletic adolescent girls. Age at menarche and skeletal age are consistent with later somatic maturation. The pattern of adolescent growth and maturation is similar to that of other gymnasts, short normal late-maturing girls, and late-maturing girls with short parents.

CONCLUSIONS

The results emphasize a primary role for constitutional factors in the selection process of female gymnasts at relatively young ages.

Growth in peak aerobic power during adolescence

PURPOSE

To model the growth of peak aerobic power during adolescence in both sexes followed longitudinally from 10 to 18 yr.

METHODS

Peak aerobic power (peak VO2) was measured annually during a maximal treadmill test with the Bruce protocol. Height and weight were measured semiannually. The Preece-Baines Model I growth function was used to fit curves to data for individuals with >/= six observations for peak aerobic power to estimate age at peak velocity (PV) for peak VO2 (age at PVPVO2), PVPVO2 (L x min(-1) x yr(-1)), and value at PVPVO2 (L x min(-1)) for each individual. Curves were successfully fitted for 83 individuals (48 males, 35 females). The model was also fitted to individual data for height and weight to estimate ages at peak height velocity (PHV) and peak weight velocity (PWV). Age at PVPVO2 was compared with ages at PHV and PWV. Pearson correlation coefficients were calculated between ages at PV and PV for peak VO2, height, and weight.

RESULTS

Mean ages at PVPVO2 are 12.3 +/- 1.2 yr for females and 14.1 +/- 1.2 yr for males. Peak VO2 increases in both sexes throughout adolescence, with males having higher values than females at all ages. Age at PVPVO2 occurs nearly coincident with PHV and before PWV in both sexes. Correlation coefficients among ages at PHV, PWV, and PVPVO2 suggest a general maturity factor for body size and aerobic power.

CONCLUSION

Growth in peak VO2 exhibits a clear growth spurt in both sexes during adolescence. The growth spurt occurs earlier in females but is of greater magnitude in males.

Body mass index, waist circumference, and clustering of cardiovascular disease risk factors in a biracial sample of children and adolescents

OBJECTIVE

To derive optimal body mass index (BMI) and waist circumference thresholds for children and adolescents, to predict risk factor clustering.

DESIGN

Cross-sectional receiver operating characteristic curve analysis.

SETTING

The Bogalusa Heart Study, a community-based study of cardiovascular disease risk factors in early life.

PARTICIPANTS

A total of 2597 black and white children and adolescents, 5 to 18 years of age, who were examined between 1992 and 1994.

MAIN OUTCOME MEASURES

The presence or absence of > or =3 age-adjusted risk factors (low high-density lipoprotein cholesterol level, high low-density lipoprotein cholesterol level, high triglyceride level, high glucose level, high insulin level, and high blood pressure) was predicted from age-adjusted BMI and waist circumference values.

RESULTS

The areas under the receiver operating characteristic curves were significantly different from 0.5 for both BMI and waist circumference for all gender/race groups, ranging from 0.73 to 0.82. The optimal BMI thresholds were at the 53rd and 50th percentiles for white and black male subjects, respectively, and at the 57th and 51st percentiles for white and black female subjects, respectively. Similarly, the optimal waist circumference thresholds were at the 56th and 50th percentiles for white and black male subjects, respectively, and at the 57th and 52nd percentiles for white and black female subjects, respectively. The sensitivity and specificity at the thresholds were similar for all gender/race groups, ranging from 67% to 75%.

CONCLUSIONS

The use of BMI and waist circumference for the prediction of risk factor clustering among children and adolescents has significant clinical utility. In this sample, race and gender differences in the optimal thresholds were minimal.

Maturity-associated variation in the growth and functional capacities of youth football (soccer) players 13?15�years

The objective was to estimate the contribution of experience, body size and maturity status to variation in the functional capacities of adolescent football (soccer) players. The sample included 69 players 13.2-15.1 years of age from three clubs which competed in the highest division for their age group in the first Portuguese national division. Height and weight were measured and stage of pubic hair development was assessed at clinical examination. The number of years of experience in football was obtained at interview. Three tests of functional capacity were administered: 30-m dash (running speed), vertical jump (explosive power) and a yo-yo intermittent endurance test (aerobic resistance). Multiple linear regression analysis was used to estimate the relative contributions of age, stage of sexual maturity, height, weight and years of formal training in football to the three indicators of functional capacity. Stage of puberty, body size and years of training accounted for 21% to 50% of the variance in the three tasks. Sexual maturity status was the primary contributor to the variance in the intermittent shuttle run, whereas weight and height were the primary contributors to the explained variance in the 30-m dash and vertical jump, respectively. In conclusion, biological maturity status significantly influences the functional capacity of adolescent football players 13-15 years of age. Training is a significant contributor to aerobic resistance, whereas weight and height are significant contributors to the sprint and vertical jump, respectively.