Early sport specialization: roots, effectiveness, risks

Year-round training in a single sport beginning at a relatively young age is increasingly common among youth. Contributing factors include perceptions of Eastern European sport programs, a parent's desire to give his or her child an edge, labeling youth as talented at an early age, pursuit of scholarships and professional contracts, the sporting goods and services industry, and expertise research. The factors interact with the demands of sport systems. Limiting experiences to a single sport is not the best path to elite status. Risks of early specialization include social isolation, overdependence, burnout, and perhaps risk of overuse injury. Commitment to a single sport at an early age immerses a youngster in a complex world regulated by adults, which is a setting that facilitates manipulation - social, dietary, chemical, and commercial. Youth sport must be kept in perspective. Participants, including talented young athletes, are children and adolescents with the needs of children and adolescents.

Correlates of aerobic fitness in urban and rural Portuguese adolescents

BACKGROUND

Improving physical fitness is often an objective of programmes aimed at preventing obesity among youth.

AIM

To evaluate the association between cardiorespiratory fitness (CRF) and area of residence controlling for several correlates in adolescents.

SUBJECTS AND METHODS

CRF was assessed with the progressive aerobic cardiovascular endurance run (PACER) test in a cross-sectional sample of 362 Portuguese adolescents (165 males, 197 females) of 13-16 years of age. Youth were classified by area of residence as urban or rural. Gender, age, weight status, parental education, screen time (inactivity) and moderate-to-vigorous physical activity (MVPA) were statistically controlled. Logistic regression analysis was used.

RESULTS

Adolescents of both sexes from rural settings were 76% more likely to be classified as aerobically fit compared to those from urban areas. The odds ratio for CRF in the final model was similar in boys (OR = 0.24, 95% CI 0.06-0.99, p < 0.05) and girls (OR = 0.24, 95% CI 0.07-0.76, p < 0.05). MVPA and weight status were important predictors of CRF in Portuguese adolescents of 13-16 years of age. Maternal education was an additional predictor in girls.

CONCLUSION

CRF and rural/urban settings were significantly related in this sample of Portuguese adolescents of both sexes.

Body mass index and individual physical fitness tests in Taiwanese youth aged 9-18 years

OBJECTIVE

To evaluate the relationship between body mass index (BMI) and four components of physical fitness in a national cross-sectional sample of Taiwanese youth.

METHODS

A subsample of 102 765 youth (50 940 girls, 51 825 boys) 9-18 years was selected from a nationwide sample. Height, weight and four fitness items were measured: sit and reach (flexibility), standing long jump (power), sit-ups (abdominal muscular strength/endurance), and 800/1 600 m run/walk (cardiorespiratory endurance). BMI was calculated. Sex-specific regressions using a non-linear quadratic model of each fitness item on BMI were done in four age groups: 9-10, 11-12, 13-15, 16-18 years.

RESULTS

The relationship between BMI and fitness varied among tests. Lower fitness in three items (sit-ups, jump, distance run) was evident in boys and girls with higher BMIs in each age group. Slopes of decline with increasing BMI varied by age group and sex. Relationships became parabolic for the three fitness items with age and peaks of the parabola were sharper in adolescent boys than girls. Relationships for the sit and reach contrasted with the other tests and differed among age groups and between sexes.

CONCLUSION

BMI significantly and differentially influenced individual fitness tests, but effects varied with age and sex. Higher BMIs were generally associated with lower fitness.

Body Composition of Young Athletes

Absolute and relative components of body mass are a primary focus in studies of body composition. Components change with growth and maturation, requiring care in selecting methods of assessment in children and adolescents. Although sex differences are apparent in fat-free mass (FFM), fat mass (FM), and relative fatness (% Fat) during childhood, they are more clearly defined during adolescence and adulthood. Body composition is one of many determinants of sport performance, but % Fat tends to be the primary focus of discussion in young athletes. The influence of training for sport on bone mineral has received more attention in recent years because of methodological advances in assessment and concern for potential negative effects of altered menstrual function on bone. Relative fatness of young athletes in several sports is summarized, and issues related to sport training and body composition in young athletes are considered. Suggestions for dealing with body composition in young athletes are provided.

Cross-validation of the Beunen-Malina method to predict adult height

The purpose of this study was to cross-validate the Beunen-Malina method for non-invasive prediction of adult height. Three hundred and eight boys aged 13, 14, 15 and 16 years from the Madeira Growth Study were observed at annual intervals in 1996, 1997 and 1998 and re-measured 7-8 years later. Height, sitting height and the triceps and subscapular skinfolds were measured; skeletal age was assessed using the Tanner-Whitehouse 2 method. Adult height was measured and predicted using the Beunen-Malina method. Maturity groups were classified using relative skeletal age (skeletal age minus chronological age). Pearson correlations, mean differences and standard errors of estimate (SEE) were calculated. Age-specific correlations between predicted and measured adult height vary between 0.70 and 0.85, while age-specific SEE varies between 3.3 and 4.7 cm. The correlations and SEE are similar to those obtained in the development of the original Beunen-Malina method. The Beunen-Malina method is a valid method to predict adult height in adolescent boys and can be used in European populations or populations from European ancestry. Percentage of predicted adult height is a non-invasive valid method to assess biological maturity.

Community well-being and growth status of indigenous school children in rural Oaxaca, southern Mexico

OBJECTIVE

To evaluate the relationship between community well-being based on an index of marginalization and growth status of indigenous rural school children in Oaxaca.

METHODS

Heights and weights of a cross-sectional sample of 11,454 children, 6-14 years, from schools for indigenous rural children (escuelas albergue) in 158 municipios in Oaxaca were measured in 2007. Tertiles of an index of marginalization were used to classify the 158 municipios into three categories of community well-being: lowest (highest marginalization), low, and moderate (lowest marginalization). Multivariate analysis of covariance, controlling for age, relative isolation and population size, was used to compare body size of children by category of community well-being. Contributions of marginalization, isolation and population size to variation in body size were estimated with sex-specific linear regression.

RESULTS

Children from municipios lowest in well-being were shorter and lighter than children from municipios low and moderate in well-being. Marginalization and relative isolation accounted for 23% (boys) and 21% (girls) of the variance in height and for 21% of the variance in weight of girls. Marginalization was the predictor of weight in boys (23%).

CONCLUSION

Community well-being was reflected in the growth status of rural indigenous school children. Compromised growth status was consistent with poor health and nutritional conditions that were and are characteristic of rural areas in the state of Oaxaca.

Concurrent validation of estimated activity energy expenditure using a 3-day diary and accelerometry in adolescents

Estimates of daily energy expenditure are important to studies of physical activity and energy balance. Objective measures are not always feasible and further research is needed to validate survey instruments and diaries. The study validates estimated activity energy expenditure (AEE) based on a 3-day diary protocol relative to AEE derived from uniaxial accelerometry in adolescents, 265 girls and 227 boys (12.5-16.4 years). Participants completed the diary and wore a GT1M Actigraph accelerometer on the same days. Height and weight were measured. Correlations between protocols were significant (P<0.001) but moderate, r=0.65 in males and r=0.69 in females. The highest correlation occurred among males on Friday, r=0.74 (P<0.01). Controlling for body mass, partial correlations between protocols decreased to 0.44 and 0.35 in males and females, respectively. About 97% of the cases fell within the limits of agreement in a Bland-Altman plot. The criterion of inclusion for the accelerometer excluded 18% of the initial sample. In summary, the 3-day diary was completed without any major problems and provided a reasonably valid alternative for assessing AEE. Concordance between methods was slightly lower for individuals with higher values of AEE.

Growth, maturation, functional capacities and sport-specific skills in 12-13 year-old- basketball players

AIM

The influence of maturity status on body size, functional capacities and basketball-specific skills was evaluated and multivariate relationships between domains of variables were examined in 80 male basketball players 12.0-13.9 years.

METHODS

Height, body mass and two skinfolds were measured. Stage of pubic hair (PH) was assessed clinically. Functional capacity was assessed with the vertical jump (squat jump, countermovement jump), 2-kg medicine ball throw, hand grip strength, 60-second sit-ups and endurance shuttle run. Performances on four basketball skills were tested: shooting, passing, dribbling and defensive movements. Analysis of covariance with age as the covariate was used to test differences among players by stage of puberty. Associations among body size, adiposity, functional capacities and skills were evaluated with canonical correlation analysis.

RESULTS

Maturity status explained a significant portion of variance in body size (F=50.13, P<0.01, h2=057, for height; F=13.47, P<0.01, h2=0.26, for weight). The effect of pubertal status was significant for the jumps and upper limb strength, but not for sit-ups or aerobic endurance. Canonical correlations showed an inverse relationship of height and adiposity with skill tests, and a positive relationship between skills and a combination of abdominal muscular strength (sit-ups) and aerobic endurance.

CONCLUSION

Skill appeared to be independent of pubertal status and the tallest group of basketball players did not attain better scores in basketball-specific skill tests.

Secular trends in established and novel cardiovascular risk factors in Welsh 12-13 year olds: a comparison between 2002 and 2007

BACKGROUND

This study examines CVD risk factors trends in Welsh adolescents between 2002 and 2007.

PARTICIPANTS AND METHODS

CVD risk factor data was examined from two cross-sectional studies. The first study (73 participants; aged 12.9 ± 0.3 years) was completed in 2002. The second study (90 participants; aged 12.9 ± 0.4 years) was conducted in 2007. Measurements included body mass index (BMI), waist circumference (WC), total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglyceride, fibrinogen (Fg) and high-sensitivity C-reactive protein (hs-CRP).

RESULTS

In boys, mean BMI and WC were lower in 2007, although not significantly (p ≥ 0.05). In 2007, there were improvements in mean lipid, Fg and hs-CRP concentrations in both sexes (p < 0.05). In 2002, 42.8% of boys and 34.2% of girls were overweight or obese; in 2007, this was 23.7% and 28.9% for boys and girls, respectively. More adolescents in 2002 exceeded the recommended levels for lipids, Fg and hs-CRP.

CONCLUSION

This is the only study to examine CVD risk factor trends in Welsh adolescents. Although overweight continues to be widespread in 12-13 year olds, this study did not identify significant mean changes in overweight and obesity between 2002 and 2007. Overall, the data presented a positive trend in lipid profile and inflammatory factors.

Motor coordination as predictor of physical activity in childhood

This study considers relationships among motor coordination (MC), physical fitness (PF) and physical activity (PA) in children followed longitudinally from 6 to 10 years. It is hypothesized that MC is a significant and primary predictor of PA in children. Subjects were 142 girls and 143 boys. Height, weight and skinfolds; PA (Godin-Shephard questionnaire); MC (Körperkoordination Test für Kinder); and PF (five fitness items) were measured. Hierarchical linear modeling with MC and PF as predictors of PA was used. The retained model indicated that PA at baseline differed significantly between boys (48.3 MET/week) and girls (40.0 MET/week). The interaction of MC and 1 mile run/walk had a positive influence on level of PA. The general trend for a decrease in PA level across years was attenuated or amplified depending on initial level of MC. The estimated rate of decline in PA was negligible for children with higher levels of MC at 6 years, but was augmented by 2.58 and 2.47 units each year, respectively, for children with low and average levels of initial MC. In conclusion MC is an important predictor of PA in children 6-10 years of age.

Growth status of indigenous school children 6-14 years in the Tarahumara Sierra, Northern Mexico, in 1990 and 2007

AIMS

The study evaluated the growth status and secular change in body size of indigenous Tarahumara children in northern Mexico.

METHODS

Heights and weights of Tarahumara children 6-14 years were measured in 1990 (n = 601) and 2007 (n = 583); the BMI was calculated. International criteria defined weight status while United States reference data defined stunting.

RESULTS

Estimated secular gains in height from 1990 to 2007 were greatest in 6-7 year-old boys and declined with age to a small, non-significant secular decline in boys 12-14 years. Among girls secular gains in height were similar at 6-7 and 8-9 years, largest at 10-11 years and small and non-significant at 12-14 years. Secular gains in weight were similar among 6-7 and 8-9 year-old boys and girls, were greater in girls than in boys at 10-11 years and showed a small, non-significant secular decline in boys and girls 12-14 years. Secular change in the BMI paralleled those for weight. The prevalence of stunting declined from 1990 to 2007 in both sexes and all age groups except 12-14 year youth. Overweight was more prevalent in girls than boys in both years and increased from 4% to 7% in boys and 9% to 13% in girls. Obesity was not common among boys and girls in each age group and in both years. Stunting and overweight/obesity were not related in either 1990 or 2007.

CONCLUSION

Positive secular changes in growth status have occurred in Tarahumara children 6-11 years in contrast to negligible changes among children 12-14 years. The results suggest recent improvements in health and nutrition sufficient to support a positive secular trend in younger children.

Variation in relative fat distribution associated with maturational timing: The Wrocław Growth study

Complete longitudinal data of 136 boys aged 8-16 years and 124 girls aged 8-15 years were used to evaluate the association between maturational timing and the relative distribution of subcutaneous adipose tissue, specifically a trunk-oriented pattern of distribution. Age at peak height velocity (PHV) was the indicator of maturational timing and three skinfolds (triceps, subscapular, abdomen) were the indicators of subcutaneous fatness. Principal components analysis of the three skinfolds was used to identify indicators of relative subcutaneous adipose tissue distribution. Age at PHV and chronological age significantly influenced scores on the first principal components, which indicated centripetal fat patterning. The data suggest that early maturing subjects accumulate more subcutaneous adipose tissue on the lower trunk compared with later maturing peers of the same age and sex.

Secular change in height, sitting height and leg length in rural Oaxaca, southern Mexico: 1968–2000

OBJECTIVE

To evaluate secular changes in height, sitting height and estimated leg length between 1968 and 2000 in residents in a rural Zapotec-speaking community in Oaxaca, southern Mexico.

MATERIALS AND METHODS

Height and sitting height were measured in school children 6-13 years (1968; 1978, 2000), in adolescents 13-17 years (1978, 2002) and adults 19-29 years (1978, 2000). Leg length was estimated as height minus sitting height. The sitting height/ height ratio was calculated. Subjects were grouped by sex into four age categories: 6-9, 10-13, 13-17 and 19-29 years for analysis. The Preece-Baines Model I growth curve was fitted to cross-sectional means for 1978 and 2000.

RESULTS

There were no differences between children 6-9 and 10-13 years in 1968 and 1978 with the exception of the sitting height ratio in girls 6-9 years. Children of both sexes 6-13 years and adolescent boys 13-17 years were significantly larger in the three dimensions in 2000 compared to 1978; adolescent girls differed only in height and sitting height. Adult males in 2000 were significantly taller with longer legs than those in 1978, but the samples did not differ in sitting height and the ratio. Adult females in 1978 and 2000 did not differ significantly in the three dimensions. Rates of secular change in height and sitting height between 1978 and 2000 were reasonably similar in the three age groups of male children and adolescents, but the rate for estimated leg length was highest in 10-13-year-old boys. Secular gains were smaller in adult males, but were proportionally greater in estimated leg length. Girls 6-9 and 10-13 years experienced greater secular gains in height, sitting height and estimated leg length than adolescent and young adult females, while secular gains and rates decreased from adolescent girls to young adult women. Ages of peak velocity for height, sitting height and estimated leg length declined in boys, while only ages of peak velocity for height and estimated leg length declined in girls.

CONCLUSIONS

There are major secular increases in height, sitting height and estimated leg length of children and adolescents of both sexes since 1978. Secular gains in height are of similar magnitude in boys and girls 6-13 years, but are greater in adolescent and young adult males than females. The secular increase in height of young adults of both sexes is smaller than that among adolescents. Estimated leg length accounts for about 60% of the secular increase in height in children of both sexes. Estimated leg length and sitting height contribute equally to the secular increase in height in adolescent boys, whereas estimated leg length accounts for about 70% of the secular increase in height in young adult males. Sitting height contributes about two-thirds of the secular increase in height in adolescent and young adult females.

Youth soccer players, 11-14 years: maturity, size, function, skill and goal orientation

BACKGROUND

Participants in many youth sports are commonly combined into age groups spanning 2 years.

AIM

The study compared variation in size, function, sport-specific skill and goal orientation associated with differences in biological maturity status of youth soccer players within two competitive age groups.

METHODS

The sample included 159 male soccer players in two competitive age groups, 11-12 years (n=87) and 13-14 years (n=72). Weight, height, sitting height and four skinfolds, four functional capacities, four soccer skills and goal orientation were measured. Skeletal maturity was assessed using the Fels method. Each player was classified as late, on time or early maturing based on the difference between skeletal and chronological ages. ANOVA was used to compare characteristics of players across maturity groups.

RESULTS

Late, on time and early maturing boys are represented among 11-12-year-olds, but late maturing boys are under-represented among 13-14-year-olds. Players in each age group advanced in maturity are taller and heavier than those on time and late in skeletal maturity, but players of contrasting maturity status do not differ, with few exceptions, in functional capacities, soccer-specific skills and goal orientation.

CONCLUSION

Variation in body size associated with maturity status in youth soccer players is similar to that for adolescent males in general, but soccer players who vary in maturity status do not differ in functional capacities, soccer-specific skills and goal orientation.

Physical activity in youth from a subsistence agriculture community in the Valley of Oaxaca, southern Mexico

Observations of activities of contemporary subsistence agricultural communities may provide insights into the lifestyle of youth of 2 to 3 generations ago. The purpose of this study was to document age- and sex-associated variation in household activities and daily steps walking to school of youth 9-17 years in an indigenous subsistence agricultural community in Oaxaca, southern Mexico. Activities during leisure were also considered. A cross-sectional survey of a rural Zapotec-speaking community was undertaken, and respondents included 118 boys and 152 girls, aged 8.7-17.9 years. Household and leisure activities were documented by questionnaire and subsequent interview. Household activities were classified by estimated intensity for before and after school and on the weekend, and an estimate of METS per day accumulated while doing chores was derived. Number of steps from home to school was estimated. Contingency table analysis and MANCOVA controlling for age was used to evaluate results. Household activities tended to cluster at light and moderate intensities in girls and at moderate to moderate-to-vigorous intensities in boys. Estimated METS per day in approximately 2 h of chores differed significantly by sex. Secondary school girls expended significantly more METS per day in chores than primary school girls, but there was no difference by school level in boys. The daily round trip from home to school was approximately 2400 steps for primary students and approximately 2700 and approximately 3100 steps for secondary boys and girls, respectively. Television viewing and participation in sports were major leisure activities for boys and girls. Daily household chores, walking, and leisure activities suggest moderately active and moderately-to-vigorously active lifestyles in girls and boys, respectively, in this indigenous subsistence agricultural community.

Physical activity: the present in the context of the past

In the broad sense, modern humans have lived in an environment in which physical activity and associated movement skills were central, especially in the context of physical competition with other animals. The physically active lifestyle of earlier human populations has been emphasized, especially the cardiovascular endurance component and energy expenditure, but less attention has been devoted to the gross and fine motor skills that are essential components of this lifestyle. Motor skills developed through practice are important determinants of success and survival in preindustrial societies. In industrial and postindustrial societies, on the other hand, the role of physical activity is different, with prowess in certain areas of physical expertise (e.g., accuracy with projectiles, muscular strength, among others) and prolonged exertion (i.e., cardiovascular endurance) less important for survival. The combined effects of the transition to a sedentary lifestyle and attendant dietary changes have resulted first an epidemic of coronary heart disease and more recently an epidemic of overweight/obesity in postindustrial societies. Although mortality associated with coronary heart disease has declined, due largely to biomedical advances, overweight and obesity have increased concomitantly with population reduction in physical activity (energy expenditure) and increased calorie (energy) consumption. The current scenario begs several questions which have implications for contemporary human biology related to sustaining the pace of cultural change on a biological base that is increasingly being compromised by physical inactivity, overweight, and obesity.

Epidemiologic transition in an isolated indigenous community in the Valley of Oaxaca, Mexico

The objective of the present study is to analyze age-specific mortality in a rural indigenous community in the throes of a secular increase in size in the Valley of Oaxaca, southern Mexico, over 30 years, 1970-1999. Variation in mortality by age group was analyzed over time for evidence of an epidemiological transition. The seasonal rain pattern in the Valley of Oaxaca (83% from May through September) was evaluated for its relationship with mortality in wet and dry months. Mortality and causes of death changed markedly over the 30-year interval. Infant and preschool mortality, overall mortality, and causes of death changed from the 1970s through the 1990s. Prereproductive deaths (<15 years) predominated in the 1970s and were largely due to gastrointestinal and respiratory diseases, with periodic outbreaks of measles. Deaths of adults 65+ years predominated in the 1990s and were largely due to degenerative diseases usually associated with aging. The marked changes in age and causes of death over the three decades (epidemiologic transition from Stage I to Stage II) occurred concurrently with significant secular increases in body size in children, adolescents, and young adults, highlighting improved health and nutritional conditions in the community which is in early Stage II of the demographic transition. The demographic transition to Stage II is a leading indicator (15-25 years lag) for the onset of the secular trend, while the epidemiologic transition to Stage II is a predictor that the secular increase is in process in the study community.

Natural selection and demographic transition in a Zapotec-speaking genetic isolate in the Valley of Oaxaca, southern Mexico

OBJECTIVE

The study analyzed the potential for natural selection and the demographic transition in an isolated Amerindian population in the process of secular change in body size.

SETTING

A genetically isolated, Zapotec-speaking community located in the Valley of Oaxaca, southern Mexico, has been studied regularly from the mid-1960s to 2000. Children, adolescents and young adults have experienced a recent secular increase in body size since 1978 after a major period of no change.

METHODS

Potential for natural selection and the demographic transition were analyzed over a 100-year period, ca 1900-2000. National census data, results from anthropological surveys and community archives and reports were used.

RESULTS

Opportunity for natural selection changed markedly over the last century. Demographic transition to Stage II occurred ca 1955 and preceded a secular increase in body size. The crossover between curves for mortality (I(m)) and fertility (I(f)) occurred at approximately the time of onset of the secular trend among children, adolescents and young adults, i.e. those born since the early 1970s.

CONCLUSIONS

The 'classic' demographic transition occurred in the mid-1950s and preceded the secular increase in body size. A 'critical mass' of environmental improvement appears to be necessary to activate secular improvements in growth status, possibly turning on a gene complex that interacts with the improved environmental conditions. The lead time from the onset of demographic transition phase II to beginning of the secular trend is approximately 25 years (one generation) in this community.

Sex differences in exercise behavior during adolescence: is biological maturation a confounding factor?

PURPOSE

To test the hypothesis that sex-related differences in exercise behavior during adolescence are confounded by biological age.

METHODS

Biological age and leisure-time exercise activity were assessed in 103 male and 83 female British Year 9 students (mean = 14.04 years, SD = 0.31). To assess exercise behavior, participants completed the Leisure-Time Exercise Questionnaire (LTEQ). Percentage of predicted adult height attained at measurement was used as an estimate of biological maturity status. Males reported more frequent engagement in strenuous forms of exercise and total exercise activity than females.

RESULTS

Sex differences in exercise behavior were attenuated and nonsignificant when biological maturity was controlled for.

CONCLUSIONS

Sex-related differences in biological maturity contribute to sex-related differences in exercise behavior during adolescence.

National athletic trainers' association position statement: preventing, detecting, and managing disordered eating in athletes

OBJECTIVE

To present recommendations for the prevention, detection, and comprehensive management of disordered eating (DE) in athletes.

BACKGROUND

Athletes with DE rarely self-report their symptoms. They tend to deny the condition and are often resistant to referral and treatment. Thus, screenings and interventions must be handled skillfully by knowledgeable professionals to obtain desired outcomes. Certified athletic trainers have the capacity and responsibility to play active roles as integral members of the health care team. Their frequent daily interactions with athletes help to facilitate the level of medical surveillance necessary for early detection, timely referrals, treatment follow-through, and compliance.

RECOMMENDATIONS

These recommendations are intended to provide certified athletic trainers and others participating in the health maintenance and performance enhancement of athletes with specific knowledge and problem-solving skills to better prevent, detect, and manage DE. The individual biological, psychological, sociocultural, and familial factors for each athlete with DE result in widely different responses to intervention strategies, challenging the best that athletics programs have to offer in terms of resources and expertise. The complexity, time intensiveness, and expense of managing DE necessitate an interdisciplinary approach representing medicine, nutrition, mental health, athletic training, and athletics administration in order to facilitate early detection and treatment, make it easier for symptomatic athletes to ask for help, enhance the potential for full recovery, and satisfy medicolegal requirements. Of equal importance is establishing educational initiatives for preventing DE.

Overweight and obesity in a rural Amerindian population in Oaxaca, Southern Mexico, 1968-2000

The purpose of this study was to evaluate secular change in the prevalence of overweight and obesity in a rural Zapotec Indian community in southern Mexico between 1968 and 2000. Cross-sectional surveys of children 6-13 years, adolescents 13-17 years, and adults 19 years of age and older resident in a rural community in Oaxaca were conducted in 1968/1971, 1978, and 2000. Individuals present in the 1968, 1978, and 2000 surveys provided a small longitudinal component. Height and weight were measured; the BMI was calculated. International criteria for overweight and obesity were used. Overweight and obesity were virtually absent in school children 6-13 years in 1968 and 1978 and in adolescents in 1978. Small proportions of children (boys, 5%; girls, 8%) and adolescents (boys, 3%; girls, 15%) were overweight in 2000; two children (1%) and no adolescents were obese. Among adults, 7% of males and 19% of females were overweight and <1% of males and 4% of females were obese in 1971/1978, but 46% of males and 47% of females were overweight; and 5% of males and 14% of females were obese in 2000. The trends for children, adolescents, and adults were confirmed in the longitudinal subsamples. In conclusion, overweight and obesity are not presently a major problem in children and adolescents in this rural Zapotec community. Overweight, in particular, and to a lesser extent obesity have increased in prevalence among adults since the late 1970s. The results suggest adulthood as a critical period for onset of overweight and obesity in this sample.

Overweight and obesity among youth participants in American football

OBJECTIVE

To estimate the prevalence of overweight and obesity among participants in youth American football 9 to 14 years of age.

STUDY DESIGN

Cross-sectional, 653 boys, 8.7 to 14.6 years. Height and weight were measured; body mass index (BMI) was calculated. Overweight and obesity were defined by international (International Obesity Task Force [IOTF]) and United States (Centers for Disease Control [CDC]) criteria. Prevalence and 95% confidence interval were calculated. Player age, height, and weight and midparent height were used to predict mature height; current height was expressed as a percentage of predicted mature height as an estimate of maturity status.

RESULTS

Overall 45.0% (41.2% to 48.9%) and 42.6% (38.8% to 46.5%) of players were overweight or obese by CDC and IOTF criteria, respectively. Prevalence was highest in early maturing boys. Based on position-activity at time of injury (n = 180), overweight and obesity were more common among offensive and defensive linemen.

CONCLUSION

Overweight and obesity were more prevalent in youth football players than in national samples of American boys. Allowing for limitations of the BMI and the relative stability of the BMI from adolescence into adulthood, a relatively large number of football participants may be at risk for later overweight or obesity, and the risk appears to be greater for offensive and defensive line positions.

Validation of a noninvasive maturity estimate relative to skeletal age in youth football players

OBJECTIVE

To validate a non-invasive measure of biological maturity (percentage of predicted mature height at a given age) with an established indicator of maturity [skeletal age (SA)] in youth American football players.

DESIGN

Cross-sectional.

SETTING

Two communities in central Michigan.

PARTICIPANTS

143 youth football players 9.27 to 14.24 years.

METHODS

Height and weight were measured, and hand-wrist radiographs were taken. SA assessed with the Fels method was the criterion measure of maturity status. Chronological age (CA), height, and weight of the player and midparent height were used to predict mature height; current height of the player was expressed as a percentage of his predicted mature height as a noninvasive estimate of biological maturity status.

MAIN OUTCOME MEASURE

Boys' maturation was classified as late, on time, or early maturing on the basis of the difference between SA and CA and of present height expressed as a percentage of predicted mature height. Kappa coefficients and Spearman rank-order correlations were calculated. Characteristics of players concordant and discordant for maturity classification with SA and percentage of predicted mature height were compared with MANCOVA.

RESULTS

Concordance between methods of maturity classification was 62%. The Kappa coefficient, 0.46 (95% CI 0.19 to 0.59) and Spearman rank-order correlation, rs = 0.52 (P < 0.001) were moderate. Players discordant for maturity status varied in midparent height and percentage of predicted mature height, but not in predicted mature height.

CONCLUSION

Percentage of predicted mature height is a reasonably valid estimate of biological maturity status in this sample of youth football players.

Gene-environment interaction in skeletal maturity and body dimensions of urban Oaxaca Mestizo schoolchildren

OBJECTIVE

The study analyzed the relationship between skeletal age (SA) and the difference between skeletal and chronological ages (SA-CA) and body size among growth-stunted and well-nourished children.

METHODS AND MATERIALS

Tanner-Whitehouse 2 (TW2) 20 bone, radius-ulna-short (RUS) bone, and carpal SAs were analyzed in three cross-sectional samples of school children aged 6-13 years: Mestizo children (n = 396) from the city of Oaxaca, southern Mexico, and American Black (n = 570) and White (n = 432) from Philadelphia. The Oaxaca children were mild-to-moderately undernourished while the Philadelphia children were well nourished. The total sample included 1398 radiographs assessed with the Tanner-Whitehouse protocol by a single, experienced rater. Maturity scores were converted to TW2 20 bone, RUS and carpal SAs.

RESULTS

Correlations of SA and SA-CA differences with body dimensions (height, sitting height, leg length, weight, triceps skinfold, arm and estimated midarm muscle circumferences) were consistent and approximately equal in magnitude for the well-nourished samples but were different among Oaxaca children. SAs of Philadelphia children were significantly more highly correlated with body dimensions than were SA-CA differences compared to Oaxaca Mestizo children. Patterns of RUS and carpal SA correlations with body size (height, sitting height, and leg length) in Oaxaca children were different from the Philadelphia samples. Oaxaca children tended to have advanced RUS SA and delayed carpal SA.

CONCLUSION

Long bone complexes mature earlier than round bone complexes in Oaxaca children compared to Philadelphia Black and White children, resulting in short stature in Oaxaca children. Results suggest a gene-environment interaction effect on the program for skeletal growth and maturation in undernourished Oaxaca children compared to well-nourished Black and White children from Philadelphia.

TW3 and Fels skeletal ages in elite youth soccer players

BACKGROUND

Skeletal age (SA) tends to be advanced for chronological age (CA) in adolescent male soccer players.

AIM

The study compared SA assessments with the TW3 and Fels methods in a sample of male, elite youth soccer players.

METHODS

SAs were assessed with the Tanner-Whitehouse 3 (TW3) radius-ulna-short bone (RUS) and Fels methods in a sample of 40 elite youth soccer players 12.5-16.1 years of age. Players were classified as late, on time or early on the basis of relative SA, the difference between SA and CA. Players who reached skeletal maturity were labeled mature.

RESULTS

SA was in advance of CA. Among 14 players >15.0 years, two are skeletally mature with the Fels method (CA 15.7 and 15.9 years), while 11 are skeletally mature with the TW3 method (CA 15.0-16.1 years).

CONCLUSION

The TW3 and Fels methods yield different SAs in elite youth soccer players. Significantly more 15-year-old boys are classified as skeletally mature with the TW3 method than with the Fels method. These observations have implications for international age group competitions as well as for medico-legal circumstances that require CA verification. SA is not a valid measure of CA and should not be used as such.

INFLUENCE OF HEIGHT ON ATTAINED LEVEL OF EDUCATION IN MALES AT 19 YEARS OF AGE

In this study it is hypothesized that taller individuals are more likely to move up the scale of educational attainment compared with shorter individuals from the same social background. Three national cohorts of 19-year-old males were considered: 29,464 born in 1967 and surveyed in 1986, 31,062 born in 1976 and surveyed in 1995, and 30,851 born in 1982 and surveyed in 2001. Four social variables were used to describe the social background of each conscript in the three surveys: degree of urbanization, family size, and parental and maternal educational status. The educational status of each conscript was classified into two groups: (1) those who were secondary school students or graduates, or who had entered college, and (2) those who had completed their education at the primary school level or who had gone to a basic trade school. Multiple binomial logistic regressions were used to estimate the relative risk of achieving higher educational status by 19-year-old males relative to height and the four social factors. Consistently across the three cohorts the odd ratios (ORs) indicate that height exerts an independent and significant effect on the attained level of education at the age of 19 years in males (1986: OR=1·24, p<0·001; 1995: OR=1·24, p<0·001; 2001: OR=1·20, p<0·001). Two possible, not mutually exclusive, selective mechanisms are postulated and discussed: ‘passive’ and ‘active’ action.

BMI and health-related physical fitness in Taiwanese youth 9-18 years

PURPOSE

The purpose of the study was to evaluate the cross-sectional relationship between BMI and a physical fitness index (PFI) based on four indicators of fitness in a national sample of Taiwanese youth.

METHODS

Height, weight, and four measures of physical fitness (sit-ups completed in 60 s, standing long jump, sit and reach, and 800- or 1600-m run/walk) were measured in a national sample of 102,765 Taiwanese youth 9-18 yr of age: 50,940 girls and 51,825 boys. BMI was calculated for each subject. Within each sex-specific half-year age group, students were classified into five BMI categories based on national percentiles: very low, BMI < 5th percentile; low, BMI >or= 5th but < 15th percentiles; normal, BMI >or= 15th but < 85th percentiles; high, BMI >or= 85th but < 95th percentiles; and very high, BMI >or= 95th percentiles. Z-scores based on sex- and age-specific means and standard deviations were calculated, and the sum of z-scores for the four fitness tests was used as a PFI. Differences in PFI between BMI categories within each sex-specific half-year age group were compared with ANOVA with Bonferroni adjustments. Sex-specific regressions of PFI on BMI, using a nonlinear quadratic model, were done in four broader age categories.

RESULTS

Relationships between BMI and PFI are nonlinear and vary with age from late childhood through adolescence. With increasing age during adolescence, the relationship becomes parabolic, and the peaks of the parabola are sharper in adolescent boys than girls.

CONCLUSION

PFI declines in a curvilinear manner with increasing BMI among youth 9-18 yr of age, but the slope of the relationship varies with age.

Comparisons of physical characteristics and performances among female collegiate rowers

The physical characteristics and performances of female collegiate rowers were examined from two perspectives: level (novice, varsity) and years of participation (0, 1, 2, 3) in collegiate rowing. The participants were 90 female collegiate rowers from three US Division I university teams, of the National Collegiate Athletic Association (NCAA). Height, body mass, sitting height, arm span, skinfolds, limb circumferences, and skeletal breadths were measured. Leg length was estimated and Heath-Carter anthropometric somatotypes were calculated. Performance measures included lower-back flexibility, vertical jump, and 2-km time on a rowing ergometer. Descriptive statistics were calculated for the total sample and by level and years of experience. Multivariate analysis of variance and a Bonferroni-adjusted alpha level (P < 0.05) were used to test differences. Varsity rowers had significantly more rowing experience ( approximately 0.5 years) before college, higher vertical jumps ( approximately 3 cm), faster 2-km times ( approximately 25 s), and lower endomorphic characteristics than novice rowers. Anthropometric and performance differences among rowers by years of experience were negligible with the exception of slower 2-km times ( approximately 32 s) in rowers with no collegiate experience than rowers with collegiate experience. In conclusion, collegiate rowers differ to some extent in physical and performance characteristics by level and experience.