A Genetic Epidemiological Mega Analysis of Smoking Initiation in Adolescents.

INTRODUCTION: Previous studies in adolescents were not adequately powered to accurately disentangle genetic and environmental influences on smoking initiation (SI) across adolescence. METHODS: Mega-analysis of pooled genetically informative data on SI was performed, with structural equation modeling, to test equality of prevalence and correlations across cultural backgrounds, and to estimate the significance and effect size of genetic and environmental effects according to the classical twin study, in adolescent male and female twins from same-sex and opposite-sex twin pairs (N = 19 313 pairs) between ages 10 and 19, with 76 358 longitudinal assessments between 1983 and 2007, from 11 population-based twin samples from the United States, Europe, and Australia. RESULTS: Although prevalences differed between samples, twin correlations did not, suggesting similar etiology of SI across developed countries. The estimate of additive genetic contributions to liability of SI increased from approximately 15% to 45% from ages 13 to 19. Correspondingly, shared environmental factors accounted for a substantial proportion of variance in liability to SI at age 13 (70%) and gradually less by age 19 (40%). CONCLUSIONS: Both additive genetic and shared environmental factors significantly contribute to variance in SI throughout adolescence. The present study, the largest genetic epidemiological study on SI to date, found consistent results across 11 studies for the etiology of SI. Environmental factors, especially those shared by siblings in a family, primarily influence SI variance in early adolescence, while an increasing role of genetic factors is seen at later ages, which has important implications for prevention strategies. IMPLICATIONS: This is the first study to find evidence of genetic factors in liability to SI at ages as young as 12. It also shows the strongest evidence to date for decay of effects of the shared environment from early adolescence to young adulthood. We found remarkable consistency of twin correlations across studies reflecting similar etiology of liability to initiate smoking across different cultures and time periods. Thus familial factors strongly contribute to individual differences in who starts to smoke with a gradual increase in the impact of genetic factors and a corresponding decrease in that of the shared environment.

Role of intensive training in the growth and maturation of artistic gymnasts.

Short stature and later maturation of youth artistic gymnasts are often attributed to the effects of intensive training from a young age. Given limitations of available data, inadequate specification of training, failure to consider other factors affecting growth and maturation, and failure to address epidemiological criteria for causality, it has not been possible thus far to establish cause-effect relationships between training and the growth and maturation of young artistic gymnasts. In response to this ongoing debate, the Scientific Commission of the International Gymnastics Federation (FIG) convened a committee to review the current literature and address four questions: (1) Is there a negative effect of training on attained adult stature? (2) Is there a negative effect of training on growth of body segments? (3) Does training attenuate pubertal growth and maturation, specifically, the rate of growth and/or the timing and tempo of maturation? (4) Does training negatively influence the endocrine system, specifically hormones related to growth and pubertal maturation? The basic information for the review was derived from the active involvement of committee members in research on normal variation and clinical aspects of growth and maturation, and on the growth and maturation of artistic gymnasts and other youth athletes. The committee was thus thoroughly familiar with the literature on growth and maturation in general and of gymnasts and young athletes. Relevant data were more available for females than males. Youth who persisted in the sport were a highly select sample, who tended to be shorter for chronological age but who had appropriate weight-for-height. Data for secondary sex characteristics, skeletal age and age at peak height velocity indicated later maturation, but the maturity status of gymnasts overlapped the normal range of variability observed in the general population. Gymnasts as a group demonstrated a pattern of growth and maturation similar to that observed among short-, normal-, late-maturing individuals who were not athletes. Evidence for endocrine changes in gymnasts was inadequate for inferences relative to potential training effects. Allowing for noted limitations, the following conclusions were deemed acceptable: (1) Adult height or near adult height of female and male artistic gymnasts is not compromised by intensive gymnastics training. (2) Gymnastics training does not appear to attenuate growth of upper (sitting height) or lower (legs) body segment lengths. (3) Gymnastics training does not appear to attenuate pubertal growth and maturation, neither rate of growth nor the timing and tempo of the growth spurt. (4) Available data are inadequate to address the issue of intensive gymnastics training and alterations within the endocrine system.

Functional fitness and physical activity of Portuguese community-residing older adults.

The purposes of this study were to generate functional-fitness norms for Portuguese older adults, to determine age and sex differences, and to analyze the physical activity-associated variation in functional fitness. The sample was composed of 802 older adults, 401 men and 401 women, age 60-79 yr. Functional fitness was assessed using the Senior Fitness Test. Physical activity level was estimated via the Baecke questionnaire. The P50 values decreased from 60 to 64 to 75 to 79 yr of age. A significant main effect for age group was found in all functional-fitness tests. Men scored significantly better than women in the chair stand, 8-ft up-and-go, and 6-min walk. Women scored significantly better than men in chair sit-and-reach and back scratch. Active participants scored better in functional-fitness tests than their average and nonactive peers. This study showed a decline in functional fitness with age, better performance of men, and increased proficiency in active participants.

Functional fitness and bone mineral density in the elderly.

UNLABELLED: Bone quality has been associated with genetic factors and several environmental influences. This study suggests that although functional fitness should be considered in clinical assessments of bone health, body composition appears to have a higher relevance in the explanation of bone health/strength in older people. PURPOSE: This study aims to describe the association between functional fitness (FF), other constitutive factors, and bone health/strength in a large community-dwelling sample of elderly active Portuguese. METHODS: This cross-sectional study included 401 males and 401 females aged 60-79 years old. Bone mineral density (BMD) of the total body, lumbar spine (LS), and hip region was determined by dual-energy X-ray absorptiometry (DXA). In addition, femur strength index (FSI) was determined. FF was assessed using the Senior Fitness Test. Demographic information and a health history were obtained by telephone interview through questionnaire. RESULTS: Aerobic endurance and body strength were positively related with hip BMD region in males (0.10 < r < 0.16; p < 0.01-0.05) and females (0.13 < r < 0.28; p < 0.01). No significant correlation was found between any FF test and LS BMD, except for upper-body strength in females. After controlling for other constitutive predictors (sex, age, height, body mass (BM), total fat mass (TFM), and total lean tissue mass (TLTM)), FF had a minor contribution only in prediction of BMD at multisites and FSI. The total explained variance for all determinants was moderate (R² = 0.35 for femoral neck (FN) BMD, R² = 0.27 for LS BMD, R² = 0.49 total body BMD, and R² = 0.22 for FSI). CONCLUSIONS: Sex, age, height, BM, TLTM, and TFM entered as the most significant contributors for BMD and FSI. Although FF parameters are typically considered in clinical assessments of bone health/strength in older people, body composition appears to have a higher relevance in the explanation of BMD and strength.

Interrelationships among invasive and non-invasive indicators of biological maturation in adolescent male soccer players.

The relationships among indicators of biological maturation were evaluated and concordance between classifications of maturity status in two age groups of youth soccer players examined (11-12 years, n = 87; 13-14 years, n = 93). Data included chronological age (CA), skeletal age (SA, Fels method), stage of pubic hair, predicted age at peak height velocity, and percent of predicted adult height. Players were classified as on time, late or early in maturation using the SA-CA difference, predicted age at peak height velocity, and percent of predicted mature height. Factor analyses indicated two factors in players aged 11-12 years (maturity status: percent of predicted mature height, stage of pubic hair, 59% of variance; maturity timing: SA/CA ratio, predicted age at peak height velocity, 26% of variance), and one factor in players aged 13-14 years (68% of variance). Kappa coefficients were low (0.02-0.23) and indicated poor agreement between maturity classifications. Spearman rank-order correlations between categories were low to moderate (0.16-0.50). Although the indicators were related, concordance of maturity classifications between skeletal age and predicted age at peak height velocity and percent predicted mature height was poor. Talent development programmes call for the classification of youth as early, average, and late maturing for the purpose of designing training and competition programmes. Non-invasive indicators of maturity status have limitations for this purpose.

Prediction of adult height in girls: the Beunen-Malina-Freitas method.

The purpose of this study was to validate and cross-validate the Beunen-Malina-Freitas method for non-invasive prediction of adult height in girls. A sample of 420 girls aged 10-15 years from the Madeira Growth Study were measured at yearly intervals and then 8 years later. Anthropometric dimensions (lengths, breadths, circumferences, and skinfolds) were measured; skeletal age was assessed using the Tanner-Whitehouse 3 method and menarcheal status (present or absent) was recorded. Adult height was measured and predicted using stepwise, forward, and maximum R (2) regression techniques. Multiple correlations, mean differences, standard errors of prediction, and error boundaries were calculated. A sample of the Leuven Longitudinal Twin Study was used to cross-validate the regressions. Age-specific coefficients of determination (R (2)) between predicted and measured adult height varied between 0.57 and 0.96, while standard errors of prediction varied between 1.1 and 3.9 cm. The cross-validation confirmed the validity of the Beunen-Malina-Freitas method in girls aged 12-15 years, but at lower ages the cross-validation was less consistent. We conclude that the Beunen-Malina-Freitas method is valid for the prediction of adult height in girls aged 12-15 years. It is applicable to European populations or populations of European ancestry.

Comprehensive fine mapping of chr12q12-14 and follow-up replication identify activin receptor 1B (ACVR1B) as a muscle strength gene.

Muscle strength is important in functional activities of daily living and the prevention of common pathologies. We describe the two-staged fine mapping of a previously identified linkage peak for knee strength on chr12q12-14. First, 209 tagSNPs in/around 74 prioritized genes were genotyped in 500 Caucasian brothers from the Leuven Genes for Muscular Strength study (LGfMS). Combined linkage and family-based association analyses identified activin receptor 1B (ACVR1B) and inhibin ß C (INHBC), part of the transforming growth factor ß pathway regulating myostatin - a negative regulator of muscle mass - signaling, for follow-up. Second, 33 SNPs, selected in these genes based on their likelihood to functionally affect gene expression/function, were genotyped in an extended sample of 536 LGfMS siblings. Strong associations between ACVR1B genotypes and knee muscle strength (P-values up to 0.00002) were present. Of particular interest was the association with rs2854464, located in a putative miR-24-binding site, as miR-24 was implicated in the inhibition of skeletal muscle differentiation. Rs2854464 AA individuals were ∼2% stronger than G-allele carriers. The strength increasing effect of the A-allele was also observed in an independent replication sample (n=266) selected from the Baltimore Longitudinal Study of Aging and a Flemish Policy Research Centre Sport, Physical Activity and Health study. However, no genotype-related difference in ACVR1B mRNA expression in quadriceps muscle was observed. In conclusion, we applied a two-stage fine mapping approach, and are the first to identify and partially replicate genetic variants in the ACVR1B gene that account for genetic variation in human muscle strength.

Prevalence of overweight, obesity and physical activity levels in children from Azores Islands.

BACKGROUND: Childhood overweight and obesity are increasing all over the world and have been associated with low levels of physical activity (PA). AIMS: To determine the prevalence of overweight, obesity and PA levels in Azorean children according to age and sex; and to determine the association between levels of PA and prevalence of overweight and obesity. SUBJECTS AND METHODS: Weight, height and PA levels were measured in 3699 children aged 6-10 years, from the Azores Islands, Portugal. Overweight and obesity were classified according to the cut-offs of Cole et al. (BMJ 320:1240-1243, 2000) . RESULTS: In girls, prevalences of overweight and obesity were 22.8% and 13.2%, and in boys 17.6% and 12.3%, respectively. No age trends were found in the prevalence of overweight or obesity; however, girls had a higher risk of being overweight (OR = 1.4, 95% CI = 1.2-1.7) than boys. Levels of PA were higher in boys compared to girls (F(1) = 52.8, p < 0.001). A protective effect of PA practice (very active versus less active) was observed for obesity (OR = 0.7; 95% CI = 0.5-0.9). CONCLUSION: The results demonstrate the existence of high prevalence of overweight and obesity in children from the Azores Islands, which is associated with low levels of PA.

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.

Timing of adolescent somatic maturity and midlife muscle function: a 34-yr follow-up.

UNLABELLED: Midlife muscle function is associated with disability and premature mortality later in life. Biological maturity is associated with muscle function during growth; however, it is unknown whether biological maturity during adolescence is associated with muscle mass and function in middle-aged healthy men. PURPOSE: The purpose of this study is to evaluate if late maturation during adolescence is associated with better muscle function in middle-aged men. METHODS: One hundred and thirty-three middle-aged men 45 to 49 yr were included. During adolescence, height was measured at annual intervals, and age at peak height velocity was derived from the individual growth curves and was used to classify participants into early-, average-, and late-maturing groups. Outcome measurements and tests included lean body mass (dual-energy x-ray absorptiometry), muscle-bone areas, isometric strength, and muscle power. Stature, body mass, cardiorespiratory fitness (V O2peak), and physical activity level were included as confounding characteristics. RESULTS: Contrasting maturity groups did not differ in the confounding characteristics (size, mass, aerobic power, and physical activity). Furthermore, no differences were observed for lean mass and muscle-bone areas. Late-maturing adults had greater strength and power, and average differences were between 0.7 and 0.9 SD units (P < 0.05). CONCLUSIONS: Late maturation during adolescence is associated with better muscle function at middle age.

Genome-wide linkage scan for contraction velocity characteristics of knee musculature in the Leuven Genes for Muscular Strength Study.

The torque-velocity relationship is known to be affected by ageing, decreasing its protective role in the prevention of falls. Interindividual variability in this torque-velocity relationship is partly determined by genetic factors (h(2): 44-67%). As a first attempt, this genome-wide linkage study aimed to identify chromosomal regions linked to the torque-velocity relationship of the knee flexors and extensors. A selection of 283 informative male siblings (17-36 yr), belonging to 105 families, was used to conduct a genome-wide SNP-based (Illumina Linkage IVb panel) multipoint linkage analysis for the torque-velocity relationship of the knee flexors and extensors. The strongest evidence for linkage was found at 15q23 for the torque-velocity slope of the knee extensors (TVSE). Other interesting linkage regions with LOD scores >2 were found at 7p12.3 [logarithm of the odds ratio (LOD) = 2.03, P = 0.0011] for the torque-velocity ratio of the knee flexors (TVRF), at 2q14.3 (LOD = 2.25, P = 0.0006) for TVSE, and at 4p14 and 18q23 for the torque-velocity ratio of the knee extensors TVRE (LOD = 2.23 and 2.08; P = 0.0007 and 0.001, respectively). We conclude that many small contributing genes are involved in causing variation in the torque-velocity relationship of the knee flexor and extensor muscles. Several earlier reported candidate genes for muscle strength and muscle mass and new candidates are harbored within or in close vicinity of the linkage regions reported in the present study.

Clustering of metabolic risk factors in young adults: genes and environment.

OBJECTIVE: Evidence of a genetic basis of metabolic risk factors (MRFs) is growing. Studies examining the genetic and environmental basis of the clustering of MRFs, grouped together in the metabolic syndrome (MetS), are however sparse. The aim of this study therefore was to study the heritabilities of the MRFs and the genetic and environmental correlations between the MRFs. METHODS: Study participants were 768 Caucasian twins coming from 418 pairs (18-34 years). MRFs were those included in the National Cholesterol Education Program Adult Treatment Panel III definition of the MetS. Multivariate path analysis on the continuous MRFs of the MetS was implemented. RESULTS: Heritabilities ranged between 47.0% and 80.2% (men) and 58.5% and 77.9% (women) for the individual MRFs. Evidence was found for overarching genetic (A) and environmental (E) sources of variance, both however loading mainly on waist circumference. Furthermore, the model included a 'lipids' and a 'blood pressure'-factor both in part attributable to A and E. The majority of the variance however was MRF-specific. CONCLUSION: Based on our sample of young adults with a low prevalence of the MetS, it can be concluded that both genes and environment contribute significantly to the clustering of the MRFs although the majority of the variation is MRF-specific. Therefore, future QTL searches in young adults may want to focus on MRF-specific loci, rather than 'cluster-phenotypes' such as the MetS.

Genetic and environmental determination of tracking in subcutaneous fat distribution during adolescence.

BACKGROUND: The distribution of fat and adipose tissue is an important predictor of disease risk. Variation in fat distribution during adolescence is correlated with fat distribution in adulthood. OBJECTIVE: The objective was to gain insight into the relative contribution of genes and environment to the stability of subcutaneous fat distribution from early adolescence into young adulthood. DESIGN: Ratio of trunk to extremity skinfold thickness (TER) data from the Leuven Longitudinal Twin Study (n = 105 Belgian twin pairs followed from 10 to 18 y of age) was entered into a longitudinal path analysis. RESULTS: The best-fitting model included additive genetic sources of variance and nonshared environment. Heritabilities ranged between 84.3% (95% CI: 63.9-92.3%) and 88.6% (95% CI: 76.5-94.1%) in boys and between 78.4% (95% CI: 59.3-88.3%) and 88.3% (95% CI: 77.0-93.8%) in girls. The majority of the phenotypic tracking (boys: 0.40-0.78; girls: 0.38-0.72) could be attributed to the moderate-to-high genetic correlations (rG) (between 0.27-0.84 and 0.38-0.80 for the various age intervals in boys and girls, respectively). This rG could be attributed to both genetic sources of variance, which are the same throughout adolescence, as well as genetic sources of variance that are "switched-on" at a certain age, the effect of which is then transmitted to subsequent observations. Environmental correlations (rE) in boys ranged between 0.51 and 0.70 but contributed relatively little to phenotypic tracking because the amount of variance explained by the environment was low (11.4-15.7%). In girls rE was low to moderate at best (0.09-0.48). CONCLUSION: Phenotypic tracking in subcutaneous fat distribution during adolescence is predominantly explained by additive genetic sources of variance.

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.

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.

Indicators of biological maturation and secular changes in biological maturation.

Commonly used indicators of biological maturation are discussed, including sexual, skeletal, morphological, and dental maturity, and the hypothalamus-pituitary-end organ axes that regulate the growth and maturation processes. Interrelationships among indicators and the tempo, timing, and sequence of maturational events are also considered. Environmental factors that influence the level of maturity at a given point in time and the process of maturation are also discussed: undernutrition, obesity, ethnic/racial background, social class, familial characteristics, climate, and altitude. Recommendations for the design of studies of maturational events are made, and an overview of secular changes before and after 1970 is provided. The review concludes with specific recommendations for the inclusion of a maturity indicator or maturity indicators in the construction of an international growth standard for preadolescent and adolescent children

Genetic and environmental causes of tracking in explosive strength during adolescence.

PURPOSE: To determine whether the observed phenotypic stability in explosive strength during adolescence, as measured by inter-age correlations in vertical jump (VTJ), is mainly caused by genetic and/or environmental factors. METHODS: Subjects are from the Leuven Longitudinal Twin Study (LLTS) (n = 105 pairs, equally divided over five zygosity groups). VTJ data were aligned on age at peak height velocity (APHV) to attenuate the temporal fluctuations in inter-age correlations caused by differences in timing of the adolescent growth spurt. Simplex models were fitted using structural equation modelling. RESULTS: After aligning the data on APHV, the annual inter-age correlations show a clear simplex structure over a 4 year interval. The best fitting models included additive genetic and unique environmental sources of variation. Heritability estimates ranged between 60.8% (CI 37.7%-77.2%) and 87.3% (CI 74.2%-94.0%) for boys and between 76.5% (CI 56.7%-89.0%) and 88.6% (CI 77.8%-94.1%) for girls. Up to 56.4% and 62.8% of the total variation at the last measurement occasion is explained by additive genetic factors that already explained a significant amount of variation at previous measurement occasions in boys and girls respectively. It thus can be concluded that the observed stability of explosive strength during adolescence is mainly caused by a stable genetic influence in boys and girls. CONCLUSIONS: Additive genetic factors seem to be the main cause of the observed phenotypic stability in VTJ performance in boys and girls during adolescence.

Genetic and environmental determination of tracking in static strength during adolescence.

The purpose of this study was to determine whether the observed phenotypic stability in static strength during adolescence, as measured by interage correlations in arm pull, is mainly caused by genetic and/or environmental factors. Subjects were from the Leuven Longitudinal Twin Study (n = 105 pairs, equally divided over 5 zygosity groups). Arm-pull data were aligned on age at peak height velocity to attenuate the temporal fluctuations in interage correlations caused by differences in timing of the adolescent growth spurt. Developmental genetic models were fitted using structural equation modeling. After the data were aligned on age at peak height velocity, the annual interage correlations conformed to a quasi-simplex structure over a 4-yr interval. The best-fitting models included additive genetic and unique environmental sources of variation. Additive genetic factors that already explained a significant amount of variation at previous measurement occasions explained 44.3 and 22.5% of the total variation at the last measurement occasion in boys and girls, respectively. Corresponding values for unique environmental sources of variance are 31.2 and 44.5%, respectively. In conclusion, the observed stability of static strength during adolescence is caused by both stable genetic influences and stable unique environmental influences in boys and girls. Additive genetic factors seem to be the most important source of stability in boys, whereas unique environmental factors appear to be more predominant in girls.

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.

Adolescent correlates of adult physical activity: a 26-year follow-up.

PURPOSE: It is hypothesized that adolescent physical activity, fitness, anthropometric dimensions, fatness, biological maturity, and family characteristics contribute to the variation in physical activity at 40 yr of age, and that these associations vary with age. METHODS: Subjects were 166 males followed from 1969 to 1996, between the ages of 14 and 40 yr from the Leuven Longitudinal Study on Lifestyle, Fitness and Health. Sports participation, fitness, anthropometric dimensions, fatness, and biological maturity were observed during the growth period. Also, sociocultural characteristics of the family were examined. The work, leisure time, and sport activity index of the Baecke Questionnaire and activity counts of a triaxial accelerometer were used as outcome variables at 40 yr. RESULTS: When upper and lower activity groups (quintiles) at 40 yr were contrasted, moderate associations were found (R2c varied between 0.1419 and 0.3736). No or low associations were found with the leisure time index. Body dimensions, fitness scores, sports practice, and family characteristics contributed to the explained variance in work, sport index, and activity counts. Multiple correlations were low (R2 = 0.037-0.085) for the work and leisure time activities, and were somewhat higher (R2 = 0.06-0.156) for the sport index and the activity counts in the total sample. CONCLUSION: Adolescent somatic dimensions, fitness, sports participation, parental sociocultural characteristics, and sport participation contributed to a small-to-moderate extent to the contrast between high and low active adults.