Is PPARα intron 7 G/C polymorphism associated with muscle strength characteristics in nonathletic young men?

Peroxisome proliferator-activated receptor alpha (PPARα), a ligand-dependent transcription factor, regulates fatty acid metabolism in heart and skeletal muscle. The intron 7 G/C polymorphism (rs4253778) has been associated with athletic performance. The rare C-allele was predominant in power athletes, whereas the G-allele was more frequent in endurance athletes. In the present study, we investigated the association between this polymorphism and strength characteristics in nonathletic, healthy young adults (n = 500; age 24.2 ± 4.4 years). Knee torque was measured during concentric knee flexion and extension movements at 60°/s, 120°/s, and 240°/s during 3, 25, and 5 repetitions, respectively. Also, resistance to muscle fatigue (i.e. work last 20% repetitions/work first 20% repetitions *100) was calculated. Differences in knee strength phenotypes between GG homozygous individuals and C-allele carriers were analyzed. The polymorphism did not influence the ability to produce isometric or dynamic knee flexor or extensor peak torque during static or dynamic conditions in this population (0.23 < P < 0.95). Similar results were found for the endurance ratio, a measure for resistance to muscle fatigue. In conclusion, the PPARα intron 7 G/C polymorphism does not seem to influence strength characteristics in a nonathletic population.

Genome-wide linkage scan for resistance to muscle fatigue.

Repeated, intense use of muscles leads to a decline in performance known as muscle fatigue. Resistance to muscle fatigue depends on age, sex, muscle fiber type, activation by the nervous system and training. Heritability of muscle strength phenotypes ranges between 31% and 78%, although little is known about heritability of muscle fatigue. A first aim of this study was to estimate the heritability for fatigue resistance after a short bout of intense exercise of the knee musculature. The main purpose was to identify chromosomal regions linked to muscle fatigue applying genome-wide linkage analyses. A selection of 283 informative male siblings (17-36 years old), belonging to 105 families, was used to conduct a genome-wide SNP-based multipoint linkage analysis. Heritabilities for resistance to muscle fatigue ranged from 21% to 54%. The strongest linkage signal was found at 19q13.11 (LOD=2.158; P<0.0001) and at 1q32.1 (LOD=2.142; P<0.0001) for resistance to fatigue of the knee flexors; however, no marker reached genome-wide significance. Several other regions with LOD>1.5 were found (1p31.3, 3q29, 8p22, 11q25 and 19q12). When replicated in an independent sample, these results warrant further fine mapping studies aiming to detect genes that underlie variation in muscle fatigue.

Correlates of changes in BMI of children from the Azores islands.

OBJECTIVE: To model changes in body mass index (BMI), including its stability, and to investigate the association between physical activity, 1-mile run/walk and levels of gross motor coordination and BMI during 5 consecutive years. DESIGN: A longitudinal study of children 6 years of age at baseline followed at annual intervals over 5 years. SUBJECTS: A total of 285 children (143 boys and 142 girls) were enrolled in grade 1 (age 6 years) and followed through grade 5 (age 10 years). MEASUREMENTS: BMI was recorded and physical activity was assessed by questionnaire, aerobic fitness was evaluated with the 1-mile run/walk and gross motor coordination was measured with the KTK test battery (Körperkoordination test für Kinder). Multilevel modelling techniques were for the primary analysis. RESULTS: Changes in BMI showed similar curvilinear trends in boys and girls, with ample inter-individual crossing trajectories that is, low tracking. Longitudinal changes in physical activity (PA) and aerobic fitness were not significantly associated with BMI-changes during the 5 years. Children who were more proficient in their motor coordination showed lower values of BMI during the 5 years. CONCLUSIONS: BMI trajectories of both boys and girls show low tracking of BMI-values. Considerable inter-individual variation exists both in baseline BMI-values and changes (velocity and acceleration) over time. PA and fitness were not associated with BMI-changes, but gross motor function was negatively associated with BMI-changes. No gender-specific associations were found. If confirmed in other populations these observations could be translated in the promotion of physical activities that improve gross motor function in children aged 6-10 years. This seems to be of major importance for the physical education curriculum of primary school children.

A growth curve to model changes in sport participation in adolescent boys.

The aims of this study are twofold: (1) to present the latent growth model, its strategy and usefulness in modelling sport participation over a 6-year period in youngsters (2) and to study the impact of biological maturation in sport participation changes. A standardized sport participation questionnaire using h/week/year as the unit of analysis was applied to 588 Belgium boys 13-18 years of age followed longitudinally for 6 years. Skeletal age was used to estimate biological maturation. Growth curve modelling with robust estimation was used. Sport participation changes showed a curvilinear trend: baseline values (3.18+/-0.13 h/week/year), a linear trend that indicates the rate of change (0.70+/-0.11) and a quadratic trend indicating deceleration, i.e. a change in the rate of change (-0.07+/-0.02) were all statistically significant (P<0.05), as well as inter-individual differences in these three parameters. Up to 16.8 years, the rate of sports participation increased 0.70 h/week/year and then declined. Biological maturation did not show any association with adolescent changes in sport participation.

Genetics and sports: an overview of the pre-molecular biology era.

Estimated genetic and environmental contributions to individual differences in physical performance phenotypes, responsiveness to intermittent, aerobic and strength training, and specific skill training protocols are the focus of this chapter. Data are derived primarily from twin and family studies, although methods of analysis vary considerably. Estimates of heritability span a wide range for several performance phenotypes and the responsiveness to training. This is explained, in part, by differences in sample characteristics and analytical strategies. Corresponding data for skill acquisition are very limited. Data dealing with the effects of age, sex, maturation and ethnicity on heritability estimates are lacking, and information on behavioral phenotypes that may be related to performance is not available.

Parent-of-origin specific linkage and association of the IGF2 gene region with birth weight and adult metabolic risk factors.

OBJECTIVE: The maternally imprinted insulin-like growth factor 2 (IGF2) gene is an important fetal growth factor and is also suggested to have postnatal metabolic effects. In this study, we examined whether common polymorphisms in IGF2 (6815_6819delAGGGC, 1156T>C and 820G>A (ApaI)) and a microsatellite marker in the close vicinity of IGF2 were linked to or associated with birth weight and adult metabolic risk factors. DESIGN AND PARTICIPANTS: Polymorphisms were genotyped in 199 monozygotic complete twin pairs, 109 dizygotic complete twin pairs, 15 single twins, 231 mothers and 228 fathers recruited from the East Flanders Prospective Twin Survey. Conventional and parent-of-origin specific linkage and association analyses were carried out with birth weight, adult body height and parameters quantifying obesity, insulin sensitivity and dyslipidaemia measured at adult age (mean age 25 years). RESULTS: In the parent-of-origin specific association analysis, in which only the paternally inherited allele was incorporated, the 1156T>C SNP (single nucleotide polymorphism) showed significant association with IGF-binding protein 1 (IGFBP1) levels (T and C (mean (95% CI)): 13.2 (12.1-14.3) and 16.2 (14.6-18.0) ng ml(-1), P=0.002). No linkage was observed in either the conventional or in the parent-of-origin specific linkage analysis. CONCLUSION: This study suggests that paternally inherited alleles of a common polymorphism in the IGF2 gene affect IGFBP1 levels.

Sedentary behaviour, physical activity and a continuous metabolic syndrome risk score in adults.

OBJECTIVE: The association of sedentary behaviour and leisure time physical activity with a validated continuous metabolic syndrome risk score was investigated in adults. SUBJECTS/METHODS: A number of 992 adults (559 men) without cardiovascular disease or diabetes. Subjects reported time spent in leisure time physical activity and television watching/computer activities. A validated metabolic syndrome risk score, based on waist circumference, triglycerides, blood pressure, fasting plasma glucose and high-density lipoprotein cholesterol, was used. The metabolic syndrome risk score and time spent in sedentary behaviour and physical activity were analysed as continuous variables using multiple linear regression. RESULTS: Metabolic syndrome risk was positively associated with time spent watching television/computer activities, irrespective of physical activity level, and after adjustment for age, education level, smoking status and dietary intake in women aged > or =45 years (beta=0.184, P<0.05). Independent of the time being sedentary, moderate to vigorous leisure time physical activity was inversely associated with metabolic syndrome risk in men (<45 years: beta=-0.183, P<0.01; > or =45 years: beta=-0.192, P<0.01) and women aged > or =45 years (beta=-0.203, P<0.01). CONCLUSIONS: Although cross-sectional, the present results support inclusion of efforts to decrease sedentary behaviour in metabolic syndrome prevention strategies for women aged > or =45 years, besides promotion of moderate to vigorous physical activity, since both behavioural changes might show additional effects.

Common SNPs in LEP and LEPR associated with birth weight and type 2 diabetes-related metabolic risk factors in twins.

OBJECTIVE: Children born small for gestational age are at increased risk of developing type 2 diabetes in adulthood. The satiety signal leptin that regulates food intake and energy expenditure might be a possible molecular link, as umbilical cord leptin levels are positively correlated with birth weight. In the present study, we examined whether common single nucleotide polymorphisms (SNPs) in the leptin (LEP; 19G>A) gene and its receptor (LEPR; Q223R and K109R) are associated with birth weight and adult metabolic risk factors for type 2 diabetes in twins. DESIGN: SNPs were genotyped in 396 monozygotic and 232 dizygotic twins (286 men and 342 women, mean age 25 years) recruited from the East Flanders Prospective Twin Survey. Data were analysed using linear mixed models. RESULTS: The LEPR K109R SNP was associated with birth weight (KK, KR and RR (95% confidence interval, CI): 2511 (2465-2557), 2575 (2516-2635) and 2726 (2606-2845) gram; P(additive)=0.001). Also the LEPR Q223R SNP showed a significant association with weight at birth (QQ, QR and RR (95% CI): 2492 (2431-2554), 2545 (2495-2595) and 2655 (2571-2740) gram; P(additive)=0.003). Furthermore, an interaction between the LEPR K109R and the Q223R SNP on birth weight was observed (P=0.014). G allele carriers of the LEP 19G>A SNP had higher high-density lipoprotein (HDL) cholesterol levels compared to 19A homozygotes (GX vs AA (95% CI): 1.62 (1.58-1.66) vs 1.49 (1.40-1.58) mmol l(-1); P(recessive)=0.013). CONCLUSIONS: This study indicates that leptin may act as a growth-promoting signal during fetal development, and suggests a possible role for the LEPR in explaining the inverse relationship between birth weight and the development of metabolic diseases in adulthood. Additionally, these results suggest that the LEP 19G>A SNP affect HDL cholesterol levels.

Genome-wide linkage scan for maximum and length-dependent knee muscle strength in young men: significant evidence for linkage at chromosome 14q24.3.

BACKGROUND: Maintenance of high muscular fitness is positively related to bone health, functionality in daily life and increasing insulin sensitivity, and negatively related to falls and fractures, morbidity and mortality. Heritability of muscle strength phenotypes ranges between 31% and 95%, but little is known about the identity of the genes underlying this complex trait. As a first attempt, this genome-wide linkage study aimed to identify chromosomal regions linked to muscle and bone cross-sectional area, isometric knee flexion and extension torque, and torque-length relationship for knee flexors and extensors. METHODS: In total, 283 informative male siblings (17-36 years old), belonging to 105 families, were used to conduct a genome-wide SNP-based multipoint linkage analysis. RESULTS: The strongest evidence for linkage was found for the torque-length relationship of the knee flexors at 14q24.3 (LOD = 4.09; p<10(-5)). Suggestive evidence for linkage was found at 14q32.2 (LOD = 3.00; P = 0.005) for muscle and bone cross-sectional area, at 2p24.2 (LOD = 2.57; p = 0.01) for isometric knee torque at 30 degrees flexion, at 1q21.3, 2p23.3 and 18q11.2 (LOD = 2.33, 2.69 and 2.21; p<10(-4) for all) for the torque-length relationship of the knee extensors and at 18p11.31 (LOD = 2.39; p = 0.0004) for muscle-mass adjusted isometric knee extension torque. CONCLUSIONS: We conclude that many small contributing genes rather than a few important genes are involved in causing variation in different underlying phenotypes of muscle strength. Furthermore, some overlap in promising genomic regions were identified among different strength phenotypes.

Anthropometry, carbohydrate and lipid metabolism in the East Flanders Prospective Twin Survey: heritabilities.

AIMS/HYPOTHESIS: We determined the genetic contribution of 18 anthropometric and metabolic risk factors of type 2 diabetes using a young healthy twin population. METHODS: Traits were measured in 240 monozygotic (MZ) and 138 dizygotic (DZ) twin pairs aged 18 to 34 years. Twins were recruited from the Belgian population-based East Flanders Prospective Twin Survey, which is characterised by its accurate zygosity determination and extensive collection of perinatal and placental data, including information on chorionicity. Heritability was estimated using structural equation modelling implemented in the Mx software package. RESULTS: Intra-pair correlations of the anthropometric and metabolic characteristics did not differ between MZ monochorionic and MZ dichorionic pairs; consequently heritabilities were estimated using the classical twin approach. For body mass, BMI and fat mass, quantitative sex differences were observed; genetic variance explained 84, 85 and 81% of the total variation in men and 74, 75 and 70% in women, respectively. Heritability estimates of the waist-to-hip ratio, sum of four skinfold thicknesses and lean body mass were 70, 74 and 81%, respectively. The heritability estimates of fasting glucose, fasting insulin, homeostasis model assessment of insulin resistance and beta cell function, as well as insulin-like growth factor binding protein-1 levels were 67, 49, 48, 62 and 47%, in that order. Finally, for total cholesterol, LDL-cholesterol, HDL-cholesterol, total cholesterol:HDL-cholesterol ratio, triacylglycerol, NEFA and leptin levels, genetic factors explained 75, 78, 76, 79, 58, 37 and 53% of the total variation, respectively. CONCLUSIONS/INTERPRETATION: Genetic factors explain the greater part of the variation in traits related to obesity, glucose intolerance/insulin resistance and dyslipidaemia.

Polymorphisms in the vitamin D receptor gene are associated with muscle strength in men and women.

INTRODUCTION: Vitamin D receptor (VDR) polymorphisms have been associated with fracture risk and muscle strength, although evidence for the latter is limited and conflicting. METHODS: BsmI, TaqI and FokI VDR polymorphisms were genotyped in 253 men (54.9 +/- 10.2 yr) and 240 women (41.5 +/- 13.2 yr). Haplotypes were constructed for BsmI and TaqI. Handgrip, isometric (at 60 degrees , 120 degrees and 180 degrees joint angle) and eccentric torques (60 degrees /s) of knee extension and flexion were analysed using AN(C)OVA. Torque-velocity curves were constructed for concentric torques at 60 degrees /s, 180 degrees /s and 240 degrees /s and analysed using multivariate AN(C)OVA. Age, height and fat-free mass were included as covariates. RESULTS: Quadriceps isometric and concentric strength were higher in female f/f homozygotes compared to F allele carriers. Adjustment for confounding factors rendered results for quadriceps isometric strength at 120 degrees non-significant. No significant association was found with BsmI-TaqI haplotype in women. In contrast, male Bt/Bt homozygotes had higher isometric quadriceps strength at 150 degrees and higher concentric quadriceps strength than bT allele carriers without and with adjustment for confounding factors. No association was observed with FokI in men. In both genders, no interaction effect was present between BsmI-TaqI haplotype and FokI. CONCLUSIONS: Different VDR gene polymorphisms are associated with quadriceps strength in men and women.

Heritability of somatotype components: a multivariate analysis.

OBJECTIVE: To study the genetic and environmental determination of variation in Heath-Carter somatotype (ST) components (endomorphy, mesomorphy and ectomorphy). DESIGN: Multivariate path analysis on twin data. SUBJECTS: Eight hundred and three members of 424 adult Flemish twin pairs (18-34 years of age). RESULTS: The results indicate the significance of sex differences and the significance of the covariation between the three ST components. After age-regression, variation of the population in ST components and their covariation is explained by additive genetic sources of variance (A), shared (familial) environment (C) and unique environment (E). In men, additive genetic sources of variance explain 28.0% (CI 8.7-50.8%), 86.3% (71.6-90.2%) and 66.5% (37.4-85.1%) for endomorphy, mesomorphy and ectomorphy, respectively. For women, corresponding values are 32.3% (8.9-55.6%), 82.0% (67.7-87.7%) and 70.1% (48.9-81.8%). For all components in men and women, more than 70% of the total variation was explained by sources of variance shared between the three components, emphasising the importance of analysing the ST in a multivariate way. CONCLUSIONS: The findings suggest that the high heritabilities for mesomorphy and ectomorphy reported in earlier twin studies in adolescence are maintained in adulthood. For endomorphy, which represents a relative measure of subcutaneous adipose tissue, however, the results suggest heritability may be considerably lower than most values reported in earlier studies on adolescent twins. The heritability is also lower than values reported for, for example, body mass index (BMI), which next to the weight of organs and adipose tissue also includes muscle and bone tissue. Considering the differences in heritability between musculoskeletal robustness (mesomorphy) and subcutaneous adipose tissue (endomorphy) it may be questioned whether studying the genetics of BMI will eventually lead to a better understanding of the genetics of fatness, obesity and overweight.

Quantitative trait loci for human muscle strength: linkage analysis of myostatin pathway genes.

This study reports the results of a multipoint linkage study that aims to unravel the genetic basis of muscle strength and muscle mass in humans. Myostatin (GDF8) is known to be a strong inhibitor of muscle growth in animals. However, studies examining human myostatin polymorphisms are rare and are limited to the GDF8 gene itself. Here, the contribution to isometric and concentric knee strength of nine key proteins involved in the myostatin pathway is studied in a nonparametric multipoint linkage analysis by means of a variance components and regression method. A sample of 367 healthy young male siblings was phenotyped on an isokinetic dynamometer and genotyped for markers of the myostatin pathway genes. Three of the loci were found significantly linked with a quantitative trait locus (QTL) for knee muscle strength. First, D13S1303 showed replication of an explorative single-point linkage study with a maximum LOD score of 2.7 (P = 0.0002). Second, maximum LOD scores of 3.4 (P = 0.00004) and 3.3 (P = 0.00005) were observed for markers D12S1042 and D12S85, respectively, at 12q12-14. Finally, marker D12S78 showed an LOD score of 2.7 at 12q22-23. We conclude that several genes involved in the myostatin pathway, but not the myostatin gene itself, are important QTLs for human muscle strength. An additional set of valuable candidate genes that were not part of the myostatin pathway was found in the chromosome 12 and 13 genomic regions.

Somatic growth of a school-aged population from Mozambique: trend and biosocial meaning.

A cross-sectional study of children and adolescents from Maputo, Mozambique, was carried out in order to (1) describe the current growth status of children and adolescents from Maputo, (2) evaluate the relative status of the growth and development of youth from Maputo compared to WHO international standards, (3) assess the relationship between socioeconomic status and growth and development, and (4) assess the impact that the civil war (1980-1992) had on the health status of children and adolescents living in Maputo. The sample is composed of 2,271 subjects (1,098 boys and 1,173 girls), age 6 to 17 years. Somatic measures included height, weight, and skinfold thicknesses from which nutritional indicators were calculated and plotted against WHO norms. Subjects were divided into three groups according to their socioeconomic status. Data from a cross-sectional study done in the same areas in 1992 was used to analyze the impact of war. Beginning at 11 years, Maputo students are always shorter and weigh less than the WHO standards. BMI in boys from 11 years and in girls from 12 years is somewhat lower than the WHO norms. A social gradient is evident, favoring those students with higher socioeconomic status. Height, weight, BMI, fat mass, and lean body mass are always higher in the 1999 sample than in the 1992 study. We conclude that (1) there is a substantial difference in height and weight values of Maputo children and adolescents compared to WHO standards; (2) there is a clear advantage of being of higher socioeconomic status; (3) socioeconomic status, hygiene, and sanitation are the main factors responsible for the greater values of the 1999 sample; and (4) differences between the stature of students with higher socioeconomic status and the WHO norms are almost irrelevant. This last aspect reveals the importance of socioeconomic factors in determining the growth process, implying its importance in facilitating the "expression" of the genotypes available in the population.

Skeletal maturity and socio-economic status in Portuguese children and youths: the Madeira growth study.

BACKGROUND: Skeletal maturity is used to evaluate biological maturity status. Information about the association between socio-economic status (SES) and skeletal maturity is limited in Portugal. AIMS: The aim of this study is to document the skeletal maturity of youths in Madeira and to evaluate variation in maturity associated with SES. SUBJECTS AND METHODS: The study involved 507 subjects (256 boys and 251 girls) from the Madeira Growth Study, a mixed-longitudinal study of five cohorts (8, 10, 12, 14 and 16 years of age) followed at yearly intervals over 3 years (1996-1998). A total of 1493 observations were made. Skeletal age was estimated from radiographs of the hand and wrist using the Tanner-Whitehouse 2 method (TW2). Social class rankings were based on method. Five social rankings were subsequently grouped into three SES categories: high, average and low. RESULTS: Median for the radius, ulna and short finger bones (RUS scores) in the total sample of boys and girls increased curvilinearly across age whereas median for the 7 (without pisiform) carpal bones (Carpal scores) increased almost linearly. The 20-bone maturity scores demonstrated distinctive trends by gender: the medians for boys increased almost linearly while the medians for girls increased curvilinearly. SES differences were minimal. Only among children aged 10-11 years were high SES boys and girls advanced in skeletal maturity. Madeira adolescents were advanced in skeletal maturity compared with Belgian reference values. CONCLUSION: The data suggests population variation in TW2 estimates of skeletal maturation. Skeletal maturity was not related to SES in youths from Madeira.

Association between bone, body composition and strength in premenarcheal girls and postmenopausal women.

AIM: The study examined whether associations between bone, body composition and strength are age dependent. SUBJECTS AND METHODS: Two age levels (premenarcheal girls and postmenopausal women on HRT) were studied in a 10-month follow-up. Bone, lean and fat mass were measured by dual-energy X-ray absorptiometry (DXA), and strength was measured using an isokinetic dynamometer. RESULTS: In girls, significant correlations were found between mass (lean, fat and body mass), strength and most bone characteristics (r = 0.15-0.93). At the proximal femur changes in bone mineral density (BMD) were moderately related to changes in body composition. In the women, body mass and lean mass were significantly correlated with most bone characteristics (r = 0.34-0.82). Low to moderate correlations were observed between changes in bone and changes in body composition. After controlling for lean mass the relation between strength and bone was no longer significant. CONCLUSIONS: In premenarcheal girls, bone is partly determined by mass, with lean mass the most important predictor at the femoral sites. In postmenopausal women, lean mass is an important determinant of bone mineral content (BMC) and BMD, but changes in BMD are related to changes in fat. The relation between strength and BMD is mainly attributable to the relation between lean mass and BMD. The contributory effects of soft tissue to bone change over different life periods.

Linkage of myostatin pathway genes with knee strength in humans.

This study was the first to explore the potential role of the myostatin (GDF8) pathway in relation to muscle strength and estimated muscle cross-sectional area in humans using linkage analysis with a candidate gene approach. In young male sibs (n = 329) 11 polymorphic markers in or near 10 candidate genes from the myostatin pathway were genotyped. Muscle mass was estimated by anthropometric measurements, and maximal knee strength was evaluated using isokinetic dynamometers (Cybex NORM). Single-point nonparametric variance components and linear quantitative trait locus regression linkage analysis methods were used. Linkage patterns were observed between knee extension and flexion peak torque with markers D2S118 (GDF8), D6S1051 (CDKN1A), and D11S4138 (MYOD1), and a maximum LOD score of 2.63 (P = 0.0002) was observed with D2S118. The ratios of peak torque over muscle and bone area of the midthigh of the lower contraction velocity (60 degrees/s) showed more frequently significant LOD scores than the torques at high velocity (240 degrees/s). Although myostatin is physiologically more related to muscle mass through possible effects of hyperplasia and hypertrophy than it is to strength, only two estimated muscle cross-sectional areas were marginally linked (LOD 1.06 and 1.07, P = 0.01) with marker D2S118 near GDF8 (2q32.2). The present results gave suggestive evidence that the myostatin pathway might be important for strength phenotypes, and GDF8, CDKN1A, and MYOD1 are potential candidate regions for a further and denser mapping with respect to these phenotypes.

Influence of weight-bearing exercises on bone acquisition in prepubertal monozygotic female twins: a randomized controlled prospective study.

The aim of this study was to determine whether high-impact exercises have an osteogenic effect in 21 prepubertal female monozygotic twins aged 8.7 (SD 0.7) years. Bone mineral density (aBMD), bone mineral content (BMC), bone area, and body composition were derived from DXA. Skeletal maturity was assessed by the Tanner-Whitehouse technique. Anthropometric dimensions (28 dimensions) were measured and also used to derive adiposity and muscularity indices, and information about physical activity was obtained by questionnaire. These measurements were taken before and after the exercise period. The exercise program consisted of high-impact exercises. During 9 months, one girl of each twin pair performed the exercises 3 times a week under supervision of a teacher while their sisters served as control group. At baseline there were no differences between the groups. After 9 months, exercisers (Ex) and controls (Con) had similar increases in height and weight. Significant lower adiposity was observed in the exercise group vs the control group. None of the bone indices differed significantly between the two groups. When the analyses were done for a subgroup of twin pairs (n = 12) who did not participate in high-impact sports during their leisure time, significant differences were obtained for aBMD and BMC of the proximal femur in favor of the exercise group. These results indicate that for prepubertal girls who are not involved in sport activities or who are only involved in low-impact sport activities this exercise program has an osteogenic effect on the proximal femur, but for girls who are already involved in high-impact sports this protocol does not have any additional effect on the bone status.

Heritability of somatotype components from early adolescence into young adulthood: a multivariate analysis on a longitudinal twin study.

BACKGROUND: Several studies with different designs have attempted to estimate the heritability of somatotype components. However they often ignore the covariation between the three components as well as possible sex and age effects. Shared environmental factors are not always controlled for. AIM: This study explores the pattern of genetic and environmental determination of the variation in Heath-Carter somatotype components from early adolescence into young adulthood. SUBJECTS AND METHODS: Data from the Leuven Longitudinal Twin Study, a longitudinal sample of Belgian same-aged twins followed from 10 to 18 years (n = 105 pairs, equally divided over five zygosity groups), is entered into a multivariate path analysis. Thus the covariation between the somatotype components is taken into account, gender heterogeneity can be tested, common environmental influences can be distinguished from genetic effects and age effects are controlled for. RESULTS: Heritability estimates from 10 to 18 years range from 0.21 to 0.88, 0.46 to 0.76 and 0.16 to 0.73 for endomorphy, mesomorphy and ectomorphy in boys. In girls, heritability estimates range from 0.76 to 0.89, 0.36 to 0.57 and 0.57 to 0.76 for the respective somatotype components. Sex differences are significant from 14 years onwards. More than half of the variance in all somatotype components for both sexes at all time points is explained by factors the three components have in common. CONCLUSIONS: The finding of substantial genetic influence on the variability of somatotype components is further supported. The need to consider somatotype as a whole is stressed as well as the need for sex- and perhaps age-specific analyses. Further multivariate analyses are needed to confirm the present findings.