Genetic architecture of subcortical brain regions: common and region‐specific genetic contributions

Understanding the aetiology of patterns of variation within and covariation across brain regions is key to advancing our understanding of the functional, anatomical and developmental networks of the brain. Here we applied multivariate twin modelling and principal component analysis (PCA) to investigate the genetic architecture of the size of seven subcortical regions (caudate nucleus, thalamus, putamen, pallidum, hippocampus, amygdala and nucleus accumbens) in a genetically informative sample of adolescents and young adults (N = 1038; mean age = 21.6 ± 3.2 years; including 148 monozygotic and 202 dizygotic twin pairs) from the Queensland Twin IMaging (QTIM) study. Our multivariate twin modelling identified a common genetic factor that accounts for all the heritability of intracranial volume (0.88) and a substantial proportion of the heritability of all subcortical structures, particularly those of the thalamus (0.71 out of 0.88), pallidum (0.52 out of 0.75) and putamen (0.43 out of 0.89). In addition, we also found substantial region‐specific genetic contributions to the heritability of the hippocampus (0.39 out of 0.79), caudate nucleus (0.46 out of 0.78), amygdala (0.25 out of 0.45) and nucleus accumbens (0.28 out of 0.52). This provides further insight into the extent and organization of subcortical genetic architecture, which includes developmental and general growth pathways, as well as the functional specialization and maturation trajectories that influence each subcortical region.     

Maxillary volume growth in childhood

Nasomaxillary abnormalities in form, position, and development in children are often prominent features of craniosynostosis, and in particular, craniofacial dysostosis. While attempting to quantitatively assess the volumetric maxillary deficiency in these patients, it became apparent that there was no "normal" reference range for maxillary volumes throughout childhood that could be used for comparison. The aim of this study was to generate a model for measuring maxillary volume and subsequent changes throughout childhood. The technique of segmentation was applied to magnetic resonance images obtained in 55 healthy children (30 boys, 25 girls), aged 1 month to 184 months (15.33 years). Maxillary volumes were plotted against age for boys and girls to create a model for normal maxillary growth during the first 15 years of life. Maxillary volumes were larger in boys at all ages. However, the pattern of maxillary growth in boys and girls was similar and could be divided into three periods, each lasting approximately 5 years. During the first 5 years of life, there is a steady increase in maxillary volume, at the end of which the maxilla has reached 53 percent of the volume recorded at 15 years. There is an accelerated rate of growth between 5 and 11 years, which corresponds to the development and eruption of the permanent dentition. Thereafter, until the age of 15 years, the rate of growth of the maxilla plateaus. Maxillary volume in the first 12 months of life is, on average, 29 cm3 in boys and 25 cm3 in girls. By 15 years of age, it has increased to an average of 73.0 cm3 in boys and 59.4 cm3 in girls (an increase by a factor of 2.5 in boys and 2.4 in girls). The difference between the two sexes is statistically significant for the entire series (boys: mean maxillary volume = 56.55 cm3, SD = 24.61; girls: mean maxillary volume = 40.68, SD = 17.69, p = 0.009, one-way analysis of variance).     

The Influence of Sex Steroids on Structural Brain Maturation in Adolescence

Puberty reflects a period of hormonal changes, physical maturation and structural brain reorganization. However, little attention has been paid to what extent sex steroids and pituitary hormones are associated with the refinement of brain maturation across adolescent development. Here we used high-resolution structural MRI scans from 215 typically developing individuals between ages 8–25, to examine the association between cortical thickness, surface area and (sub)cortical brain volumes with luteinizing hormone, testosterone and estradiol, and pubertal stage based on self-reports. Our results indicate sex-specific differences in testosterone related influences on gray matter volumes of the anterior cingulate cortex after controlling for age effects. No significant associations between subcortical structures and sex hormones were found. Pubertal stage was not a stronger predictor than chronological age for brain anatomical differences. Our findings indicate that sex steroids are associated with cerebral gray matter morphology in a sex specific manner. These hormonal and morphological differences may explain in part differences in brain development between boys and girls.     

Genetic and environmental influences on Anxious/Depression during childhood: a study from the Netherlands Twin Register

For a large sample of twin pairs from the Netherlands Twins Register who were recruited at birth and followed through childhood, we obtained parental ratings of Anxious/Depression (A/D). Maternal ratings were obtained at ages 3 years (for 9025 twin pairs), 5 years (9222 pairs), 7 years (7331 pairs), 10 years (4430 pairs) and 12 years (2363 pairs). For 60-90% of the pairs, father ratings were also available. Multivariate genetic models were used to test for rater-independent and rater-specific assessments of A/D and to determine the genetic and environmental influences on individual differences in A/D at different ages. At all ages, monozygotic twins resembled each other more closely for A/D than dizygotic twins, implying genetic influences on variation in A/D. Opposite sex twin pairs resembled each other to same extent as same-sex dizygotic twins, suggesting that the same genes are expressed in boys and girls. Heritability estimates for rater-independent A/D were high in 3-year olds (76%) and decreased in size as children grew up [60% at age 5, 67% at age 7, 53% at age 10 (60% in boys) and 48% at age 12 years]. The decrease in genetic influences was accompanied by an increase in the influence of the shared family environment [absent at ages 3 and 7, 16% at age 5, 20% at age 10 (5% in boys) and 18% at age 12 years]. The agreement between parental A/D ratings was between 0.5 and 0.7, with somewhat higher correlations for the youngest group. Disagreement in ratings between the parents was not merely the result of unreliability or rater bias. Both the parents provided unique information from their own perspective on the behavior of their children. Significant influences of genetic and shared environmental factors were found for the unique parental views. At all ages, the contribution of shared environmental factors to variation in rater-specific views was higher for father ratings. Also, at all ages except age 12, the heritability estimates for the rater-specific phenotype were higher for mother ratings (59% at age 3 and decreasing to 27% at age 12 years) than for father ratings (between 14 and 29%). Differences between children, even as young as 3 years, in A/D are to a large extent due to genetic differences. As children grow up, the variation in A/D is due in equal parts to genetic and environmental influences. Anxious/Depression, unlike many other common childhood psychopathologies, is influenced by the shared family environment. These findings may provide support for why certain family therapeutic approaches are effective in the A/D spectrum of illnesses.     

Effects of Heritability,Shared Environment,and Nonshared Intrauterine Conditions on Child and Adolescent BMI

Heritability studies of BMI, based upon twin samples, have identified genetic and shared environmental components of BMI, but have been largely silent about the nonshared environmental factors. Intrauterine factors have been identified as having significant long‐term effects on BMI and may be a critical source of nonshared environmental influence. Extant studies based on samples of either unrelated individuals or twins cannot separate the effects of genetics, shared environments, and nonshared intrauterine conditions because the one lacks variation in the degree of relatedness and the other has insufficient variation in intrauterine conditions. This study improves upon these prior studies by using a large, sibling‐based sample to examine heritability, shared environmental, and nonshared intrauterine influences on BMI during two age periods in childhood (6–8 years; 12–14 years). The primary interest was in determining the effects of the intrauterine environment on BMI as a component of the nonshared environment and in determining whether there were sex‐specific differences in heritability and/or in the intrauterine factors. These were estimated using regression‐based techniques introduced by DeFries and Fulker. Heritability of BMI was estimated to be 0.20–0.28 at 6–8 years and 0.46–0.61 at 12–14 years. Differences in heritability were found at 12–14 years between same‐sex as compared to mixed‐sex pairs. The shared environmental effect was significant at 6–8 years but insignificant at 12–14 years. Differences in birth weight were significant in all groups at 6–8 years suggesting long‐term effects of the nonshared intrauterine environment; at 12–14 years, birth weight was no longer significant for girls.     

Individual differences in adolescent religiosity in Finland: familial effects are modified by sex and region of residence.

Data from 16-year-old Finnish twin pairs were used to estimate familial effects on religiosity and the modification of those effects by sex and residential region. The sample of 2265 twin boys and 2521 twin girls formed 779 monozygotic and 1614 dizygotic pairs, 785 of the same sex and 829 of opposite sex. We compared religiosity scores of twins living in more rural and traditional northern Finland with those living in the more urban and secular southern region. Girls had higher religiosity scores than did boys, and twins living in northern Finland had higher religiosity scores than those resident in southern Finland. Correlations for monozygotic twins were slightly higher than those for dizygotic twins, and covariance modeling found modest heritability of religiosity [11% (95% CI 0-24) for girls; 22% (95% CI 6-38) for boys], and substantial shared environmental effects [60% (95% CI 49-69) and 45% (95% CI 31-57)] among girls and boys, respectively. The correlation between shared environmental effects in boys and girls was estimated to be 0.84 (95% CI 0.73-0.99). In analyses distinguishing region of residence, girls living in southern Finland were found to have significantly higher unshared environmental effects than girls in northern Finland, while boys living in the urban south appeared to have lower shared environmental effects, and higher additive genetic effects, than boys living in the rural north.     

Are there differences in brain morphometry between twins and unrelated singletons? A pediatric MRI study

Twins provide a unique capacity to explore relative genetic and environmental contributions to brain development, but results are applicable to non‐twin populations only to the extent that twin and singleton brains are alike. A reason to suspect differences is that as a group twins are more likely than singletons to experience adverse prenatal and perinatal events that may affect brain development. We sought to assess whether this increased risk leads to differences in child or adolescent brain anatomy in twins who do not experience behavioral or neurological sequelae during the perinatal period. Brain MRI scans of 185 healthy pediatric twins (mean age = 11.0, SD = 3.6) were compared to scans of 167 age‐ and sex‐matched unrelated singletons on brain structures measured, which included gray and white matter lobar volumes, ventricular volume, and area of the corpus callosum. There were no significant differences between groups for any structure, despite sufficient power for low type II (i.e. false negative) error. The implications of these results are twofold: (1) within this age range and for these measures, it is appropriate to include healthy twins in studies of typical brain development, and (2) findings regarding heritability of brain structures obtained from twin studies can be generalized to non‐twin populations.     

Genetic and environmental contributions to weight, height, and BMI from birth to 19 years of age: an international study of over 12,000 twin pairs

Objective

To examine the genetic and environmental influences on variances in weight, height, and BMI, from birth through 19 years of age, in boys and girls from three continents.

Design and Settings

Cross-sectional twin study. Data obtained from a total of 23 twin birth-cohorts from four countries: Canada, Sweden, Denmark, and Australia. Participants were Monozygotic (MZ) and dizygotic (DZ) (same- and opposite-sex) twin pairs with data available for both height and weight at a given age, from birth through 19 years of age. Approximately 24,036 children were included in the analyses.

Results

Heritability for body weight, height, and BMI was low at birth (between 6.4 and 8.7% for boys, and between 4.8 and 7.9% for girls) but increased over time, accounting for close to half or more of the variance in body weight and BMI after 5 months of age in both sexes. Common environmental influences on all body measures were high at birth (between 74.1–85.9% in all measures for boys, and between 74.2 and 87.3% in all measures for girls) and markedly reduced over time. For body height, the effect of the common environment remained significant for a longer period during early childhood (up through 12 years of age). Sex-limitation of genetic and shared environmental effects was observed.

Conclusion

Genetics appear to play an increasingly important role in explaining the variation in weight, height, and BMI from early childhood to late adolescence, particularly in boys. Common environmental factors exert their strongest and most independent influence specifically in pre-adolescent years and more significantly in girls. These findings emphasize the need to target family and social environmental interventions in early childhood years, especially for females. As gene-environment correlation and interaction is likely, it is also necessary to identify the genetic variants that may predispose individuals to obesity.     

Human sympathoadrenal system and adrenal cortex in prepubertal and pubertal periods

A complex study of the functional state of the sympathoadrenal system and adrenal cortex in 10–15-year-old children of both sexes was carried out using the indices of daily excretion of adrenaline, noradrenaline, 17-ketosteroids, and 17-hydroxycorticosteroids. A synchronism in the functional activity of the mediator component of the sympathoadrenal system as well as of the androgenic and glucocorticoid functions of the adrenal cortex was observed with age and during pubertal development of children. At the same time, heterochronic maturation was observed in the sex groups: in girls at the age of 10 and 12 years and in boys at the age of 14–15 years. The changes of different direction and intensity in the excretion of the studied hormones and hormonal metabolites were observed in the sex and age groups. A sharp increase in the daily excretion of glucocorticoid metabolites accompanied by a considerable decrease in the age index of noradrenaline secretion was observed in 14-and 15-year-old boys from beginning to end of school year; in addition, an increase in the daily excretion of sex hormones was observed at the age of 15 years. In girls, these indices varied within the age range, which points to a more sophisticated neuroendocrine control of physiological functions in girls during puberty.     

Circulatory and respiratory responses to muscular exercise in Czech and Norwegian children

This paper presents a comparison between Czech and Norwegian rural healthy children with regard to the functional characteristics of the circulatory and respiratory system based upon work physiological variables and measurements of some pulmonary volumes. The study included randomised samples of boys and girls at the age of 8, 12 and 16 years, 66 Czech boys and 63 girls, 54 Norwegian boys and 57 girls. At the age of 8 years the maximal aerobic power was closely similar in both countries, but in the older age groups the Norwegian children exhibited lower physical fitness. The maximal heart rate was close to 200 min-1 on the average without any sex, age or ethnic differences. In agreement with the higher maximal aerobic power the 12 and 16 year old Czech children had lower submaximal heart rates for the same oxygen uptake than the Norwegian children. The forced vital capacity and forced expiratory volume in one second was significantly higher on the average in Czech than in Norwegian children but the latter, expressed in percent age of the former, averaged 87 to 91% without any sex, age or ethnic differences. The maximal ventilation volumes during muscular exercise reached higher values in Czech than in Norwegian children of the same age, but the mean maximal respiratory rate was close to 60 min-1, being independent of age, sex and cultural differences. During heavy exercise only 40 to 50% of the vital capacity and 45 to 55% of the forced expiratory volume were taken into account and this index of pulmonary function did not differ with sex, age or ethnic differences.     

Genetic and environmental influences on BMI from late childhood to adolescence are modified by parental education

To investigate how parental education modifies genetic and environmental influences on variation in BMI during adolescence, self-reported BMI at 11-12, 14, and 17 years of age was collected from a population sample of 2,432 complete Finnish twin pairs born in 1983-1987. Based on parental report, twins were divided to those with high (both parents high school graduates), mixed level (one parent a graduate, the other not), and limited (neither parent a graduate) parental education. Genetic and environmental influences on variation in BMI in different education classes were modeled using twin analysis. Heritability of BMI among 11-12-year-olds with high parental education was 85-87% whereas it was 61-68% if parental education was limited or mixed level. Common environmental effect, i.e., effect of environmental factors shared by family members, was found (17-22%) if parental education was limited or mixed level but not if it was high. With increasing parental education, common environmental variance in BMI decreased at age 14 among boys (from 22 to 3%) and girls (from 17 to 10%); heritability increased among boys from 63 to 78%, but did not change among girls. The common environmental component disappeared and heritability of BMI was larger at the age of 17 in all parental education classes. To conclude, common environment did not affect variation of adolescent BMI in high-educated families but did so in families with limited parental education. This suggests that intervention and prevention campaigns could effectively target families identified by limited parental education.     

Human sympathoadrenal system and adrenal cortex in prepubertal and pubertal periods

A complex study of the functional state of the sympathoadrenal system and adrenal cortex in 10-15-year-old children of both sexes was carried out using the indices of daily excretion of adrenaline, noradrenaline, 17-ketosteroids, and 17-hydroxycorticosteroids. A synchronism in the functional activity of the mediator component of the sympathoadrenal system as well as of the androgenic and glucocorticoid functions of the adrenal cortex was observed with age and during pubertal development of children. At the same time, heterochronic maturation was observed in the sex groups: in girls at the age of 10 and 12 years and in boys at the age of 14-15 years. The changes of different direction and intensity in the excretion of the studied hormones and hormonal metabolites were observed in the sex and age groups. A sharp increase in the daily excretion of glucocorticoid metabolites accompanied by a considerable decrease in the age index of noradrenaline secretion was observed in 14- and 15-year-old boys from beginning to end of school year; in addition, an increase in the daily excretion of sex hormones was observed at the age of 15 years. In girls, these indices varied within the age range, which points to a more sophisticated neuroendocrine control of physiological functions in girls during puberty.     

A case‐control study of brain structure and behavioral characteristics in 47,XXX syndrome

Trisomy X, the presence of an extra X chromosome in females (47,XXX), is a relatively common but under‐recognized chromosomal disorder associated with characteristic cognitive and behavioral features of varying severity. The objective of this study was to determine whether there were neuroanatomical differences in girls with Trisomy X that could relate to cognitive and behavioral differences characteristic of the disorder during childhood and adolescence. MRI scans were obtained on 35 girls with Trisomy X (mean age 11.4, SD 5.5) and 70 age‐ and sex‐matched healthy controls. Cognitive and behavioral testing was also performed. Trisomy X girls underwent a semi‐structured psychiatric interview. Regional brain volumes and cortical thickness were compared between the two groups. Total brain volume was significantly decreased in subjects with Trisomy X, as were all regional volumes with the exception of parietal gray matter. Differences in cortical thickness had a mixed pattern. The subjects with Trisomy X had thicker cortex in bilateral medial prefrontal cortex and right medial temporal lobe, but decreased cortical thickness in both lateral temporal lobes. The most common psychiatric disorders present in this sample of Trisomy X girls included anxiety disorders (40%), attention‐deficit disorder (17%) and depressive disorders (11%). The most strongly affected brain regions are consistent with phenotypic characteristics such as language delay, poor executive function and heightened anxiety previously described in population‐based studies of Trisomy X and also found in our sample.     

A highly specific heterologous enzyme immunoassay for 5 alpha-androstane-3 alpha, 17 beta-diol 17-glucuronide (androstanediol-17G) and developmental patterns of urinary androstanediol-17G excretions

We established a highly specific enzyme immunoassay (EIA) for 5 alpha-androstane-3 alpha, 17 beta-diol 17-glucuronide (androstanediol-17G). Rabbit antisera raised against 5 alpha-androstane-3 alpha, 11 alpha, 17 beta-triol 17-glucuronide 11-glutaryl bovine serum albumin and a heterologous tracer of androstanediol-17G conjugated with horseradish peroxidase at the glucuronic acid group were used. The EIA showed excellent specificity: there were no remarkable cross-reactivities with related androgens. The assay range for urine samples was 0.3-30 ng/ml. Recoveries of standards added to samples were 100-108%. Intra-assay and inter-assay coefficients of variation were 2.9-4.4% and 5.7-7.9%, respectively. The EIA was applied to urine samples of 407 males and 322 females to determine developmental patterns and normal ranges of androstanediol-17G excretions in 11 age groups (0 y, 1 y, 2-3 y, 4-5 y, 6-7 y, 8-9 y, 10-11 y, 12-13 y, 14-15 y, 16-17 y, and over 18 y). Urinary androstanediol-17G/creatinine (androstanediol-17G/Cre) ratios in both sexes were high in infancy, tended to decrease during childhood, and began to increase near adolescence. While androstanediol-17G/Cre ratio in girls increased at 8-9 y and reached a plateau during adolescence, that in boys increased at 10-11 y and continued to increase throughout adolescence. Androstanediol-17G/Cre ratios in girls were higher than those in boys at 6-7 y (P < 0.05) and at 8-9 y (P < 0.01). Androstanediol-17G/Cre ratios in boys were higher than those in girls at 12-13 y and at older ages (P < 0.01). These developmental patterns are parallel to age-related changes in androgenicity and serum androstanediol-17G, suggesting that urinary androstanediol-17G/Cre ratio could be a good marker for androgenicity in childhood.     

Sex differences in weight in infancy and the British 1990 national growth standards.

OBJECTIVES: To determine if there is a sex difference in infancy in the new British national standards for weight (based on data from 1990). DESIGN: Weight data in a birth cohort were compared with the 1990 standards and Tanner and Whitehouse (1966) standards up to age 12 months. SETTING: Newcastle upon Tyne. SUBJECTS: 3418 term infants. RESULTS: Our cohort showed a mean difference in standard deviation scores of 0.42 between boys and girls (P < 0.0001) when compared with the 1990 standards. Two and a half times as many girls as boys had weights below the 3rd centile during the first year, with an equivalent excess of boys above the 97th centile (P < 0.0001). Similar results were found with Tanner and Whitehouse standards. CONCLUSIONS: These differences could result in substantial sex bias in the identification of poor growth in early childhood. The standards need modification.     

Genetic contributions to the association between height and intelligence: Evidence from Dutch twin data from childhood to middle age

A positive association between intelligence (IQ) and height has been reported previously. It is generally assumed that this association reflects the effect of childhood environment on IQ, but there is still little research supporting directly this hypothesis. We studied the association between height and IQ in 209 Dutch twin pairs at the ages of 5, 7, 10 and 12 years, 208 twin pairs at 16 and 18 years of age and 567 twin pairs and their siblings in adulthood. The heritability of height was high in all cohorts and across all ages (a² = 0.93 − 0.96). In adulthood, heritability was also high for full-scale IQ (FSIQ: a² = 0.83–0.84) and somewhat lower for verbal IQ (VIQ: a² = 0.66–0.84). In early childhood, the heritability was lower, and common environmental factors had a substantial effect on FSIQ and VIQ. A positive association of height and IQ was found in early childhood and adolescence. In adulthood, a correlation was found between height and FSIQ in young adulthood and between height and VIQ in middle age. All correlations could be ascribed to genetic factors influencing both height and IQ. Thus, these results show that the association between height and IQ should not be directly regarded as evidence for childhood living conditions affecting IQ, but the effect of genetic factors affecting independently or interacting with environmental factors should be considered as well.     

Changes in lung, airway, and chest wall function in boys and girls between 8 and 12 yr

Maximum expiratory flows, maximum inspiratory and expiratory pressures, and lung volumes were measured in 248 8-yr-old and 215 12-yr-old healthy school children. Eight-year-old girls had smaller total lung capacity but higher volume-corrected expiratory flows than boys. Maximum expiratory flow and total lung capacity increased more in girls than in boys between 8 and 12 yr. Girls had a greater increase in residual volume (0.23 liter for girls, 0.16 liter for boys) as well as lower maximum expiratory and inspiratory pressures (P less than 0.001). Girls have smaller lung volumes than boys, so one would expect smaller airways in girls, but girls generate greater flows, indicating that their airways are possibly wider than those of boys. There is also evidence of unequal growth of the airways and air spaces between 8 and 12 yr. Chest wall development appears less in girls than boys and the difference becomes more marked at 12 yr.     

A factor analysis of cranial base and vault dimensions in children

Lengths within the cranial base and vault were measured in cephalometric radiographs of 220 boys and 177 girls ranging in age from 0 to 15 years; all these children are participants in The Fels Longitudinal Growth Study. The present study is based on mixed longitudinal data derived from 1640 radiographs for boys and 1260 radiographs for girls. Factor analysis was applied separately for boys and girls for each age group; i.e., 0–3, 4–6, 7–9, 10–12, and 13–15 years. For the 0–3 year age group, two factors were extracted in each sex, whereas four factors were extracted in the rest of the age groups. The factor structures are similar in the three older age groups of boys (7–9, 10–12, and 13–15 years). The first four factors for these groups are labelled, respectively: cranial vault size, posterior cranial base length, presphenoid length, and basisphenoid length. The order of the third and fourth factors is reversed in the 7–9 year olds. For girls, the factors extracted were also the same in both the 7–9 and 10–12 year age groups, even though the order of factors was different between age groups; i.e., anterior cranial base length, cranial vault size, basisphenoid length, and basioccipital length. Differential growth rates among cranial base dimensions probably cause changes in factor patterns. Obliteration of the spheno-occipital synchondrosis is suggested as the mechanism responsible for the change of factor pattern in the girls. Closure of this synchondrosis would have occurred too late to affect the patterns in boys.     

Age- and sex-related characteristics and mechanisms of adaptations during the prepubertal and pubertal periods of development

Integrated study of the functional state of the sympathoadrenal system and the adrenal cortex in children of both sexes aged 10–15 years. The study was conducted on the basis of the daily adrenaline, noradrenaline, 17-ketosteroid, and 17-oxycorticosteroid excretion values, which allowed certain synchrony to be established in the manifestation of the activity of the transmitter link of the sympathoadrenal system and the adrenal cortex androgenic and glucocorticoid functions with age, during sexual maturation. The heterogeneous character of maturation was found in the sex groups: in girls at an age of 10 and 12 years and in the boys at an age of 14–15 years. Changes in the excretion of the hormones and hormone metabolites with different directions and rates in the age-sex groups were observed throughout the academic year. In 14- to 15-year-old boys, a sharp increase in the daily excretion of the glucocorticoid metabolites accompanied by a substantial decrease in the age-related noradrenaline excretion values and the sex hormone metabolite values at an age of 15 years was observed. In the girls, these values varied within the age range, which indicates a more perfect character of the neuroendocrine regulation of their physiological functions in the period of sexual maturation.     

Age- and gender-related development of stretch shortening cycle during a sub-maximal hopping task

The aim of this study was to analyse the effects of age and gender (and their interaction) on a stretch shortening cycle solicited during a hopping task. For this aim, 147 girls and 148 boys aged 11 to 20 years, who were enrolled in middle school or secondary school with no experience in sport activity, or training less than three times per week, performed 3×5 hops in place. Leg-stiffness, jump-height and reactive-strength indices were assessed using an accelerometer (Myotest). The participants were selected in order to form five age groups: 11 12, 13-14, 15-16, 17-18 and 19-20 years. Regression analysis between force and centre of mass displacement revealed spring-mass behaviour for all groups (r²=.73-.89), meaning that beginning at the age of 11 years, children are able to perform complex inter-muscular coordination of the lower limbs, revealing efficient neural control early in childhood. Leg stiffness increased from 24.7 ± 10.6 kN · m⁻¹ at 11-12 years to 44.1 ± 14 kN · m⁻¹ in boys, with a small increase until 16 years (+17%) and a large increase between 17 and 20 years (+32.7%). In girls, leg stiffness increased from 26.6 ± 9 kN · m⁻¹ at 11-12 years to 39.4 ± 10.9 kN · m⁻¹ at 19-20 years, with a curious decrease in leg stiffness at 17-18 years, probably due to an increase in the percentage of fat at this age (25%). While no gender effect was found, the reactive-strength index revealed that, from 15-16 years onward, boys were better able to produce high levels of force in a shorter time than girls. The age of 15-16 years is a threshold of maturity and gender differentiation, where the boys investigated are more efficient in the stretch shortening cycle.