Planning Steps Forward in Development: In Girls Earlier than in Boys

The development of planning ability in children initially aged four and five was examined longitudinally with a retest-interval of 12 months using the Tower of London task. As expected, problems to solve straightforward without mental look-ahead were mastered by most, even the youngest children. Problems demanding look-ahead were more difficult and accuracy improved significantly with age and over time. This development was strongly moderated by sex: In contrast to coeval boys, four year old girls showed an impressive performance enhancement at age five, reaching the performance of six year olds, whereas four year old boys lagged behind and caught up with girls at the age of six, the typical age of school enrollment. This sex-specific development of planning was clearly separated from overall intelligence: young boys showed a steeper increase in raw intelligence scores than girls, whereas in the older groups scores developed similarly. The observed sex differences in planning development are evident even within a narrow time window of twelve months and may relate to differences in maturational trajectories for girls and boys in dorsolateral prefrontal cortex.     

Autonomic Regulation of Heart Rate and Distinctive Features of Oculomotor Activity in Eight- to Nine-Year-Old Boys and Girls during the Reading of Texts of Different Complexities

Distinctive features of autonomic regulation of the heart rate and spatiotemporal parameters of eye movements during the reading of texts of different complexities levels from a computer screen have been analyzed in girls and boys eight to nine years of age. Sex-related differences in heart rate variability (HRV) pattern were already observed in the resting state, since parasympathetic effects were stronger in boys than in girls. Parasympathetic activity decreased in boys who were reading texts of different complexities. The most pronounced decrease was observed during the reading of the first (simple) text. The changes in girls were mostly due to an increase in sympathetic activity and were less pronounced than in boys. Oculomotor activity analysis revealed differences in reading process strategy: reading was more fragmented (discrete) in the girls and more integrated in the boys. However, reading skills were not fully developed in children of eight to nine years of age, since “syllabized” reading was observed in girls and boys alike.     

Sensorimotor Reactivity of Children Living in a Radionuclide-Contaminated Zone

Schoolchildren aged 8 to 13 years were examined in Gomel. The children's sensorimotor reaction to light and acoustic stimuli is characterized with regard for their age and sex on the basis of the latency of sensorimotor reactions (LSMR), which shortened significantly with age in children of either sex. This developed unevenly in the children examined, as may be seen from the quite broad ranges of the LSMR fluctuation in each age group. The boys had a stronger sensorimotor reaction to both light and acoustic stimuli than the girls. At the same time, both the boys and the girls reacted to the acoustic stimulus more actively than to the light stimulus.     

Gender differentiations of cognitive-motor functioning in prepubertal and pubertal children

The aim of this study was to determine cognitive and motor status factors in female and male children aged 10-14, as well as developmental and/or integration functions according to gender. The study included 162 girls and 134 boys aged 10-14, divided into four groups: 84 girls aged 10-12 (mean age 11.26, SD 0.68), 84 boys aged 10-12 (mean age 11.41, SD 0.50), 78 girls aged 13-14 (mean age 13.52, SD 0.63) and 50 boys aged 13-14 (mean age 13.21, SD 0.53). The significance of quantitative differences between boys and girls in the overall system of variables was defined based on the results of canonic discriminant analysis of variance, and within each variable based on the results on univariate analysis of variance (ANOVA). In the younger age group (10-12 years), girls were superior to boys in a test assessing flexibility (Seated straddle stretch), whereas, compared to girls, boys had greater strength of the trunk (Crossed-arm sit-ups), greater explosive strength ofjump and sprint type (Standing broad jump and 20 m dash), and coordination (Obstacle course backwards and Steps laterally). In the older age group (13-14 years) differences in flexibility were even more prominent in favor of girls, whereas the differences in explosive strength increased in favor of boys, especially of the throwing type with better agility (Steps laterally), balance (Board balance) and greater static strength of arms and shoulders (Bent-arm hang). In order to determine qualitative differences between pubertal and prepubertal girls and boys, the matrix of variable inter-correlations was factorized by the procedure of principal components procedure, that were then transformed to promax solution. The results showed that cognitive functioning had a significant role in the motor efficacy of girls and boys aged 10 to 14. In the age group of 10-12 years, in females, cognitive functioning is related to the motor system which integrates the regulation of muscle tone with agility/coordination, whereas in males there is a relation between cognitive abilities and the regulator of speed of upper extremities movement frequency. In the age group of 13-14 years, in females, cognitive functioning is involved in forming the factors for regulation of coordination and the intensity of energy mobilization in lower extremities, and to some degree, in the factor for regulation of intensity of energy mobilization in upper extremities and strength of the trunk, whereas in males the integration of synergetic regulation of movement in terms of balance and agility in terms of speed of direction change is carried out with significant involvement of cognitive abilities.     

Sexual dimorphism in bone growth as a function of body size in moderately malnourished Guatemalan preschool age children

The sexual dimorphism in second metacarpal bone growth was investigated in 710 malnourished Guatemalan children one to seven years old to determine if the sex differences seen are only the result of differences in stature and weight. The study sample was mixed-longitudinal and consisted of 1,586 annual examinations. Boys have greater mean stature, weight, periosteal diameter, medullary diameter and cortical area than girls the same age, while girls have greater age specific mean cortical thickness and percent cortical area than boys. When the effects of stature, weight and age are removed boys still have significantly larger periosteal and medullary diameters and less cortical thickness and percent cortical area than girls. These differences between boys and girls therefore cannot be explained by sex differences in body size. However, no sex differences in cortical area remain after accounting for differences in stature, weight and age.     

Sexual dimorphism in mandibular growth of French-Canadian children 6 to 10 years of age

Polynomial regression is used to model the mandibular growth of 28 girls and 26 boys who were followed longitudinally from 6 to 10 years of age. The pooled-within individual designs indicate that ramus height follows a linear pattern of size increase; corpus and total mandibular lengths display curvilineal, decelerating, patterns of growth over the age range. Multivariate analyses of variance reveal significant sex differences in size, favoring boys, for the two length measures at 6 years of age. Growth velocity for corpus length is also significantly greater in boys than in girls. Sexual dimorphism in the growth of total mandibular length is more complex, including differences in velocity and deceleration. Ramus height shows no significant pattern of variation between boys and girls for either size or growth velocity.     

Changes in blood lipids and blood pressure during adolescence.

A total of 625 adolescents from three general practices participated in a cross-sectional study of cardiovascular disease risk factors. The girls had higher serum total and high density lipoprotein (HDL) cholesterol concentrations than the boys, while the boys had higher serum triglyceride concentrations. Smoking (equally prevalent in both sexes) was associated with lower HDL cholesterol concentrations, particularly in boys, while in girls use of oral contraceptives was associated with higher total cholesterol and lower HDL cholesterol concentrations showed striking associations with age, height, and sexual maturation in boys, but not in girls. Triglyceride concentrations were associated with age in boys. Systolic blood pressure and serum urate concentrations were higher in boys and rose steeply with age, but no age association was seen for urate concentrations or systolic blood pressure in girls or for diastolic pressures in either sex. Girls, however, had higher diastolic pressures. There was a strong association between urate concentration and the other cardiovascular disease risk factors, especially HDL cholesterol. Adolescence is associated with considerable changes in cardiovascular disease risk factors, and there are striking sex differences in these changes.     

Fetal growth: boys before girls

At term birth, boys are heavier than girls. This difference is thought to be generated in part by androgen action; its time course has not been deciphered. Androgen action may not only increase weight gain, but may also alter its time course. We have tested this hypothesis by examining the difference in gestational age of 281,894 boys and girls with weights between 500-4,749 g. The age at which children are born with a given weight was found to depend on gender: boys were consistently younger than girls (p < 0.001), the age difference being most pronounced in the lower birth weight classes. Thus, the gender difference in fetal growth appears to be rather pronounced before the third trimester and relatively less marked towards term. In conclusion, the male conceptus seems to grow not only more, but also earlier than the female. Hence, some critical time windows of development may be slightly different in boys and girls, and this phenomenon may be one of the bases for gender differences in the sensitivity to fetal programming. Copyrightz1999S. KargerAG,Basel     

Ethnic Differences in Subcutaneous Adiposity and Waist Girth in Children and Adolescents

The purpose of this study was to examine ethnic differences in adiposity as measured by sum of skinfolds (SKF) and waist circumference (WC) in children and adolescents, after statistical adjustment for the BMI and age. A cross sectional sample of 3,218 (55% white, 49% male) children and adolescents aged 5–18 years who participated in the Bogalusa Heart Study (1992–1994) were included in these analyses. Sex‐specific ANOVAs, adjusted for BMI and age, for each 2‐year age group compared measures of adiposity (SKF and WC) between ethnic groups. No significant differences in the proportions of children and adolescents who were overweight and obese by ethnicity or sex were found. Mean SKF in normal weight (P < 0.0001) and overweight (P < 0.0001) categories was higher for white than black children of both sexes. Across most age categories, white boys and girls had significantly higher SKF than black boys and girls, respectively (P ≤ 0.05). Across most age categories, white boys had significantly higher WC than black boys (P ≤ 0.05) with no difference in the girls, when adjusted for BMI and age. Measures of adiposity in childhood and adolescence were significantly higher in white children compared to black children, when adjusted for BMI and age. Throughout childhood and adolescence, white boys and girls had higher SKF and white boys had higher WC. Differences in adiposity between ethnic groups should be considered in disease risk assessment and stratification as they are observed even for a given BMI level.     

Boys and girls on the playground: sex differences in social development are not stable across early childhood

Sex differences in human social behaviors and abilities have long been a question of public and scientific interest. Females are usually assumed to be more socially oriented and skillful than males. However, despite an extensive literature, the very existence of sex differences remains a matter of discussion while some studies found no sex differences whereas others reported differences that were either congruent or not with gender stereotypes. Moreover, the magnitude, consistency and stability across time of the differences remain an open question, especially during childhood. As play provides an excellent window into children's social development, we investigated whether and how sex differences change in social play across early childhood. Following a cross-sectional design, 164 children aged from 2 to 6 years old, divided into four age groups, were observed during outdoor free play at nursery school. We showed that sex differences are not stable over time evidencing a developmental gap between girls and boys. Social and structured forms of play emerge systematically earlier in girls than in boys leading to subsequent sex differences in favor of girls at some ages, successively in associative play at 3-4 years, cooperative play at 4-5 years, and social interactions with peers at 5-6 years. Preschool boys also display more solitary play than preschool girls, especially when young. Nevertheless, while boys catch up and girls move on towards more complex play, sex differences in social play patterns are reversed in favor of boys at the following ages, such as in associative play at 4-5 years and cooperative play at 5-6 years. This developmental perspective contributes to resolve apparent discrepancies between single-snapshot studies. A better understanding of the dynamics of sex differences in typical social development should also provide insights into atypical social developments which exhibit sex differences in prevalence, such as autism.     

Scaling peak VO2 to body mass in young male and female distance runners.

This study examined age- and sex-associated variation in peak oxygen consumption (VO2) of young male and female distance runners from an allometric scaling perspective. Subjects were from two separate studies of 9- to 19-yr-old distance runners from the mid-Michigan area, one conducted between 1982 and 1986 (Young Runners Study I, YRS I) and the other in 1999-2000 (Young Runners Study II, YRS II). Data from 27 boys and 27 girls from YRS I and 48 boys and 22 girls from the YRS II were included, and a total of 139 and 108 measurements of body size and peak VO2 in boys and girls, respectively, were available. Subjects were divided into whole year age groups. A 2 x 9 (sex x age group) ANOVA was used to examine differences in peak VO2. Intraindividual ontogenetic allometric scaling was determined in 20 boys and 17 girls measured annually for 3-5 yr. Allometric scaling factors were calculated using linear regression of log-transformed data. Results indicated that 1) absolute peak VO2 increases with age in boys and girls, 2) relative peak VO2 (ml x kg(-1) x min(-1)) remains relatively stable in boys and in girls, 3) relative peak VO2 (ml x kg(-0.75) x min(-1)) increases throughout the age range in boys and increases in girls until age 15 yr, and 4) peak VO2 adjusted for body mass (ml/min) increases with age in boys and girls. The overall mean cross-sectional scaling factor was 1.01 +/- 0.03 (SE) in boys and 0.85 +/- 0.05 (SE) in girls. Significant age x sex interactions and significant scaling factors between sexes identify the progressive divergence of peak VO2 between adolescent male and female distance runners. Mean ontogenetic allometric scaling factors were 0.81 [0.71-0.92, 95% confidence interval (CI)] and 0.61 (0.50-0.72, 95% CI) in boys and girls, respectively (P = 0.002). There was considerable variation in individual scaling factors (0.51-1.31 and 0.28-0.90 in boys and girls, respectively). The results suggest that the interpretation of growth-related changes in peak VO2 of young distance runners is dependent upon the manner of expressing peak VO2 relative to body size and/or the statistical technique employed.     

Assessment of developmental age: cross-sectional analysis of secondary sexual characteristics

The developmental age of a growing person does not necessarily correspond to his or her chronological age. The two sexes differ considerably in their developmental tempo, and there are tempo differences also within the same sex. Early developers appear older, late developers appear younger than their chronological age might suggest. Based on a sample of 8675 German boys and 8689 girls of the same ethnicity, aged between 8 and 17 years sex differences of height, weight and secondary sexual characteristics are analyzed. Girls on average, develop faster than boys. Their peak of highest increments of height occurs at 10.2 years and is positioned early within the events of sexual maturity. The peak of highest increments of height in boys occurs at age 11.2 on average and is positioned relatively early within the sequences of secondary sexual characteristics. Maturing development starts with breast-stage 2 in girls at age 10.9 and penis-stage as well as scrotum-stage 2 in boys at age 11.1 on average. The development of pubic hair follows and menarche in girls at age 12.7, respectively spermarche in boys at age 13.8, marks the border to theoretical fertility. There are remarkable differences in the tempo of sexual development between the different types of body shape. In girls the pyknomorphic types are the early developers. Breast stage 2 for instance occurs at age 10.1 in the stocky and corpulent pyknomorphic girls and at age 13.0 in the tall and slender leptomorphic girls. This is different in boys. Here are much less differences between the types of body shape, but generally it is the leptomorphic type, at whom the stages of his secondary sexual characteristics are developed a little earlier.     

Gender-specific growth patterns of transversal body dimensions in Croatian children and youth (2 to 18 years of age)

In a cross-sectional study of growth, 5,260 healthy children of both sexes from Zagreb (Croatia) aged 2 to 18 years were measured. Six transversal body dimensions were studied: biacromial, transverse chest, antero-posterior chest, biiliocristal, bicondylar humerus and bicondylar femur diamters. A significant increase in body diameters has been observed until the age of 14 to 15 in girls and until the age of 16 in boys, showing that girls have a 1 to 2 years shorter period of growth. Compared to boys of the same age, they achieved larger amounts of final transversal bone size throughout the whole growth period. The most pronounced example was the knee diameter that in girls attained 95% of adult size as early as the age of 10. In both genders, the adult size is achieved earlier in widths of the extremities than in those of the trunk. The studied transversal body segments showed different growth dynamics, which is gender-specific. While sexual dimorphism in pelvic and shoulder diameters emerged with pubertal spurt, gender differences in chest and extremities' diameters started early in life. In all ages, boys had larger chest, elbow and knee diameters. In pubertal age boys gained a significantly larger biacromial diameter (from the age of 13 onwards), while girls exceeded them in biiliocristal diameter (from 10 to 14 years). The findings of gender differences were compared to those reported for other European populations and their growth patters were discussed comparing viewpoints.     

Serum selenium levels in healthy slovak children and adolescents

Blood serum selenium levels were measured in 891 healthy children and adolescents (aged 11–18 yr, 450 girls and 441 boys) residing in both rural and urban areas from eight regions of Slovakia. Subjects were divided into four age groups (11–12 y, 13–14 y, 15–16 y, and 17–18 y). Serum selenium concentration was determined by the electrothermal atomic absorption spectrometric method. The mean (±SD) serum selenium concentrations were 0.750 ±0.255 μmol/L in girls and 0.773 ±0.235 μmol/L in boys. A large proportion of the individuals (25.7% in girls, 18.1% in boys) exhibited serum selenium levels under 0.57 μmol/L (45 μg/L). An increasing trend of the serum selenium values with age has been observed in both boys (p < 0.01) and girls (p < 0.05). Boys had higher serum selenium levels in the all age groups but the differences were not statistically significant.     

Sex, age and caste differences in somatotypes of Rajput and scheduled caste adolescents from the Sirmour District of Himachal Pradesh, India

Somatotypes of a cross-sectional sample of 544 rural adolescents ranging in age from 11 to 17 years are described. The sample included 269 Rajput (141 girls and 128 boys) and 275 Scheduled Caste (135 girls and 140 boys) subjects. Each subject was somatotyped using the Heath-Carter anthropometric somatotype protocol (Carter & Heath 1990). In all, ten anthropometric measurements namely height, weight, bicondylar diameters of humerus and femur, flexed mid-upper-arm and calf circumferences, and triceps, subscapular, supraspinale and calf skinfolds were taken. The mean somatotypes of the Rajput boys and girls were 1.62- 3.30-3.85 (mesomorphic-ectomorph) and 2.42-2.90-3.99 (balanced ectomorph), respectively. The mean somatotypes of the Scheduled Caste subjects were 1.51-3.02-3.74 (mesomorphic-ectomorph) for boys and 2.38-2.64-3.70 (balanced ectomorph) for girls. A one-way ANOVA revealed that females of both the caste groups were significantly (p < or = 0.05) more endomorphic than the males. The sex differences in other two components were not significant (p +/- 0.05). Caste differences, as revealed by a one-way ANOVA analysis, were not significant (p +/- 0.05) in both sexes. With the exception of the Rajput girls, the differences in whole somatotypes between those in an early phase of adolescence and those in an advanced phase of adolescence were not significant (p = 0.05). The results indicate that populations exposed to same environmental situations for a long period of time tend to show similarity in physique. A one-way MANOVA analysis, which used Wilk's Lambda as test statistics, revealed that from 11-17 years there was no significant change (p < or = 0.05) in component dominance of mean somatotypes in the boys and girls of the present sample. Among males of a majority of the Indian populations, ectomorphy dominates over endomorphy and mesomorphy from 11 to 17 years.     

Sex matters during adolescence: testosterone-related cortical thickness maturation differs between boys and girls

Age-related changes in cortical thickness have been observed during adolescence, including thinning in frontal and parietal cortices, and thickening in the lateral temporal lobes. Studies have shown sex differences in hormone-related brain maturation when boys and girls are age-matched, however, because girls mature 1-2 years earlier than boys, these sex differences could be confounded by pubertal maturation. To address puberty effects directly, this study assessed sex differences in testosterone-related cortical maturation by studying 85 boys and girls in a narrow age range and matched on sexual maturity. We expected that testosterone-by-sex interactions on cortical thickness would be observed in brain regions known from the animal literature to be high in androgen receptors. We found sex differences in associations between circulating testosterone and thickness in left inferior parietal lobule, middle temporal gyrus, calcarine sulcus, and right lingual gyrus, all regions known to be high in androgen receptors. Visual areas increased with testosterone in boys, but decreased in girls. All other regions were more impacted by testosterone levels in girls than boys. The regional pattern of sex-by-testosterone interactions may have implications for understanding sex differences in behavior and adolescent-onset neuropsychiatric disorders.     

Comparison of Attitudes and Behaviors Related to Nutrition,Body Size,Dieting, and Hunger in Russian,Black-American,and White-American Adolescents

Attitudes and behaviors related to nutrition are known to differ between white-American and black-American adolescents, however, little is known about teenagers from Russia. We hypothesized that, compared with white-American or black-American teenagers, Russian teenagers would prefer a larger body size, be less likely to diet, and be less concerned about being overweight. Self-administered questionnaires were completed by 196 students in Moscow, 326 white-American, and 239 black-American adolescents who attended school in North Carolina (mean age = 16). Ideal body mass index (BMI) was calculated from measured height and the response to the question, “What do you consider to be your ideal weight?” Mean ideal BMI was higher in black-American boys (25.1) and girls (21.4) than in white-American boys (22.1) and girls (19.2), and Russian boys (21.8) and girls (19.1). After controlling for BMI, black-American girls were less than half as likely to report dieting compared with white-American girls. There were no significant differences among white-American girls and Russian girls, and there were no ethnic differences between boys in the prevalence of dieting. White-American girls and black-American girls were much more likely to identify being overweight as an important nutritional concern than were Russian girls (odds ratios >10), and there were no ethnic differences among boys. We conclude that preferences for body size, the prevalence of dieting, and concerns about being overweight were similar in Russian and white-American teens, with the exception of Russian teenaged girls who were less likely than American girls to identify being overweight as an important concern. Overall, weight-related attitudes and behaviors in Russian teenagers were more similar to those of white-American teenagers than those of black-American teenagers.     

Estimating height from arm span measurement in Malawian children

Arm span and standing height were measured in 289 boys and 337 girls aged 6-15 years who were free from physical deformities which can affect stature or arm span. The arm span exceeded height in all age groups of boys and in older girls. At the age of 7, 11 and 12 years girls were significantly taller than the boys and had longer arm span while at the age of 15 years, the trend was opposite. The mean difference between the two anthropometric parameters for boys was 5.45 +/- 4.21 cm (t = 3.556, p < 0.001) and for girls was 4.94 +/- 4.96 cm (t = 3.542, p < 0.001). Correlation coefficient between height and arm span measurements for Malawian boys was 0.983 and for girls was 0.986. Height, arm span and height-arm span difference increased with age of children while height to arm span ratio decreased. The gender difference in height-arm span differences was only significant at the age of 15 years. Multiple regression and cross validation were performed. Height of Malawian children of both sexes can be estimated from equation: Height (cm) = 15.756 + (0.168 x age) + (0.839 x arm span) (SEE = 0.760, R2 = 0.988).