Ventilatory anaerobic threshold in healthy children. Age and sex differences

The ventilatory anaerobic threshold (VAT) during graded exercise was defined as the oxygen uptake (VO2) immediately below the exercise intensity at which pulmonary ventilation increased disproportionally relative to VO2. Since VAT is considered to be a sensitive and noninvasive measure for evaluating cardiorespiratory endurance performance, the purpose of the present study was to determine normal values in children. We examined 257 healthy children (140 boys and 117 girls) varying in age from 5.7 to 18.5 years, during treadmill exercise. The data were analyzed in relation to sex and age. In boys the lowest VO2max (ml X min-1 X kg-1) was found in the youngest age group (5-6 year). In girls, on the other hand, no significant increase occurred with age. For VAT, expressed as ml O2 X min-1 X kg-1 or as a percent of VO2max, a significant decrease was found in boys and girls with age. This suggests an increase in lactacid anaerobic capacity during growth. In contrast to observations in adults, only low correlations were found between VO2max and VAT (r = 0.28 in boys and r = 0.52 in girls), which suggests that the development of the underlying physiological mechanism does not occur at the same rate in growing children. These data provide normal values for VAT that can be used for clinical exercise testing in the pediatric age group.     

Forty years trends in timing of pubertal growth spurt in 157,000 Danish school children

Background

Entering puberty is an important milestone in reproductive life and secular changes in the timing of puberty may be an important indicator of the general reproductive health in a population. Too early puberty is associated with several psychosocial and health problems. The aim of our study was to determine if the age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV) during puberty show secular trends during four decades in a large cohort of school children.

Methods and Findings

Annual measurements of height were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen Municipality. 135,223 girls and 21,612 boys fulfilled the criteria for determining age at OGS and age at PHV. These physiological events were used as markers of pubertal development in our computerized method in order to evaluate any secular trends in pubertal maturation during the study period (year of birth 1930 to 1969). In this period, age at OGS declined statistically significantly by 0.2 and 0.4 years in girls and boys, respectively, whereas age at PHV declined statistically significantly by 0.5 and 0.3 years in girls and boys, respectively. The decline was non-linear with a levelling off in the children born between 1940 and 1955. The duration of puberty, as defined by the difference between age at OGS and age at PHV, increased slightly in boys, whereas it decreased in girls.

Conclusion

Our finding of declining age at OGS and at PHV indicates a secular trend towards earlier sexual maturation of Danish children born between 1930 and 1969. Only minor changes were observed in duration of puberty assessed by the difference in ages at OGS and PHV.     

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.     

Causes of precocious puberty in children referred for evaluation in hospital conditions

INTRODUCTION: Symptoms of precocious puberty (PP) in children always arouse anxiety in their parents. Many children with PP are being hospitalized for the detailed diagnostic work-up. The aim of our study was to analyze the frequency of the variants of PP in children referred to our department. MATERIAL: Retrospective analysis of 119 children (103 girls and 16 boys) referred for hospitalization in the years 2003-2005 due to signs of precocious puberty was performed. RESULTS: Premature thelarche, benign variant of puberty, was diagnosed in 62 (53%) girls, in the mean age of 3.39 (+/- 2.33) years. Their mean height was within 0.7 +/- 1.1 SD. Premature pubarche was diagnosed 30 (25%) children--22 girls and 8 boys in the mean age was 7.24 (+/- 0.81) years. Their mean height was 1.3 +/- 1.0 SD and was significantly higher than normal (p < 0.0001). Premature menarche was diagnosed in 8 (7%) girls in the mean age 4.81 +/-2.26 years. Mean height in this group was normal for age (0.9+/-0.8 SD). PP was diagnosed in 19 (16%) children (11 girls and 8 boys) in the mean age 5.91 +/- 1.63 years. Mean height in this group was 1.6 +/- 0.7 SD, and was significantly higher than the mean for age (p<0.0005). GnRH-dependent type was present in 15 children, diagnosed as idiopathic in 9 girls and 1 boy. In 5 children (4 boys and 1 girl) pathology of central nervous system was found. In 4 children GnRH-independent precocious puberty was diagnosed--in 3 caused by congenital adrenal hyperplasia and in 1 boy by tumour of testis (leydigioma). CONCLUSIONS: Girls with precocious thelarche without growth acceleration present the benign variant of puberty and need clinical follow up only. Boys with clinical signs of precocious puberty should be carefully evaluated to rule out the organic cause.     

Age-related changes and sex differences in postural control adaptability in children during periodic floor oscillation with eyes closed

We investigated age-related changes and sex differences in adaptability of anticipatory postural control in children. Subjects comprised 449 children (4-12 years old) and 109 young adults (18-29 years old). Subjects stood with eyes closed on a force-platform fixed to a floor oscillator. We conducted five trials of 1-minute oscillation (0.5 Hz frequency, 2.5 cm amplitude) in the anteroposterior direction. Postural steadiness was quantified as the mean speed of the center of pressure in the anteroposterior direction (CoPy). In young adults, CoPy speed decreased rapidly until the third trial for both sexes. Adaptability was evaluated by changes in steadiness. The adaptability of children was categorized as "good," "moderate," and "poor," compared with a standard variation of the mean CoPy speed regression line between the first and fifth trials in young adults. Results were as follows: (1) anticipatory postural control adaptability starts to develop from age 6 in boys and 5 in girls, and greatly improves at age 7-8 in boys and 6 in girls; (2) the adaptability of children at age 11-12 (74% of boys and 63% of girls were categorized as "good") has not yet reached the same level as for young adults; (3) the adaptability at age 11-12 for girls is temporarily disturbed due to early puberty.     

Physical activity levels of normal-weight and overweight girls and boys during primary school recess

Objective: This study aimed to compare moderate‐to‐vigorous physical activity (MVPA) and vigorous physical activity (VPA) in normal‐weight and overweight boys and girls during school recess. Research Methods and Procedures: Four hundred twenty children, age 6 to 10 years, were randomly selected from 25 schools in England. Three hundred seventy‐seven children completed the study. BMI was calculated from height and weight measurements, and heart rate reserve thresholds of 50% and 75% reflected children's engagement in MVPA and VPA, respectively. Results: There was a significant main effect for sex and a significant interaction between BMI category and sex for the percent of recess time spent in MVPA and VPA. Normal‐weight girls were the least active group, compared with overweight boys and girls who were equally active. Fifty‐one boys and 24 girls of normal weight achieved the 40% threshold; of these, 30 boys and 10 girls exceeded 50% of recess time in MVPA. Eighteen overweight boys and 22 overweight girls exceeded the 40% threshold, whereas 8 boys and 8 girls exceeded the 50% threshold. Discussion: Overweight boys were significantly less active than their normal‐weight male counterparts; this difference did not hold true for girls. Even though nearly double the number of normal‐weight children achieved the 40% of MVPA during recess compared with overweight children, physical activity promotion in school playgrounds needs to be targeted not only at overweight but at other health parameters, as 40 overweight children met the 40% MVPA target proposed for recess.     

Age- and sex-related differences in brainstem auditory evoked potentials in secondary school students living in Northern European Russia

Brainstem auditory evoked potentials (BAEPs) were studied in 46 1st- to 11th-year students (22 boys and 24 girls) of a rural secondary school in Arkhangel’sk oblast. The objective of this work was to study age- and sex-related differences in BAEP characteristics in children and adolescents, living in the North and assess the BAEP characteristics as compared to reference values. In all three age groups of students, interpeak intervals I–III, III–V, and I–V characterizing the peripheral and central conduction times were shorter in girls than in boys. Interpeak interval III–V tended to increase with age only in boys (at puberty), with a significant increase in the latencies of waves I, III, and V. The BAEP characteristics in the subjects examined included a shorter peak latency and a greater amplitude of wave I (except senior students), relatively prolonged interpeak interval I–III, and more pronounced sex-related differences in BAEPs, especially at puberty. These findings show that it is necessary to revise regional reference values for BAEPs, differentiated by sex and age, including at puberty.     

Cardiorespiratory fitness predicts changes in adiposity in overweight Hispanic boys

We have previously shown that cardiorespiratory fitness predicts increasing fat mass during growth in white and African-American youth, but limited data are available examining this issue in Hispanic youth. Study participants were 160 (53% boys) overweight (BMI>or=85th percentile for age and gender) Hispanic children (mean+/-s.d. age at baseline=11.2+/-1.7 years). Cardiorespiratory fitness, assessed by VO2max, was measured through a maximal effort treadmill test at baseline. Body composition through dual-energy X-ray absorptiometry and Tanner stage through clinical exam were measured at baseline and annually thereafter for up to 4 years. Linear mixed models were used to examine the gender-specific relationship between VO2max and increases in adiposity (change in fat mass independent of change in lean tissue mass) over 4 years. The analysis was adjusted for changes in Tanner stage, age, and lean tissue mass. In boys, higher VO2max at baseline was inversely associated with the rate of increase in adiposity (beta=-0.001, P=0.03); this effect translates to a 15% higher VO2max at baseline resulting in a 1.38 kg lower fat mass gain over 4 years. However, VO2max was not significantly associated with changes in fat mass in girls (beta=0.0002, P=0.31). In overweight Hispanic boys, greater cardiorespiratory fitness at baseline was protective against increasing adiposity. In girls however initial cardiorespiratory fitness was not significantly associated with longitudinal changes in adiposity. These results suggest that cardiorespiratory fitness may be an important determinant of changes in adiposity in overweight Hispanic boys but not in girls.     

达斡尔族学生皮下脂肪发育的研究

作者内蒙古莫力达瓦达斡尔族自治旗１７５９例中小学生项项皮褶厚度及体脂发育情况进行了调查研究。结果表明：（１）达斡尔族学生进入青春期后,随着年龄的增长,男性躯干部皮变厚,四肢部皮褶变薄,女性躯干、四肢部皮褶均增厚。（２）１２岁后,女性皮褶厚度显著大于男性。（３）青春发育早期,男性体脂逐渐有下降,女性于１２－１４岁体脂迅速增加。（４）总体说来,达斡尔族学生并不偏于肥胖。     

Stature and body weight growth patterns from longitudinal data of Japanese children born during World War II

Stature and body weight data of 100 boys and 100 girls from 7 to 17 years of age in Shimodate City who were born during World War II were longitudinally analyzed. The children were significantly smaller and lighter throughout their growth period than those born 11 years after the end of the war. The correlation coefficient between statures at each age and at age 17 showed a gradual increase with increasing age, while that between statures at each age and at age 7 decreased with age. However, a drop in the correlation coefficient was found during puberty, at age 11 for girls and at age 13 for boys. Comparing the normalized distance from mean values of stature and body weight at age 7, at puberty, and at age 17, only 51% of the children continued to be in the same relative position for both height and weight, 6% of boys and 4% of girls showing a decreasing pattern for both and 4% of boys and 7% of girls showing an increasing pattern for both. Thus, about 60% of the children of either sex presented parallel stature and body weight growth patterns for ages from 7 to 17.     

Cardiorespiratory fitness and sedentary activities are associated with adiposity in adolescents

Objective: To determine whether physical activity, sedentary activities, and/or cardiorespiratory fitness are related to waist circumference in adolescents, as previously reported in adults. Research Methods and Procedures: The study subjects were a representative sample of Spanish adolescents (N = 2859; 1357 boys, 1502 girls; age, 13 to 18.5 years), all of whom were involved in the AVENA (Food and Assessment of the Nutritional Status of Adolescents) study. BMI, waist circumference, pubertal maturation status, and cardiorespiratory fitness were measured in all. Leisure‐time physical activity, sedentary activities, active commuting to school, and socioeconomic status were assessed by self‐reported questionnaires. Results: No relationship was found between leisure‐time physical activity and BMI or waist circumference. In contrast, and in both boys and girls and after adjustment for confounding variables, cardiorespiratory fitness was found to be inversely associated with waist circumference and BMI, independent of sedentary activities or physical activity (p ≤ 0.001). The maximum oxygen consumption explained 13% of the variance in waist circumference in boys and 16% in girls. Sedentary activities were independently and directly related to waist circumference in both boys and girls (p ≤ 0.05) and to BMI in boys (p ≤ 0.05). Sedentary activities explained 10% of the variance in waist circumference in boys and 18% in girls. The BMI‐adjusted waist circumference was inversely correlated with cardiorespiratory fitness in overweight‐obese boys (p ≤ 0.05) and showed a trend toward significance in girls (p ≤ 0.1). Discussion: Both moderate to high levels of cardiorespiratory fitness and sedentary activities, but not physical activity, are associated with lower abdominal adiposity, as measured by waist circumference.     

Diagnostic utility of a low-dose gonadotropin-releasing hormone test in the context of puberty disorders

OBJECTIVES: The 10-microg gonadotropin-releasing hormone (GnRH) test assesses pituitary gonadotroph responsiveness, whereas the 100-microg dose assesses maximal secretory capacity. Our aims were to establish normative data for the low-dose test in children and to evaluate the test in diagnosing common pubertal disorders. METHODS: We retrospectively classified 107 children who underwent 10-microg GnRH tests into normal prepubertal (20 boys, 10 girls), normal early pubertal (10 boys, 16 girls), constitutional delay of puberty (CDP, 13 prepubertal boys >12 years), hypogonadotropic hypogonadism (HH, 5 prepubertal boys >12 years), central precocious puberty (CPP, 19 girls) or premature thelarche/variant (13 girls). RESULTS: Peak LH response was higher in prepubertal boys >12 years compared with younger boys (p < 0.01) but showed no further change in early puberty. CDP boys had LH responses similar to prepubertal boys >12 years. HH boys showed an absent LH response which diagnosed HH with 100% sensitivity and 96% specificity. Thelarche girls had LH:FSH peak ratios lower than normal prepubertal (p = 0.001), pubertal (p < 0.05) or CPP (p = 0.001) girls. CONCLUSIONS: We have established normative values for the low-dose GnRH test in children. The test successfully differentiated HH from CDP in boys, and contributed to the differential diagnosis of CPP and premature thelarche in girls.     

Effect of computer work on the state of physiological functions in children aged 7 to 10 years

We studied the age- and sex-related functional characteristics of the central nervous system (CNS), cardiovascular system (CVS), lability of the visual sensory system, and mental capacity before and after a continuous computer work for 15 min in children aged 7, 8, 9, and 10 years. The results of the research showed that the resistance of the physiological systems of the body to loads associated with computer work increases in primary school children with age. We also observed sex-related differences: many parameters of functional performance during computer work at the age of 8 years were better in girls than in boys, which was due to a higher rate of development; at the age of 10 years, girls had a larger number of adverse changes in the functional state of the body compared with boys, which is possibly due to the onset of puberty.     

Age at Puberty and the Emerging Obesity Epidemic

Background

Recent studies have shown that puberty starts at younger ages than previously. It has been hypothesized that the increasing prevalence of childhood obesity is contributing to this trend. The purpose of this study was to analyze the association between prepubertal body mass index (BMI) and pubertal timing, as assessed by age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV), and the secular trend of pubertal timing given the prepubertal BMI.

Methodology/Principal Findings

Annual measurements of height and weight were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen municipality; 156,835 children fulfilled the criteria for determining age at OGS and PHV. The effect of prepubertal BMI at age seven on these markers of pubertal development within and between birth cohorts was analyzed. BMI at seven years was significantly inversely associated with age at OGS and PHV. Dividing the children into five levels of prepubertal BMI, we found a similar secular trend toward earlier maturation in all BMI groups.

Conclusion/Significance

The heavier both boys and girls were at age seven, the earlier they entered puberty. Irrespective of level of BMI at age seven, there was a downward trend in the age at attaining puberty in both boys and girls, which suggests that the obesity epidemic is not solely responsible for the trend.     

Muscle phosphocreatine kinetics in children and adults at the onset and offset of moderate-intensity exercise.

The splitting of muscle phosphocreatine (PCr) plays an integral role in the regulation of muscle O2 utilization during a "step" change in metabolic rate. This study tested the hypothesis that the kinetics of muscle PCr would be faster in children compared with adults both at the onset and offset of moderate-intensity exercise, in concert with the previous demonstration of faster phase II pulmonary O2 uptake kinetics in children. Eighteen peri-pubertal children (8 boys, 10 girls) and 16 adults (8 men, 8 women) completed repeated constant work-rate exercise transitions corresponding to 80% of the Pi/PCr intracellular threshold. The changes in quadriceps [PCr], [Pi], [ADP], and pH were determined every 6 s using 31P-magnetic resonance spectroscopy. No significant (P>0.05) age- or sex-related differences were found in the PCr kinetic time constant at the onset (boys, 21+/-4 s; girls, 24+/-5 s; men, 26+/-9 s; women, 24+/-7 s) or offset (boys, 26+/-5 s; girls, 29+/-7 s; men, 23+/-9 s; women 29+/-7 s) of exercise. Likewise, the estimated theoretical maximal rate of oxidative phosphorylation (Qmax) was independent of age and sex (boys, 1.39+/-0.20 mM/s; girls, 1.32+/-0.32 mM/s; men, 2.36+/-1.18 mM/s; women, 1.51+/-0.53 mM/s). These results are consistent with the notion that the putative phosphate-linked regulation of muscle O2 utilization is fully mature in peri-pubertal children, which may be attributable to a comparable capacity for mitochondrial oxidative phosphorylation in child and adult muscle.     

Aerobic parameters of exercise as a function of body size during growth in children

To examine the relationship between body weight in children and aerobic parameters of exercise, we determined the anaerobic threshold (AT), maximum O2 uptake (VO2max), work efficiency, and response time for O2 uptake (RT-VO2) in 109 healthy children (51 girls and 58 boys, range 6-17 yr old) using a cross-sectional study design. Gas exchange during exercise was measured breath by breath. The protocol consisted of cycle ergometry and a linearly increasing work rate (ramp) to the limit of the subject's tolerance. Both AT and VO2max increased systematically with body weight, whereas work efficiency and RT-VO2 were virtually independent of body size. The ratio of AT to VO2max decreased slightly with age, and its mean value was 60%. AT scaled to body weight to the power of 0.92, not significantly different from the power of 1.01 for VO2max. Thus both the AT and the VO2max increase in a highly ordered manner with increasing size, and as judged by AT/VO2max, the onset of anaerobic metabolism during exercise occurred at a relatively constant proportion of the overall limit of the gas transport system. We conclude that in children cardiorespiratory responses to exercise are regulated at optimized values despite overall change in body size during growth.     

Blood pressure during exercise in healthy children

During maximal dynamic exercise the blood pressure (BP) was measured in 497 healthy 9- to 18-year-old children. Systolic BP increased more in the postpubertal groups than in the prepubertal ones. It was also higher in the boys than in the girls of the same age. This was due to a higher work load in boys than girls. Twenty-two subjects had a systolic BP of 200 mmHg or more during the exercise. Only 2 had a resting systolic BP exceeding the mean by 2 standard deviations or more. Three postpubertal boys reached a systolic BP of 240 mmHg at heart rate 170. None had an elevated resting BP. It may be concluded that it cannot be predicted on the basis of the resting BP whether or not an individual is going to have an excessive increase in systolic BP during exercise. The increase in systolic BP to dangerous levels, e.g. 240 mmHg or more, during exercise can only be excluded by means of an individual exercise test.     

Precocious or early puberty and growth failure in girls treated for acute lymphoblastic leukaemia

We have studied 41 children with early or precocious puberty who have been treated for acute lymphoblastic leukaemia with prophylactic cranial irradiation (1,800-2,400 cGy) accompanied by intrathecal methotrexate and systemic chemotherapy. Mean age at radiotherapy was 3.9 years (range 1.7-7.7) in the girls and 4.8 years (range 2.6-7.8) in the boys. Mean age at the onset of puberty was 8.6 years (range 6.7-9.7) in the girls and 9.3 years (range 7.8-10.3) in the boys. Of the 41 children with early puberty (greater than 1.4 SD from the mean) 36 were females and 5 were males. 21 of the 36 girls had an absent or inadequate growth acceleration of puberty. 7 of 12 girls who had a pharmacological test of growth hormone (GH) secretion had GH insufficiency (peak level less than 20 mU/l). Early or precocious puberty combined with GH insufficiency may produce severe growth failure and we have used a treatment regimen of a gonadotrophin-releasing hormone analogue, in order to reduce the rate of epiphyseal maturation, combined with biosynthetic GH to increase or sustain growth rate. We have treated 4 girls in this manner. During a mean treatment period of 0.86 years, height SDS for bone age rose from a mean of -1.06 to -0.59. Longer treatment periods will be required to assess the effect on final height.     

Practice Variation in the Management of Girls and Boys with Delayed Puberty

Objective: Delayed puberty is a common condition, and typical management includes “watchful waiting” and/or sex-steroid therapy. We sought to characterize treatment practices and to assess provider comfort with the management of delayed puberty in girls and boys.Methods: A national survey of pediatric endocrine providers assessed definitions of delayed puberty, practices around sex-steroid therapy, reasons for treatment, and comfort in managing delayed puberty in girls and boys.Results: Of 184 respondents (12% participation rate), 64% and 71% used the traditional age cutoffs for defining delayed puberty of 13 years for girls and 14 years for boys, respectively. Nearly half (45%) of providers would treat boys relatively earlier than girls, compared to 18% who would treat girls relatively earlier (P<.0001). Providers were more likely to cite bone density as a reason to treat girls and alleviating patient and parental distress, accelerating growth, and “jump starting” puberty as reasons to treat boys. Greater experience in endocrine practice was associated with greater comfort managing delayed puberty in both boys and girls. Approximately 80% of providers agreed that clinical guidelines are needed for the management of delayed puberty.Conclusion: There is a high degree of variability in the clinical management of delayed puberty, and our results suggest that providers are more hesitant to treat girls compared to boys and have different reasons for treating each. It remains to be determined if these discrepancies in treatment are justified by biologic differences between girls and boys or represent nonevidence-based disparities in care.Abbreviation: U.S. = United States