Differences in the GH-IGF-I axis in children of different weight and fitness status.

OBJECTIVE: To determine if differences in the GH-IGF-I axis exist between children of high and low aerobic fitness who are obese or of normal weight. DESIGN: 124 children (ages 8-11) divided into four groups based on BMI and VO2max (mL O2/kg fat free mass(FFM)/min): normal weight--high-fit (NH), normal weight--low-fit (NL), obese--high-fit (OH), and obese--low-fit (OL). Height, weight, skinfolds, body mass index (BMI), body fat percentage and predicted VO2max (both ml/kg/min and ml/kg(FFM)/min) were assessed. Resting growth hormone (GH), total insulin-like growth factor 1 (total IGF-I), free insulin-like growth factor 1(free IGF-I), and insulin were measured using morning fasting blood samples. RESULTS: GH was greater in the NH group compared to the OL group only (p<0.01). No group differences existed for either total IGF-I (p=0.53) or free IGF-I (p=0.189). Insulin was greater in the OH and OL groups than the NH and NL groups (p<0.01). With groups combined (or overall), insulin and free IGF-I were related to fitness (insulin--ml/kg/min: r=-0.226, p<0.05 and ml/kg(FFM)/min: r=-0.212, p<0.05; free IGF-I--ml/kg/min: r=-0.219, p<0.01 and ml/kg(FFM)/min: r=-0.272, p<0.05). CONCLUSIONS: Fitness may contribute to the obesity related reduction of GH that may be involved with weight gain.

Relationship between cardiovascular risk factors and adipokines in adolescents.

UNLABELLED: This study evaluated the associations of adipokines with cardiovascular risk factors. SUBJECTS/METHODS: 60 normal weight (BMI ≤75th percentile) and 60 overweight (BMI ≥95th percentile) adolescents aged 10-14 years. Resting systolic and diastolic blood pressures (SBP, DBP) and waist circumference were obtained in duplicate. Circulating adiponectin, resistin, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), total cholesterol (TC), high-density lipoprotein (HDL), and triglycerides (TG) were measured from fasting plasma samples. RESULTS: Simple correlations showed that SBP was significantly related (p < 0.05) to adiponectin (r = -0.185), resistin (r = 0.207), and IL-6 (r = 0.238); HDL was significantly related to adiponectin (r = 0.398) and TNF-α (r = -0.227). TG was only related to adiponectin (r = -0.292, p < 0.05). Multiple regression models controlling for puberty and ethnicity indicated that adiponectin (R(2) = 0.152, p < 0.05), resistin (R(2) = 0.152, p < 0.05), and IL-6 (R(2) = 0.170, p < 0.05) were associated with SBP. The association between adiponectin and HDL was stronger in normal weight versus overweight adolescents (R(2) = 0.336, p < 0.05). None of the other models showed differences in the associations by weight status. CONCLUSIONS: In adolescents, SBP but not DBP was associated with most adipokines. HDL, but not TC, was also associated with some adipokines. TG were only associated with adiponectin. Associations were mostly related to adiposity.

Interrelationships among changes in leptin, insulin, cortisol and growth hormone and weight status in youth.

OBJECTIVE: While acute alterations in leptin, insulin, cortisol and growth hormone (GH) levels have been reported in children following weight change interventions, little is known about natural hormonal changes as children grow and how these changes are affected by unprovoked weight status changes. The purpose of this investigation was to compare changes in leptin, insulin, cortisol and GH levels in youth who maintained their weight status vs. those who moved from normal weight to overweight or vice versa. METHODS: Data were collected from 120 youth at baseline (9.8±1.0 years) and two years later. Participants were selected from a larger cohort to represent all scenarios of weight status: normal weight [>5(th) and <85(th) body mass index (BMI) percentile] at both time points (NN), overweight (≥85(th) BMI percentile) at both time points (OO), normal weight status who changed to overweight (NO) and overweight status which changed to normal weight (ON). Hormonal concentrations were measured from fasting venous blood. RESULTS: In youth who changed their weight status, there were significant associations (p<0.05) between changes in BMI percentile and changes in leptin, insulin and cortisol (partial R(2)=0.35, 0.13 and 0.11, respectively), after accounting for race, sex and changes in pubertal status and aerobic power. Our key findings were that youth who became overweight (NO) showed greater changes for leptin (+205% vs. -21%) and cortisol (-33% vs. +13%), p<0.05 than those who reverted from overweight to normal weight (ON). CONCLUSION: Natural changes in weight status in youth show a relationship with changes in leptin, insulin and cortisol levels and the hormonal changes appear to be more sensitive to increases, rather than reductions, in weight status.

A school-based intervention for diabetes risk reduction.

BACKGROUND: We examined the effects of a multicomponent, school-based program addressing risk factors for diabetes among children whose race or ethnic group and socioeconomic status placed them at high risk for obesity and type 2 diabetes. METHODS: Using a cluster design, we randomly assigned 42 schools to either a multicomponent school-based intervention (21 schools) or assessment only (control, 21 schools). A total of 4603 students participated (mean [+/- SD] age, 11.3 [+/- 0.6 years; 54.2% Hispanic and 18.0% black; 52.7% girls). At the beginning of 6th grade and the end of 8th grade, students underwent measurements of body-mass index (BMI), waist circumference, and fasting glucose and insulin levels. RESULTS: There was a decrease in the primary outcome--the combined prevalence of overweight and obesity--in both the intervention and control schools, with no significant difference between the school groups. The intervention schools had greater reductions in the secondary outcomes of BMI z score, percentage of students with waist circumference at or above the 90th percentile, fasting insulin levels (P=0.04 for all comparisons), and prevalence of obesity (P=0.05). Similar findings were observed among students who were at or above the 85th percentile for BMI at baseline. Less than 3% of the students who were screened had an adverse event; the proportions were nearly equivalent in the intervention and control schools. CONCLUSIONS: Our comprehensive school-based program did not result in greater decreases in the combined prevalence of overweight and obesity than those that occurred in control schools. However, the intervention did result in significantly greater reductions in various indexes of adiposity. These changes may reduce the risk of childhood-onset type 2 diabetes. (Funded by the National Institutes of Health and the American Diabetes Association; ClinicalTrials.gov number, NCT00458029.)

The Relationship between Changes in Weight Status and Insulin Resistance in Youth.

This study examined changes in insulin resistance (IR) in 120 youth over two years. IR was quantified via homeostatic model (HOMA-IR), and weight status changes were quantified via body mass index (BMI). When all participants were considered, the mean HOMA-IR and BMI increased 13.4% and 1.65 units, respectively. Change in BMI z-score and percent change in HOMA-IR were moderately associated (r = 0.39). Follow-up analyses were performed for the following weight groups: NN (normal at baseline and two years later), NO (normal to overweight), ON (overweight to normal), and OO (overweight at both points). The NO group had a greater change in HOMA-IR (+50%) compared to other groups: ON (-8%), NN (+2%), and OO (-0.1%) (P < .05). The association between changes in BMI z-score and HOMA-IR was r = 0.49 when only the NO and ON groups were included. These results reinforce the importance of preventing youth from becoming overweight to control IR.

Obesity and cholesterol in Japanese, French, and U.S. children.

The number of children at risk for overweight/obesity has increased dramatically in the last decade worldwide. This study compares measures of obesity (body mass index [BMI] and body fat percentage) and total cholesterol in 4,013 fourth-grade students from three countries, France, Japan, and the United States. Data were analyzed using t test, chi-square, and analysis of variance to determine differences between groups and by multiple linear regression. All variables differed significantly by group. BMI was highest in U.S. children. Body fat percentage was also highest in U.S. children and lowest in French children. Total cholesterol was highest in French children and lowest in U.S. White children. There were modest but significant associations between BMI and cholesterol in all groups except French children; associations varied by gender. Results indicate there was great variation in measures of obesity and cholesterol by country. The association between obesity and cholesterol may vary by culture, ethnicity, and gender.

Risk factors for type 2 diabetes in a sixth- grade multiracial cohort: the HEALTHY study.

OBJECTIVE: HEALTHY is a 3-year middle school intervention program designed to reduce risk factors for type 2 diabetes. The prevalence of diabetes risk factors at baseline in a cohort of 6,358 sixth-grade students is reported. RESEARCH DESIGN AND METHODS: Forty-two schools at seven U.S. sites were randomly assigned to intervention or control. Students participated in baseline data collection during fall of 2006. RESULTS: Overall, 49.3% of children had BMI >or=85th percentile, 16.0% had fasting blood glucose >or=100 mg/dl (<1% had fasting blood glucose >or=126 mg/dl), and 6.8% had fasting insulin >or=30 microU/ml. Hispanic youth were more likely to have BMI, glucose, and insulin levels above these thresholds than blacks and whites. CONCLUSIONS: Sixth-grade students in schools with large minority populations have high levels of risk factors for type 2 diabetes. The HEALTHY intervention was designed to modify these risk factors to reduce diabetes incidence.

Do surrogate markers for adiposity relate to cytokines in adolescents?

PURPOSE: To determine the associations between field-collected surrogates of adiposity and concentrations of resistin, tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), and adiponectin in youth. METHODS: Cross-sectional data from 60 normal weight and 60 overweight adolescents, ages 10-14 years, were retrospectively examined. Body mass index (BMI) percentile, sum of subscapular and triceps skinfolds (SSF), and waist circumference (WC) were used to classify weight status (BMI) or adiposity (SSF and WC). Percentiles for each surrogate were used for comparison groups. Fasting TNF-alpha, IL-6, resistin, and adiponectin concentrations were measured in plasma. RESULTS: Multiple regression models, controlling for sex and ethnicity, indicated that TNF-alpha was associated with BMI percentile (R(2) = 0.107, P < 0.05) and SSF (R(2) = 0.085, P < 0.05), whereas resistin was associated with SSF (R(2) = 0.118, P < 0.05). Adiponectin was associated with all 3 adiposity markers: BMI percentile (R(2) = 0.298, P < 0.05), SSF (R(2) = 0.297, P < 0.05), and waist (R(2) = 0.278, P < 0.05). Analyses of variance indicated higher TNF-alpha and lower adiponectin concentrations in youth with a BMI higher than the 95th percentile (P = 0.014; P < 0.001) or SSF higher than the 95th percentile (P = 0.025; P < 0.001). Youth with WC higher than the 90th percentile had higher resistin (P = 0.029), higher IL-6 (P = 0.028), and lower adiponectin (P < 0.001) concentrations. CONCLUSIONS: Of the 3 surrogates examined, differences in cytokine concentrations were mostly observed in youth who had WC percentiles higher than the 90th percentiles versus WC lower than the 75th percentiles. Alternatively, from the multiple-regression models SSF, an estimate of subcutaneous adiposity was the surrogate most consistently related to all cytokines, although the degrees of associations were low. The results suggest that although some surrogates were more strongly associated to certain cytokines, WC and SSF seemed more closely associated with cytokines than a BMI percentile indicating obesity.

Middle-school children's understanding of physical activity: "if you're moving, you're doing physical activity".

This qualitative descriptive study explored the understanding of physical activity from the perspectives of middle-school children (n = 12; ages 11-15 years) who participated in 15 collaborative exploratory meetings (approximately 1.5 hours/meeting) that were audiorecorded. Content analysis was completed; a pediatric nurse specialist and the participating children validated the findings. The children understood physical activity concretely, considering everything they did as physical activity based on their primary criterion of body movement. The children adeptly recalled activities and activity time duration, but struggled with categorizing the intensity of their activities. Domains of activity included home and school; social activities crossed both arenas. The study contributes to our knowledge of children's understanding of physical activity, highlighting the concreteness of the children's thinking, including their perspectives on evidence and conclusions based on their notions of evidence. Implications for nursing are discussed.

Influence of physical activity on change in weight status as children become adolescents.

UNLABELLED: Physical activity (PA) has been shown to have a positive effect on weight status, but habitual physical activity declines as youth age, yet some adolescents do not gain weight. PURPOSE: To determine if changes in weight status over 5 years during adolescence are associated with changes in PA levels. PROCEDURES: A longitudinal study of 377 girls and 388 boys tested initially at ages 9-11 years old and 5 years later (age 14-16 years old). The sample was grouped by initial and final weight status: N-N = youth with BMIs < 85(th) percentile at both points (n = 456; 60%); O-O = overweight youth with BMIs > or = 85(th) percentile at both time points (n = 186; 24%); O-N = overweight youth whose BMI declined to < 85(th) percentile (n = 66; 9%); N-O = normal weight youth who became overweight (n = 57; 7%). Stature and body mass were measured and habitual PA levels were obtained during the survey. RESULTS: Total PA scores, moderate (MPA) and vigorous activity (VPA) declined by 65-70% for all groups (p = 0.002). Girls in the O-N groups had less of a decline in PA than the girls in the N-O group (p < 0.05). No differences were evident for the boys. These results were consistent even when adjusted for developmental stage or race/ethnicity. DISCUSSION: Overweight children as young as 9 years old are already participating in less PA than normal weight youth. Although PA declined from childhood to adolescence, overweight girls with normalized weight status, had less of a decline in MPA or VPA than normal weight girls who became overweight. The data highlight the complexity of the interrelationship between physical activity and weight gain or loss. These data suggest that habitual physical activity levels, especially in girls, may have a role in adolescents attaining a healthy weight status.

Adolescents with metabolic syndrome have a history of low aerobic fitness and physical activity levels.

PURPOSE: Metabolic syndrome (MS) is a clustering of cardiovascular disease risk factors that identifies individuals with the highest risk for heart disease. Two factors that may influence the MS are physical activity and aerobic fitness. This study determined if adolescent with the MS had low levels of aerobic fitness and physical activity as children. METHODS: This longitudinal, exploratory study had 389 participants: 51% girls, 84% Caucasian, 12% African American, 1% Hispanic, and 3% other races, from the State of North Carolina. Habitual physical activity (PA survey), aerobic fitness (VO2max), body mass index (BMI), blood pressure, and lipids obtained at 7-10 y of age were compared to their results obtained 7 y later at ages 14-17 y. RESULTS: Eighteen adolescents (4.6%) developed 3 or more characteristics of the MS. Logistic regression, adjusting for BMI percentile, blood pressure, and cholesterol levels, found that adolescents with the MS were 6.08 (95%CI = 1.18-60.08) times more likely to have low aerobic fitness as children and 5.16 (95%CI = 1.06-49.66) times more likely to have low PA levels. CONCLUSION: Low levels of childhood physical activity and aerobic fitness are associated with the presence of the metabolic syndrome in adolescents. Thus, efforts need to begin early in childhood to increase exercise.

The association between insulin resistance and cytokines in adolescents: the role of weight status and exercise.

Increased adiposity is associated with insulin resistance (IR) and an inflammatory response in adults. We tested the hypotheses that cytokines associated with adiposity are also correlated with IR in early adolescents and that these relationships are moderated by weight status, levels of vigorous physical activity (VPA), or maximal aerobic power (pVO2max). Body mass, stature, and a fasting blood sample were obtained from 120 midpubertal adolescents (60 girls and 60 boys). Habitual VPA was obtained by a survey. Predicted VO2max was determined using a cycle ergometer test. Weight status was based on body mass index (BMI) percentiles (normal weight=BMI<75th percentile, overweight=BMI>95th percentile). Glucose, insulin, adiponectin, resistin, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 were measured; and IR index was based on the Homeostatic Model Assessment. Adiponectin, resistin, and TNF-alpha were associated with IR in all adolescents (R2=0.329, P<.001; R2=0.152, P=.001; and R2=0.141, P=.002; respectively); but interleukin-6 was not (R2=0.148, P=.114). The degree of association between adiponectin and IR was stronger in overweight than in normal-weight adolescents (P<.050). When regression models included weight status, neither TNF-alpha nor resistin was significantly related to IR (P>.050). Exercise did not moderate the association between these cytokines and IR. However, higher levels of VPA and/or pVO2max were associated with higher adiponectin, lower resistin, and lower TNF-alpha in at least one of the sexes. Our results indicate that the pathophysiology of obesity is already established in early adolescents. Increased adiposity, resulting in reduced adiponectin and increased resistin and TNF-alpha, may link these cytokines with IR in adolescents.

Insulin and weight status in adolescents: independent effects of intensity of physical activity and peak aerobic power.

Differences in insulin concentrations between normal weight or overweight adolescents (n = 437) were determined depending on their habitual physical activity (PA) and aerobic power (pVO2max). Tertiles were computed for PA (survey) and pVO2max (submaximal predicted cycle test). Independent of their weight, adolescents in the upper 2 tertiles for vigorous PA had lower insulin concentrations than those in the bottom tertile (p < .05). Adolescents in the top tertile for pVO2max expressed per kg fat-free mass also had lower insulin concentrations than those in the medium and bottom tertiles (p = .002). In youth, vigorous physical activity and aerobic power are associated with fasting insulin independent of weight status.

Influence of aerobic power and percent body fat on cardiovascular disease risk in youth.

PURPOSE: To describe how the relationships between aerobic power or percent body fat and cardiovascular disease (CVD) risk differ by age. METHODS: A sample of 1,824 young persons was divided into age groups (8-10, 11-13, and 14-16 years). Aerobic power (VO(2)max) was predicted using a submaximal cycle ergometer test, whereas percent body fat was assessed using the sum of skinfolds. Six CVD risk factors were measured: high-density lipoprotein cholesterol, total cholesterol, triglycerides, systolic and diastolic blood pressures, and fasting insulin. These risk factors were classified into risk categories (none, borderline, or at risk) and summed to determine a total CVD risk score. RESULTS: The percentages of participants with elevated risk scores was low, despite the high mean percent body fat and low mean aerobic power. Correlations among the six risk variables and either body fat or aerobic power were strongest in the youngest participants. In the multiple regression models adjusted for gender and SES, percent body fat was a stronger predictor of CVD risk score than aerobic power. The variance in risk score attributed to fatness was greatest in the youngest participants and declined in older age groups. CONCLUSIONS: Percent body fat had a greater influence on CVD risk than aerobic power. The relationship between body fat and total risk score was strongest in the youngest participants. Thus, interventions to improve CVD risk in youth should target body fat reduction beginning at an early age.

The children's computerized physical activity reporter: children as partners in the design and usability evaluation of an application for self-reporting physical activity.

The objectives of this three-phased study were to design and evaluate the usability of a computerized questionnaire, The Children's Computerized Physical Activity Reporter, designed with and for middle school children's self-report of physical activity. Study design was qualitative, descriptive, and collaborative, framed in a usability engineering model, with 22 participating children (grades 6-8; mean age, 12.5 years; range, 11-15 years) of three ethnic backgrounds. In Phase 1, children's understanding of physical activity and needs for reporting were determined, which were then translated in Phase 2 to the design features and content of the questionnaire; content validity, readability, and algorithm reliability were completed. Phase 3 involved children's evaluation of the questionnaire's usability (ease of use, efficiency, and aesthetics). The children all liked the questionnaire but identified several usability issues within instructions and reports. Working collaboratively with children was highly effective in ascertaining their understanding of physical activity and their self-reporting needs. Thus, the questionnaire's design was created from children's understanding of physical activity and their needs for recalling activities. The development of the questionnaire and its usability evaluation contribute to understanding children's physical activity and to the importance of designing for usability. Additional research is needed to ascertain reliability and validity of data derived from its use and to explore its usefulness in clinical or research venues.

Changing our future: obesity and the metabolic syndrome in children and adolescents.

Obesity, or overweight, in childhood is a major risk factor for the metabolic syndrome in adolescence, as the prevalence in US children tripled between 1970 and 2000. An increase in the metabolic syndrome in youth has followed this increase. In population-based studies, the prevalence of the syndrome ranged from 3.6% to 4.2%. In smaller studies with many overweight youth, the prevalence was 28.7% to 39.7% in those who were overweight and 49.7% in those who were severely obese. Overweight children are likely to have hyperinsulinemia, high-density lipoprotein cholesterol, high triglycerides, and hypertension, which are components of the metabolic syndrome. Nurses have an important role in screening for these metabolic syndrome components. Screening is especially important in boys and girls who are overweight and in girls with early menarche. A problem when screening children and adolescents is determining normative values, but guidelines are available. Prevention and management of the metabolic syndrome are not specific to the syndrome, but rather should be focused on the underlying problem of overweight and related problems that comprise the syndrome. We must use all avenues available to us, including influencing public and school policies, and pay close attention to overweight and metabolic syndrome components in our clinical practice, whether with children or adults. Preventing and managing the metabolic syndrome should be a family matter, and the necessary lifestyle changes will benefit the entire family.

Prevalence of abnormal lipid and blood pressure values among an ethnically diverse population of eighth-grade adolescents and screening implications.

OBJECTIVES: Our goal was to report the prevalence of elevated blood pressure and lipid levels among eighth-grade adolescents from 3 US locations and differences by gender, ethnicity, and overweight percentile group. METHODS: Fasting blood samples and blood pressure levels were obtained from 1717 eighth-grade students from 12 predominantly minority schools in 3 states (Texas, California, and North Carolina) during spring 2003. Age, gender, ethnicity, weight, and height were ascertained and BMI calculated. The presence of abnormal total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and triglycerides, prehypertension, hypertension, at risk for overweight, and overweight were calculated and compared with the findings of previous youth studies. We examined whether prevalence differed by gender, ethnicity, or BMI group. RESULTS: A total of 23.9% of participants had high blood pressure, 16.7% had borderline total cholesterol, 4.0% had high total cholesterol, 10.5% had borderline low-density lipoprotein cholesterol, 3.9% had high low-density lipoprotein cholesterol, 13.3% had low high-density lipoprotein cholesterol, and 17.2% had high triglycerides. A total of 19.8% of participants were at risk of overweight (BMI > or = 85th percentile, < 95th percentile) and 29% were overweight (BMI > or = 95th percentile). The prevalence of risk factors was associated (P < .05) with the overweight group and differed by age and gender. CONCLUSIONS: Prevalence of elevated blood pressure was higher in this sample than in previous national surveys in which subjects were less overweight. Associations between overweight and both elevated lipid and blood pressure levels suggest that adolescents overweight or at risk for overweight should be screened for elevated blood pressure and lipid levels.

Central obesity, the metabolic syndrome, and plasminogen activator inhibitor-1 in young adults.

PURPOSE: To determine the association of central obesity with the components of the metabolic syndrome (i.e., hyperinsulinemia, hypertension, hypertriglyceridemia, low levels of high-density lipoprotein cholesterol [HDL-C]) and plasma levels of plasminogen activator inhibitor-1 (PAI-1) in young adults. We hypothesized that central obesity as determined by waist circumference would be predictive of components of the metabolic syndrome and of PAI-1. DATA SOURCES: Participants in this descriptive study consisted of 85 healthy young adults aged 19-22 years, 62% women who fasted for 12 h prior to data collection in the General Clinical Research Center at a major university hospital medical center in the southeastern United States. CONCLUSIONS: The majority of the participants had one or more components of the metabolic syndrome (n= 43, 51%). Central obesity was present in 14.1% and was more common in women than men (chi(2)= 5.11; p= 0.021). Central obesity was significantly and positively correlated with elevated blood pressure (BP) and levels of insulin and PAI-1 while being negatively correlated with HDL-C. In multiple regression analyses, diastolic BP, insulin, and HDL-C were predictors of waist circumference (R(2)= 0.615). In a separate multiple regression, PAI-1 was predicted by waist circumference (R(2)= 0.331). IMPLICATIONS FOR PRACTICE: Many otherwise healthy young adults have one or more components of the metabolic syndrome. Assessment and institution of preventative measures for obesity and the components of the metabolic syndrome should begin in childhood. Furthermore, determination of waist circumference especially in young women may aid the practitioner to identify those at risk for the metabolic syndrome earlier in their disease trajectory. Furthermore, insulin resistance is believed to occur initially in the trajectory of the metabolic syndrome, making it a principal contender for suitable interventions to reduce risk for both type 2 diabetes and cardiovascular disease (CVD). Homeostatic model assessment for insulin resistance was used to assess for insulin resistance among the euglycemic participants. Recording the presence of insulin resistance will aid the practitioner in determining if a low-risk patient is in peril for development of type 2 diabetes and/or CVD. Early cardiovascular risk recognition is vital to clinical practice as it allows more time for the practitioner to counsel patients for the essential planning needed to make lifestyle changes.

Energy costs of physical activities in children and adolescents.

PURPOSE: The primary aim was to determine the energy expenditure (EE: kcal.kg(-1).h(-1)) in terms of caloric cost and metabolic equivalents of activities commonly performed by children and adolescents. Secondary aims were to determine at what age and pubertal developmental stage values approach those of adults. METHODS: In this descriptive study, 295 volunteer youth 8-18 yr of age completed 18 common physical activities (including rest) while EE was measured continuously with a portable metabolic system. Three sets of activities were assigned in random order for each subject. Activities ranged from television viewing and video game play to running and rope skipping. Pubertal development was estimated from a self-report questionnaire. RESULTS: At rest, VO(2) and EE were highest in the youngest children and decreased with advancing age and higher pubertal stage in both genders. The age-adjusted and puberty-adjusted energy expenditure values were generally lower than the compendium MET values for sedentary and moderate activities but were more varied for high-intensity activities. However, the ratio of activity EE to REE was comparable in children and adults. CONCLUSIONS: Energy expenditure per kilogram of body mass at rest or during exercise is greater in children than adults and varies with pubertal status, thus using the definition of a MET in the compendium of physical activities without adjustment is inadequate for energy estimation in children, until a child reaches Tanner Stage 5. However, the ratio of activity EE to resting EE in children appears to be similar or slightly less than in the compendium, suggesting that the compendium MET increments used with our adjusted EE values more closely approximate the true EE of activities in children than present adult norms.

The relationship between leptin, metabolic hormones, exercise and body composition in adolescents.

During adolescence, little is known about the relationship between leptin and metabolic hormones and how these are modified by body composition and exercise. This study determined: 1) the relationships between leptin, triiodothyronine, cortisol, and insulin, and 2) whether these relationships were modified by body composition and exercise. Fasting hormonal concentrations were assessed from 80 girls and 80 boys, aged 11-18 yr. In a multiple regression model, including the hormones and gender, only gender and insulin were significant predictors of leptin (R2 = 0.394; p <0.001). In a second model, including body fat and exercise, the levels of body fat, gender, free triidothyronine and cortisol explained 59.6% of the variance in leptin (p <0.05). The results suggest that in adolescents, the relationship between leptin and insulin is mediated by body fat. Leptin is negatively associated with cortisol in boys and with thyroid hormones in girls; these hormones possibly interact to sustain normal growth and maturation.