Obese adolescents exhibit a constant ratio of GH isoforms after whole body vibration and maximal voluntary contractions.

BACKGROUND: Growth hormone (GH) is a heterogeneous protein composed of several molecular isoforms, the most abundant ones being the 22 kDa- and 20 kDa-GH. Exercise-induced secretion of GH isoforms has been extensively investigated in normal-weight individuals due to antidoping purposes, particularly recombinant human GH (rhGH) abuse. On the other hand, the evaluation of exercise-induced responses in GH isoforms has never been performed in obese subjects. METHODS: The acute effects of whole body vibration (WBV) or maximal voluntary contraction (MVC) alone and the combination of MVC with WBV (MVC + WBV) on circulating levels of 22 kDa- and 20 kDa-GH were evaluated in 8 obese male adolescents [mean age ± SD: 17.1 ± 3.3 yrs.; weight: 107.4 ± 17.8 kg; body mass index (BMI): 36.5 ± 6.6 kg/m2; BMI standard deviation score (SDS): 3.1 ± 0.6]. RESULTS: MVC (alone or combined with WBV) significantly stimulated 22 kDa- and 20 kDa-GH secretion, while WBV alone was ineffective. In particular, 22 kDa- and 20 kDa-GH peaks were significantly higher after MVC + WBV and MVC than WBV. In addition, 22 kDa-GH (but not 20 kDa-GH) peak was significantly higher after MVC + WBV than MVC. Importantly, the ratio of circulating levels of 22 kDa- to 20 kDa-GH was constant throughout the time window of evaluation after exercise and similar among the three different protocols of exercise. CONCLUSIONS: The results of the present study confirm the ability of MVC, alone and in combination with WBV, to stimulate both 22 kDa- and 20 kDa-GH secretion in obese patients, these responses being related to the exercise workload. Since the ratio of 22 kDa- to 20 kDa-GH is constant after exercise and independent from the protocols of exercise as in normal-weight subjects, hyposomatotropism in obesity does not seem to depend on an unbalance of circulating GH isoforms. Since the present study was carried out in a small cohort of obese sedentary adolescents, these preliminary results should be confirmed in further future studies enrolling overweight/obese subjects with a wider age range.

Unexpectedly increased anorexigenic postprandial responses of PYY and GLP-1 to fast ice cream consumption in adult patients with Prader-Willi syndrome.

OBJECTIVE: The effect of eating rate on the release of anorexigenic gut peptides in Prader-Willi syndrome (PWS), a neurogenetic disorder clinically characterized by hyperphagia and excessive obesity, has not been investigated so far. DESIGN AND PATIENTS: Postprandial PYY and GLP-1 levels to fast (5 min) and slow (30 min) ice cream consumption were measured in PWS adult patients and age-matched patients with simple obesity and normal-weighted subjects. Visual analog scales (VASs) were used to evaluate the subjective feelings of hunger and satiety. RESULTS: Fast ice cream consumption stimulated GLP-1 release in normal subjects, a greater increase being observed with slow feeding. Fast or slow feeding did not change circulating levels of GLP-1 in obese patients, while, unexpectedly, fast feeding (but not slow feeding) stimulated GLP-1 release in PWS patients. Plasma PYY concentrations increased in all groups, irrespective of the eating rate. Slow feeding was more effective in stimulating PYY release in normal subjects, while fast feeding was more effective in PWS patients. Slow feeding evoked a lower hunger and higher satiety compared with fast feeding in normal subjects, this finding being not evident in obese patients. Unexpectedly, fast feeding evoked a lower hunger and higher satiety in PWS patients in comparison with slow feeding. CONCLUSIONS: Fast feeding leads to higher concentrations of anorexigenic gut peptides and favours satiety in PWS adult patients, this pattern being not evident in age-matched patients with simple obesity, thus suggesting the existence of a different pathophysiological substrate in these two clinical conditions.

Concurrent comparison of the measurement properties of generic and disease-specific questionnaires in obese inpatients.

BACKGROUND: The concurrent comparison of questionnaires assessing health-related quality of life in the same population is necessary for better appreciating their performance and to select the best instrument for a given purpose (e.g. clinical trials and observational studies). AIM: The aim of this study was to compare the measurement properties of two disease-specific and generic questionnaires: the Obesity-related Well-Being (ORWELL97), the Obesity-Related Disability test (TSD-OC), the EuroQoL, and the World Health Organization Quality of Life questionnaire. MATERIALS/SUBJECTS: Two-hundreds and forty-nine obese inpatients [age 47 (standard deviation, SD 15) years, body mass index 44.4 (SD 5.2) kg/m(2), 69 % female] completed the four questionnaires before and after a 3-week multidisciplinary weight reduction program. Standard measurement properties were calculated and compared. RESULTS: Intra-class correlation coefficient ranged from 0.73 to 0.90 for most of the instruments and subscales. The standard error of measurement ranged from 9 to 21 % for the generic instruments, and from 9 to 44 % for the specific questionnaires. Missing data and ceiling effects were found for TSD-OC. Responsiveness was similar for all the instruments. The correlations between the change scores of the instruments were small (<0.37). CONCLUSIONS: It was not possible to identify a "best" instrument, but overall the ORWELL97 seems to show better measurement properties. The two specific instruments measured different constructs and they did not show a clear superior performance compared to the generic questionnaires.

Effect of mechanical and metabolic factors on motor function and fatigue in obese men and women: a cross-sectional study.

BACKGROUND: Mechanical overload and poor quality of contractile elements related to metabolic abnormalities concur to motor disability of obesity. The independent contribution of these factors to motor dysfunction in obese individuals is scarcely defined. AIM: Aim of the study is to test the hypothesis that metabolic factors may independently affect motor function in obesity. METHODS: Leg maximum power output per unit body mass (W Mb), per unit fat-free mas (W FFM) and fatigue in daily functioning were assessed in 635 obese [body mass index (BMI)≥ 35 kg/m(2)] individuals (286 men, 349 women) aged 19-78 yr. The independent effects of age, BMI, insulin resistance and the five components of the metabolic syndrome on W Mb, W FFM and fatigue were evaluated by multivariate analysis. RESULTS: A multiple regression analysis revealed that in both genders W Mb (denoting the individual's performance capability during anaerobic tasks) was independently reduced by age (p<0.001), BMI (p<0.05-0.001) and abnormalities of glucose metabolism (p<0.06-0.01), while W FFM (representing the muscle intrinsic anaerobic capability) was affected only by age (p<0.001) and glucose metabolism impairment (p<0.06-0.01). In both genders fatigue was increased by age (p<0.001) and BMI (p<0.05-0.01), but augmented by low levels of HDL-cholesterol in men only (p<0.05). CONCLUSIONS: Besides depending on mechanical overload and age, low muscle power output in obese individuals was independently associated also with metabolic abnormalities related to impaired glucose homeostasis. Fatigue and performance, although similarly influenced by age and body mass excess, are affected by different metabolic factors.

Relationship between fatty liver and glucose metabolism: a cross-sectional study in 571 obese children.

BACKGROUND AND AIMS: Early onset type 2 diabetes mellitus (T2DM) is associated with obesity, insulin resistance and impaired beta-cell function. Non-alcoholic fatty liver disease (NAFLD) may be an independent risk factor for T2DM. We investigated the relationship between NAFLD and glucose metabolism in a large sample of obese children. METHODS AND RESULTS: A total of 571 obese children (57% males and 43% females) aged 8-18 years were consecutively studied at a tertiary care centre specialised in paediatric obesity. Liver ultrasonography was used to diagnose NAFLD after exclusion of hepatitis B and C and alcohol consumption. Oral-glucose tolerance testing (OGTT) was performed; insulin sensitivity was evaluated by using the insulin sensitivity index (ISI) and beta-cell function by using the ratio between the incremental areas under the curve (AUC) of insulin and glucose (incAUCins/incAUCglu). A total of 41% of the obese children had NAFLD. Impaired glucose tolerance or T2DM was present in 25% of the children with NAFLD versus 8% of those without it (p<0.001). Children with NAFLD had higher body mass index (BMI), fasting glucose, 120-min OGTT glucose, incAUCins/incAUCglu and lower ISI as compared with children without NAFLD (p≤0.002). At bootstrapped multivariable median regression analysis controlling for gender, age, pubertal status and BMI, NAFLD was an independent predictor of 120-min OGTT glucose and ISI, but not of incAUCins/incAUCglu. Similar findings were obtained using continuous liver steatosis as the predictor, instead of dichotomous NAFLD. CONCLUSION: NAFLD was present in 41% of our obese children and was associated with higher insulin resistance, but not with impaired beta-cell function.

Impact of percent body fat on oral glucose tolerance testing: a cross-sectional study in 1512 obese children.

BACKGROUND: Although an association between insulin resistance (IR) and body adiposity has been reported in obese children, this relationship has not been studied as thoroughly as in adults. AIM: We evaluated the association between oral glucose tolerance testing (OGTT) and percent body fat (PBF) in a sample of 1512 obese children followed at a Pediatric Obesity Clinic. SUBJECTS AND METHODS: Six hundred and twenty-eight male and 884 female obese children aged 6 to 18 yr were consecutively enrolled into the study. OGTT was performed with administration of 1.75 g of glucose per kg of body weight (up to 75 g). PBF was estimated through bioelectrical impedance analysis (BIA) using a population- specific formula recently published by our group. Multivariable median regression was used to evaluate the association between 4 outcomes [glucose area under the curve (AUC), insulin AUC, insulin sensitivity index (ISI), and insulinogenic index (IGI)] and gender, age or pubertal status and PBF. RESULTS: Median PBF was 52% (range 26 to 70%). After correction for age and gender, a 10% increase of PBF was associated with a decrease of -0.50 [95% confidence interval (CI): -0.65 to -0.35] units of ISI and an increase of 0.15 units of IGI (95%CI 0.07 to 0.24). CONCLUSIONS: In obese children, PBF is inversely associated with IR and directly associated to ß-cell response as detected by OGTT.

The cholestyramine-induced decrease of PYY postprandial response is negatively correlated with fat mass in obese women.

Obese patients have decreased fasting and postprandial levels of peptide YY (PYY), an anorexigenic peptide produced by the L cells of the gastrointestinal mucosa. Fatty nutrients are the most powerful stimulus for PYY release. Cholestyramine, an anion exchanger which adsorbs bile salts, reduces digestion of lipids. The aim of the present study was to investigate the effects of cholestyramine or placebo on PYY secretion in obese women administered a high-fat meal [n=8; age: 30.9±2.7 years; BMI: 47.3±3.3 kg/m2]. Postprandial PYY levels in obese women given placebo significantly increased in plasma at 30, 60, 90, and 120 min after meal ingestion. Cholestyramine administration significantly reduced postprandial PYY response at 15, 30, and 60 min. Percent fat mass (FM%) was negatively correlated with the percent increment of plasma PYY concentrations induced by meal administration at 30 min; conversely, there was a positive correlation between FM% and the percent decrement of plasma PYY concentrations induced by cholestyramine at the same time interval. These correlations failed to reach statistical significance when related to BMI. This study implies that in the obese state the altered PYY response to food consumption is a consequence of a dysfunction of L cells, which become less sensitive to the positive feedback effect of lipids.

Growth hormone and lactate responses induced by maximal isometric voluntary contractions and whole-body vibrations in healthy subjects.

BACKGROUND: In contrast with maximal voluntary resistance exercise, which is allegedly considered a potent GH stimulus in young subjects, evaluation of GH response to whole-body vibrations (WBV) has yielded conflicting results. METHODS: The acute effects of WBV alone (test A), maximal voluntary isometric contractions (MVC) (test B), and combination of WBV and MVC (test C) on serum GH and blood lactate (LA) levels were studied in 9 healthy adult males. Muscle soreness was assessed 24 and 48 h after exercise by a visual analogue scale. RESULTS: GH responses were significantly higher after tests B and C than after test A (GH peaks: 18.8 ± 9.5 ng/ml or 20.8 ± 13.7 ng/ml, respectively, vs 4.3 ± 3.5 ng/ml; p<0.05), with no difference between tests B and C. LA concentrations significantly increased after tests A, B, and C, being significantly higher after tests B and C than after test A (LA peaks: 2.0 ± 0.5 mmol/l or 6.7 ± 2.3 mmol/l, respectively, vs 7.6 ± 0.9 mmol/l; p<0.05). Peak LA values were significantly correlated to GH peaks in the 3 tests (r=0.48; p<0.05). Muscle soreness was significantly higher 24-48 h after tests B and C than after test A, no significant differences being present between tests B and C. CONCLUSIONS: WBV stimulates GH secretion and LA production, with no additive effect when combined with repeated isometric voluntary contractions. Optimization of protocols based on WBV seems important to maximize the positive effects of this intervention on the somatotropic function.

Changes in plasma levels of ghrelin, leptin, and other hormonal and metabolic parameters following standardized breakfast, lunch, and physical exercise before and after a multidisciplinary weight-reduction intervention in obese adolescents.

OBJECTIVE: To investigate in severely obese adolescents the effects of a 3-week multidisciplinary weight-reduction intervention involving moderate energy restriction, individualised physical activity and behavior therapy on the response of some hormonal and metabolic parameters to meals and exercise. DESIGN: Clinical longitudinal study on inpatients in a specialised institution. SUBJECTS: A total of 20 obese adolescents (10 boys and 10 girls) aged 12-17 yr [body mass index (BMI): 37.7±6.1 kg/m2; fat mass (FM): 44.8±13.2 kg]. MEASUREMENTS: The changes in plasma concentration of leptin, ghrelin, GH, IGF-I, insulin, glucose, and non-esterified fatty acids (NEFA) in response to standardised meals and exercise bouts were measured before and after the weight-reduction intervention. At the same times, body composition was assessed by bioelectrical impedance as well as appetite sensations using a visual analog scale. RESULTS: At the end of the intervention, the adolescents had lost body weight and FM (expressed both in kg and %) (p<0.05), without any significant fat-free mass loss (in % terms). In response to both meals and exercise, after the 3-week intervention, plasma leptin concentration decreased significantly (p<0.05), whereas the other hormones (insulin, ghrelin, GH, and IGF-I) and metabolic parameters (glucose and NEFA) did not change. Interestingly, appetite was not affected by the intervention. CONCLUSION: This 3-week multidisciplinary intervention in obese adolescents induced a significant body weight loss with beneficial changes in body composition. However, despite there being no change in metabolic parameters and ghrelin in response to meals and exercise after the intervention, plasma concentrations of leptin were decreased. The failure of ghrelin levels to increase by this approach might explain the good control of appetite observed at the end of the study.

Factor analysis of metabolic syndrome components in severely obese girls and boys.

AIMS AND METHODS: Factor analysis is a multivariate correlation technique frequently employed to characterise the aggregation of abnormalities underlying the metabolic syndrome (MS), but scarcely used in obese adolescents. Aim of the study was to investigate the clustering of anthropometric and metabolic variables related to the MS in 487 obese pubertal adolescents (140 boys, 347 girls) in the range of age 11-18 yr employing the factor analysis with exploratory approach. RESULTS: Principal component analysis reduced 11 correlated physiological variables to 4 uncorrelated factors that explained 68.7% of the variance in the original parameters in boys, and 68.4% in girls. In boys, these factors were: obesity/ hypertension, insulin resistance, dyslipidemia, and hyperglycemia, with elements related to obesity and fat distribution loaded also in dyslipidemia and insulin resistance. In girls no commonalities were detected, but elements of dyslipidemia and insulin resistance were loaded in a single factor, whereas elements of obesity and hypertension were loaded in separate factors. CONCLUSIONS: The identification of 4 independent factors suggests a multiple physiological origin of the MS also in youngsters. The measures of adiposity were correlated with development of hypertension, insulin resistance, and dyslipidemic phenomena in boys only, whereas in girls anthropometric measures were not correlated with any tested component of the MS, possibly disclosing the protective effect of female sex hormones in the juvenile age span.

GH responses to whole body vibration alone or in combination with maximal voluntary contractions in obese male adolescents.

BACKGROUND: The anabolic, lipolytic and anti-inflammatory effects of exercise-stimulated GH secretion could be usefully exploited in the multidisciplinary rehabilitative programs of obese patients, who are reported to suffer from hyposomatotropism. To date, evaluation of GH responses to whole body vibration (WBV) in combination with maximal voluntary contractions (MVC) has been performed in normal-weight subjects, but not obese patients. Thus, aim of the present study was to investigate the effects of WBV and MVC, alone and combined, on GH responsiveness in obese subjects. METHODS: The acute effects of WBV or MVC alone and the combination of MVC with WBV (MVC + WBV) on serum GH, cortisol and IGF-I and blood lactate (LA) levels were evaluated in 8 obese male adolescents [mean age ±â€¯SD: 17.1 ±â€¯3.3 yrs.; weight: 107.4 ±â€¯17.8 kg; body mass index (BMI): 36.5 ±â€¯6.6 kg/m2; BMI standard deviation score (SDS): 3.1 ±â€¯0.6]. RESULTS: WBV and MVC (alone or combined) significantly stimulated GH secretion. In particular, GH peaks and net areas under the curve (nAUCs) were significantly higher after MVC + WBV and MVC than WBV, without any difference between MVC + WBV and MVC groups; anyway, an additive effect on GH levels immediately after the execution of MVC + WBV test was found in comparison with MVC test. LA peaks significantly increased after each exercise (vs. basal condition), being significantly higher after MVC + WBV and MVC than WBV, without any difference between MVC + WBV and MVC groups. Peak LA values were significantly correlated with GH peaks and nAUCs. In contrast to the unchanged IGF-I levels, MVC + WBV and MVC (but not WBV) significantly stimulated cortisol secretion. CONCLUSIONS: The results of the present study confirm the ability of MVC and WBV to stimulate GH secretion in obese patients. Rehabilitative programs combining different types of exercise eliciting a potent GH response seem to be important to counteract the hyposomatotropism of obese patients. Due to its limited stress upon joints without provoking an excessive fatigue, WBV could be usefully employed in the initial stages of a weight loss program alone or in combination with more potent GH releasing stimuli, such as MVC.

Comparison of predictive equations for resting energy expenditure in severely obese Caucasian children and adolescents.

The objective of the present study was to compare resting energy expenditure (REE) calculated by different predictive equations (McDuffie, Derumeaux, Tverskaya, Schofield, FAO/WHO/ UNU, Harris-Benedict and Lazzer-Sartorio) to REE measured in severely obese Caucasian children and adolescents. Two hundred and eighty-seven obese children and adolescents (121 males, 166 females, mean age: 14.5 yr, mean body mass index (BMI) z-score: 3.3) participated in this study. REE was measured (MREE) by indirect calorimetry and body composition by bioelectrical impedance analysis. The FAO/WHO/UNU equations showed the lowest mean difference between predicted resting energy expenditure (PREE) and MREE (+0.2%, p=ns), but the higher SD (+/-1.16 MJ) and the PREE were accurate in 26% of subjects. The Tverskaya, Derumeaux and Harris-Benedict equations significantly underestimated REE in all children and adolescents (-7.6, -4.1, and -2.4%, respectively, p<0.05), while the Schofield and McDuffie equations overestimated REE (+2.5, +5 and 25%, respectively, p<0.05). By contrast, the Lazzer-Sartorio equations showed the greater agreement and accuracy (in 55% of subjects) between mean PREEs and MREE for all children and adolescents, as well as for boys and girls (+1.6%, p=ns). In conclusion, Lazzer-Sartorio equations showed an accurate estimation of REE in groups of severely obese children and adolescents, resulting in lower mean differences and SD and higher accuracy between PREE and MREE than the other equations considered in this study.

Hedonic eating in Prader-Willi syndrome is associated with blunted PYY secretion.

Hedonic and homeostatic hunger represent two different forms of eating: just for pleasure or following energy deprivation, respectively. Consumption of food for pleasure was reported to be associated with increased circulating levels of both the orexigenic peptide ghrelin and some specific endocannabinoids in normal-weight subjects and patients with morbid obesity. To date, the effects of palatable food on these mediators in Prader-Willi syndrome (PWS) are still unknown. To explore the role of some gastrointestinal orexigenic and anorexigenic peptides and endocannabinoids (and some related congeners) in chocolate consumption, we measured changes in circulating levels of ghrelin, cholecystokinin (CCK), peptide YY (PYY), anandamide (AEA), 2-arachidonoyl-glycerol (2-AG), palmitoylethanolamide (PEA) and oleoylethanolamide (OEA) in eight satiated adult PWS patients after consumption of chocolate and, on a separate day, of a non-palatable isocaloric food with the same macronutrient composition. Evaluation of hunger and satiety was also performed by visual analogic scale. The anticipatory phase and the consumption of food for pleasure were associated with decreased circulating levels of PYY. An increase in PEA levels was also observed. By contrast, circulating levels of ghrelin, CCK, AEA, 2-AG and OEA did not differ before and after the exposure/ingestion of either chocolate or non-palatable foods. Hunger and satiety were similar in the hedonic and non-palatable sessions. In conclusion, when motivation to eat is promoted by highly palatable foods, a depressed post-prandial PYY secretion is observed in PWS. Although preliminary, these findings seem to hypothesize a possible role of PYY agonists in the management of PWS patients. Abbreviations: AEA, Anandamide; 2-AG, 2-arachidonoyl-glycerol; CB1, cannabinoid receptor type 1; OEA, oleoylethanolamide; PEA, palmitoylethanolamide; PWS: Prader-Willi syndrome; VAS, visual analog scales.

Prediction of basal metabolic rate in obese children and adolescents considering pubertal stages and anthropometric characteristics or body composition.

BACKGROUND/OBJECTIVES: To develop and crossvalidate new equations for predicting basal metabolic rate (BMR) in obese children and adolescents in relation to pubertal stages, anthropometric characteristics or body composition. SUBJECTS/METHODS: A total of 1696 obese Caucasian children and adolescents (mean body mass index z-score: 3.5±0.8) participated in this study. BMR was determined by indirect calorimetry and fat-free mass (FFM) and fat mass (FM) by bioelectrical impedance analysis. Equations were derived by stepwise multiple regression analysis using a calibration cohort of 848 subjects, and the equations were crossvalidated with a Bland and Altman method in the remaining 848 subjects. RESULTS: Two new specific equations based on gender (1: males; 0: females), pubertal stages (from 1 to 5, assessed according Marshall & Tanner methods) and body weight (BW, kg), stature (m) or body composition (kg) were generated as follows: (1) BMR=(BW × 0.044)+(stature × 2.836)-(pubertal stage × 0.148)+(gender × 0.781)-0.551 (adjusted coefficient of determination (R(2)adj)= 0.69 and root mean squared error (RMSE)=0.954 MJ); (2) BMR=(FFM × 0.082)+(FM × 0.037)-(pubertal stage × 0.125)+(gender × 0.706)+2.528 (R(2)adj= 0.70 and RMSE=0.943 MJ). In the crossvalidation group, mean-predicted BMR was not significantly different from the mean-measured BMR (MBMR) for all children and adolescents, as well as for boys and girls (difference<2 %), and the limits of agreement (±2 s.d.) were +1.95 and -1.98 MJ/d, (P=NS). BMR was predicted accurately (90-110% of MBMR) in 67% of subjects. CONCLUSION: The new prediction equations considering the pubertal stages allow an accurate and more appropriate (vs equations using chronological age) estimation of BMR in obese children and adolescents.

Comparison of dual-energy X-ray absorptiometry, air displacement plethysmography and bioelectrical impedance analysis for the assessment of body composition in morbidly obese women.

BACKGROUND/OBJECTIVES: We evaluated the agreement of air displacement plethysmography (ADP) and bioelectrical impedance analysis (BIA) with dual-energy X-ray absorptiometry (DXA) for the assessment of percent fat mass (%FM) in morbidly obese women. SUBJECTS/METHODS: Fifty-seven women aged 19-55 years and with a body mass index (BMI) ranging from 37.3 to 55.2 kg/m(2) were studied. Values of %FM were obtained directly from ADP and DXA, whereas for BIA we estimated fat-free mass (FFM) from an equation for morbidly obese subjects and calculated %FM as (weight-FFM)/weight. RESULTS: The mean (s.d.) difference between ADP and DXA for the assessment of %FM was -2.4% (3.3%) with limits of agreement (LOA) from -8.8% to 4.1%. The mean (s.d.) difference between BIA and DXA for the assessment of %FM was 1.7% (3.3%) with LOA from -4.9% to 8.2%. CONCLUSION: ADP-DXA and BIA-DXA are not interchangeable methods for the assessment of body composition in morbidly obese women.

GH responses to two consecutive bouts of neuromuscular electrical stimulation in healthy adults.

BACKGROUND: It is well established that repeated GHRH administration or repeated voluntary exercise bouts are associated with a complete blunting of GH responsiveness when the administration of the second stimulus follows the first one after a 2-h interval. AIM: To evaluate GH responses to neuromuscular electrical stimulation (NMES) in healthy adults. METHODS: Six volunteers (mean age+/-s.d. 31.7+/-5.5 years) were studied before and after two consecutive bouts of NMES exercise (a series of 20 contractions at the maximum of individual tolerance, frequency: 75 Hz, pulse duration: 400 mus, on-off ratio: 6.25-20 s) administered at a 2-h interval. RESULTS: Baseline GH levels (mean: 0.3+/-0.2 ng/ml) significantly increased after the first NMES (peak: 4.2+/-3.7 ng/ml), with a complete normalization after 120 min (0.3+/-0.3 ng/ml). The administration of the second bout of NMES of comparable characteristics also resulted in a significant GH increase (peak: 5.2+/-3.2 ng/ml), which was comparable with that observed after the previous one. GH net incremental area under the curve after the first and second bouts of NMES were not significantly different (155.1+/-148.5 and 176.9+/-123.3 ng/ml per h, P=0.785). CONCLUSIONS: Unlike repeated pharmacological stimuli and voluntary exercise bouts, subsequent sessions of NMES administered at a 2-h interval appear to circumvent feedback mechanisms and to re-induce the GH responses, thus indicating a possible different underlying mechanism elicited by different GH-releasing stimuli.

Age- and gender-related variations of leg power output and body composition in severely obese children and adolescents.

A low level of physical activity is considered to be both a determinant factor and a negative effect of childhood obesity, notably contributing to its development and maintenance, but the motor capabilities of obese children of different ages have scarcely been evaluated. The purpose of the study is to depict the general trends of muscle anaerobic performance in a cohort of obese Italian children. Three-hundred-six obese children (141 males, 165 females), aged 10-17 yr with body mass index (BMI) range 28.9-62.0 kg/m2 (mean BMI z-score: 2.71 +/- 0.56 SD; range: 1.6-4.5), were cross-sectionally studied. Lower limb maximal anaerobic power output (W) was assessed with the Margaria stair climbing test, and a consistent subgroup of 77 subjects (37 males, 40 females) was also selected for accessory study of body composition with bioimpedance analysis (BIA), in order to evaluate the relationships between fat-free mass (FFM) and W. In both genders, W increased significantly for effect of age and degree of obesity [three-factor multivariate analysis of variance (MANOVA), p < 0.001], but, while no difference was found between boys and girls in the age groups of 10-11 and 12-13 yr (post-hoc Tukey test, p > 0.05), boys in the age groups 14-15 and 16-17 yr were more powerful than girls of the same age (p < 0.001), wherease the relative W per unit body mass W BM) was higher (two-factor MANOVA) in boys (p < 0.01) of all age groups (p > 0.05). In the subgroup tested with BIA, the amount of FFM increased significantly [two-factor analysis of variance (ANOVA), p < 0.001] according to age, being similar in males and females in lower age groups (post-hoc Tukey test, p > 0.05), but higher in boys of older groups (post-hoc Tukey test, p < or = 0.001), so that all differences between age groups and genders disappeared (two-factor MANOVA) when W was expressed per unit FFM (p > 0.05). A significant linear correlation was found between FFM and W, (R2 = 0.66, p < 0.001). In conclusion, no difference in absolute W can be detected between obese boys and girls up to the age of 13, but W differences observed in older age groups appear to be consistent with a concomitant gender-related variation in body composition. The capability of performing external work in short bursts (as represented by trends in WBM) is lower in girls of all ages, and merits consideration on the clinical ground.

Surface melting of the vortex lattice.

We discuss the effect of an (ab) surface on the melting transition of the pancake-vortex lattice in a layered superconductor within a density functional theory approach. Both discontinuous and continuous surface melting are predicted for this system, although the latter scenario occupies the major part of the low-field phase diagram. The formation of a quasiliquid layer below the bulk melting temperature inhibits the appearance of a superheated solid phase, yielding an asymmetric hysteretic behavior which has been seen in experiments.

Dissociation of vortex stacks into fractional-flux vortices.

We discuss the zero field superconducting phase transition in a finite system of magnetically coupled superconducting layers. Transverse screening is modified by the presence of other layers resulting in topological excitations with fractional flux. Vortex stacks trapping a full flux and present at any finite temperature undergo a dissociation transition which corresponds to the depairing of fractional-flux vortices in individual layers. We propose an experiment with a bilayer system allowing us to identify the dissociation of bound vortex molecules.