Exercise performance and magnetic resonance imaging-determined thigh muscle volume in children

This study examined the relationships between thigh muscle volume (TMV) and aerobic and anaerobic performance in children. A total of 32 children, 16 boys and 16 girls, aged 9.9 (0.3) years completed a treadmill running test to exhaustion for the determination of peak oxygen uptake (peak V˙O₂) and a Wingate Anaerobic Test (WAnT) for the determination of peak power (PP) and mean power (MP). The volume of the right thigh muscle was determined using magnetic resonance imaging. TMV was not significantly different in boys and girls [2.39 (0.29) l vs 2.18 (0.38) l, P > 0.05]. Peak V˙O₂ and MP were significantly higher in boys than girls (P < 0.01) whether expressed in absolute, mass-related or allometrically scaled terms. Absolute PP was not significantly different in boys and girls but mass-related and allometrically scaled values were higher in boys (P < 0.01). TMV was correlated with absolute peak V˙O₂, PP and MP in both sexes (r = 0.52–0.89, P < 0.01). In boys, mass-related PP was correlated with TMV (r =0.53, P < 0.01), and in girls mass-related peak V˙O₂ was correlated with TMV (r = −0.61, P < 0.01). However, in neither sex were allometrically scaled peak V˙O₂, PP or MP correlated with TMV (P > 0.05). There were no significant differences between boys and girls in terms of peak V˙O₂, PP or MP when expressed in a ratio to TMV or allometrically scaled TMV. In conclusion, this study has demonstrated that, when body size is appropriately accounted for using allometric scaling, TMV is unrelated to indices of aerobic and anaerobic power in 10-year-old children. Furthermore, there appear to be no qualitative differences in the muscle function of boys and girls in respect of aerobic and anaerobic function. Accepted: 4 February 1997     

Gender-related differences in maximum mechanical power output in short-term activities in children and adolescents

The study was designed to examine the gender-related differences in maximum mechanical power output in various short-burst activities during growth. The subject sample consisted of four subgroups: 9 boys (14.11 +/- 0.6 yr), 9 boys (10.67 +/- 0.71 yr), 7 girls (14.29 +/- 0.49 yr), 7 girls (10.57 +/- 0.54 yr). We measured peak power (PP), mean power (MP), fatigue index (FI) during 30-s WAnT, squat jump height (SJH) and power (SJP), and counter movement jump height (CMJH) and power (CMJP), maximum speed over 20-metre distance (S20). Lactation concentration was measured in the 3rd and 5th minutes after the WAnT Ratio normalisation and ANCOVA were used to remove the influence of the differences in muscle (MM) and body mass (BM). Male adolescents had higher absolute values of PP (P < 0.05), MP (P < 0.05) than female. Ratio normalisation showed that boys had higher PP/BM (P < 0.05), PP/MM (P < 0.05), MP/BM (P < 0.05), MP/MM (P < 0.06) than girls. The ANCOVA adjustment for MM showed differences between genders in PP (P < 0.001), MP (P < 0.001), SJH (P < 0.05), SJP (P < 0.05) and CMJP (P < 0.001), whereas the ANCOVA adjustment for BM showed differences only in PP (P < 0.001), MP (P < 0.001). Prepubertal boys had higher absolute values only in SJP (P < 0.05). We concluded that variations in body composition could not be the only key to gender-related differences in power output in short-burst activities.     

Mechanically braked elliptical Wingate test: modification considerations, load optimization, and reliability

The 30-second, all-out Wingate test evaluates anaerobic performance using an upper or lower body cycle ergometer (cycle Wingate test). A recent study showed that using a modified electromagnetically braked elliptical trainer for Wingate testing (EWT) leads to greater power outcomes because of larger muscle group recruitment. The main purpose of this study was to modify an elliptical trainer using an easily understandable mechanical brake system instead of an electromagnetically braked modification. Our secondary aim was to determine a proper test load for the EWT to reveal the most efficient anaerobic test outcomes such as peak power (PP), average power (AP), minimum power (MP), power drop (PD), and fatigue index ratio (FI%) and to evaluate the retest reliability of the selected test load. Delta lactate responses (ΔLa) were also analyzed to confirm all the anaerobic performance of the athletes. Thirty healthy and well-trained male university athletes were selected to participate in the study. By analysis of variance, an 18% body mass workload yielded significantly greater test outcomes (PP = 19.5 ± 2.4 W·kg, AP = 13.7 ± 1.7 W·kg, PD = 27.9 ± 5 W·s, FI% = 58.4 ± 3.3%, and ΔLa = 15.4 ± 1.7 mM) than the other (12-24% body mass) tested loads (p < 0.05). Test and retest results for relative PP, AP, MP, PD, FI%, and ΔLa were highly correlated (r = 0.97, 0.98, 0.94, 0.91, 0.81, and 0.95, respectively). In conclusion, it was found that the mechanically braked modification of an elliptical trainer successfully estimated anaerobic power and capacity. A workload of 18% body mass was optimal for measuring maximal and reliable anaerobic power outcomes. Anaerobic testing using an EWT may be more useful to athletes and coaches than traditional cycle ergometers because a greater proportion of muscle groups are worked during exercise on an elliptical trainer.     

Practice effect of the Wingate anaerobic test

The purpose of this study was to investigate the presence of a practice effect on the Wingate anaerobic test (WAnT). Twenty-five young adult men (mean age = 20 years) performed 2 trials of the WAnT, which were separated by 7 days. Mean peak power (PP) and mean power (MP) for trials I and II were compared using a 1-way repeated measures analysis of variance to determine if a practice effect existed. Mean PP and MP scores were significantly higher (p < 0.025) on trial II (867.64 and 634.68 W for PP and MP, respectively) than on trial I (764.48 and 604.92 W), indicating that a practice effect occurred. Effect size (Cohen's d) for PP and MP was 0.72 and 0.35, indicating a large effect and small effect, respectively. Therefore, at least 1 full administration should be performed prior to a baseline power output measurement.     

Physiological and sport-specific skill response of olympic youth soccer athletes

Although many studies have been focused on soccer athletes, no comprehensive studies have been conducted on adolescent soccer athletes in the United States. Therefore, the purpose of this study was to quantify the physiological and sport-specific skill characteristics of Olympic Developmental Program (ODP) soccer athletes by age group and game experience. Following written, informed consent, 59 male athletes (age = 14.6 +/- 2.0 years; wt = 60.5 +/- 1.4 kg; ht = 172.4 +/- 1.2 cm) completed a battery of tests to determine aerobic power (VO(2)max), heart rate (HR(max)), ventilation (VE(max)), respiratory exchange ratio (RER), anaerobic threshold (AT), blood pressure (BP(rest/max)), anaerobic power/capacity [peak power (PP), mean power (MP), total work output (TWO), fatigue index (FI)], leg power [vertical squat jump (VJS), countermovement jump (VJC)], body composition [percent body fat (%BF), lean body mass (LBM)], joint range of motion (trunk, back, hip, knee, and ankle), and agility/sport-specific skills (T-test, line drill test, juggling test, Johnson wall volley, and modified-Zelenka circuit). Factor analyses with subsequent multivariate analyses of variance (MANOVAs) indicated significant main effects across age (p = 0.0001) but not by game experience (p = 0.82). Older athletes exhibited greater height, weight, LBM, VE(max), Time(max), PP, TWO, and VSJ values than younger athletes. Although not significant, there were differences with increasing age in the agility tests (T-test, wall volley, and juggling test). In conclusion, improvements in anaerobic power, agility, and sport-specific skill should be addressed at this developmental level of competition.     

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.     

A new approach to assessing maximal aerobic power in children: the Odense School Child Study

In two experiments maximal aerobic power (VO2max) calculated from maximal mechanical power (Wmax) was evaluated in 39 children aged 9-11 years. A maximal multi-stage cycle ergometer exercise test was used with an increase in work load every 3 min. In the first experiment oxygen consumption was measured in 18 children during each of the prescribed work loads and a correction factor was calculated to estimate VO2max using the equation VO2max = 12.Wmax + 5.weight. An appropriate increase in work rate based on height was determined for boys (0.16 W.cm-1) and girls (0.15 W.cm-1) respectively. In the second experiment 21 children performed a maximal cycle ergometer exercise test twice. In addition to the procedure in the first experiment a similar exercise test was performed, but without measurement of oxygen uptake. Calculated VO2max correlated significantly (p less than 0.01) with those values measured in both boys (r = 0.90) and girls (r = 0.95) respectively, and the standard error of estimation for VO2max (calculated) on VO2max (measured) was less than 3.2%. Two expressions of relative work load (%VO2max and %Wmax) were established and found to be closely correlated. The relative work load in %VO2max could be predicted from the relative work load in %Wmax with an average standard error of 3.8%. The data demonstrate that calculated VO2max based on a maximal multi-stage exercise test provides an accurate and valid estimate of VO2max.     

The relationship of lean limb volume to performance in the handgrip and standing long jump tests in boys and girls, aged 11.6–13.2 years

Twenty-three girls and 19 boys performed the handgrip and standing long jump (SLJ) tests. Their total forearm and leg volumes were calculated from circumference and length measurements and the lean volumes (bone + muscle) were calculated by making allowance for skinfold thickness. Although the boys were older than the girls (12.8 and 12.4 years), there was no significant difference in their heights or body masses. The absolute performances of the boys were superior to those of the girls in both tests (handgrip 234 and 205 N and SLJ 1.53 and 1.34 m), but when jumping performance was expressed as distance x body mass, there was no significant difference. In both tests, performance in terms of unit lean limb volume showed no significant gender difference. When performance was related to lean limb volume, both boys and girls showed a linear relationship in the two tests, with no significant difference between them. This absence of a gender difference contrasts with the results of a previous study on young adults and comparison shows that the relationships between lean limb volume and performance in the two tests for both boys and girls lie just below those of the young, adult females. The difference between the girls and the young adult females was just significant in the handgrip (p less than 0.05), but not significant in the SLJ (p greater than 0.25), whereas the differences between the boys and young adult males were significant (p less than 0.01) in both tests. Thus it would appear that a gender difference in the performance of skeletal muscle develops during adolescence and possible contributory factors are discussed.     

Sweat lactate in exercising children and adolescents of varying physical maturity.

This study attempts to explain some of the individual variability in sweating pattern by comparing prepubescents and pubescents. Sweating rate and muscular anaerobic capacity are higher in adults than in children; thus we hypothesized that sweat gland anaerobic metabolism, as reflected by lactate excretion, might be higher with advanced physical maturity (PM). Lactate concentration in sweat ([LAC]sw) was measured at various stages of PM in boys who exercised in the heat. The subjects were divided into three groups on the basis of Tanner staging: prepubertal (PP, n = 16), midpubertal (MP, n = 15), and late pubertal (LP, n = 5). Subjects cycled at 50% of maximal O2 uptake for three 20-min bouts, with 10-min rest periods, in 42 degrees C and 18% relative humidity. Sweat samples were harvested, and population density of activated sweat glands was determined after each exercise bout. [LAC]sw during bout 1 was higher in PP than in LP [PP = 22.2 +/- 2.2, MP = 19.5 +/- 1.4, LP = 14.3 +/- 1.3 (SE) mmol/l]. In all groups, [LAC]sw decreased during subsequent bouts, and there were no intergroup differences in [LAC]sw during bout 3 (PP = 11.2 +/- 0.4, MP = 10.6 +/- 0.5, LP = 9.7 +/- 0.2 mmol/l). [LAC]sw was inversely related to sweating rate. Lactate excretion rate per gland was greater with the increase in PM (PP = 61.0 +/- 8.2, MP = 79.1 +/- 11.3, LP = 99.9 +/- 11.0 pmol/min; P = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ethnic Differences in Physical Activity and Inactivity Patterns and Overweight Status

Objective: To examine the relationship between physical activity and inactivity patterns and overweight in U.S. adolescents using baseline and 1-year change in activity and inactivity data. Research Methods and Procedures: Nationally representative data from 12,759 participants (6997 non-Hispanic whites, 2676 non-Hispanic blacks, 2185 Hispanics, and 901 Asians) in the National Longitudinal Study of Adolescent Health (1995 and 1996). Data on moderate to vigorous and low-intensity physical activity, TV/video viewing, and video game/computer use were obtained from questionnaires. Multivariate models assessed the association of overweight (body mass index ≥ 95th percentile Centers for Disease Control and Prevention/National Center for Health Statistics 2000 curves) with initial (and 1-year change) activity and inactivity levels, controlling for age, ethnicity, socioeconomic status, urban residence, cigarette smoking, and region of residence. Results: Overweight prevalence was positively associated with high level TV/video viewing among white boys (odds ratio [OR] = 1.52; 95% confidence interval [1.08 to 2.14]) and girls (OR = 2.45 [1.51 to 3.97]). The odds of overweight decreased with high levels of moderate to vigorous physical activity among white boys (OR = 0.81 [0.76 to 0.87]), non-Hispanic black boys (OR = 0.86 [0.76 to 0.98]) and girls (OR = 0.88 [0.78 to 0.99]), and Hispanic boys (OR = 0.90 [0.83 to 0.97]) and girls (OR = 0.91 [0.84 to 0.99]). Discussion: Predicted probabilities generated from the logistic regression models, which examined the experimental effects of altering hours of TV/video viewing and bouts of moderate to vigorous physical activity, show lower overweight among adolescents who watched less TV per week combined with frequent moderate to vigorous physical activity than those who watched more TV per week combined with fewer bouts of weekly moderate to vigorous physical activity. Predicted probabilities suggest important sex and ethnic differences in these associations.     

Predicting anaerobic capabilities in 11-13-year-old boys

Anaerobic exercise is involved in many recreational and competitive sport activities. This study first established regression equations to predict maximal anaerobic power and then cross-validated these prediction equations. Using stepwise multiple regression analysis prediction equations for relative (watts per kilogram of body mass) and absolute (watts) mean and peak anaerobic power using the 30-second Wingate Test as the power measure were determined for 40 boys (age, 11-13 years). Percentage of body fat, free-fat weight, midthigh circumference, and 30-m dash were the independent predictive variables with the generated regression equations subsequently cross-validated using 20 different boys (age, 11-13 years). Significant correlations (Pearson r) were found for the cross-validation subjects between the measured power outputs and predicted power outputs for relative mean power (r = 0.48, p < 0.05), absolute mean power (r = 0.77, p < 0.01), and absolute peak power (r = 0.76, p < 0.01). Using paired t-tests, no significant mean differences (p > 0.05) were found for the same subjects between actual and predicted power outputs for relative mean power, absolute mean power, and absolute peak power. Prediction of maximal anaerobic power from selected anthropometric measurements and 30-m dash appears tenable in 11-13-year-old boys and can be accomplished in a simple cost- and time-effective manner.     

The influence of physical activity on lean mass accrual during adolescence: a longitudinal analysis.

During childhood, physical activity is likely the most important modifiable factor for the development of lean mass. However, the effects of normal growth and maturation must be controlled. To distinguish effects of physical activity from normal growth, longitudinal data are required. One hundred nine boys and one hundred thirteen girls, participating in the Saskatchewan Pediatric Bone Mineral Accrual Study, were repeatedly assessed for 6 yr. Age at entry was 8-15 yr. Stature, body mass, and physical activity were assessed biannually. Body composition was assessed annually by dual-energy X-ray absorptiometry. Physical activity was determined using the physical activity questionnaires for children and adolescence. Biological age was defined as years from age of peak height velocity. Data were analyzed using multilevel random-effects models. In boys, it was found that physical activity had a significant time-dependent effect on lean mass accrual of the total body (484.7+/-157.1 g), arms (69.6+/-27.2 g), legs (197.7+/-60.5 g), and trunk (249.1+/-91.4 g) (P<0.05). Although the physical activity effects were similar in the girls (total body: 306.9+/-96.6 g, arms: 31.4+/-15.5 g, legs: 162.9+/-40.0 g, and trunk: 119.6+/-58.2 g; P<0.05), boys for the same level of activity accrued, depending on the site, between 21 and 120% more absolute lean mass (g). In conclusion, habitual physical activity had a significant independent influence on the growth of lean body mass during adolescence, once biological maturity and stature were controlled.     

Physiological and performance characteristics of adolescent club volleyball players

The objective of this investigation was to examine the physical and performance characteristics of adolescent club volleyball players. Twenty-nine adolescent girls, aged 12 to 17 years (14.31 +/- 1.37) were participants in this investigation. All athletes were members of a competitive volleyball club. The following group values were obtained: height (HT) = 1.69 +/- 0.08 m, weight (WT) = 59.6 +/- 8.2 kg, body fat percentage (BF%) = 20.9 +/- 4.5, lean body mass (LBM) = 46.7 +/- 4.9 kg, modified sit-and-reach (MSR) = 38.7 +/- 7.1 cm, shoulder rotation (SR) = 29.4 +/- 5.6 cm, isometric hand grip (IHG) = 34.5 +/- 5.5 kg, isometric leg strength (ILS) = 77.4 +/- 18.1 kg, vertical jump (VJ) = 35.5 +/- 6.2 cm, standing broad jump (SBJ) =178.8 +/- 20.3 cm, 1-minute sit-ups (SU) = 47.0 +/- 6.7, T-test (TT) = 11.2 +/- 0.8 seconds., shuttle test (SHT) = 9.7 +/- 0.4 seconds, stork stand (SS) = 8.1 +/- 4.1 seconds, serving velocity (SVV) =16.1 +/- 4.5 m.s(-1), and spiking velocity (SKV) = 16.9 +/- 2.4 m.s(-1). For purposes of analysis, players were divided into 2 age groups: 12 to 14 years (group A) and 15 to 17 years (group B). Significant differences (p < 0.05) were found between age groups for the following values: HT, WT, LBM, IHG, ILS, SBJ, and SVV. Values for group B were greater for each variable. Significant correlations include age and IHG (r = 0.75), age and ILS (r = 0.51), age and SBJ (r = 0.67), age and SVV (r = 0.71), LBM and IHG (r = 0.90), LBM and ILS (r = 0.62), LBM and SVV (r = 0.58), SVV and IHG (r = 0.60), and SKV and SS (r = 0.60). Our results suggest that age, experience, LBM, shoulder, hip, and thigh girths, strength, and balance are key physical performance characteristics of adolescent girls who play volleyball. Potentially, this type of information will allow coaches and athletes to identify physical and performance data specific to age groups for purposes of evaluation and player development.     

Increased bone mineral density and serum leptin in non-obese girls with precocious pubarche: relation to low birthweight and hyperinsulinism.

BACKGROUND: Hyperinsulinism and hyperandrogenism have the capacity to increase bone mineral density (BMD) and serum leptin, independently of body fat mass. We therefore assessed lumbar BMD and serum leptin in girls with the sequence of a low birthweight and precocious pubarche (PP) in childhood, in whom hyperinsulinism and hyperandrogenism have been described. METHODS: Fifty-two non-obese PP girls were studied (age range 6.9-14.9 years). Serum leptin was also measured in 42 control girls, matched for age, body mass index and pubertal stage. RESULTS: BMD SDS, measured by dual-energy X-ray absorptiometry, was elevated in PP girls compared to the population reference (0.39 +/- 0.18 SDS; p = 0.03) and bone age, assessed from hand radiographs, was significantly advanced compared to chronological age (1.2 +/- 0.1 years; p < 0.0005). CONCLUSION: Compared to control girls, PP girls had higher leptin levels for degree of body mass index (PP girls: 9.4 +/- 0.6 ng/ml; controls: 7.8 +/- 0.6 ng/ml; p = 0.01). In PP girls, serum leptin was inversely related to birthweight (r = -0.32, p = 0.01) and positively related to free androgen index (FAI) (r = 0.71, p < 0.0005). BMD SDS was also inversely related to birthweight (r = -0.26, p < 0.05) and positively related to serum leptin (r = 0.42, p < 0.05), FAI (r = 0.45, p < 0.05) and mean serum insulin during oral glucose tolerance testing (MSI) (r = 0.59, p < 0.0005). In multiple regression, MSI was the strongest determinant of BMD SDS (beta = 0.50, p = 0.002). In conclusion, elevated BMD and serum leptin in non-obese PP girls were related to degrees of low birthweight, hyperinsulinism and hyperandrogenism. The characteristic hyperinsulinism of PP girls is proposed to be the key variable in this constellation.     

A comparison of zooplankton production estimates obtained from three commonly used methods and a computer simulation program

SUMMARY 1. Zooplankton production in a eutrophic reservoir was estimated by three common methods.
2. Estimates of daily production from the growth increment method and the birth and death rate versions of the biomass turnover method were poorly correlated ( r =0.58–0.60). Estimates of daily production rates from the above two versions of the biomass turnover method were strongly correlated ( r =0.90).
3. The mortality rate version of the biomass turnover method is illogical and yields anomalous results.
4. The growth increment method assumes steady state conditions and zero deaths within each stage and hence calculates potential production for each stage.
5. Estimates from a new computer simulation (PROD) were strongly correlated with ( r =0.92) but lower than those from the growth increment method. Estimates from PROD were more poorly correlated ( r =0.78) with those from the biomass turnover method.
6. There is a strong need for improved methods for estimating secondary production; computer based methods would seem to be the most promising.     

Single versus serial assessment of skeletal age: Either,both or neither?

Assessments of skeletal age are a valuable adjunct to the clinical evaluation of physical maturity but are more meaningful when considered in relation to chronological age, especially over time, than as separate entities. Data on 51 girls from the Child Research Council study series gave a correlation coefficient of 0.51 between skeletal age (SA) at menarche and chronological age (CA) at menarche — a value in close agreement with data reported from other studies. With a range in SA of 11.58 to 14.89 years, these data were examined further for changes in SA related to timing of adolescence. SA was greater than CA in each of the nine girls whose menarche occurred between 10.5 and 12 years of age. SA was equal to CA in one girl, greater than CA in eight girls and less than CA in 11 girls with menarche between 12.15 and 13.4 years. Of the 22 girls with menarche after 13.5 years, one had SA = CA at 14.89 years and the other 21 all had SA less than CA. An r of 0.84 was calculated between the values of CA minus SA at menarche and CA at menarche. Similar relationships were found between SA and CA at age of maximum increment in growth in height for these girls and for 53 boys in the study series. Longitudinal data for height, weight and SA for four boys and five girls demonstrate the problems of prediction of the timing of adolescence and of adult size from skeletal ages in the childhood years.     

Maximal oxygen uptake in Danish adolescents 16-19 years of age

A random sample of schoolchildren, 119 boys and 153 girls, was tested in the fall of 1983. The data presented here are anthropometric data (height, weight, fat % and vital capacity) and oxygen uptake directly measured on a bicycle ergometer. The mean height and weight for boys were 179.1 cm and 67.7 kg, and those for girls were 168.0 cm and 59.6 kg. The mean fat content was 9.1% for boys and 19.1% for girls, and their mean vital capacities were 4.91 and 3.61 respectively. The boys had a high maximal oxygen uptake (51.7 ml X kg-1 X min-1) showing no reduction over the age span studied. The girls' maximal oxygen uptake was lower (overall mean 40.0 ml X kg-1 X min-1) with a small reduction from 16 to 19 years of age. When comparing maximal oxygen uptake per kg lean body mass in the two sexes, the boys had 18.4% higher values than the girls, indicating that girls of this age have the lower fitness level. The results of maximal aerobic power measurement in the boys compare well with findings from other investigations using direct measurements, indicating that the fitness of teenage boys is kept at a high level. Comparable data from various countries for girls show different pictures, but it appears that in general they have a low fitness level.     

Pronounced adrenarche and precocious pubarche in boys

In girls, pronounced adrenarche with precocious pubarche (PP) has been related to reduced fetal growth and to a cluster of endocrine-metabolic abnormalities. We examined whether these associations are also evident in boys with PP. The study population consisted of matched groups of boys (n = 58; age range 5-15 years) without or with a history of PP. After stratification for pubertal development, non-PP and PP boys displayed comparable results for the studied variables, including serum insulin-like growth factor I, sex hormone binding globulin, insulin-like growth factor binding proteins 1 and 3, indices of circulating glucose and insulin responsiveness to an oral glucose load, and birth weight SD score. In conclusion, the present results indicate that adrenarche-driven PP in boys is, in contrast to PP in girls, not associated with a cluster of endocrine-metabolic abnormalities and is not related to reduced fetal growth. These observations support the view that adrenarche-driven PP in boys may be regarded as a variant of normal development. Copyrightz1999S.KargerAG,Basel     

Cold exposure during military operations: effects on anaerobic performance

This study examined the effects of military field operations (MFO) under different environmental conditions on anaerobic performance. US Marines were tested in the field under the following conditions: 1) noncold environment (NC; n = 30, 10-32 degrees C) and 2) cold environment (CO; n = 32, -2 to -22 degrees C). Subjects performed 30-s Wingate tests (WIN) pre- and immediately post-MFO to assess anaerobic performance. The MFO consisted of approximately 4.5 days of combat training maneuvers while carrying field equipment (packs and weapon, approximately 25 kg). WIN measures obtained were absolute and relative mean power (MP), 5-s peak power (PP), and fatigue index (% decline). Significant main effects (P less than 0.01) were observed for time (pre-post MFO). Reductions occurred in absolute MP [651.8 +/- 30.3 to 616.4 +/- 28.5 (SE) W] and PP (897.8 +/- 41.6 to 857.0 +/- 39.1 W); however, no effect on fatigue index was seen. Significant interaction effects (P less than 0.05) were observed in relative measures. Reductions (pre-post) in MP (NC = 8.64 +/- 0.16 to 8.37 +/- 0.14 W/kg; CO = 8.91 +/- 0.26 to 8.04 +/- 0.15 W/kg) and PP (NC = 11.80 +/- 0.24 to 11.61 +/- 0.33 W/kg; CO = 12.23 +/- 0.35 to 11.20 +/- 0.19 W/kg) were greater under CO than NC conditions. These changes were found despite significant (P less than 0.05) but comparable pre-post weight reductions in both CO and NC conditions.(ABSTRACT TRUNCATED AT 250 WORDS)