Associations of adiposity with measured and self-reported academic performance in early adolescence

Objective: To examine the associations of adiposity with measured and self‐reported academic performance independently of demographics and physical activity among U.S. adolescents. Research Methods and Procedures: We surveyed 666 students 11 to 14 years old from seven middle schools in Los Angeles, CA. Weight and height were measured. Actual grade point average was obtained from school records. Self‐reported school grades and physical activity time were measured by questionnaire. Adiposity measures included BMI, BMI percentile (≥85th percentile defined as at‐risk‐of‐overweight), and percentage body fat (bioimpedance). Results: After adjusting for gender, ethnicity, age, and physical activity time, overweight at‐risk status, BMI, and percentage body fat were negatively related to only self‐reported (p < 0.01) but not measured grades. Level of moderate‐to‐vigorous physical activity time was negatively related to measured and self‐reported grades, independently of adiposity (p < 0.01). Discussion: To our knowledge, this is the first study to examine both body mass and body fat in relation to measured and self‐reported school grades. Adiposity did not relate to actual academic performance in a sample of predominantly Latino and Asian‐American adolescents. The use of measured vs. self‐reported academic outcomes may represent different constructs and influence study conclusions. Cultural factors may also play a role in our findings, but this requires further study.     

Physical Fitness and Physical Activity in Obese and Nonobese Flemish Youth

Objective: To assess different aspects of physical fitness and physical activity in obese and nonobese Flemish youth. Research Methods and Procedures: A random sample of 3214 Flemish schoolchildren was selected and divided into an “obese” and “nonobese” group based on body mass index and sum of skinfolds. Physical fitness was assessed by the European physical fitness test battery. Physical activity was estimated by a modified version of the Baecke Questionnaire. Results: Obese subjects had inferior performances on all tests requiring propulsion or lifting of the body mass (standing‐broad jump, sit‐ups, bent‐arm hang, speed shuttle run, and endurance shuttle run) compared with their nonobese counterparts (p < 0.001). In contrast, the obese subjects showed greater strength on handgrip (p < 0.001). Both groups had similar levels of leisure‐time physical activity; however, nonobese boys had a higher sport index than their obese counterparts (p < 0.05). Discussion: Results of this study show that obese subjects had poorer performances on weight‐bearing tasks, but did not have lower scores on all fitness components. To encourage adherence to physical activity in obese youth, it is important that activities are tailored to their capabilities. Results suggest that weight‐bearing activities should be limited at the start of an intervention with obese participants and alternative activities that rely more on static strength used.     

Age-related changes of bone mineral density in human calcaneus, talus, and scaphoid bone

To examine whether the bone mineral density (BMD) decreases uniformly with aging in any spongy bones, the authors investigated age-related changes of BMD in the calcaneus, talus, and scaphoid bone. After the ordinary dissection by medical students was finished, calcanei, tali, and scaphoid bones were resected from the subjects, and BMDs were measured by dual-energy X-ray absorptiometry. Their BMDs seemed to decrease gradually with aging in the calcanei, tali, and scaphoid bones. It was found that there were statistically significant relationships between age and BMD in the men’s and women’s scaphoid bones, women’s tali, and women’s calcanei, but not in the men’s tali and calcanei. It should be noted that there were significant relationships between age and BMD in both men’s and women’s scaphoid bones. In regard to relationship in BMD between the bones of the upper and lower limbs in individuals, it was found that the relationship between the calcaneus and talus was higher than that between the calcaneus and scaphoid bone. This suggests that there is a higher relationship in BMD between the two tarsal bones compared with that between the tarsal and carpal bones.     

Correlates of adherence to a physical activity program in young African-American girls

Objective: The goal was to identify correlates of adherence to a structured physical activity (PA) program. Research Methods and Procedures: Subjects were 136 8‐ to 12‐year‐old African‐American girls. Potential correlates at baseline were: 1) fitness index (FI: % body fat from DXA and cardiovascular fitness from treadmill test), and 2) self‐esteem, anxiety, attitude to school and teachers, relationship with parents, and interpersonal relations (Behavioral Assessment System for Children). The 10‐month PA program included 80 minutes of PA offered 5 days/wk. Regression tree classification was used to model attendance. Results: Six splits occurred (34% total variance explained). Less anxious subjects attended more often than highly anxious subjects (3 days/wk vs. 1.5 days/wk) did. Subjects with a healthier FI attended more often than those with a less healthy FI (3 days/wk vs. 0.5 days/wk) did. Younger subjects attended more often than older ones (3 days/wk vs. 2.5 days/wk) did. The next two splits were again with anxiety (3.5 days/wk vs. 3 days/wk) and FI (3 days/wk vs. 2.5 days/wk). Finally, subjects with higher levels of self‐esteem attended more often than those with lower levels (3.5 days/wk vs. 2 days/wk) did. Discussion: Subjects who were self‐confident, younger, fitter, and less anxious were more likely to participate regularly. This suggests that children who may be more likely to benefit from a PA program are less likely to participate. To enhance participation in PA programs, especially in older African‐American girls: 1) psychological concerns should be identified and addressed before enrollment, and 2) programs should be designed to be appealing to children of all fitness levels.     

Cardiorespiratory fitness and sedentary activities are associated with adiposity in adolescents

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

Longitudinal patterns of breakfast eating in black and white adolescent girls

Objective: The objective was to describe the pattern of breakfast eating over time (“breakfast history”) and examine its associations with BMI and physical activity. Research Methods and Procedures: This longitudinal investigation of patterns of breakfast eating included 1210 black and 1161 white girls who participated in the 10‐year, longitudinal National Heart, Lung, and Blood Institute Growth and Health Study (NGHS). Three‐day food records were collected during annual visits beginning at ages 9 or 10 up to age 19. Linear regression and path analysis were used to estimate the associations between breakfast history, BMI, and physical activity. Results: Among girls with a high BMI at baseline, those who ate breakfast more often had lower BMI at the end of the study (age 19), compared with those who ate breakfast less often. Path analysis indicated that energy intake and physical activity mediated the association between patterns of breakfast eating over time and BMI in late adolescence. Discussion: The association between regular breakfast consumption over time and moderation of body weight among girls who began the study with relatively high BMI suggests that programs to address overweight in children and adolescents should emphasize the importance of physical activity and eating breakfast consistently.     

1.8 mT不同频率正弦交变电磁场对青年大鼠骨密度及骨形态计量的影响比较

比较不同频率的正弦交变电磁场对SD青年大鼠骨密度及骨形态计量指标的影响,筛选可有效提升大鼠骨密度的频率参数。将32只8周龄SD雌性大鼠随机分为4组:对照组、15 Hz组、30 Hz组、45 Hz组;除对照组外,实验组大鼠每天都给予相应频率的1.8 m T正弦交变电磁场干预,干预时间为90 min。磁场干预8周后,双能X射线骨密度仪检测大鼠全身骨密度、右侧股骨骨密度和椎骨骨密度,ELISA分析血清中骨形成与骨吸收生化指标的含量,右侧胫骨进行荧光间距测量与骨形态计量分析。相比于对照组,15 Hz组、45 Hz组大鼠的全身骨密度、股骨骨密度、椎骨骨密度均明显升高(P0.05),血清中骨钙素与骨保护素含量也显著提升(P0.05);实验组大鼠的胫骨双荧光间距与骨组织静态参数均高于对照组(P0.05)。结果表明,15 Hz、45 Hz正弦交变电磁场可有效提升青年大鼠的骨密度,从而可预防骨质疏松的发生。     

Physical,Behavioral, and Body Image Characteristics in a Tri‐Racial Group of Adolescent Girls

Objectives: The purpose of this study was to evaluate physical characteristics, nutrient intake, physical activity level, and body image in white (CC), African‐American (AA), and Hispanic‐American (HA) female adolescents. Research Methods and Procedures: High school volunteers were solicited for this study. Self‐reported information was used to determine subject characteristics, family income, physical activity, body image, and nutrient intake. Physical evaluations were used to determine body mass index, percent body fat, fat distribution, resting heart rate, and blood pressure (BP). Results: Results showed that AA girls displayed significantly higher diastolic BP than HA girls (p = 0.029). CC adolescents showed greater physical activity (p = 0.010) and lower adiposity than HA adolescents (p = 0.048), as well as lower subscapular skinfold than AA adolescents (p = 0.018). AA adolescents selected a higher ideal body size than CC girls (p = 0.038). There was also a significant difference in percentage carbohydrates (p < 0.034) and cholesterol consumed (p < 0.016) among groups, with CC girls showing the highest values for carbohydrates and lowest values for cholesterol intake among groups. Discussion: Given our findings of higher adiposity and lower physical activity levels in HA adolescents and greater diastolic BP levels and subscapular skinfold in AA adolescents, more interventions should be targeted toward improving health‐related variables among minority populations.     

Roles of physical activity and cardiorespiratory fitness on sex difference in insulin resistance in late elementary years

[Purpose]

Little is known about the potential role of lifestyle factors in sex differences in insulin resistance in late elementary school children.

[Methods]

In this cross-sectional study, we compared sex differences in Tanner scales, body fat, physical activity (PA) and fitness, and insulin resistance markers in elementary school children (boys, n = 69 and girls, n = 81) aged 12-13 years. Body composition was assessed with a standardized protocol. Cardiorespiratory fitness was measured as oxygen consumption during an incremental treadmill exercise. Fasting blood samples were collected for blood chemistry assays including lipids, glucose, insulin and homeostasis model assessment for insulin resistance (HOMA-IR), leptin, and adiponectin. Daily PA was measured with an accelerometer for 7 consecutive days, and they were classified as low-, moderate-, and vigorous-PA. Independent t-tests were used to compare mean differences in the measured variables between boys and girls. There were significant sex differences in Tanner scales, body mass index, percent body fat, and waist circumference (WC).

[Results]

Girls had significantly higher values in Tanner scales (p < 0.001) and percent body fat (p < 0.001) than boys. Boys had significantly higher values in body mass index (p = 0.019) and waist circumference (p < 0.001) than girls. Boys also had significantly higher values in VO_2max (p < 0.001) and low (p < 0.001), moderate (p < 0.001), and vigorous (p < 0.001) PAs. With respect to metabolic risk factors, girls had significantly higher serum levels of triglycerides (p = 0.005), insulin (p < 0.001), and HOMA-IR (p < 0.001) and significantly lower high-density lipoprotein cholesterol (p = 0.015) than boys.

[Conclusion]

In summary, the current findings of the study showed that the increased risk for insulin resistance in girls over boys is associated with higher Tanner scale and percent body fat in conjunction with poor cardiorespiratory fitness and physical inactivity, suggesting that exercise intervention to promote physical activity and fitness is imperative for general health promotion of school children, with a special focus on girls.     

Reduced adiposity in ob/ob mice following total body irradiation and bone marrow transplantation

Objective: The objective of this study was to assess long‐term metabolic consequences of total body irradiation (TBI) and bone marrow transplantation. Severe obesity develops due to both hypertrophy and hyperplasia of adipocytes. We hypothesized that TBI would arrest adipose tissue growth and would affect insulin resistance (IR). Research Methods and Procedures: We exposed 2‐month‐old female ob/ob mice to 8 Grays of TBI followed by bone marrow transplantation and tested the animals for body weight (BW) gain, body composition, blood glucose, and insulin sensitivity. Results: Two months after TBI, irradiated mice stopped gaining BW, whereas non‐treated mice continued to grow. At the age of 9.5 months, body mass of irradiated mice was 60.6 ± 1.4 grams, which was only 61% of that in non‐treated ob/ob controls (99.4 ± 1.6 grams). Body composition measurements by DXA showed that decreased BW was primarily due to an impaired fat accumulation. This could not result from the production of leptin by bone marrow‐derived adipocyte progenitors because inhibition of the obese phenotype was identical in recipients of both B6 and ob/ob bone marrow. Inability of the irradiated mice to accumulate fat was associated with hepatomegaly, lower levels of monocyte chemoattractant protein‐1 expression in adipose tissue, and increased IR. Discussion: Our data argue in favor of the hypothesis that inability of adipose tissue to expand may increase IR. This mouse model may be valuable for studies of late‐onset radiation‐induced IR in humans.     

强度不同的间歇跑台训练对生长期大鼠骨代谢及相关激素的影响

目的:探讨强度不同的间歇跑台训练对生长期大鼠骨代谢的影响,以期为青少年训练强度的制定提供理论支持。方法:选取4周龄雄性wistar大鼠70只,根据体重随机搭配分成7组(n=10):即对照组和运动组。运动组按照大鼠摄氧量分为:65%组,70%组,75%组,80%组,85%组和90%组。跑台训练9周,每周训练6 d,每组训练分3次,每次不低于10 min,中间间隔30 min。最后一次运动后24 h,取股骨和血进行骨密度(BMD)、骨量(BMC)和血清中的碱性磷酸酶(AKP),抗酒石酸酸性磷酸酶(Str-ACP)的测定。结果:①70%组股骨的BMD(0.1393±0.0031)、BMC(0.4525±0.0335)显著高于对照组(BMD:0.1200±0.0095,BMC:0.3238±0.0485)和其他各运动组(65%组BMD:0.1339±0.0062、BMC:0.4058±0.0492,75%组BMD:0.1296±0.0015、BMC:0.3869±0.0254,80%组BMD:0.1223±0.0082、BMC:0.3454±0.0483,85%组BMD:0.1250±0.0044、BMC:0.3731±0.0381,90%组BMD:0.1171±0.0047、BMC:0.3051±0.0286)(P<0.05),90%组的BMD、BMC低于对照组但未达到显著水平,其他各运动组均高于对照组;②各运动组血清AKP均显著高于对照组,其中65%组(41.015±2.114)、70%组(46.035±2.611)、75%组(43.834±3.155)、80%组(38.043±4.073)血清AKP非常显著高于对照组(26.875±1.188)(P<0.01),70%组和75%组血清AKP显著高于80%组、85%组、90%组(P<0.05),同时70%组血清AKP显著高于65%组(P<0.05),这说明70%VO2max的训练强度成骨细胞最活跃。各运动组血清StrACP均显著高于对照组,随着训练强度的增加,血清StrACP水平呈上升趋势,80%组(22.430±1.591)、85%组(23.990±1.870)、90%组(28.009±1.839)血清StrACP显著高于65%组(18.503±2.429)、70%组(16.447±2.120)和75%组(17.769±1.642)(P<0.05),90%组血清StrACP均显著高于80%组和85%组(P<0.05)。结论:70%VO2max的中等强度间歇跑台训练使生长期大鼠骨量、骨密度增加最明显。     

Sympathectomy alters bone architecture in adult growing rats

Sympathetic nervous system (SNS) fibres and alpha- and beta-receptors are present in bone, indicating that the SNS may participate in bone metabolism. The importance of these observations is controversial because stimulation or inhibition of the SNS has had various effects upon both anabolic and catabolic activity in this tissue. In this study we evaluated the effects of pharmacological sympathectomy, using chronic treatment of maturing male rats with 40 mg of guanethidine/kg i.p., upon various parameters in bone. Double labelling with tetracycline injection was also performed 20 and 2 days before sacrifice. Bone mass, mineral content, density and histomorphometric characteristics in different skeletal regions were determined. Bone metabolic markers included urinary deoxypyridinoline and serum osteocalcin measurements. Guanethidine significantly reduced the accretion of lumbar vertebral bone and of mineral content and density, compared to controls. Femoral bone mineral content and density were also significantly reduced, compared to controls. Histomorphometric analyses indicated these effects were related to a reduction of cortical bone and mineral apposition rate at femoral diaphysials level. Both markers of bone metabolism were reduced in controls as they approached maturity. Guanethidine significantly decreased serum osteocalcin compared to controls, while urinary deoxypyridinoline was unchanged. These data indicate that guanethidine-induced sympathectomy caused a negative balance of bone metabolism, leading to decreased mass by regulating deposition rather than resorption during modeling and remodeling of bone.     

Relationships of Age and Weekly Running Distance to BMI and Circumferences in 41, 582 Physically Active Women

Objective: To assess in women whether age‐related increases in adiposity are dependent on exercise, and, contrariwise, whether exercise‐related declines in adiposity are dependent on age. Research Methods and Procedures: Cross‐sectional analyses were conducted of 41, 582 female runners. Results: Age affected the relationships between vigorous exercise and adiposity. The decline in BMI per kilometer per week run was linear in 18 to 23 year olds and became increasingly non‐linear (convex) with age. Waist, hip, and chest circumferences declined significantly with running distance across all age groups, but the declines were significantly greater in older than younger women, particularly among shorter distance runners. The relationships between body circumferences and running distance became increasingly convex in older women. Conversely, vigorous exercise diminished the apparent increase in adiposity with age. The increase in average BMI with age was greatest in women who ran <8 km/wk, intermediate in women who ran 8 to 15 km/wk or 16 to 31 km/wk, and least in those who averaged over 32 km/wk. Before age 45, waist circumference rose for those who ran 0 to 7 km/wk, showed no significant relationship to age for those who ran 8 to 39 km/wk, and declined in those who ran 40 to 55 and 56 km/wk and more. Age related‐increases in hip and chest circumferences before 45 years old were significantly less in women who ran longer weekly distances. Discussion: These cross‐sectional associations are consistent with the hypothesis that exercise may mitigate age‐related increases in adiposity and that age affects exercise‐induced reductions in adiposity (although causality remains to be determined experimentally).     

Different "weight" of cardiac and general adiposity in predicting left ventricle morphology

Excess adiposity has been widely related to cardiac morphological changes. Nevertheless, the mechanistic link between increased adiposity and left ventricular (LV) morphology is controversial and not completely understood. In this context, several authors have recently debated the different "weight" of BMI as an index of general adiposity vs. the importance of the epicardial fat depot as a marker of local visceral adiposity in obesity-related LV changes. Studies in uncomplicated obesity suggest that the role of BMI in predicting LV abnormalities remains rather doubtful. In contrast, several lines of evidence suggest that cardiac adiposity could play an important part in the development of cardiac modifications. Epicardial fat as an index of cardiac adiposity could have a functional and mechanical role in obesity-related LV abnormalities. Epicardial fat is clinically correlated with LV mass, atrial dimensions, and diastolic function, but a causal effect of epicardial adipose tissue on cardiac chamber modifications remains to be demonstrated. Nevertheless, the close anatomical and functional relationship of epicardial adipose tissue to the adjacent myocardium should readily allow local, paracrine interactions between these tissues.