Relations of moderate and vigorous physical activity to fitness and fatness in adolescents

BACKGROUND: It is unclear how moderate and vigorous intensities of physical activity (PA) are associated with cardiovascular fitness (CVF) and percentage of body fat (%BF) in adolescents. OBJECTIVE: We tested the hypothesis that vigorous PA, to a greater degree than moderate PA, would be associated with better CVF and lower %BF. DESIGN: This was a cross-sectional study of 421 black and white high school students (x age: 16 y). PA was measured with 5 d of accelerometry and expressed in min/d of moderate or vigorous PA. CVF was measured with a multistage treadmill test and was expressed as the oxygen consumption at a heart rate of 170 bpm. %BF was measured with dual-energy X-ray absorptiometry. Multiple regressions were used to determine the degree to which variance in CVF and %BF was explained by PA, after control for age, sex, race, and the sex x race interaction. RESULTS: A higher index for CVF was associated with higher amounts of moderate and vigorous PA; more variance was explained by vigorous than by moderate PA. Lower %BF was associated with higher amounts of vigorous PA but not with the amount of moderate PA. CONCLUSION: Black and white adolescents who engaged in relatively large amounts of free-living vigorous exercise were likely to be relatively fit and lean.     

Associations between objectively assessed physical activity and indicators of body fatness in 9- to 10-y-old European children: a population-based study from 4 distinct regions in Europe (the European Youth Heart Study)

BACKGROUND: The rising prevalence of obesity in children may be due to a reduction in physical activity (PA). OBJECTIVE: Our aim was to study the associations of objectively measured PA volume and its subcomponents with indicators of body fatness. DESIGN: A cross-sectional study of 1292 children aged 9-10 y from 4 distinct regions in Europe (Odense, Denmark; the island of Madeira, Portugal; Oslo; and Tartu, Estonia) was conducted. PA was measured by accelerometry, and indicators of body fatness were the sum of 5 skinfold thicknesses and body mass index (BMI; in kg/m(2)). We examined the associations between PA and body fatness by using general linear models adjusted for potential confounding variables. RESULTS: After adjustment for sex, study location, sexual maturity, birth weight, and parental BMI, time (min/d) spent at moderate and vigorous PA (P = 0.032) and time (min/d) spent at vigorous PA were significantly (P = 0.015) and independently associated with body fatness. Sex, study location, sexual maturity, birth weight, and parental BMI explained 29% (adjusted R(2) = 0.29) of the variation in body fatness. Time spent at vigorous PA explained an additional 0.5%. Children who accumulated <1 h of moderate PA/d were significantly fatter than were those who accumulated >2 h/d. CONCLUSIONS: The accumulated amount of time spent at moderate and vigorous PA is related to body fatness in children, but this relation is weak; the explained variance was <1%.     

Association of physical activity to cardiovascular fitness and fatness in 12–13-year-old boys in different weight status

Aim

The aim was to examine the associations between physical activity (PA) and cardiovascular fitness (CVF) and fatness in boys (age 12.04?±?0.77 year) and to assess if weight status influences these associations.

Subjects and methods

Two hundred sixty-five boys participated in the study. PA was measured by accelerometry. Body fatness estimators included body mass index (BMI), body fat%, sum of five skinfolds and waist circumference. CVF was directly measured during stepwise incremental exercise test and expressed in peak oxygen uptake (VO_2peak) and maximal power output (W _max).

Results

All measured PA levels (except vigorous PA in obese boys) were significant predictors of W _max per kilogram of body mass in normal weight and obese boys. Vigorous PA, moderate-to-vigorous PA (MVPA), total PA in normal weight and vigorous PA in obese boys were significant predictors of W _max. Variation in VO_2peak per kilogram of body mass was significantly explained by moderate PA, vigorous PA, MVPA and total PA in normal weight only. For those of normal weight, vigorous PA, MVPA and total PA were negatively associated with body fat% and sum of five skinfolds. In obese boys, moderate PA and MVPA were negatively associated with BMI.

Conclusions

Time spent in vigorous PA and MVPA was associated with fatness parameters in normal weight and obese boys and with CVF parameters only in normal weight boys. Normal weight boys spent more time in vigorous PA and MVPA than overweight and obese boys and had high values in VO_2peak, VO_2peak per kilogram of body mass and W _max per kilogram of body mass.

     

Habitual physical activity and physical activity intensity: their relation to body composition in 5.0-10.5-y-old children

BACKGROUND: Concerns of a decrease in physical activity levels (PALs) of children and a concurrent increase in childhood obesity exist worldwide. The exact relation between these two parameters however has as yet to be fully defined in children. OBJECTIVE: This study examined the relation in 47 children, aged 5-10.5 y (mean age 8.4+/-0.9 y) between habitual physical activity, minutes spent in moderate, vigorous and hard intensity activity and body composition parameters. DESIGN: Total energy expenditure (TEE) was calculated using the doubly labelled water technique and basal metabolic rate (BMR) was predicted from Schofield's equations. PAL was determined by PAL=TEE/BMR. Time spent in moderate, vigorous and hard intensity activity was determined by accelerometry, using the Tritrac-R3D. Body fatness and body mass index (BMI) were used as the two measures of body composition. RESULTS: Body fat and BMI were significantly inversely correlated with PAL (r=-0.43, P=0.002 and r=-0.45, P=0.001). Times spent in vigorous activity and hard activity were significantly correlated to percentage body fat (r=-0.44, P=0.004 and r=-0.39, P=0.014), but not BMI. Children who were in the top tertiles for both vigorous activity and hard activity had significantly lower body fat percentages than those in the middle and lowest tertiles. Moderate intensity activity was not correlated with measures of body composition. CONCLUSIONS: As well as showing a significant relation between PAL and body composition, these data intimate that there may be a threshold of intensity of physical activity that is influential on body fatness. In light of world trends showing increasing childhood obesity, this study supports the need to further investigate the importance of physical activity for children.     

Patterns of physical activity in free-living adults in the Southern United States

OBJECTIVE: To examine the relationship between the amount and patterns of physical activity (PA), body fatness, and age in a heterogeneous adult population in the free living. DESIGN: Cross-sectional study of the amount of PA over a 1-week period. The amount of body movements during PA (PA counts*10(3)) and time spent on various PA intensity categories were calculated from a triaxial accelerometer and compared with subject characteristics, including body fat from hydrodensitometry. PARTICIPANTS: Adult healthy men (n=48) and women (n=72) were recruited from the Nashville, Tennessee area and their PA was monitored in their free-living environment. RESULTS: The average weekday PA counts (176.5+/-60.3, P=0.002, r(2)=0.294), PA counts day-to-day variability (47.3+/-32.7, P=0.002, r(2)=0.286), daily maximum PA counts (241.9+/-89.2, P=0.001, r(2)=0.327), minute-to-minute variability on weekdays (0.281+/-0.091, P=0.001, r(2)=0.362), and the difference between maximum and minimum daily PA counts (130.6+/-78.3, P=0.008, r(2)=0.243) were significantly and negatively correlated with body fatness. During awake time, both men and women spent 10-12 h on low intensity (1.0-2.9 metabolic equivalents (METs)) PA, approximately 1 h on moderate (3.0-5.9 MET), and less than 10 min on vigorous (>6.0 MET) PA each day. On weekends, men and women spent more time at rest (1 MET), less time on low-intensity PA, and men spent more time on moderate PA than on weekdays. CONCLUSIONS: In adults living in the Southern US the amount of free-living PA was negatively correlated with body fatness. Both men and women spent the majority of active time on low and moderate PA. PA patterns on weekends were different than on weekdays and were related to sex and age, but not to body fatness. SPONSORSHIP: National Institutes of Health, US.     

Fatness,physical activity,and television viewing in children during the adiposity rebound period: the Iowa Bone Development Study

BACKGROUND: Understanding the determinants of adiposity in young children may be particularly critical for preventing adult obesity since the age at which body fatness reaches a postinfancy low point (typically 4-6 years) is inversely associated with obesity later in life. METHODS; We examined cross-sectional associations among fatness, leanness, and physical activity in 467 children (range 4-6 years). Activity was measured using accelerometry and parental report of children's television (TV) viewing. Dual energy X-ray absorptiometry was used to quantify body composition. RESULTS: Minutes spent in vigorous activity and TV viewing were the variables most consistently and most highly associated with adiposity. Children in the lowest quartile for vigorous activity had on average (absolute) body fat percentages that were 4% greater than those children in the highest quartile for vigorous activity. Body fat percentages for children in the highest category for TV viewing were on average 3% greater than those children who watched the least amount of TV. CONCLUSIONS: Low levels of vigorous physical activity and high levels of TV viewing are associated with fatness in young children during the adiposity rebound period. This suggests that increasing children's active play may be important in preventing obesity later in life.     

A prospective study of physical activity intensity and change in adiposity in middle-aged women

PURPOSE: To determine the extent to which objectively measured intensity of physical activity (PA) predicts change in body fat (BF%) in women. DESIGN: Prospective cohort study of PA intensity and body composition in middle-aged women. SETTING: The study took place in a metropolitan Mountain West community. SUBJECTS: Two hundred and twenty-eight women participated in two assessment periods separated by 20 months. MEASURES: Each assessment period consisted of seven consecutive days of monitoring, followed by body composition testing. ANALYSIS: The general linear model using partial correlations and Mantel-Haenszel chi2 tests were performed. RESULTS: At baseline and follow-up, women who participated in vigorous PA were leaner than women who participated in moderate or light PA (p < .05). Longitudinal results indicated that a greater proportion of women who decreased PA intensity over the 20 months also increased BF% (66%), compared to participants who increased or maintained PA intensity (47%) (p < .05). CONCLUSIONS: PA intensity seems to play a role in long-term weight maintenance. Reducing PA intensity increases the risk of BF% gain in women. Efforts to help women maintain PA intensity along with other weight management strategies may prove beneficial in preventing unwanted body fat gain in middle-aged women.     

Associations between physical activity, body fat, and insulin resistance (homeostasis model assessment) in adolescents: the European Youth Heart Study

BACKGROUND: More and better data are needed to understand the action of physical activity (PA) on insulin resistance and the concomitant relation with body fat in adolescence. OBJECTIVE: We examined the relation between total PA and intensity levels with insulin resistance under special consideration of waist circumference and skinfold thickness. DESIGN: This was a cross-sectional study of 613 adolescents (352 girls, 261 boys) with a mean (+/-SD) age of 15.5 +/- 0.5 y from Sweden and Estonia. Total, low, moderate, and vigorous PA was measured by accelerometry. Body fat estimators included waist circumference and the sum of 5 skinfold thicknesses. Fasting insulin and glucose were measured, and insulin resistance was calculated according to the homeostasis model assessment (HOMA). Linear regression analysis and analysis of covariance were used to determine the association between PA and insulin resistance while considering body fat. All estimates were adjusted for sex, country, pubertal status, and indicators of body fat when applicable. RESULTS: Total, moderate, and vigorous PA were inversely correlated with HOMA. Body fat estimators were positively correlated with HOMA. Significant contrasts in HOMA concentrations were seen when comparing the lower 2 tertiles with the upper tertile of PA indicators. Repeating the analysis with body fat estimators showed significant contrasts in HOMA concentrations when comparing the lower tertiles with the upper tertile. CONCLUSION: In view of an increase in obesity in young people, the results accentuate the role of PA in sustaining metabolic balance in adolescence and the potential benefit of an increase of time spent at higher PA levels for youth with relatively elevated amounts of body fat.     

Association of physical activity with body-composition indexes in children aged 6-8 y at varied risk of obesity

BACKGROUND: Physical inactivity increases the risk of obesity, but the relations between reported levels of physical activity (PA) and measures of body fatness (BF) in children are remarkably inconsistent. OBJECTIVE: We examined the relation between objective measures of PA and body-composition indexes in nonobese children. DESIGN: A cross-sectional study was conducted in 100 children aged 6-8 y who were recruited according to their risk of future obesity: high-risk children had >/=1 obese parent [body mass index (BMI; in kg/m(2)): >30] and low-risk children had 2 nonobese biological parents (BMI: <30). Free-living activity energy expenditure (AEE) and PA level were calculated from 7-d doubly labeled water measurements, time spent in light-intensity activity was assessed by heart rate monitoring, and body composition was determined from isotopic dilution. To adjust for body size, fat mass and fat-free mass were normalized for height and expressed as fat mass index (FMI) and lean mass index (LMI), respectively. RESULTS: High-risk children had significantly higher BMI, LMI, and FMI than did low-risk children, but no group differences in PA were found. AEE and PA level were positively associated with LMI and, after adjustment for sex and fat-free mass, negatively associated with FMI but not with BMI. Boys who spent more than the median time in light-intensity activities had significantly higher FMI than did less sedentary boys. This difference was not observed in girls. CONCLUSIONS: AEE and PA level were negatively associated with BF in nonobese children. Accurate measures of body composition are essential to appropriate assessment of relations between PA and obesity risk.     

Association of Diet,Physical Activity Guidelines and Cardiometabolic Risk Markers in Children

The aim was to identify different dietary and physical activity (PA) patterns in 5- to 14-year-old children with a high prevalence of overweight and obesity using cluster analysis based on their adherence to the Spanish Society of Community Nutrition dietary guidelines and levels of PA, and to determine their associations with age, sex, body composition, and cardiometabolic risk markers. In 549 children, hierarchical cluster analysis was used to identify subgroups with similar adherence to dietary recommendations and level of PA. Three clusters were identified: Cluster 1, with the lowest level of vigorous PA and adherence to dietary recommendations; Cluster 2, with the lowest levels of moderate and vigorous PA and the highest adherence to dietary recommendations; and Cluster 3, with the highest level of PA, especially vigorous PA and a medium level adherence to dietary recommendations. Cluster 3 had lower total body fat and higher lean body mass percentages than Cluster 2. Cluster 2 had lower high-density lipoprotein cholesterol and higher low-density lipoprotein cholesterol levels than Cluster 1. The results from our study suggest that it is important to consider adherence to PA recommendations together with adherence to dietary guidelines to understand patterns of obesogenic habits in pediatric populations with high prevalence of overweight and obesity.     

Determinants of childhood overweight and obesity in China

In order to investigate the determinants of childhood overweight and obesity in China, the prevalence of overweight (including obesity) was compared according to different dietary and physical activity patterns and parental body weight status. A total of 6826 children aged 7-17 years from the 2002 China National Nutrition and Health Survey were included in the study. Information for dietary intake was collected using three consecutive 24-h recalls by trained interviewers. The amounts of cooking oil and condiments consumed were weighed. An interview-administered 1-year physical activity questionnaire was used to collect physical activity information. The results showed that the heavier the parental bodyweight, the higher the overweight prevalence in children. The prevalence ratio increased if parent(s) were overweight and/or obese, up to 12.2 if both parents were obese. Overweight children consumed significantly more dietary energy, protein and fat, but less carbohydrate than their normal weight counterparts. On average, overweight children spent 0.5 h less on moderate/vigorous activities and 2.3 h more on low intensity activities per week. The following prevalence ratios were statistically significant: walking to and from school (0.6); moderate/vigorous activities > or =45 min/d (0.8); low intensity physical activities >2 h/d (1.3); the consumption of > or =25 g/d cooking oil (1.4); > or =200 g/d meat and meat products consumption (1.5); > or =100g/d dairy products (1.8). After adjustment for parental body weight status and socioeconomic status, only cooking oil consumption and walking to and from school remained significantly related to child overweight. In conclusion, parental weight status is an import-ant determinant. Fat intake, low intensity activities and active transport to/from school may be suitable entry points for overweight prevention among Chinese school children.     

Characteristics of inactive primary care patients: baseline data from the activity counseling trial. For the Activity Counseling Trial Research Group

BACKGROUND: Although many primary care patients are inactive, being able to classify even small amounts and intensities of activity and factors associated with these activity levels could be helpful for physicians who are trying to motivate their patients to become more physically active. METHODS: Sociodemographics, physical activity, fitness, other cardiovascular risk factors, and psychosocial measures were measured at baseline in the 874 patients in the Activity Counseling Trial. Patients were categorized into three groups: (1) no moderate-to-vigorous physical activity (MVPA), (2) some moderate but no vigorous activity, and (3) some vigorous activity. Multiple logistic regression was used to determine factors cross-sectionally associated with activity intensity. RESULTS: One or more cardiovascular risk factors in addition to physical inactivity were present in 84% of participants. Maximal oxygen uptake averaged 25.2 ml/kg/min; 85% had poor to fair aerobic fitness. Physical activity averaged 32.7 kcal/kg/day, with 13.5 min of MVPA/day; 26% engaged in some vigorous activity, 11% engaged in no MVPA. In unadjusted analyses, gender, age, race, education, income, employment, smoking, alcohol use, and exercise self-efficacy were associated with activity intensity (P = 0.05-0.001). A greater percentage engaged in moderate than in vigorous activity in all subgroups. In multiple logistic regression analyses, odds ratios (95% confidence intervals) for engaging in vigorous activity were 0. 39 (0.28, 0.56) for women, 0.38 (0.19, 0.75) for 65+ compared with 35- to 44-year-olds, and 1.14 (1.06, 1.22) for 10-unit increases in performance self-efficacy score. CONCLUSIONS: Most primary care patients who are physically inactive have additional cardiovascular risk factors, particularly overweight and obesity. All subgroups pursue moderate-intensity activity more often than vigorous activity. Women, older persons, and those with lower exercise self-efficacy are less likely to engage in vigorous activity.     

Physical activity behaviours of adults in the Greater Green Triangle region of rural Australia

Objective: To assess physical activity (PA) behaviours of adults in rural Australia. Design and setting: Three cross‐sectional surveys in the Greater Green Triangle area covering the south‐east of South Australia (Limestone Coast), and south‐west (Corangamite Shire) and north‐west (Wimmera) of Victoria during 2004–2006. Participants: A total of 1546 persons, aged 25– 74 years, randomly selected from the electoral roll. Main outcome measures: Overall PA, leisure‐time PA, occupational PA, active commuting and moderate‐to‐vigorous PA. Results: Approximately 80% of participants, more women than men, engaged in 30 minutes or more of daily PA. Only 30% (95% CI 26.3, 33.0) of men and 21% (95% CI 18.3, 23.9) of women did moderate‐to‐vigorous PA for at least 20–30 minutes four or more times a week. In leisure time, most participants were moderately active; almost one‐fifth were inactive and another fifth highly active. Two‐thirds of men engaged in high‐level occupational PA, compared with one‐sixth of women. Only 30% of participants actively commuted to work. There was a tendency for a positive association between income level and leisure‐time PA. Conclusions: One‐fifth of adults in rural Australia were inactive. While there was a high prevalence of participants who engaged in daily PA, few did so at moderate‐to‐vigorous intensity to achieve health benefits. As occupational PA is difficult to change, improvements in levels of PA are more likely during leisure‐time and for some people by engaging in commuting PA.     

Self-reported physical activity using International Physical Activity Questionnaire in adolescents and young adults with visual impairment

Background

Young people with visual impairment (VI) face many environmental barriers that influence physical activity.

Assessment of body fatness in young children using the skinfold technique and BMI vs body water dilution

OBJECTIVES: To compare body fatness estimated using a skinfold technique and body mass index (BMI) with body fatness estimated using the body water dilution method in healthy Swedish children 9 or 14 months of age. METHODS: Total body fat (TBF) was calculated from total body water, estimated using the doubly labelled water method, and body weight. When expressed in per cent of body weight, these estimates (%TBF-BWD) represented reference values for body fatness. Body fatness was also calculated from skinfold thickness (%TBF-SFT) and as BMI. The children were ranked and grouped into five groups with an increasing level of body fatness using BMI, %TBF-SFT and %TBF-BWD, respectively. SUBJECTS: A total of 30 infants 9 months of age and 29 children 14 months of age. RESULTS: On average, the children (n=59) had a BMI=17.5+/-1.6 kg/m(2) and contained 27.8+/-3.7 %TBF-SFT and 29.1+/-4.4 %TBF-BWD. %TBF-BWD minus %TBF-SFT was=1.35+/-4.06%. By measuring %TBF-SFT or BMI, about 35% of the children could be classified in the correct group with respect to body fatness. Serious misclassification (ie two or more groups too high or too low) was, however, more common for %TBF-SFT (29%) than for BMI (17%). CONCLUSIONS: The capacity of BMI to place children in the correct body fatness group was poor although not quite as poor as the corresponding capacity of the skinfold technique. The latter method produced inaccurate and imprecise estimates of body fatness.     

Effect of intensity of physical activity on body fatness and fat distribution

To evaluate the effect of intensity of physical activity on body fatness and fat distribution, observations of 1366 women and 1257 men who participated in the 1981 Canada Fitness Survey were analyzed. Subjects were tested for energy expenditure of leisure-time activities and estimated maximal oxygen uptake (VO2max), body fatness was measured by subcutaneous skinfold thicknesses, and anthropometric measurements were made. Subjects of both sexes were categorized into four subgroups on the basis of their participation in leisure-time activities of various intensities. In general, subjects practicing vigorous activities on a regular basis had lower subcutaneous skinfold thicknesses and waist-to-hip ratios (WHRs) than those not performing these activities. These differences remained statistically significant after a covariance analysis was used to remove the effect of total energy expenditure of leisure-time activities on subcutaneous fat and fat distribution. Moreover, the WHR remained significantly lower in subjects performing high-intensity exercise after the effect of subcutaneous fat on fat distribution was adjusted for.     

Dietary and physical activity/inactivity factors associated with obesity in school-aged children

Diet and physical activity (PA) are essential components of nutritional status. Adequate nutrition and an active lifestyle are key factors during childhood, because food habits track into adulthood. Children spend more time in school than in any other environment away from home. Studying the diet factors and patterns of PA that affect obesity risk in children during school hours and the complete school day can help identify opportunities to lower this risk. We directly measured the time children spent performing moderate to vigorous PA (MVPA) at school, compared the amount and intensity of PA during school hours with after-school hours, and tried to determine if diet behaviors and PA or inactivity were associated with excess weight and body fat. This cross-sectional study included 143 normal-weight (NLW) and 48 obese children aged 8-10 y. Diet data were obtained from two 24-h recalls. Body composition was measured by bioimpedance. Screen time and sports participation data were self-reported. NLW children drank/ate more dairy servings than the obese children, who consumed more fruit-flavored water than the NLW group. Consumption of soft drinks, sugar-added juices, and fresh juices was low in both groups. Children were less active during school hours than after school. MVPA was lower during school hours in the obese group than in the NLW group. Schools, parents, and authorities should be more involved in promoting strategies to improve the dietary habits and PA levels of school-aged children, because this group is not achieving the recommended level of daily MVPA.     

Energy expenditure determined by self-reported physical activity is related to body fatness

OBJECTIVE: Activity self-reports are a commonly used tool in assessing daily physical activity (PA) and associated energy expenditure (EE). This study examined the effect of relative body fatness (%BF) on differences between self-reported and measured duration and associated EE in healthy adults. RESEARCH METHODS AND PROCEDURES: Men and women (n = 115, age 38+/-9 years), ranging in %BF from 7.9% to 58.9%, spent two separate days (normal and exercise) in a whole-room indirect calorimeter where EE was measured. While in the room calorimeter, subjects reported the type, intensity, and duration of each performed PA. The Compendium of Physical Activity was used to calculate the energy cost of each reported activity. The EE of all self-reported activities (EEr) was categorized into four intensity levels, synchronized, and compared with EE from the room calorimeter (EEm). RESULTS: With increasing %BF, subjects significantly overestimated duration of more strenuous activities (> or =4.5), while underestimating moderate activities (2.5 to 4.4 metabolic equivalents (METs)). Misreporting of duration and/or intensity caused an overestimation or underestimation of PA-associated EE at these levels. Reported EE sleep was lower than measured EE sleep, although both had similar durations. As a result, total EEr was similar to EEm. DISCUSSION: Individual variability of daily total PA and associated EE generated from self-reports in adults is high. Persons with a higher %BF report duration and/or intensity of moderate to high levels of PA with lower accuracy than leaner individuals. We conclude using the Compendium of Physical Activity is not suitable for the accurate estimation of self-reported EE of AA in adults with a higher %BF.     

Correlates of individual differences in body-composition changes resulting from physical training in obese children

BACKGROUND: No studies have been reported in children that assess correlates of body-composition changes in response to a physical training intervention. OBJECTIVE: The hypothesis studied was that variation in diet and physical activity would explain a significant portion of the interindividual variation in the response of body composition to physical training. DESIGN: The participants were 71 obese children aged 7-11 y (22 boys, 49 girls; 31 whites, 40 blacks). Body composition was measured by dual-energy X-ray absorptiometry, physical activity by a 7-d recall interview, and diet by two, 2-d recalls. The children underwent 4 mo of physical training. RESULTS: The mean attendance was 4 d/wk, the mean (+/-SD) heart rate for the 40-min sessions was 157 +/- 7 beats/min, and the mean energy expenditure was 946 +/- 201 kJ/session. On average, the percentage body fat decreased significantly in the total group, and total mass, fat-free soft tissue, bone mineral content, and bone mineral density increased, but there was a good deal of individual variability. Multiple regression models indicated that in general, more frequent attendance, being a boy, lower energy intake, and more vigorous activity were associated with healthier body-composition changes with physical training. Ethnicity was not retained as a correlate of the change of any component of body composition. CONCLUSIONS: In obese children, age, vigorous activity, diet, and baseline percentage body fat together accounted for 25% of the variance in the change in percentage body fat with physical training.     

Racial differences in insulin secretion and sensitivity in prepubertal children: role of physical fitness and physical activity

OBJECTIVE: To investigate in prepubertal children whether physical fitness and/or physical activity are: 1) associated with insulin secretion and sensitivity and 2) account for racial differences in insulin secretion and sensitivity. RESEARCH METHODS AND PROCEDURES: Subjects included 34 African American and 34 white nondiabetic children aged 5 to 11 years. Data were divided into two sets according to the availability of VO2max and physical activity data. Body composition was measured by dual-energy X-ray absorptiometry. Subcutaneous abdominal adipose tissue and intra-abdominal adipose tissue were examined by computed tomography. Insulin sensitivity (S1) and acute insulin response (AIR) were determined by a frequently sampled intravenous glucose tolerance test. An all-out, progressive treadmill exercise test was used for measuring VO2max. Physical activity data were collected by questionnaire. RESULTS: African American children had lower SI and higher AIR than white children, after adjusting for total body fat mass. African Americans reported higher levels of physical activity (hours/wk) than whites, but had a lower VO2max. In multiple linear regression analysis, hours/wk of activity and hours/wk of vigorous activity, but not moderate activity, were independently related to SI and AIR after adjusting for race, total body fat mass or fat distribution, and total lean tissue mass. VO2max was not related to AIR, and was inversely related to SI, after adjusting for body composition. Race remained significantly associated with both SI and AIR, even after adjusting for body composition, fat distribution, and hours/wk of activity or hours/wk of vigorous activity. DISCUSSION: In summary, overall physical activity and, especially, vigorous activity were associated with insulin secretion and sensitivity. However, neither physical activity nor VO2max explained the racial difference in insulin secretion (higher in African Americans) and sensitivity (lower in African Americans). Thus, racial (African American to white) differences in aspects of insulin action seem to be due to factors other than body composition, fat distribution, cardiovascular fitness, and amount of physical activity.