Cardiometabolic risk among rural Native American adults in a large multilevel multicomponent intervention trial

This cross-sectional analysis of the baseline evaluation sample of the Obesity Prevention and Evaluation of InterVention Effectiveness in Native Americans 2 (OPREVENT2) study included 601 Native American adults ages 18-75 living in rural reservation communities in the Midwest and Southwest United States. Participants completed a self-report questionnaire for individual and family history of hypertension, heart disease, diabetes and obestiy. Body mass index (BMI), percent body fat, and blood pressure were measured by trained research staff. About 60% of respondents had a BMI >30 kg/m2. Approximately 80% had a waist-to-hip ratio and percent body fat classified as high risk, and nearly 64% had a high-risk blood pressure measurement. Although a large proportion of participants reported a family history of chronic disease and had measurements that indicated elevated risk, relatively few had a self-reported diagnosis of any chronic disease. Future studies should examine potential connections between healthcare access and discordance in self-reported versus measured disease risks and diagnoses.

Exposure to a Multilevel, Multicomponent Obesity Prevention Intervention (OPREVENT2) in Rural Native American Communities: Variability and Association with Change in Diet Quality

The OPREVENT2 obesity prevention trial was a multilevel multicomponent (MLMC) intervention implemented in rural Native American communities in the Midwest and Southwest U.S. Intervention components were delivered through local food stores, worksites, schools, community action coalitions, and by social and community media. Due to the complex nature of MLMC intervention trials, it is useful to assess participants’ exposure to each component of the intervention in order to assess impact. In this paper, we present a detailed methodology for evaluating participant exposure to MLMC intervention, and we explore how exposure to the OPREVENT2 trial impacted participant diet quality. There were no significant differences in total exposure score by age group, sex, or geographic region, but exposure to sub-components of the intervention differed significantly by age group, sex, and geographical region. Participants with the highest overall exposure scores showed significantly more improvement in diet quality from baseline to follow up compared to those who were least exposed to the intervention. Improved diet quality was also significantly positively associated with several exposure sub-components. While evaluating exposure to an entire MLMC intervention is complex and imperfect, it can provide useful insight into an intervention’s impact on key outcome measures, and it can help identify which components of the intervention were most effective.

Increased Energy Cost of Mobility in Chronic Stroke

The purpose of this study was to compare the energy cost of completing mobility-related activities in chronic stroke to the estimated energy cost found in the compendium of physical activities, a resource that estimates and classifies energy cost of various human physical activities. Men (n=18) and women (n=10) with chronic hemiparetic gait (stroke latency: 4 ± 2 years, age: 60.4 ± 1.6 years, BMI: 31.5 ± 1.1 kg/m²) participated in the study. Portable energy cost monitoring (COSMED K4b2) was performed during five mobility activities of varying intensity to determine metabolic equivalents (METs, or oxygen consumption in multiples of resting level) for each activity. The METs achieved during the five activities were compared to the following compendium MET values for: 1) floor sweeping; 2) stepping in place; 3) over-ground walking; 4) lower speed treadmill walking (1.0 mph at 4% incline); and 5) higher speed treadmill walking (2.0 mph at 4% incline). Measurements were obtained for 10 min at rest and 5 minutes during each of the five activities. The energy cost of rest was only 85% of Compendium METS, while mobility-related activities were ~1.25-1.50 fold greater when measured in stroke vs. Compendium METS for all measures (P's<0.05), except floor sweeping, which was similar between groups. These data indicate that MET levels provided in the compendium are not applicable to chronic stroke survivors as they overestimate energy expenditure at rest and underestimate energy expenditure during physical activity, indicating poor efficiency in movement, thus elevating the oxygen cost of completing general daily activities.

Toddler physical activity study: laboratory and community studies to evaluate accelerometer validity and correlates

Background

Toddlerhood is an important age for physical activity (PA) promotion to prevent obesity and support a physically active lifestyle throughout childhood. Accurate assessment of PA is needed to determine trends/correlates of PA, time spent in sedentary, light, or moderate-vigorous PA (MVPA), and the effectiveness of PA promotion programs. Due to the limited availability of objective measures that have been validated and evaluated for feasibility in community studies, it is unclear which subgroups of toddlers are at the highest risk for inactivity. Using Actical ankle accelerometry, the objectives of this study are to develop valid thresholds, examine feasibility, and examine demographic/ anthropometric PA correlates of MVPA among toddlers from low-income families.

Methods

Two studies were conducted with toddlers (12–36 months). Laboratory Study (n = 24)- Two Actical accelerometers were placed on the ankle. PA was observed using the Child Activity Rating Scale (CARS, prescribed activities). Analyses included device equivalence reliability (correlation: activity counts of two Acticals), criterion-related validity (correlation: activity counts and CARS ratings), and sensitivity/specificity for thresholds. Community Study (n = 277, low-income mother-toddler dyads recruited)- An Actical was worn on the ankle for > 7 days (goal >5, 24-h days). Height/weight was measured. Mothers reported demographics. Analyses included frequencies (feasibility) and stepwise multiple linear regression (sMLR).

Results

Laboratory Study- Acticals demonstrated reliability (r = 0.980) and validity (r = 0.75). Thresholds demonstrated sensitivity (86 %) and specificity (88 %). Community Study- 86 % wore accelerometer, 69 % had valid data (mean = 5.2 days). Primary reasons for missing/invalid data: refusal (14 %) and wear-time ≤2 days (11 %). The MVPA threshold (>2200 cpm) yielded 54 min/day. In sMLR, MVPA was associated with age (older > younger, β = 32.8, p < 0.001), gender (boys > girls, β = −11.21, p = 0.032), maternal MVPA (β = 0.44, p = 0.002) and recruitment location (suburban > urban, β = 19.6, p < 0.001), or race (non-Black > Black, β = 18.5, p = 0.001). No association with toddler weight status.

Conclusions

Ankle accelerometry is a valid, reliable, and feasible method of assessing PA in community studies of toddlers from low-income families. Sub-populations of toddlers may be at increased risk for inactivity, including toddlers that are younger, female, Black, those with less active mothers, and those living in an urban location.

Validating accelerometry as a measure of physical activity and energy expenditure in chronic stroke

BACKGROUND

Accelerometers can objectively measure steps taken per day in individuals without gait deficits, but accelerometers also have the ability to estimate frequency, intensity, and duration of physical activity. However, thresholds to distinguish varying levels of activity intensity using the Actical brand accelerometer are standardized only for the general population and may underestimate intensity in stroke.

OBJECTIVE

To derive Actical activity count thresholds specific to stroke disability for use in more accurately gauging time spent at differing activity levels.

METHODS

Men (n = 18) and women (n = 10) with chronic hemiparetic gait (4 ± 2 years latency, 43% Caucasian, 56% African-American, ages of 47-83 years, BMI 19-48 kg/m²) participated in the study. Actical accelerometers were placed on the non-paretic hip to obtain accelerometry counts during eight activities of varying intensity: (1) watching TV; (2) seated stretching; (3) standing stretching; (4) floor sweeping; (5) stepping in place; (6) over-ground walking; (7) lower speed treadmill walking (1.0 mph at 4% incline); and (8) higher speed treadmill walking (2.0 mph at 4% incline). Simultaneous portable monitoring (Cosmed K4b2) enabled quantification of energy cost for each activity in metabolic equivalents (METs, or oxygen consumption in multiples of resting level). Measurements were obtained for 10 min of standard rest and 5 min during each of the eight activities.

RESULTS

Regression analysis yielded the following new stroke-specific Actical minimum thresholds: 125 counts per minute (cpm) for sedentary/light activity, 667 cpm for light/moderate activity, and 1546 cpm for moderate/vigorous activity.

CONCLUSION

Our revised cut points better reflect activity levels after stroke and suggest significantly lower thresholds relative to those observed for the general population of healthy individuals. We conclude that the standard, commonly applied Actical thresholds are inappropriate for this unique population.

Ankle Accelerometry for Assessing Physical Activity Among Adolescent Girls: Threshold Determination, Validity, Reliability, and Feasibility

PURPOSE

Ankle accelerometry allows for 24-hr data collection and improves data volume/integrity versus hip accelerometry. Using Actical ankle accelerometry, the purpose of this study was to (a) develop sensitive/specific thresholds, (b) examine validity/reliability, (c) compare new thresholds with those of the manufacturer, and (d) examine feasibility in a community sample (low-income, urban adolescent girls).

METHOD

Two studies were conducted with 6th- through 7th-grade girls (aged 10-14 years old): First was a laboratory study (n = 24), in which 2 Actical accelerometers were placed on the ankle and worn while measuring energy expenditure (Cosmed K4b2, metabolic equivalents [METs]) during 10 prescribed activities. Analyses included device equivalence reliability (intraclass correlation coefficient [ICC], activity counts of 2 Acticals), criterion-related validity (correlation, activity counts and METs), and calculations of sensitivity, specificity, kappa, and receiver-operating characteristic curves for thresholds. The second was a free-living study (n = 459), in which an Actical was worn for more than 7 days on the ankle (full 24-hr days retained). Analyses included feasibility (frequencies, missing data) and paired t tests (new thresholds vs. those of the manufacturer).

RESULTS

In the laboratory study, the Actical demonstrated reliability (ICC = .92) and validity (r = .81). Thresholds demonstrated sensitivity (91%), specificity (84%), kappa = .73 (p = .043), area under curve range = .81-.97. In the free-living study, 99.6% of participants wore the accelerometer; 84.1% had complete/valid data (mean = 5.7 days). Primary reasons for missing/invalid data included: improper programming/documentation (5.2%), failure to return device (5.0%), and wear-time ≤ 2 days (2.8%). The moderate-to-vigorous physical activity threshold (> 3,200 counts/minute) yielded 37.2 min/day, 2 to 4.5 times lower than that of the manufacturer's software (effect size = 0.74-4.05).

CONCLUSIONS

Validity, reliability, and feasibility evidences support Actical ankle accelerometry to assess physical activity in community studies of adolescent girls. When comparing manufacturers' software versus new thresholds, a major difference was observed.

Dietary prescription adherence and non-structured physical activity following weight loss with and without aerobic exercise

OBJECTIVES

To compare the effects of weight loss with and without exercise on 1) dietary prescription adherence and 2) non-structured activity in postmenopausal women.

DESIGN

Longitudinal study.

SETTING

Clinical research setting with facility based exercise and nutrition education.

PARTICIPANTS

Overweight and obese women, 45-76 years old.

INTERVENTION

6 months of weight loss alone (WL; N=38) or with aerobic exercise (AEX+WL; N=41).

MEASUREMENTS

Cardiorespiratory fitness (VO2max), resting metabolic rate (RMR), seven day food intake, and physical activity (by Actical accelerometers worn in a subset subgroup: WL: N=10; AEX+WL: N=15) were assessed before and after the interventions.

RESULTS

Both interventions resulted in similar weight loss (~9%) and no significant changes in RMR, while only the AEX+WL group improved VO2max (~10%). At baseline, the AEX+WL group consumed slightly more protein than the WL group (P<0.01). Macronutrient intake did not change following AEX+WL, but the WL group decreased their fat intake and increased their carbohydrates and protein intakes (Ps<0.05), which resulted in similar macronutrient intakes between groups post-intervention. Weekday total activity counts decreased 22% (P<0.05) following WL. This change tended (P=0.07) to be different than the lack of change in non-structured activity observed following AEX+WL.

CONCLUSION

Although similar dietary adherence was observed, these data suggest that postmenopausal women undergoing weight loss may benefit from the addition of exercise to prevent the decline in non-structured activity observed following weight loss alone.

Comparison of BMI and physical activity between old order Amish children and non-Amish children

OBJECTIVE

The Old Order Amish (OOA) is a conservative Christian sect of European origin living in Pennsylvania. Diabetes is rare in adult OOA despite a mean BMI rivaling that in the general U.S. non-Hispanic white population. The current study examines childhood factors that may contribute to the low prevalence of diabetes in the OOA by comparing OOA children aged 8-19 years with National Health and Nutrition Examination Survey (NHANES) data and children from Maryland's Eastern Shore (ES), a nearby, non-Amish, rural community. We hypothesized that pediatric overweight is less common in OOA children, that physical activity (PA) and BMI are inversely correlated, and that OOA children are more physically active than ES children.

RESEARCH DESIGN AND METHODS

We obtained anthropometric data in 270 OOA children and 229 ES children (166 non-Hispanic white, 60 non-Hispanic black, 3 Hispanic). PA was measured by hip-worn accelerometers in all ES children and in 198 OOA children. Instrumentation in 43 OOA children was identical to ES children.

RESULTS

OOA children were approximately 3.3 times less likely than non-Hispanic white ES children and NHANES estimates to be overweight (BMI ≥85th percentile, Centers for Disease Control and Prevention). Time spent in moderate/vigorous PA (MVPA) was inversely correlated to BMI z-score (r = -0.24, P = 0.0006). PA levels did not differ by ethnicity within the ES group, but OOA children spent an additional 34 min/day in light activity (442 ± 56 vs. 408 ± 75, P = 0.005) and, impressively, an additional 53 min/day in MVPA (106 ± 54 vs. 53 ± 32, P < 0.0001) compared with ES children. In both groups, boys were more active than girls but OOA girls were easily more active than ES boys.

CONCLUSIONS

We confirmed all three hypotheses. Together with our previous data, the study implies that the OOA tend to gain their excess weight relatively late in life and that OOA children are very physically active, both of which may provide some long-term protection against diabetes.

A cross-sectional and longitudinal study of travel by walking before and after school among eighth-grade girls

PURPOSE

To examine "travel by walking" (TBW) before and after school among eighth-grade girls.

METHODS

Participants attended 36 middle schools from Arizona, Maryland, Minnesota, Louisiana, California, and South Carolina participating in the Trial of Activity for Adolescent Girls. The cross-sectional sample consisted of 3,076 eighth-grade girls, and the longitudinal sample included 1,017 girls who participated in both sixth and eighth grades. Before- or after-school TBW status was determined from the 3-Day Physical Activity Recall. The main outcomes were body mass index and physical activity, which was measured by accelerometry, estimated for total physical activity (light, moderate, vigorous) and moderate-to-vigorous physical activity (MVPA).

RESULTS

Eighth-grade girls who reported TBW had 4 more minutes (95% confidence interval = 2.1-6.1) of MVPA before and after school than nonwalkers, and 2 more minutes of MVPA (95% confidence interval = 1.1-3.1) on an average weekday. In the longitudinal sample, girls who reported TBW before and after school in both sixth and eighth grades (consistent walkers) accumulated more minutes of MVPA for an average weekday than inconsistent walkers in both sixth (27 ± 2.2 vs. 25 ± 1.9 minutes; p = .03) and eighth (28 ± 2.6 vs. 25 ± 2.3 minutes; p = .003) grades. There were no differences in body mass index by walking status.

CONCLUSIONS

Adolescent girls who reported TBW before and after school accumulated more minutes of MVPA than nonwalkers. Efforts to prevent the decline in walking to school in middle school girls could contribute to their overall physical activity.

How active are American adolescents and have they become less active?

The aim of this study was to systematically examine patterns and time trends in US adolescents' physical activity (PA) and sedentary behaviours. We examined findings from the nationally representative Youth Risk Behavior Surveillance Surveys during 1991-2007, and fit regression models estimating average annual changes and tested time trends, and age, gender and ethnic differences. US adolescents had less PA but more sedentary behaviours than recommended, but showed no clear evidence of becoming less active. In 2007, 24.9% reported on average spending ≥3 h of screen time per day for non-school work; only 34.7% met the current PA recommendations, and it (25.6%) was even lower in girls. The prevalence of having sufficient vigorous PA changed little between 1993 and 2005 (from 65.8% to 64.1%). Encouraging changes regarding TV viewing time and physical education (PE) were detected. PE daily attendance rate and exercising >20 min during an average PE class increased significantly, while watching TV ≥3 h d⁻¹ decreased significantly in recent years. Considerable sex, age and ethnic differences existed in the patterns and trends. These national data show no clear evidence of declining PA among US adolescents in recent years. Reduced PA is not likely the major explanation of the recent increase in obesity among US adolescents.

Challenge! Health promotion/obesity prevention mentorship model among urban, black adolescents

OBJECTIVES

The objective of this study was to evaluate a 12-session home/community-based health promotion/obesity prevention program (Challenge!) on changes in BMI status, body composition, physical activity, and diet.

METHODS

A total of 235 black adolescents (aged 11-16 years; 38% overweight/obese) were recruited from low-income urban communities. Baseline measures included weight, height, body composition, physical activity (PA), and diet. PA was measured by 7-day play-equivalent physical activity (> or =1800 activity counts per minute). Participants were randomly assigned to health promotion/obesity prevention that is anchored in social cognitive theory and motivational interviewing and was delivered by college-aged black mentors or to control. Postintervention (11 months) and delayed follow-up (24 months) evaluations were conducted. Longitudinal analyses used multilevel models with random intercepts and generalized estimating equations, controlling for baseline age/gender. Stratified analyses examined baseline BMI category.

RESULTS

Retention was 76% over 2 years; overweight/obese status declined 5% among intervention adolescents and increased 11% among control adolescents. Among overweight/obese youth, the intervention reduced total percentage of body fat and fat mass and increased fat-free mass at delayed follow-up and increased play-equivalent physical activity at postintervention but not at delayed follow-up. Intervention adolescents declined significantly more in snack/dessert consumption than control adolescents at both follow-up evaluations.

CONCLUSIONS

At postintervention, there were intervention effects on diet and PA but not BMI category or body composition. At delayed follow-up, dietary changes were sustained and the intervention prevented an increase in BMI category. Body composition was improved for overweight/obese youth. Changes in body composition follow changes in diet and PA and may not be detected immediately after intervention.

Associations between patterns of objectively measured physical activity and risk factors for the metabolic syndrome

PURPOSE

To determine whether certain patterns of objectively measured physical activity (PA) are associated with the risk factors for or the diagnosis of the metabolic syndrome (MS).

DESIGN

Latent class analysis, including assessment of the associations between latent PA classes and risk factors for the MS.

SETTING

Random sample from throughout the United States using data from the 2003-2004 National Health and Nutrition Examination Survey.

SUBJECTS

A total of 3458 civilian adult noninstitutionalized U.S. citizens.

MEASURES

Daily minutes of moderate-to-vigorous PA across a 7-day week based on accelerometer measurements, as well as high blood pressure, blood glucose levels, triglyceride levels, and body mass index, along with low levels of high density lipoproteins, using clinical cut points.

RESULTS

Membership in the more active PA classes was consistently associated with lower odds of all risk factors for the MS. However, when participants were categorized into quartiles of the coefficients of variation of PA across 7 days, few differences were seen in any of the risk factors.

CONCLUSIONS

Accumulating the total weekly recommended amount of PA is consistently associated with positive health profiles, and more PA than the recommended amounts may be even better. However, the manner in which this activity is accumulated, either spread over most days of the week or compressed into just a couple of days, may have similar associations with the risk factors for the MS.

Progressive adaptive physical activity in stroke improves balance, gait, and fitness: preliminary results

PURPOSE

We conducted a non-controlled pilot intervention study in stroke survivors to examine the efficacy of low-intensity adaptive physical activity to increase balance, improve walking function, and increase cardiovascular fitness and to determine whether improvements were carried over into activity profiles in home and community.

METHOD

Adaptive physical activity sessions were conducted 3 times/week for 6 months. The main outcomes were Berg Balance Scale, Dynamic Gait Index, 6-Minute Walk Test, cardiovascular fitness (VO2 peak), Falls Efficacy Scale, and 5-day Step Activity Monitoring.

RESULTS

Seven men and women with chronic ischemic stroke completed the 6-month intervention. The mean Berg Balance baseline score increased from 33.9+/-8.5 to 46+/-6.7 at 6 months (mean+/-SD; p=.006). Dynamic Gait Index increased from 13.7+/-3.0 to 19.0+/-3.5 (p=.01). Six-minute walk distance increased from 840+/-110 feet to 935+/-101 feet (p=0.02). VO2 peak increased from 15.3+/-4.1 mL/kg/min to 17.5+/-4.7 mL/kg/min (p=.03). There were no significant changes in falls efficacy or free-living ambulatory activity.

CONCLUSION

A structured adaptive physical activity produces improvements in balance, gait, fitness, and ambulatory performance but not in falls efficacy or free-living daily step activity. Randomized studies are needed to determine the cardiovascular health and functional benefits of structured group physical activity programs and to develop behavioral interventions that promote increased free-living physical activity patterns.

A longitudinal study of sedentary behavior and overweight in adolescent girls

The aim of this study is to examine sedentary and light activity in relation to overweight in adolescent girls. Adolescent girls were randomly recruited from 36 schools participating in the Trial of Activity for Adolescent Girls (TAAG). Assessments included age, ethnicity, socioeconomic status, and body composition estimated from weight, height, and triceps skinfold. Sedentary and light activity was measured for 6 days using accelerometry in 6th and in 8th grade among two randomly sampled cross-sections of girls. Sedentary activity increased from the 6th to 8th grade by 51.5 min/day. In the 8th grade, a significantly higher number of hours in sedentary activity for each of the 6-days of measurement were evident with higher tertiles of percent body fat (30-35%, >35% fat) (P < 0.05), but not across all increasing tertiles of BMI (5th to 85th, 85th to 95th, and >95th percentiles). The increase in sedentary activity was observed on weekdays, but not on weekends for percent body fat tertiles. In the cohort of girls measured in both 6th and 8th grades, the mean cross-sectional coefficient estimates were significant for percent body fat, but not BMI for sedentary and light activities. Adolescent girls from the 6th to 8th grade are shifting their time from light to more sedentary activity as measured by accelerometers. In addition, the increase in sedentary activity is not associated with an adverse effect on BMI or percent body fat. The eventual impact of this shift to a more sedentary lifestyle on body composition and other outcomes needs to be evaluated further.

Patterns of objectively measured physical activity in the United States

PURPOSE

We used latent class analysis (LCA) to assess patterns of physical activity among adults, using the 7 d of accelerometer data from the 2003-2004 NHANES.

METHODS

For each participant, we determined the daily minutes of moderate-to-vigorous physical activity (MVPA), vigorous physical activity (VPA), and minutes of MVPA that occurred in bouts of 10 min. Participants were then categorized into patterns of activity, using LCA and adjusting for sociodemographic characteristics.

RESULTS

For overall MVPA, five classes of physical activity were defined, including two least active classes, which averaged less than 25 min of MVPA per day and represented 78.7% of the total study population. The most active class averaged 134 min of MVPA per day and comprised 0.9% of the population. The results for bout minutes of MVPA were similar to the patterns produced for overall MVPA, with the exception of a "weekend warrior" class with moderate levels of physical activity Monday through Friday but with a much higher level of activity on the weekend, particularly on Sunday. This class represented 1.8% of the population. Only 1.4% of all days achieved 10 min or more of VPA, and in 91.1% of all days, participants accumulated less than 1 min of VPA. The LCA analysis of VPA did not produce stable results, because of the small number of participants registering any minutes of VPA.

CONCLUSION

Our results indicate that a very large portion of the U.S. population may be classified into patterns of physical activity that represent low levels of MVPA throughout the week. The LCA analysis provided a novel approach for assessing patterns of objectively measured physical activity in epidemiologic studies.

An integrated multi-institutional diabetes prevention program improves knowledge and healthy food acquisition in northwestern Ontario First Nations

This article presents the impact results of a feasibility study in Canada for prevention of risk factors for diabetes in seven northwestern Ontario First Nations. Baseline and follow-up data were collected before and after the 9-month intervention program in schools, stores, and communities that aimed to improve diet and increase physical activity among adults. Regression analyses indicate a significant change in knowledge among respondents in intervention communities (p < .019). There was also a significant increase in frequency of healthy food acquisition among respondents in the intervention communities (p < .003). There were no significant changes in physical activity or body mass index in either intervention or comparison groups. The multi-institutional approach demonstrated promising results in modifying selected risk factors for diabetes First Nations communities.

Objectively assessed associations between physical activity and body composition in middle-school girls: the Trial of Activity for Adolescent Girls

Declining levels of physical activity probably contribute to the increasing prevalence of overweight in US youth. In this study, the authors examined cross-sectional and longitudinal associations between physical activity and body composition in sixth- and eighth-grade girls. In 2003, girls were recruited from six US states as part of the Trial of Activity for Adolescent Girls. Physical activity was measured using 6 days of accelerometry, and percentage of body fat was calculated using an age- and ethnicity-specific prediction equation. Sixth-grade girls with an average of 12.8 minutes of moderate-to-vigorous physical activity (MVPA) per day (15th percentile) were 2.3 times (95% confidence interval: 1.52, 3.44) more likely to be overweight than girls with 34.7 minutes of MVPA per day (85th percentile), and their percent body fat was 2.64 percentage points greater (95% confidence interval: 1.79, 3.50). Longitudinal analyses showed that percent body fat increased 0.28 percentage points less in girls with a 6.2-minute increase in MVPA than in girls with a 4.5-minute decrease (85th and 15th percentiles of change). Associations between MVPA in sixth grade and incidence of overweight in eighth grade were not detected. More population-based research using objective physical activity and body composition measurements is needed to make evidence-based physical activity recommendations for US youth.

Weekend and weekday patterns of physical activity in overweight and normal-weight adolescent girls

OBJECTIVE

To describe the patterns (specifically comparing weekdays and weekends classified by intensities) of physical activity (PA) measured by accelerometry in adolescent girls.

RESEARCH METHODS AND PROCEDURES

Healthy sixth grade girls (n=1603), 11 to 12 years old, were randomly recruited from 36 schools participating in the Trial of Activity in Adolescent Girls. Age, ethnicity, socioeconomic status, weight, and height were taken. PA patterns were measured for 6 days using accelerometry.

RESULTS

Adolescent girls spend most of their time in sedentary (52% to 57% of the day) and light activity (40% to 45% of the day) on weekdays and weekends. In all girls, total PA comprised 44.5% of the day (41.7% light, 2.2% moderate, and 0.7% vigorous) with sedentary activity comprising 55.4%. Moderate-to-vigorous PA (MVPA) was higher (p<0.001) on weekdays than weekends in all girls, but MVPA was lower in at-risk of overweight+overweight girls (p<0.001) on both weekdays and weekends compared with normal-weight girls.

DISCUSSION

Adolescent girls are more active at moderate and vigorous intensities on weekdays than on weekends, and at-risk of overweight and those overweight spend less time engaging in MVPA than normal-weight girls.

Travel by walking before and after school and physical activity among adolescent girls

OBJECTIVE

To examine how "travel by walking" before and after school contributes to total physical activity of adolescent girls.

DESIGN

Cross-sectional sample.

SETTING

Thirty-six middle schools from Arizona, Maryland, Minnesota, Louisiana, California, and South Carolina participating in the Trial of Activity for Adolescent Girls (TAAG).

PARTICIPANTS

Seventeen hundred twenty-one sixth-grade girls consented to participate; adequate information was available for 1596 participants (93%).

MAIN EXPOSURE

Travel by walking before school, after school, and before and after school combined assessed from the 3-Day Physical Activity Recall.

MAIN OUTCOME MEASURE

Mean minutes of physical activity measured by accelerometry were estimated for total physical activity (light, moderate, vigorous), moderate to vigorous activity (MVPA), and MVPA of 3 metabolic equivalents.

RESULTS

Travel by walking was reported by 14% of participants before school and 18% after school. Girls who reported travel by walking before and after school (combined) had 13.7 more minutes (95% confidence interval, 1.2-26.3) of total physical activity and 4.7 more minutes (95% confidence interval, 2.2-7.2) of MVPA than girls who did not report this activity. Before-school and after-school walkers (but not both) accumulated 2.5 more minutes (95% confidence interval, 0.10-4.9) and 2.2 more minutes (95% confidence interval, 0.24-4.2) of MVPA on an average weekday, respectively, than nonwalkers.

CONCLUSION

Our results provide evidence that walking to and from school increases weekday minutes of total physical activity and MVPA for middle-school girls.

Associations of body size and composition with physical activity in adolescent girls

PURPOSE

To examine whether components of body composition (size, fat mass, and fat-free mass) were related to physical activity.

METHODS

A random sample of 60 eligible sixth grade girls at each of 36 schools (six schools per region and six regions in total sample); complete measurements on 1,553 girls. Physical activity was assessed over 6 d in each girl using an accelerometer, and body composition was assessed using a multiple regression equation using body mass index and triceps skinfold. Minutes of moderate-to-vigorous and vigorous physical activity were estimated from accelerometer counts per 30 s above threshold values determined from a previous study.

RESULTS

Significant inverse relationships were found for all measures of body size and composition and all physical activity indices. The combination of fat and fat-free mass expressed as a weight and as an index (divided by height squared) along with race, SES, site, and school were most highly associated with physical activity in multiple regression analysis, accounting for 14-15% of the variance in physical activity. Fat mass was more closely related to moderate-to-vigorous physical activity (MVPA) and vigorous physical activity (VPA) than fat-free mass with higher standardized regression coefficients.

CONCLUSION

We conclude that both fat mass or fat mass index as well as fat-free mass or fat-free mass index make independent contributions in association with physical activity levels. These indices are recommended for future studies.

Physical activities in adolescent girls: variability in energy expenditure

BACKGROUND

Understanding interindividual variability of energy expended in common activities is important for determining precise estimates of energy expenditure in surveillance studies and clinical trials. The purpose of this study was to describe the variability in energy expenditure for selected physical activities among adolescent girls.

METHODS

Seventy-four adolescent girls (aged 13 to 14 years) participated in this cross-sectional investigation. Data were collected in 2001 and analyzed in 2004. Energy expenditure was measured by indirect calorimetry for ten activities and during a submaximal cycle ergometer test, which was used to estimate cardiorespiratory fitness. Variability in energy expended for the various activities was expressed by standard deviation, coefficient of variation, and range for three different energy expenditure variables: relative VO2 (milliliters per kilogram per minute), absolute VO2 (liters per minute(-1)), and calculated metabolic rate (kilojoules per minute).

RESULTS

Depending on the expression of energy expenditure, coefficients of variation ranged from a low of 13.2% for climbing stairs to a high of 38.4% for playing a computer game. Some lower-intensity activities were associated with greater variability in energy expenditure. Bicycling showed consistently higher coefficients of variation across expressions of energy expenditure (29.1%, 37.7%, and 33.5% for relative VO2, absolute VO2, and calculated metabolic rate, respectively).

CONCLUSIONS

Energy expenditure for common activities is highly variable in adolescent girls. The coefficient of variation was higher in some activities of lower intensity, regardless of energy expenditure expression. This variance may influence the evaluation of physical activity interventions, particularly with regard to issues such as a prescribed dose of activity and the statistical power to detect change.

Prevalence of overweight among Baltimore City schoolchildren and its associations with nutrition and physical activity

OBJECTIVE

To determine the prevalence of overweight and at-risk-for-overweight in schoolchildren from Baltimore City.

RESEARCH METHODS AND PROCEDURES

Ten schools within city limits were randomly selected from each tertile of income, using eligibility for free school lunch as a proxy. A total of 209 third grade students from eight public schools in Baltimore City were surveyed in May 2000. Anthropometric data including height, weight, subscapular and triceps skinfold thickness, and percentage body weight from bioelectrical impedance were collected. Nutrition-related knowledge, attitudes, and behaviors were assessed using a validated questionnaire. Physical activity was assessed by questionnaire.

RESULTS

Based on International Obesity Taskforce reference values for BMI-for-age, 20.7% of girls and 17.2% of boys were overweight (BMI > 95th percentile) and 15.3% of girls and 14.1% of boys were at-risk-for-overweight (BMI between the 85th and 95th percentiles). The prevalence of overweight and at-risk-for-overweight did not vary by self-reported physical activity levels or by nutrition-related knowledge and behaviors.

DISCUSSION

The high prevalence of overweight and at-risk-for-overweight in this sample of inner-city children from Baltimore City highlights a need for targeted preventive and treatment interventions.

Accelerometry-measured activity or sedentary time and overweight in rural boys and girls

OBJECTIVE

The aim of this study was to examine the association between overweight and physical activity or sedentary time measured by accelerometry in rural boys and girls 7 to 19 years old.

RESEARCH METHODS AND PROCEDURES

A cross-sectional study was conducted involving 130 girls and 99 boys in elementary, middle, and high school in rural Maryland. After weight, height, and body composition were measured, children wore an Actiwatch accelerometer for 6 days. Comparisons for activity counts were made between normal and overweight or at risk for overweight (at-risk/overweight) participants (>or=85th percentile of BMI). The associations between body composition and accelerometry-defined activity levels (sedentary, light, moderate, and vigorous) were analyzed by age group for boys and girls.

RESULTS

Differences in total activity in counts per day or counts per minute were not observed between normal and at-risk/overweight boys or girls in all age groups. No associations between measures of body composition and time spent in an activity level were seen in boys. Fat mass and percentage fat were positively correlated to time spent in sedentary activity (range r = 0.42 to 0.54, all p < 0.01) for girls. In contrast, fat mass and percentage fat were negatively related to time spent in light activity (range, r = -0.40 to -0.51, p < 0.05) for girls.

DISCUSSION

In girls, but not boys, greater body fat is associated with greater time spent being inactive, and lower levels of body fat are associated with more time spent in light activity. Physical activity interventions targeting inactive children in rural communities are warranted.

Pregnancy-related changes in physical activity, fitness, and strength

PURPOSE

The objective was to examine the pregnancy-related changes in physical activity, fitness, and strength in women of varying body mass indices (BMI).

METHODS

Women (N = 17 low BMI, N = 34 normal BMI, and N = 12 high BMI, mean age +/- SD = 30.7 +/- 4.1 yr) were studied before pregnancy (0 wk) and postpartum (6 and 27 wk) for body composition and for physical activity, fitness, and strength. Physical activity was assessed by questionnaire, fitness by a maximal oxygen consumption (VO2) test on a cycle ergometer, and strength by the one-repetition maximum test. Data were analyzed by repeated measures ANOVA testing for time and BMI group.

RESULTS

Total physical activity differed qualitatively, but not quantitatively, with time. Significant time effects were observed for maximal workload, heart rate, respiration rate, ventilation, VO2, respiratory exchange ratio, and strength. VO2max, adjusted for weight, dropped by approximately 385 mL x min(-1) from 0 to 6 wk postpartum (P < 0.0001) and by approximately 234 mL x min(-1) from 0 to 27 wk postpartum (P < 0.01). The high-BMI group had a lower VO2max (adjusted for weight or fat-free mass) than the normal-BMI group (P < 0.05). Strength decreased for the leg press by 24% (P < 0.02) and for the latissimus pull down by 8% (P < 0.01) from 0 to 6 wk postpartum, and then increased by 44 and 12%, respectively (both P < 0.05), by 27 wk postpartum.

CONCLUSION

Relative to prepregnancy performance, fitness and strength declined in the early postpartum period but improved by 27 wk postpartum.

Validity and reliability of the Fels physical activity questionnaire for children

PURPOSE

The aim was to evaluate the reliability and validity of the Fels physical activity questionnaire (PAQ) for children 7-19 yr of age.

METHODS

A cross-sectional study was conducted among 130 girls and 99 boys in elementary (N=70), middle (N=81), and high (N=78) schools in rural Maryland. Weight and height were measured on the initial school visit. All the children then wore an Actiwatch accelerometer for 6 d. The Fels PAQ for children was given on two separate occasions to evaluate reliability and was compared with accelerometry data to evaluate validity.

RESULTS

The reliability of the Fels PAQ for the girls, boys, and the elementary, middle, and high school age groups range was r=0.48-0.76. For the elementary school children, the correlation coefficient examining validity between the Fels PAQ total score and Actiwatch (counts per minute) was 0.34 (P=0.004). The correlation coefficients were lower in middle school (r=0.11, P=0.31) and high school (r=0.21, P=0.006) adolescents. The sport index of the Fels PAQ for children had the highest validity in the high school participants (r=0.34, P=0.002).

CONCLUSION

The Fels PAQ for children is moderately reliable for all age groups of children. Validity of the Fels PAQ for children is acceptable for elementary and high school students when the total activity score or the sport index is used. The sport index was similar to the total score for elementary students but was a better measure of physical activity among high school students.

Comparison of two approaches to structured physical activity surveys for adolescents

PURPOSE

To compare the test-retest reliability, convergent validity, and overall feasibility/ usability of activity-based (AB) and time-based (TB) approaches for obtaining self-reported moderate-to-vigorous physical activity (MVPA) from adolescents.

METHODS

Adolescents (206 females and 114 males) completed two 3-d physical activity recalls using the AB and TB surveys, which contained identical lists of physical activities. The participants wore an MTI Actigraph accelerometer for the same period.

RESULTS

The TB instrument took about 3 min longer to complete (P = 0.022). Overall 2-d test-retest correlations for MVPA were similar for the two surveys (r = 0.676 and 0.667), but the girls had higher reliability on the AB survey than the boys (girls: r = 0.713; boys: r = 0.568). The overall 3-d correlations for MVPA surveys and Actigraph counts varied by gender (girls: AB = 0.265 vs TB = 0.314; boys: AB = 0.340 vs TB = 0.277). Correlations for vigorous physical activity and Actigraph counts were higher for the AB than for the TB (r = 0.281 vs 0.162). As the interval between completing the surveys and the days being recalled increased, reliability and validity were lower, especially for the AB survey.

CONCLUSION

For both genders, either approach is acceptable for obtaining MVPA information on a single day, but the TB approach appears to be slightly favored over the AB approach for obtaining multiple days of MVPA. A 3-d recall period appears to be too long for accurate recall of MVPA information from either instrument. For both genders, the surveys overestimated activity levels; thus, self-reports should be supplemented with objective data.

Defining accelerometer thresholds for activity intensities in adolescent girls

PURPOSE

To derive a regression equation that estimates metabolic equivalent (MET) from accelerometer counts, and to define thresholds of accelerometer counts that can be used to delineate sedentary, light, moderate, and vigorous activity in adolescent girls.

METHODS

Seventy-four healthy 8th grade girls, age 13 - 14 yr, were recruited from urban areas of Baltimore, MD, Minneapolis/St. Paul, MN, and Columbia, SC, to participate in the study. Accelerometer and oxygen consumption (.-)VO(2)) data for 10 activities that varied in intensity from sedentary (e.g., TV watching) to vigorous (e.g., running) were collected. While performing these activities, the girls wore two accelerometers, a heart rate monitor and a Cosmed K4b2 portable metabolic unit for measurement of (.-)VO(2). A random-coefficients model was used to estimate the relationship between accelerometer counts and (.-)VO(2). Activity thresholds were defined by minimizing the false positive and false negative classifications.

RESULTS

The activities provided a wide range in (.-)VO(2) (3 - 36 mL x kg x min) with a correspondingly wide range in accelerometer counts (1- 3928 counts x 30 s). The regression line for MET score versus counts was MET = 2.01 +/- 0.00171 (counts x 30 s) (mixed model R = 0.84, SEE = 1.36). A threshold of 1500 counts x 30 s defined the lower end of the moderate intensity (approximately 4.6 METs) range of physical activity. That cutpoint distinguished between slow and brisk walking, and gave the lowest number of false positive and false negative classifications. The threshold ranges for sedentary, light, moderate, and vigorous physical activity were found to be 0 - 50, 51- 1499, 1500 - 2600, and >2600 counts x 30 s, respectively.

CONCLUSION

The developed equation and these activity thresholds can be used for prediction of MET score from accelerometer counts and participation in various intensities of physical activity in adolescent girls.

Energy requirements during pregnancy based on total energy expenditure and energy deposition

BACKGROUND

Energy requirements during pregnancy remain controversial because of uncertainties regarding maternal fat deposition and reductions in physical activity.

OBJECTIVE

This study was designed to estimate the energy requirements of healthy underweight, normal-weight, and overweight pregnant women and to explore energetic adaptations to pregnancy.

DESIGN

The energy requirements of 63 women [17 with a low body mass index (BMI; in kg/m(2)), 34 with a normal BMI, and 12 with a high BMI] were estimated at 0, 9, 22, and 36 wk of pregnancy and at 27 wk postpartum. Basal metabolic rate (BMR) was measured by calorimetry, total energy expenditure (TEE) by doubly labeled water, and activity energy expenditure (AEE) as TEE - BMR. Energy deposition was calculated from changes in body protein and fat. Energy requirements equaled the sum of TEE and energy deposition.

RESULTS

BMR increased gradually throughout pregnancy at a mean (+/-SD) rate of 10.7 +/- 5.4 kcal/gestational week, whereas TEE increased by 5.2 +/- 12.8 kcal/gestational week, which indicated a slight decrease in AEE. Energy costs of pregnancy depended on BMI group. Although total protein deposition did not differ significantly by BMI group (mean for the 3 groups: 611 g protein), FM deposition did (5.3, 4.6, and 8.4 kg FM in the low-, normal-, and high-BMI groups; P = 0.02). Thus, energy costs differed significantly by BMI group (P = 0.02). In the normal-BMI group, energy requirements increased negligibly in the first trimester, by 350 kcal/d in the second trimester, and by 500 kcal/d in the third trimester.

CONCLUSION

Extra energy intake is required by healthy pregnant women to support adequate gestational weight gain and increases in BMR, which are not totally offset by reductions in AEE.

School-level intraclass correlation for physical activity in adolescent girls

PURPOSE

The Trial for Activity in Adolescent Girls (TAAG) is a multi-center group-randomized trial to reduce the usual decline in moderate to vigorous physical activity (MVPA) among middle-school girls. In group-randomized trials, the group-level intraclass correlation (ICC) has a strong inverse relationship to power and a good estimate of ICC is needed to determine sample size. As a result, we conducted a substudy to estimate the school-level ICC for intensity-weighted minutes of MVPA measured using an accelerometer.

METHODS

To estimate the ICC, each of six sites recruited two schools and randomly selected 45 eighth grade girls from each school; 80.7% participated. Each girl wore an Actigraph accelerometer for 7 d. Readings above 1500 counts per half minute were counted as MVPA. These counts were converted into metabolic equivalents (MET) and summed over 6 a.m. to midnight to provide MET-minutes per 18-h day of MVPA. Minutes of MVPA per 18-h day also were calculated ignoring the MET value.

RESULTS

The unadjusted school-level ICC for minutes of MVPA was 0.0205 (95%CI: -0.0079, 0.1727) and for MET-minutes of MVPA was 0.0045 (95% CI: -0.0147, 0.1145). Adjustment for age and BMI had no measurable effect, whereas adjustment for ethnicity reduced both ICC; adjusted values were 0.0175 (95% CI: -0.0092, 0.1622) for minutes of MVPA and 0.0000 (95% CI: -0.0166, 0.0968) for MET-minutes of MVPA. This information was used to calculate the number of schools and girls needed for TAAG to have 90% power to detect a 50% reduction in the decline of MET-minutes of MVPA between sixth and eighth grade.

CONCLUSIONS

The results called for 36 schools in TAAG, with 120 girls invited for measurements at each school, and a minimum participation rate of 80%.

Physical activity self-report and accelerometry measures from the Girls health Enrichment Multi-site Studies

BACKGROUND

Valid and reliable physical activity checklists are needed to assess effectiveness of interventions. This study tested the validity and reliability of the Girls health Enrichment Multi-site Studies (GEMS) Activity Questionnaire.

METHODS

Two-hundred and ten African-American girls completed the GEMS Activity Questionnaire (GAQ), a checklist of 28 physical and 7 sedentary activities, including TV viewing, inquiring whether performed on the previous day ("yesterday"), and whether usually performed ("usual"). The girls wore an accelerometer (used as the criterion for validity) for three consecutive days at baseline and after a 12-week pilot intervention. Data from 172 girls at baseline and follow-up were usable for this report.

RESULTS

Girls were (mean +/- SD) 8.8 +/- 0.8 years old with a BMI of 22.3 +/- 5.9 kg/m2. The intraclass correlation (ICC) examining reliability for the accelerometer across 3 days at baseline for the combined group was fair (ICC = 0.33, P < 0.21). The test-retest reliability coefficient for the 18-item MET-weighted GAQ yesterday scores for the comparison group of girls was 0.57 (P < 0.001). At baseline and follow-up, nonsignificant correlations were observed between 3-day accelerometer counts/minute and GAQ 18-item usual score for both comparison and intervention groups. A significant correlation was found between change in accelerometer minutes of moderate-to-vigorous activity (MVPA) between 12 noon and 6 PM and change in GAQ physical activities in the comparison girls (R = 0.35, P < 0.01). The TV-usual score was correlated with 3-day accelerometer counts/minute (R = -0.19, P = 0.02) at baseline for the total sample.

CONCLUSIONS

Correlations between the GAQ and accelerometer were low, indicating low validity. Although the GAQ may be helpful in describing types of physical activities performed, it needs further development to improve its psychometric properties.

A longitudinal study of fitness and activity in girls predisposed to obesity

PURPOSE

To determine whether physical activity and fitness change in girls with and without a predisposition to obesity from 8 to 10 yr of age.

METHODS

Normal-weight girls (N = 91) were recruited at 8 yr of age according to parental body mass index (BMI): LN = girls with two lean (BMI < 25 kg.m-2) parents, LNOB = girls with one obese and one lean parent, and OB = girls with two obese (BMI > 28 kg.m-2) parents. A longitudinal study was undertaken with annual assessments at 8, 9, and 10 yr of age. The primary outcomes were fitness ([OV0312]O2peak) measured by treadmill testing, and physical activity measured by heart rate monitoring and by questionnaire. Sedentary behavior was assessed by questionnaire.

RESULTS

[OV0312]O2peak (mL.kg-1.min-1) did not change over time; however, [OV0312]O2peak (L.min-1 and mL.kg-1.min-1), time on the treadmill, and treadmill stage were different across groups (P < 0.02). Girls with LNOB parents had a lower absolute [OV0312]O2 than the LN girls by 2.5 mL.kg-1.min-1 (P < 0.05). The OB group had a 3.9 mL.kg-1.min-1 lower [OV0312]O2 than the LN group (P < 0.001). The girls of LN parents also exercised longer on the treadmill (P < 0.05) than girls with OB parents. The percent of the day spent active on the weekday and weekend did not change over time or between groups. Time spent watching TV during the school year and summer was similar over the study period and between groups.

CONCLUSION

Our data suggest that fitness and physical activity remain fairly constant in girls from 8 to 10 yr of age, but girls of obese parents tend to be less fit.

Predictors of body fat gain in nonobese girls with a familial predisposition to obesity

BACKGROUND

Conflicting evidence exists on the causal factors underlying the development of excess adiposity in children.

OBJECTIVE

We determined the effect of energy expenditure (EE), muscle energetics, and physical fitness on weight and fat gain in prepubertal girls with or without a predisposition to obesity.

DESIGN

Normal-weight girls (n = 101) were recruited at 8 y of age according to parental body mass index. Eighty-eight girls completed the 2-y study, and the groups were as follows: LN, girls with 2 lean parents; LNOB, girls with 1 obese and 1 lean parent; and OB, girls with 2 obese parents. Measurements of weight, height, and body composition were taken 1 and 2 y after baseline. Girls underwent baseline measurements of EE by 24-h calorimetry and doubly labeled water, of muscle metabolism by (31)P nuclear magnetic resonance, and of fitness.

RESULTS

Fat mass (FM) and percentage body fat (%BF) differed significantly between the groups at years 1 and 2; the OB group had higher FM (P = 0.03) and %BF (P = 0.046) at year 1 and higher FM (P = 0.047) at year 2 than did the LN group. After adjustment for baseline weight, group, time, ethnicity, and Tanner stage, sleep EE, basal EE, 24-h EE, and peak oxygen uptake were negatively associated with FM and %BF (P < 0.04). After adjustment for the same variables, muscle oxidative capacity and free-living total EE were negatively and positively predictive, respectively, of changes in %BF between 8 and 10 y of age (both P = 0.04).

CONCLUSIONS

Nonobese girls with 2 obese parents have a significant risk of developing obesity. High free-living total EE and low muscle oxidative capacity predict high rates of fat gain.

Validity and reliability of activity measures in African-American girls for GEMS

PURPOSE

To determine the reliability and validity of physical activity monitors and self-report instruments suitable for young African-American girls.

METHODS

A validation study was conducted by the Girls health Enrichment Multi-site Studies (GEMS) research team to compare an accelerometer with a pedometer and two self-report instruments for assessing physical activity in African-American girls, age 8-9 yr. Girls (N= 68) attended two clinic visits spaced 4 d apart. Each girl wore a MTI/CSA accelerometer (used as the criterion standard for validity) and a pedometer simultaneously for four consecutive days. Girls completed on two occasions a 24-h physical activity checklist of yesterday and usual activities, including sedentary activities (GEMS Activity Questionnaire, GAQ), and a 3-d computerized self-report instrument (Activitygram).

RESULTS

Girls were (mean +/- SD) 9.0 +/- 0.6 yr old and had a body mass index of 19.4 kg x m. Reliability measured by intraclass correlations (ICC) and Pearson correlation coefficients (r) were calculated for the MTI/CSA (ICC = 0.37, P< 0.0001), pedometer (ICC = 0.08, = 0.094), Activitygram (ICC = 0.24) (P = 0.005), and GAQ for physical (r = 0.80, P< 0.0001) and sedentary (r = 0.3-0.5, P< 0.005) activities. Significant Pearson correlations between the MTI/CSA and the other instruments, as a measure of validity, were observed for the 4-d average pedometer score (r = 0.47, P< 0.0001), 3-d average Activitygram score (r = 0.37, P= 0.002), and the average of the two yesterday and two usual GAQ activity scores for a subset of 18 physical activities questions (r = 0.27, = 0.03; and r = 0.29,P = 0.02, respectively). The MTI/CSA was uncorrelated with single day scores from the three other instruments.

CONCLUSION

The reliability of the instruments tested was acceptable, except the pedometer. Validity correlations were significant when more than one day was used. Self-report instruments need further development for improved reliability and validity.

Energy requirements of women of reproductive age

BACKGROUND

The energy requirements of women have been based on total energy expenditure (TEE) derived from the factorial approach or as multiples of basal metabolic rate (BMR).

OBJECTIVE

This study was designed to reevaluate the energy requirements of healthy, moderately active underweight, normal-weight, and overweight women of reproductive age.

DESIGN

The energy requirements of 116 women [n = 13 with a low body mass index (BMI), n = 70 with a normal BMI, and n = 33 with a high BMI] were estimated from TEE measured by the doubly labeled water method. Twenty-four-hour EE and BMR were measured by room respiration calorimetry, activity EE was estimated from nonbasal EE as TEE - BMR, and physical activity level was calculated as TEE/BMR. Body composition was derived from a multicomponent model. Fitness, strength, and physical activity level were assessed, and fasting serum indexes were measured.

RESULTS

Energy requirements differed among the low-BMI (8.9 +/- 0.9 MJ/d), normal-BMI (10.1 +/- 1.4 MJ/d), and high-BMI (11.5 +/- 1.9 MJ/d) groups (P = 0.02-0.001, all pairwise comparisons). Major predictors of BMR, 24-h EE, and TEE were weight, height, and body composition; minor predictors were fasting metabolic profile and fitness. Fat-free mass and fat mass accounted for the differences in EE seen between the BMI groups. The mean physical activity level of 1.86 suggested that the multiples of BMR used to estimate energy requirements have been underestimated.

CONCLUSION

Recommended energy intakes for healthy, moderately active women of reproductive age living in industrialized societies should be revised on the basis of TEE.

Metabolic adaptation to high-fat and high-carbohydrate diets in children and adolescents

BACKGROUND

Difficulty adapting to high-fat (HF) and high carbohydrate (HC) diets may predispose children to obesity and diabetes.

OBJECTIVE

We tested the hypothesis that children have metabolic flexibility to adapt to HF and HC diets.

DESIGN

In protocol 1, 12 children aged 6-9 y and 12 adolescents aged 13-16 y were randomly assigned in a crossover design to consume low-fat (LF), HC (25% and 60% of energy, respectively) or HF, low-carbohydrate (LC) (55% and 30% of energy, respectively) diets. In protocol 2, 12 adolescents aged 13-16 y were randomly assigned in a crossover design to consume an LF-HC diet with 11% or 40% of carbohydrate as fructose. Total energy expenditure, nonprotein respiratory quotients (NPRQs), and substrate utilization were measured by using 24-h calorimetry. Effects of sex, puberty, body fat (dual-energy X-ray absorptiometry), intraabdominal fat (magnetic resonance imaging), and fitness on substrate utilization were tested.

RESULTS

Substrate utilization was not affected by puberty, body fat, intraabdominal fat, or fitness. Total energy expenditure was not affected by diet. In protocol 1, NPRQs and carbohydrate and fat utilization were significantly affected by diet (P = 0.001) and sex (P = 0.005). NPRQs and carbohydrate utilization increased with the LF-HC diet. NPRQs decreased and fat utilization increased with the HF-LC diet; changes in substrate utilization were less pronounced in females than in males. In protocol 2, 24-h NPRQs and 24-h substrate utilization were not significantly affected by fructose, although net carbohydrate and fat utilization were significantly lower and higher, respectively, with the high-fructose diet during fasting (P = 0.01) and in the subsequent feeding period (P = 0.05).

CONCLUSION

Healthy, nonobese children and adolescents adapt appropriately to HF and HC diets.

Effects of dietary macronutrient content on glucose metabolism in children

Effects of carbohydrate, fat, and fructose intake on substrate and hormone concentrations, glucose production, gluconeogenesis, and insulin sensitivity were determined in healthy, nonobese prepubertal children (n = 12) and adolescents (n = 24) using a cross-over design. In one group (12 prepubertal children and 12 adolescents), subjects were studied after 7 d of isocaloric, isonitrogenous diets providing either 60% carbohydrate and 25% fat [high carbohydrate (H(CHO))/low fat (L(F))] or 30% carbohydrate and 55% fat [low carbohydrate (L(CHO))/high fat (H(F))], and in a second group (12 adolescents) H(CHO)/L(F) diets containing either 40% or 10% fructose was used. All subjects adapted to changes in carbohydrate and fat intakes primarily by appropriately adjusting their substrate oxidation rates to match the intakes, with only minor changes in parameters of glucose metabolism. Changing from a L(CHO)/H(F) to H(CHO)/L(F) diet resulted in increased insulin sensitivity (stable labeled iv glucose tolerance test) in adolescents [from 3.2 +/- 0.7 x 10(-4) to 5.0 +/- 1.4 x 10(-4) (min(-1))/( micro U.ml(-1)) (mean +/- SE)] but not in prepubertal children [9.4 +/- 2.5 x 10(-4) to 9.9 +/- 1.5 x 10(-4) (min(-1))/( micro U.ml(-1))], whereas beta-cell sensitivity was unaffected in both groups. Insulin sensitivity was higher in prepubertal children than in adolescents (P < 0.05). The dietary fructose content did not affect any measured parameter. We conclude that in the short term, dramatic changes in fat and carbohydrate intakes (regardless of fructose content) did not adversely affect glucose and lipid metabolism in healthy nonobese children. In the adolescents, the high carbohydrate diet resulted in increased insulin sensitivity, thus facilitating insulin-mediated glucose uptake.

Familial resemblance of body composition in prepubertal girls and their biological parents

BACKGROUND

Heritability estimates for body mass index (BMI; in kg/m(2)) in children generally have been derived from twin and adoption studies. However, BMI does not reflect total or regional body composition.

OBJECTIVE

We evaluated the familial resemblance of body composition between prepubertal girls of normal weight and body fatness and their parents by using state-of-the-art technology.

DESIGN

The subjects were 101 girls [mean age: 8.5 +/- 0.4 y; percentage body fat (%BF): 12-30%] and their biological parents. Weight, height, and body composition [fat mass (FM), fat-free mass (FFM), and %BF] were measured with dual-energy X-ray absorptiometry (DXA) and total body potassium (TBK).

RESULTS

Weight, height, and BMI showed low-to-moderate similarity between the girls and both their parents (r = 0.29-0.44, P < 0.01). The girls' FM, FFM, and %BF were significantly related to both parents' body composition. Cross-generational equations were developed for DXA, eg, child's %BF = 12.4 + (0.158 paternal %BF) + (0.145 maternal %BF) (adjusted r(2) = 0.16, P < 0.001). Regional analysis with DXA showed that the adjusted r(2) values for the arm, trunk, and leg regions, respectively, were 0.17, 0.33, and 0.31 for lean tissue mass and 0.11, 0.14, and 0.09 for FM. TBK showed a similar relation between parents and girls (r = 0.28-0.47, P < 0.01). Significant heritability (h(2) +/- SE) was detected for BMI (0.35 +/- 0.17, P = 0.03) and %BF measured with DXA (0.50 +/- 0.12, P = 0.0001).

CONCLUSION

The body composition of prepubertal girls of normal weight and body fatness is significantly related to the body composition of both biological parents.

Skeletal muscle energetics assessed by (31)P-NMR in prepubertal girls with a familial predisposition to obesity

OBJECTIVE

To determine whether skeletal muscle energetics, measured by in vivo (31)P-nuclear magnetic resonance spectroscopy during plantar flexion exercise, differ between multiethnic, prepubertal girls with or without a predisposition to obesity.

DESIGN

Cross-sectional study.

SUBJECTS

Girls (mean age and body fat+/-s.d.=8.6+/-0.3 y and 22.6+/-4.2%) were recruited according to parental leanness or obesity defined as follows: LN (n=22), two lean parents, LNOB (n=18), one lean and one obese parent; and OB (n=15), two obese parents.

MEASUREMENTS

A 3 min, rest-exercise-recovery plantar flexion protocol was completed. Work was calculated from the force data. Spectra were analyzed for inorganic intracellular phosphate (P(i)), phosphocreatine (PCr), P(i)/PCr (ratio of the low and high energy phosphates indicating the bioenergetic state of the cell), intracellular pH, and adenosine triphosphate (ATP). Magnetic resonance imaging was used to determine calf muscle volume.

RESULTS

BMI was lower in the girls in the LN group (15.9+/-1.5 kg/m(2)) compared to the OB group (16.7+/-1.3 kg/m(2)) of girls (P<0.05), with no difference with the LNOB group (16.7+/-1.9 kg/m(2)). Adjusted for muscle volume and cumulative work, no differences in P(i), PCr, P(i)/PCr, pH, or ATP were observed among the LN, LNOB and OB groups at rest, the end of exercise, and after 60 and 300 s of recovery. From rest to the end of exercise, P(i) and P(i)/PCr (mean+/-s.d.: 0.2+/-0.1 vs 1.5+/-1.0) increased, whereas PCr and pH (7.04+/-0.06 vs 6.95+/-0.10) decreased (all P<0.001). By 60 s of recovery, P(i) and P(i)/PCr decreased, whereas PCr and pH increased (all P<0.001).

CONCLUSIONS

Skeletal muscle energetics, specifically P(i)/PCr and pH measured during plantar flexion exercise, do not differ between prepubertal girls with or without a familial predisposition to obesity.

Body composition in prepubertal girls: comparison of six methods

OBJECTIVE

To compare estimates of fat mass (FM), fat-free mass (FFM) and percentage body fat (%fat) by six different methods in prepubertal girls.

DESIGN

Cross-sectional study.

SUBJECTS

Normal-weight, multi-ethnic, prepubertal girls (age=8.5+/-0.4 y, n=101).

MEASUREMENTS

Body composition was measured in each child by anthropometry (skinfold thickness using Slaughter equation), dual-energy X-ray absorptiometry (DXA), total body potassium (TBK), isotope dilution for total body water measurement (TBW), multifrequency bioelectrical impedance spectroscopy (BIS), and total body electrical conductivity (TOBEC).

RESULTS

TOBEC and skinfold thickness yielded the lowest values of FM followed by DXA, TBK, TBW and BIS, with BIS giving the highest value of FM. All methods were significantly different for FFM, FM and %fat (P<0.001), except FFM by DXA and TBK. The Bland-Altman limits of agreement among the methods reveal that they are not directly interchangeable for FM, FFM, or %fat. The largest mean difference for FM was between TOBEC and BIS (-2.90 kg), whereas the smallest mean difference was between TOBEC and skinfold thickness (-0.14 kg). For FFM, the largest mean difference was also between TOBEC and BIS (2.83 kg), but the smallest mean difference for FFM was between DXA and TBK (-0.03 kg). For %fat, the mean differences were larger, -10.5% for TOBEC and BIS and+9.7% for skinfold thickness and BIS. The closest two techniques for %fat were TOBEC and skinfold thickness (mean difference of -0.62%) and DXA and TBK (-1.81%).

CONCLUSIONS

We found that estimates of body composition in prepubertal 8-y-old girls are highly method-dependent and that the six methods studied (DXA, TBK, TBW, TOBEC, BIS and anthropometry) are not directly interchangeable.

Energy expenditure, physical activity, and obesity in children

Although there are physiologic and genetic influences on the various components of energy metabolism and body weight regulation, and a major portion of individual differences in body weight can be explained by genetic differences, it seems unlikely that the increased global prevalence of obesity has been driven by a dramatic change in the gene pool. It is more likely and more reasonable that acute changes in behavior and environment have contributed to the rapid increase in obesity and that genetic factors may be important in the deferring individual susceptibilities to these changes. The most striking behavioral changes that have occurred have been an increased reliance on high-fat and energy-dense "fast foods," with larger portion sizes, coupled with an ever-increasing sedentary lifestyle. The more sedentary lifestyle is caused by an increased reliance on technology and labor-saving devices, which has reduced the need for physical exertion for everyday activities. Examples of energy-saving devices that have resulted in a secular decline in physical activity include: Increased use of automated transport rather than walking or biking Central heating and use of automated equipment, such as washing machines, in the household. Reduction in physical activity in the workplace because of computers, automated equipment, and electronic mail. Increased use of television and computers for entertainment and leisure activities. Use of elevators and escalators rather than stairs. Increased concern for crime, which has reduced the likelihood of outdoor playing. Poor urban planning that does not provide adequate biking paths or even sidewalks in some communities. Thus, the increasing prevalence, numerous health risks, and astounding economic costs of obesity clearly justify widespread efforts toward prevention efforts. These prevention efforts should begin in childhood because the behaviors are learned and continue through the lifetime.

Glucose production, gluconeogenesis, and insulin sensitivity in children and adolescents: an evaluation of their reproducibility

The prevalence of overweight and obese children has doubled, and the incidence of type 2 diabetes in children (0-19 y) has increased 4-fold during the past several decades. As a result we can anticipate an increased number of metabolic studies in children. There are few data on measures of glucose metabolism in normal children, and virtually none relating to their reproducibility. The aims of this study were 1) to provide new data on energy expenditure and glucose, lipid, and protein metabolism in nonobese, healthy children and adolescents; 2) to evaluate their reproducibility; and 3) on the basis of these data, to perform power calculations for metabolic studies. Eight nonobese subjects (8-16 y) were studied on two occasions, preceded by 7 d of a diet with identical energy content and macronutrient distribution. Gluconeogenesis, measured by deuterium oxide, accounted for 50% of glucose production. Insulin sensitivity, measured by the labeled minimal model, averaged 4.9 x 10(-4) mL(mU x min)(-1). Glucose appearance rate was significantly higher (p < 0.01) in the children than in the adolescents. Furthermore, we demonstrated that for energy intake and expenditure, plasma concentrations of glucose and C-peptide, and rates of appearance of glucose and leucine, a 10% difference can be detected in fewer than five subjects with a power of 80% and a type I error of 5%. Insulin concentration, gluconeogenesis, insulin secretory indices, insulin sensitivity, and glucose effectiveness were more variable, but with the above power a difference of 25% could be detected in 7-11 subjects using a paired study design.

Relations of parental obesity status to physical activity and fitness of prepubertal girls

OBJECTIVE

To determine whether physical activity and fitness differ among normal-weight-for-height, multiethnic, prepubertal girls whose parents are lean, obese, or both.

SETTING

Conducted in Houston, Texas.

STUDY PARTICIPANTS

Normal-weight white, black, and Hispanic prepubertal girls (mean age +/- standard deviation: 8.5 +/-.4 years) participated in this study. Girls were recruited according to parental leanness or obesity defined as follows: girls with 2 lean parents (LN group; n = 30); girls with 2 obese parents (OB group; n = 27); and girls with 1 lean and 1 obese parent (LNOB group; n = 44). Intervention. Each child wore a heart rate monitor for two 24-hour periods, underwent a treadmill exercise test, answered an activity questionnaire, and completed energy expenditure measurements by basal calorimetry and doubly labeled water.

OUTCOME MEASURES

The amount of time spent above 125% and 150% of basal heart rate (BHR) was calculated during each 24-hour period (n = 84). Fitness (n = 97), habitual physical activity (n = 101), and physical activity level (PAL = total energy expenditure/basal metabolic rate; n = 101) were also measured.

RESULTS

The times spent above 125% and 150% of BHR were similar among LN, LNOB, and OB groups. Black girls spent less time than did white girls on the weekend above 125% BHR and above 150% BHR. No significant familial or ethnic differences in peak oxygen consumption or habitual physical activity were observed. PALs were as follows: LN = 1.6 +/-.21; LNOB = 1.64 +/-.27; OB = 1.58 +/-. 20; white = 1.63 +/-.23; black = 1.58 +/-.24; and Hispanic = 1.65 +/-.25. PAL was related to time spent above 125% BHR and 150% BHR (r =.31,.39).

CONCLUSIONS

Physical activity and fitness of normal-weight prepubertal girls predisposed to obesity did not differ from girls without a family history of obesity. obesity, children, energy metabolism, exercise, heart rate monitoring.

Effects of familial predisposition to obesity on energy expenditure in multiethnic prepubertal girls

BACKGROUND

The prevalence of childhood obesity is increasing and the causes of this are unknown.

OBJECTIVE

The objective of this study was to determine whether energy expenditure (EE), measured by 24-h calorimetry and doubly labeled water, differed in normal-weight-for-height, multiethnic prepubertal girls with or without a familial predisposition to obesity.

DESIGN

Normal-weight, prepubertal white (n = 52), African American (n = 30), and Hispanic (n = 19) girls with a mean (+/-SD) age of 8.5 +/- 0.4 y were studied according to parental leanness and overweight or obesity. The girls were grouped according to whether they had 2 lean parents (n = 30), 2 obese parents (n = 27), or 1 lean and 1 obese parent (n = 44). Basal metabolic rate (BMR), sleeping metabolic rate (SMR), 24-h EE, respiratory quotient, heart rate, and activity were measured by 24-h room calorimetry; free-living total EE (TEE), activity-related EE (AEE), and physical activity level were measured by doubly labeled water. EE was standardized by fat-free mass (FFM).

RESULTS

There were no significant differences among familial groups in weight, height, fat mass, FFM, or percentage body fat. African American girls had a higher FFM than did white or Hispanic girls (P < 0.05). BMR, SMR, 24-h EE, respiratory quotient, heart rate, and activity levels were not significantly different among familial groups. Additionally, there were no significant familial group differences in TEE, AEE, or physical activity level. However, BMR, SMR, and TEE were lower in African American girls than in white girls (P < 0.05).

CONCLUSION

There was no significant difference in EE between normal-weight, multiethnic prepubertal girls predisposed to obesity and those not predisposed to obesity.

Stimulant medications decrease energy expenditure and physical activity in children with attention-deficit/hyperactivity disorder

OBJECTIVE

To determine the effect of stimulant medications used to treat children with attention-deficit/hyperactivity disorder (AD/HD) on energy expenditure, fuel utilization, and physical activity.

STUDY DESIGN

Energy expenditure and physical activity were measured, respectively, by room respiration calorimetry and microwave motion detectors in 31 children with AD/HD (26 boys and 5 girls; ages 6 to 12 years) both while they were receiving their prescribed stimulant medication and after the medication had been discontinued for at least 24 hours. Fuel utilization was calculated from calorimetry data.

RESULTS

Total and awake energy expenditure including energy expended while doing schoolwork, riding a stationary bicycle, resting, and watching a movie were from 4% to 8% lower when the children were receiving their prescribed stimulant medication. Total and awake activity were also lower while they were receiving medication (16% to 22%) and accounted for the lower rates of energy expenditure. Sleeping metabolic rate, basal metabolic rate, and fuel utilization were unaffected by medication.

CONCLUSIONS

Stimulant medications decrease physical activity, and hence, decrease the activity component of total daily energy expenditure in children with AD/HD.