Britni R. Belcher

Physical Activity in US Youth: Effect of Race/Ethnicity, Age, Gender, and Weight Status

PURPOSE To describe physical activity (PA) levels by race/ethnicity, age, gender, and weight status in a representative sample of US youth. METHODS Cross-sectional data from the 2003-2004 and 2005-2006 National Health and Nutrition Examination Survey were combined and analyzed. Youth aged 6-19 yr with at least four 10-h days of PA measured by accelerometry were included (n = 3106). Outcomes included mean counts per minute and minutes spent in moderate-to-vigorous PA (MVPA). RESULTS Among the groups, the 6- to 11-yr-olds spent more time (88 min·d) in MVPA than the 12- to 15-yr-olds (33 min·d) and 16- to 19-yr-olds (26 min·d; P < 0.001 for both). Females spent fewer minutes per day in MVPA than males (P < 0.001). Overall, obese youth spent 16 fewer minutes per day in MVPA than normal-weight youth. However, non-Hispanic white males spent three to four fewer minutes per day in vigorous PA than Mexican American (MA; P = 0.004) and non-Hispanic black (P < 0.001) males but had lower obesity rates and obese 12- to 15-yr-old MA recorded similar minutes in MVPA per day as normal-weight MA (P > 0.050). There was a significant three-way age-body mass index-race/ethnicity interaction for mean minutes per day in MVPA (P < 0.001). Adjustment for total energy intake did not qualitatively alter these results. CONCLUSIONS Females and older youth were the least active groups. Obese youth were generally less active, but this did not hold uniformly across race/ethnic groups. Cultural or biological factors could moderate the association between PA and obesity in youth.

Effects of Interrupting Children's Sedentary Behaviors With Activity on Metabolic Function: A Randomized Trial

CONTEXT Limited data suggest that interrupting sedentary behaviors with activity improves metabolic parameters in adults. OBJECTIVE We tested whether interrupting sitting with short, moderate-intensity walking bouts improved glucose tolerance in children. DESIGN Participants underwent two experimental conditions in random order on different days: continuous sitting for 3 hours or sitting interrupted by walking (3 min of moderate-intensity walking every 30 min). Insulin, C-peptide, glucose, and free fatty acids were measured every 30 minutes for 3 hours during an oral glucose tolerance test. Area under the curve (AUC) was calculated from hormone and substrate measurements. Children were given a buffet meal after each condition. SETTING The study was conducted at the National Institutes of Health Hatfield Clinical Research Center. PARTICIPANTS Twenty-eight normal-weight 7-11 year olds participated. MAIN OUTCOMES Patterns of substrate/hormone secretion and AUC, as well as energy intake, were examined by experimental condition. RESULTS Interrupting sitting resulted in a 32% lower insulin AUC (P < .001), 17% lower C-peptide AUC (P < .001), and 7% lower glucose AUC (P = .018) vs continuous sitting. Mixed model results indicated that insulin (P = .036) and free fatty acid concentrations (P = .009) were significantly lower in the interrupted vs the continuous sitting condition. Lunchtime buffet meal energy intake did not significantly differ between the conditions (975 ± 387 vs 963 ± 309 kcal; P = .85). CONCLUSIONS Interrupting sedentary time with brief moderate-intensity walking improved short-term metabolic function in non-overweight children without increasing subsequent energy intake. These findings suggest that interrupting sedentary behavior may be a promising prevention strategy for reducing cardiometabolic risk in children.

Eating breakfast more frequently is cross-sectionally associated with greater physical activity and lower levels of adiposity in overweight Latina and African American girls

BACKGROUND Eating breakfast is believed to promote a healthy body weight. Yet, few studies have examined the contribution of energy balance-related behavioral factors to this relation in minority youth. OBJECTIVE We assessed the associations between breakfast consumption and dietary intake, physical activity (PA), and adiposity before and after accounting for energy intake and PA in minority girls. DESIGN Cross-sectional data were obtained on body mass index (BMI), percentage body fat (measured by BodPod), dietary intake (measured with 3-d dietary records), and PA (measured with 7-d accelerometry) from 87 Latina and African American girls 8-17 y of age (75% Latina, 80% overweight). Dietary records were used to categorize girls as more frequent breakfast eaters (MF; 2 or 3 of 3 d; n = 57) or less frequent breakfast eaters (LF; 0 or 1 of 3 d; n = 30). Chi-square tests, ANCOVA, and multiple regression analyses were conducted. Mediation was assessed with a Sobel test. RESULTS Compared with the MF group, the LF group spent 30% less time (12.6 min/d) in moderate-to-vigorous-intensity PA (MVPA; P = 0.004) and had a higher percentage body fat (P = 0.029). MVPA accounted for 25% (95% CI: -8.8%, 58.1%; P = 0.139) of the relation between breakfast consumption and percentage body fat. We were unable to show that energy intake or MVPA was a significant mediator of the relation between breakfast consumption and adiposity in this sample. CONCLUSIONS Evidence suggests that among predominantly overweight minority girls, MVPA, but not energy intake, was associated with both breakfast consumption and adiposity; however, a lack of power reduced our ability to detect a significant mediation effect. Other unobserved variables likely contribute to this relation.

Self-Reported Versus Accelerometer-Measured Physical Activity and Biomarkers Among NHANES Youth.

BACKGROUND Discrepancies in self-report and accelerometer-measured moderate-to-vigorous physical activity (MVPA) may influence relationships with obesity-related biomarkers in youth. METHODS Data came from 2003-2006 National Health and Nutrition Examination Surveys (NHANES) for 2174 youth ages 12 to 19. Biomarkers were: body mass index (BMI, kg/m2), BMI percentile, height and waist circumference (WC, cm), triceps and subscapular skinfolds (mm), systolic & diastolic blood pressure (BP, mmHg), high-density lipoprotein (HDL, mg/dL), total cholesterol (mg/dL), triglycerides (mg/dL), insulin (μU/ml), C-reactive protein (mg/dL), and glycohemoglobin (%). In separate sex-stratified models, each biomarker was regressed on accelerometer variables [mean MVPA (min/day), nonsedentary counts, and MVPA bouts (mean min/day)] and self-reported MVPA. Covariates were age, race/ethnicity, SES, physical limitations, and asthma. RESULTS In boys, correlations between self-report and accelerometer MVPA were stronger (boys: r = 0.14-0.21; girls: r = 0.07-0.11; P < .010) and there were significant associations with BMI, WC, triceps skinfold, and SBP and accelerometer MVPA (P < .01). In girls, there were no significant associations between biomarkers and any measures of physical activity. CONCLUSIONS Physical activity measures should be selected based on the outcome of interest and study population; however, associations between PA and these biomarkers appear to be weak regardless of the measure used.

Temporal relationship between insulin sensitivity and the pubertal decline in physical activity in peripubertal Hispanic and African American females.

OBJECTIVE Little attention has been paid to possible intrinsic biological mechanisms for the decline in physical activity that occurs during puberty. This longitudinal observational study examined the association between baseline insulin sensitivity (SI) and declines in physical activity and increases in sedentary behavior in peripubertal minority females over a year. RESEARCH DESIGN AND METHODS Participants were Hispanic and African American girls (n = 55; 76% Hispanic; mean age 9.4 years; 36% obese). SI and other insulin indices were measured at baseline using the frequently sampled intravenous glucose tolerance test. Physical activity was measured on a quarterly basis by accelerometry and self-report. RESULTS Physical activity declined by 25% and time spent in sedentary behaviors increased by ∼13% over 1 year. Lower baseline SI predicted the decline in physical activity measured by accelerometry, whereas higher baseline acute insulin response to glucose predicted the decline in physical activity measured by self-report. Time spent in sedentary behavior increased by ~13% over 1 year, and this was predicted by lower baseline SI. All models controlled for adiposity, age, pubertal stage, and ethnicity. CONCLUSIONS When evaluated using a longitudinal design with strong outcome measures, this study suggests that lower baseline SI predicts a greater decline in physical activity in peripubertal minority females.

Leptin predicts a decline in moderate to vigorous physical activity in minority female children at risk for obesity

What is already known about this subject Physical activity declines as children enter puberty. Leptin is cross‐sectionally associated with physical activity, but there are conflicting findings on the magnitude and direction of this association. Leptin concentrations fluctuate during puberty, and may impact energy balance.

Effects of high sugar and high fiber meals on physical activity behaviors in Latino and African American adolescents

This crossover experimental study examined the acute effects of high‐sugar/low‐fiber (HSLF) vs. low‐sugar/high‐fiber (LSHF) meals on sedentary behavior (SB) and light‐plus activity (L+) in minority adolescents with overweight and obesity.

Future Directions for Postdoctoral Training in Cancer Prevention: Insights from a Panel of Experts

Cancer prevention postdoctoral fellowships have existed since the 1970s. The National Cancer Institute facilitated a meeting by a panel of experts in April 2013 to consider four important topics for future directions for cancer prevention postdoctoral training programs: (i) future research needs; (ii) underrepresented disciplines; (iii) curriculum; and (iv) career preparation. Panelists proffered several areas needing more research or emphasis, ranging from computational science to culture. Health care providers, along with persons from nontraditional disciplines in scientific training programs such as engineers and lawyers, were among those recognized as being underrepresented in training programs. Curriculum suggestions were that fellows receive training in topics such as leadership and human relations, in addition to learning the principles of epidemiology, cancer biologic mechanisms, and behavioral science. For career preparation, there was a clear recognition of the diversity of employment options available besides academic positions, and that program leaders should do more to help fellows identify and prepare for different career paths. The major topics and strategies covered at this meeting can help form the basis for cancer prevention training program leaders to consider modifications or new directions, and keep them updated with the changing scientific and employment climate for doctoral degree recipients and postdoctoral fellows. Cancer Epidemiol Biomarkers Prev; 23(4); 679–83. ©2014 AACR.

Effects of Interrupting Sedentary Behavior With Short Bouts of Moderate Physical Activity on Glucose Tolerance in Children With Overweight and Obesity: A Randomized, Crossover Trial

OBJECTIVE Sedentary children have greater risk of developing abnormalities in glucose homeostasis. We investigated whether interrupting sedentary behavior (sitting) with very short periods of walking would improve glucose metabolism without affecting dietary intake in children with overweight or obesity. We hypothesized that interrupting sitting with short bouts of moderate-intensity walking would decrease insulin area under the curve (AUC) during an oral glucose tolerance test (OGTT) compared with uninterrupted sitting. RESEARCH DESIGN AND METHODS Overweight/obese (BMI ≥85th percentile) children 7–11 years of age underwent two experimental conditions in random order: prolonged sitting (3 h of continuous sitting) and interrupted sitting (3 min of moderate-intensity walking at 80% of ventilatory threshold every 30 min for 3 h). Insulin, C-peptide, and glucose were measured every 30 min for 3 h during an OGTT. Each session was followed by a buffet meal. Primary outcomes were differences in OGTT hormones and substrates and in buffet meal intake by condition. RESULTS Among 35 children with complete data, mixed-model results identified lower insulin and C-peptide in the interrupted condition (P = 0.007 and P = 0.029, respectively); the intervention reduced insulin AUC by 21% (P < 0.001) and C-peptide AUC 18% (P = 0.001) and improved estimated insulin sensitivity (P = 0.013). Neither buffet total energy intake (1,262 ± 480 vs. 1,260 ± 475 kcal; P = 0.89) nor macronutrient composition of the meal (P values >0.38) differed between conditions significantly. CONCLUSIONS Interrupting sitting with brief moderate-intensity walking improved glucose metabolism without significantly increasing energy intake in children with overweight or obesity. Interrupting sedentary behavior may be a promising intervention strategy for reducing metabolic risk in such children.

Association Between Self-Reported and Objective Activity Levels by Demographic Factors: Ecological Momentary Assessment Study in Children

Background To address the limitations of the retrospective self-reports of activity, such as its susceptibility to recall bias, researchers have shifted toward collecting real-time activity data on mobile devices via ecological momentary assessment (EMA). Although EMA is becoming increasingly common, it is not known how EMA self-reports of physical activity and sedentary behaviors relate to the objective measures of activity or whether there are factors that may influence the strength of association between these two measures. Understanding the relationship between EMA and accelerometry can optimize future instrument selection in studies assessing activity and health outcomes. Objective The aim of this study was to examine the associations between EMA-reported sports or exercise using the accelerometer-measured moderate-to-vigorous physical activity (MVPA) and EMA-reported TV, videos, or video games with the accelerometer-measured sedentary time (ST) in children during matched 2-h windows and test potential moderators. Methods Children (N=192; mean age 9.6 years; 94/192, 49.0% male; 104/192, 54.2% Hispanic; and 73/192, 38.0% overweight or obese) wore an accelerometer and completed up to 7 EMA prompts per day for 8 days during nonschool time, reporting on past 2-h sports or exercise and TV, videos, or video games. Multilevel models were used to assess the relationship between the accelerometer-measured ST and EMA-reported TV, videos, or video games. Given the zero-inflated distribution of MVPA, 2-part models were used assess the relationship between the accelerometer-measured MVPA and EMA-reported sports or exercise. Results EMA-reported TV, videos, or video games were associated with a greater accelerometer-measured ST (beta=7.3, 95% CI 5.5 to 9.0, P<.001). This relationship was stronger in boys (beta=9.9, 95% CI 7.2 to 12.6, P<.001) than that in girls (beta=4.9, 95% CI 2.6 to 7.2, P≤.001). EMA-reported sports or exercise was associated with a greater accelerometer-measured MVPA (zero portion P<.001; positive portion P<.001). This relationship was stronger on weekends, in older children, and in non-Hispanic children (zero portion all P values<.001; positive portion all P values<.001). Conclusions EMA reports highly relate to accelerometer measures. However, the differences in the strength of association depending on various demographic characteristics suggest that future research should use both EMA and accelerometers to measure activity to collect complementary activity data.