Associations between Patterns of Objectively Measured Physical Activity and Risk Factors for the Metabolic Syndrome

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)

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. 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 (VO2) 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 VO2. A random-coefficients model was used to estimate the relationship between accelerometer counts and VO2. Activity thresholds were defined by minimizing the false positive and false negative classifications. Results - The activities provided a wide range in VO2 (3-36 mL·kg-1·min-1) with a correspondingly wide range in accelerometer counts (1-3928 counts·30 s-1). The regression line for MET score versus counts was MET=2.01+0.00171 (counts·30 s-1) (mixed model R2=0.84, SEE=1.36). A threshold of 1500 counts·30 s-1 defined the lower end of the moderate intensity (~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 \u3e2600 counts·30 s-1, 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

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%, 37.1%, 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 prescribed dose of activity and the statistical power to detect change

A Longitudinal Study of Sedentary Behavior and Overweight in Adolescent Girls

To examine sedentary and light activity in relation to overweight in adolescent girls

Associations of Body Size and Composition with Physical Activity in Adolescent Girls

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

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 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

A Cross-Sectional and Longitudinal Study of Travel by Walking Before and After School Among Eighth-Grade Girls

To examine “travel by walking” (TBW) before and after school among eighth grade girls

Travel by Walking Before and After School and Physical Activity Among Adolescent Girls

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

Comparison of Two Approaches to Structured Physical Activity Surveys of 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 overestimate activity levels; thus, self-reports should be supplemented with objective data

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 highter (p\u3c0.001) on weekdays than weekends in all girls, but MVPA was lower in at-risk of overweight + overweight girls (p\u3c0.001) 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