Margarita S. Treuth

Defining Accelerometer Thresholds for Activity Intensities in Adolescent Girls

Implications for Muscle Lipid Metabolism and An accumulation of intramuscular lipid has been reported with obesity and linked with insulin resistance. The purpose of this paper is to discuss: 1) mechanisms that may be responsible for intramuscular lipid accumulation with obesity, and 2) the effects of common interventions (weight loss or exercise) for obesity on skeletal muscle lipid metabolism and intramuscular lipid content. Data suggest that the skeletal muscle of morbidly obese humans is characterized by the preferential partitioning of lipid toward storage rather than oxidation. This phenotype may, in part, contribute to increased lipid deposition in both muscle and adipose tissue, and promote the development of morbid obesity and insulin resistance. Weight loss intervention decreases intramuscular lipid content, which may contribute to improved insulin action. On the other hand, exercise training improves insulin action and increases fatty acid oxidation in the skeletal muscle of obese/morbidly obese individuals. In summary, the accumulation of intramuscular lipid appears to be detrimental in terms of inducing insulin resistance; however, the accumulation of lipid can be reversed with weight loss. The mechanism(s) by which exercise enhances insulin action remains to be determined.INTRODUCTION/PURPOSE The Talk Test has been shown to be well correlated with the ventilatory threshold, with accepted guidelines for exercise prescription, and with the ischemic threshold. As such, it appears to be a valuable although quite simple method of exercise prescription. In this study, we evaluate the consistency of the Talk Test by comparing responses during different modes of exercise. METHODS Healthy volunteers (N = 16) performed incremental exercise, on both treadmill and cycle ergometer. Trials were performed with respiratory gas exchange and while performing the Talk Test. Comparisons were made regarding the correspondence of the last positive, equivocal, and first negative stages of the Talk Test with ventilatory threshold. RESULTS The %VO2peak, %VO2 reserve, %HRpeak, and %HR reserve at ventilatory threshold on treadmill versus cycle ergometer (77%, 75%. 89%, and 84% vs 67%, 64%, 82%, and 74%) were not significantly different than the equivocal stage of the Talk Test (83%, 82%, 86%, and 80% vs 73%, 70%, 87%, and 81%). The VO2 at ventilatory threshold and the last positive, equivocal and negative stages of the Talk Test were well correlated during treadmill and cycle ergometer exercise. CONCLUSIONS The results support the hypothesis that the Talk Test approximates ventilatory threshold on both treadmill and cycle. At the point where speech first became difficult, exercise intensity was almost exactly equivalent to ventilatory threshold. When speech was not comfortable, exercise intensity was consistently above ventilatory threshold. These results suggest that the Talk Test may be a highly consistent method of exercise prescription.INTRODUCTION Obesity and weight gain are negative prognostic factors for breast cancer survival. Physical activity (PA) prevents weight gain and may decrease obesity. Little information exists on PA levels among cancer survivors. We assessed PA, including the proportion of breast cancer survivors engaging in recommended levels, by categories of adiposity, age, disease stage, and ethnicity in 806 women with stage 0-IIIA breast cancer participating in the Health, Eating, Activity, and Lifestyle Study. METHODS Black, non-Hispanic white, and Hispanic breast cancer survivors were recruited into the study through Surveillance Epidemiology End Results registries in New Mexico, Western Washington, and Los Angeles County, CA. Types of sports and household activities and their frequency and duration within the third yr after diagnosis were assessed during an in-person interview. RESULTS Thirty-two percent of breast cancer survivors participated in recommended levels of PA defined as 150 min x wk(-1) of moderate- to vigorous-intensity sports/recreational PA. When moderate-intensity household and gardening activities were included in the definition, 73% met the recommended level of PA. Fewer obese breast cancer survivors met the recommendation than overweight and lean breast cancer survivors (P < 0.05). Fewer black breast cancer survivors met the recommendation compared with non-Hispanic white and Hispanic breast cancer survivors (P < 0.05). CONCLUSIONS Most of the breast cancer survivors were not meeting the PA recommendations proposed for the general adult population. Efforts to encourage and facilitate PA among these women would be an important tool to decrease obesity, prevent postdiagnosis weight gain, and improve breast cancer prognosis.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.

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.

Prediction of intra-abdominal and subcutaneous abdominal adipose tissue in healthy pre-pubertal children

OBJECTIVE: To examine the relationship of intra-abdominal adipose tissue (IAAT) and subcutaneous abdominal adipose tissue (SAAT) with body composition and anthropometry in children.DESIGN: Cross-sectional data analysis.SUBJECTS: 113 healty Caucasian and African-American, pre-pubertal children aged 4–10 y.MEASUREMENTS: IAAT and SAAT by single slice computed tomography at the level of the umbilicus; total fat and trunk fat by dual energy X-ray absorptiometry (DEXA); anthropometric evaluation by skinfolds and circumferences.RESULTS: IAAT was most strongly correlated with abdominal skinfold (r=0.88) and trunk fat by DEXA (r=0.87), and SAAT with trunk fat by DEXA (r=0.96), total fat by DEXA (r=0.93) and waist circumference (r=0.93). In stepwise regression, IAAT was best predicted by trunk fat from DEXA, total fat from DEXA, and abdominal skinfold (R2=0.85); SAAT was best predicted by trunk fat from DEXA, body weight, waist circumference and abdominal skinfold (R2=0.96). In the absence of DEXA data, IAAT was best predicted by abdominal skinfold, ethnicity and subscapular skinfold (R2=0.82) and SAAT was best predicted by waist circumference subscapular skinfold, height and abdominal skinfold (R2=0.92). The prediction equations with and without DEXA were successfully cross-validated in an independent sample of 12 additional measures of IAAT and SAAT.CONCLUSION: These data provide useful information that can help in the interpretation of anthropometric data with regard to body fat distribution. IAAT and SAAT can be accurately estimated in Caucasian and African-American prepubertal children from anthropometry with and without the availability of DEXA data.

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.

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.

The Effects of Strength Conditioning on Older Women's Ability to Perform Daily Tasks

OBJECTIVES: The objectives of this study were to determine the effects of a strength‐training program on walking speed and relative muscular stress, as measured by normalized integrated electromyographic (nIEMG) activity, while carrying a box of groceries and standing from a chair.

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.

Predicting Energy Expenditure from Accelerometry Counts in Adolescent Girls

PURPOSE Calibration of accelerometer counts against oxygen consumption to predict energy expenditure has not been conducted in middle school girls. We concurrently assessed energy expenditure and accelerometer counts during physical activities on adolescent girls to develop an equation to predict energy expenditure. METHODS Seventy-four girls aged 13-14 yr performed 10 activities while wearing an Actigraph accelerometer and a portable metabolic measurement unit (Cosmed K4b2). The activities were resting, watching television, playing a computer game, sweeping, walking 2.5 and 3.5 mph, performing step aerobics, shooting a basketball, climbing stairs, and running 5 mph. Height and weight were also assessed. Mixed-model regression was used to develop an equation to predict energy expenditure (EE) (kJ.min(-1)) from accelerometer counts. RESULTS Age (mean [SD] = 14 yr [0.34]) and body-weight-adjusted correlations of accelerometer counts with EE (kJ.min(-1)) for individual activities ranged from -0.14 to 0.59. Higher intensity activities with vertical motion were best correlated. A regression model that explained 85% of the variance of EE was developed: [EE (kJ.min(-1)) = 7.6628 + 0.1462 [(Actigraph counts per minute - 3000)/100] + 0.2371 (body weight in kilograms) - 0.00216 [(Actigraph counts per minute - 3000)/100](2) + 0.004077 [((Actigraph counts per minute - 3000)/100) x (body weight in kilograms)]. The MCCC = 0.85, with a standard error of estimate = 5.61 kJ.min(-1). CONCLUSIONS We developed a prediction equation for kilojoules per minute of energy expenditure from Actigraph accelerometer counts. This equation may be most useful for predicting energy expenditure in groups of adolescent girls over a period of time that will include activities of broad-ranging intensity, and may be useful to intervention researchers interested in objective measures of physical activity.

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 (≥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.

Effects of strength training on intra-abdominal adipose tissue in obese prepubertal girls

PURPOSE The purpose of this study was to determine the effects of strength training on fat distribution and its relationship to glucose tolerance in obese prepubertal girls. METHODS A strength training intervention study was designed in which the children exercised three times per week for 5 months. Twelve healthy, obese prepubertal girls (ages 7-10 yr, > 95th percentile weight for height) were enrolled in the study. Body composition was measured by dual-energy x-ray absorptiometry and computed tomography, and glucose tolerance was measured by a 3-h oral glucose tolerance test at baseline and after training. RESULTS Significant increases in height, weight, fat-free mass, fat mass, and subcutaneous abdominal adipose tissue occurred after training (P < 0.05), whereas intra-abdominal adipose tissue (IAAT) remained stable (N = 11). Insulin area was highly correlated with IAAT before (r = 0.91) and after (r = 0.90) training (both P < 0.01, N = 9). CONCLUSION In growing obese prepubertal girls undergoing a strength training program, IAAT remains unchanged, whereas subcutaneous abdominal fat and total body fat increased; insulin area is related to IAAT in these children.