David M. Murray

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.

Community education for cardiovascular disease prevention: risk factor changes in the Minnesota Heart Health Program.

OBJECTIVES The Minnesota Heart Health Program is a 13-year research and demonstration project to reduce morbidity and mortality from coronary heart disease in whole communities. METHODS Three pairs of communities were matched on size and type; each pair had one education site and one comparison site. After baseline surveys, a 5- to 6-year program of mass media, community organization, and direct education for risk reduction was begun in the education communities, whereas surveys continued in all sites. RESULTS Many intervention components proved effective in targeted groups. However, against a background of strong secular trends of increasing health promotion and declining risk factors, the overall program effects were modest in size and duration and generally within chance levels. CONCLUSIONS These findings suggest that even such an intense program may not be able to generate enough additional exposure to risk reduction messages and activities in a large enough fraction of the population to accelerate the remarkably favorable secular trends in health promotion activities and in most coronary heart disease risk factors present in the study communities.

Design and Analysis of Group-Randomized Trials: A Review of Recent Methodological Developments

We review recent developments in the design and analysis of group-randomized trials (GRTs). Regarding design, we summarize developments in estimates of intraclass correlation, power analysis, matched designs, designs involving one group per condition, and designs in which individuals are randomized to receive treatments in groups. Regarding analysis, we summarize developments in marginal and conditional models, the sandwich estimator, model-based estimators, binary data, survival analysis, randomization tests, survey methods, latent variable methods and nonlinear mixed models, time series methods, global tests for multiple endpoints, mediation effects, missing data, trial reporting, and software. We encourage investigators who conduct GRTs to become familiar with these developments and to collaborate with methodologists who can strengthen the design and analysis of their trials.

Changing fruit and vegetable consumption among children: the 5-a-Day Power Plus program in St. Paul, Minnesota.

OBJECTIVES A randomized school based trial sought to increase fruit and vegetable consumption among children using a multicomponent approach. METHODS The intervention, conducted in 20 elementary schools in St. Paul, targeted a multiethnic group of children who were in the fourth grade in spring 1995 and the fifth grade in fall 1995. The intervention consisted of behavioral curricula in classrooms, parental involvement, school food service changes, and industry support and involvement. Lunchroom observations and 24-hour food recalls measured food consumption. Parent telephone surveys and a health behavior questionnaire measured psychosocial factors. RESULTS The intervention increased lunchtime fruit consumption and combined fruit and vegetable consumption, lunchtime vegetable consumption among girls, and daily fruit consumption as well as the proportion of total daily calories attributable to fruits and vegetables. CONCLUSIONS Multicomponent school-based programs can increase fruit and vegetable consumption among children. Greater involvement of parents and more attention to increasing vegetable consumption, especially among boys, remain challenges in future intervention research.

Communitywide smoking prevention : Long-term outcomes of the Minnesota Heart Health Program and the Class of 1989 Study

OBJECTIVES The Class of 1989 Study is part of the Minnesota Heart Health Program (MHHP), a populationwide research and demonstration project designed to reduce cardiovascular disease in three educated communities from 1980 to 1993. This paper describes an intensive, school-based behavioral intervention on cigarette smoking, comparing long-term outcomes in one of the intervention communities with those in a matched reference community. METHODS Beginning in sixth grade (1983), seven annual waves of cohort and cross-sectional behavioral measurements were taken from one MHHP intervention community and its matched pair. All students in each community were eligible to participate (baseline n = 2401). Self-reported data collected at each period described prevalence and intensity of cigarette smoking. RESULTS There were no differences at baseline for either weekly smoking prevalence or intensity of smoking. Throughout the follow-up period, however, smoking rates as determined by these measures were significantly lower in the intervention community: 14.6% of students were weekly smokers at the end of high school compared with 24.1% in the reference community. CONCLUSIONS These results suggest that multiple intervention components such as behavioral education in schools, booster programs to sustain training, and complementary communitywide strategies may all be needed for lasting reductions in adolescent tobacco use.

The effects of community policies to reduce youth access to tobacco.

OBJECTIVES This study tested the hypothesis that adoption and implementation of local policies regarding youth access to tobacco can affect adolescent smoking. METHODS A randomized community trial was conducted in 14 Minnesota communities. Seven intervention communities participated in a 32-month community-organizing effort to mobilize citizens and activate the community. The goal was to change ordinances, merchant policies and practices, and enforcement practices to reduce youth access to tobacco. Outcome measures were derived from surveys of students before and after the intervention and from tobacco purchase attempts in all retail outlets in the communities. Data analyses used mixed-model regression to account for the clustering within communities and to adjust for covariates. RESULTS Each intervention community passed a comprehensive youth access ordinance. Intervention communities showed less pronounced increases in adolescent daily smoking relative to control communities. Tobacco purchase success declined somewhat more in intervention than control communities during the study period, but this difference was not statistically significant. CONCLUSIONS This study provides compelling evidence that policies designed to reduce youth access to tobacco can have a significant effect on adolescent smoking rates.

Promoting Physical Activity in Middle School Girls Trial of Activity for Adolescent Girls

BACKGROUND Physical activity is important for weight control and good health; however, activity levels decline in the adolescent years, particularly in girls. DESIGN Group randomized controlled trial. SETTING/PARTICIPANTS Middle school girls with English-speaking skills and no conditions to prevent participation in physical activity in 36 schools in six geographically diverse areas of the United States. Random, cross-sectional samples were drawn within schools: 6th graders in 2003 (n=1721) and 8th graders in 2005 (n=3504) and 2006 (n=3502). INTERVENTION A 2-year study-directed intervention (fall 2003 to spring 2005) targeted schools, community agencies, and girls to increase opportunities, support, and incentives for increased physical activity. Components included programs linking schools and community agencies, physical education, health education, and social marketing. A third-year intervention used school and community personnel to direct intervention activities. MAIN OUTCOME MEASURES The primary outcome, daily MET-weighted minutes of moderate-to-vigorous physical activity (MET-weighted MVPA), was assessed using accelerometry. Percent body fat was assessed using anthropometry. RESULTS After the staff-directed intervention (pre-stated primary outcome), there were no differences (mean= -0.4, 95% CI= -8.2 to 7.4) in adjusted MET-weighted MVPA between 8th-grade girls in schools assigned to intervention or control. Following the Program Champion-directed intervention, girls in intervention schools were more physically active than girls in control schools (mean difference 10.9 MET-weighted minutes of MVPA, 95% CI=0.52-21.2). This difference is about 1.6 minutes of daily MVPA or 80 kcal per week. There were no differences in fitness or percent body fat at either 8th-grade timepoint. CONCLUSION A school-based, community-linked intervention modestly improved physical activity in girls.

A Meta-Analysis of Smoking Prevention Programs After Adjustment for Errors in the Unit of Analysis

This article presents the results of a meta-analysis designed to test the prevailing view that we largely understand why adolescents start to smoke and how to delay it. This view has developed even though none of the major reviews of the last 12 years has adjusted for the important methodological problems that all of those reviews identified as common in the published literature. School-based smoking prevention programs based on peer or social-type programs, published between 1974 and 1991, were included in this meta-analysis. Treatment characteristics were used to predict an effect size after adjustment for study design and population characteristics, and in particular, after a post hoc correction for errors in the original unit of analysis. The results suggest that the average effect for peer or social-type programs is likely to be quite limited in magnitude, and that the reduction in smoking may be only 0.10 standard deviation units, or perhaps 5%. Even under optimal conditions, the reduction in smoking may be only 0.50 to 0.75 standard deviation units, or perhaps 20%-30%.

Planning for the appropriate analysis in school-based drug-use prevention studies.

School-based drug-use prevention studies often apply interventions to entire schools. A major problem for these studies results from the intragroup dependence often seen when intact social groups are assigned to study conditions. Analysis of data from 2 such studies revealed intraclass correlation coefficients between 0.02 and 0.05 for common drug use measures. Because even such modest intragroup dependence can invalidate the traditional fixed-effects analyses, researchers should adopt alternative methods that acknowledge this dependence. These alternative methods are reviewed, and appropriate methods for computing sample size requirements are illustrated. Investigators should consider these analysis issues when planning future studies, because the number of schools required for an unbiased analysis may be substantially greater than for the traditional methods.

Predictors of weight gain in the Pound of Prevention study.

OBJECTIVES: This study examined cross-sectional and prospective relationships between macronutrient intake, behaviors intended to limit fat intake, physical activity and body weight.DESIGN: The overall goal was to identify diet and exercise behaviors that predict and/or accompany weight gain or loss over time. Specific questions addressed included: (a) are habitual levels of diet or exercise predictive of weight change; (b) are habitual diet and exercise levels associated cross-sectionally with body weight; and (c) are changes in diet and exercise associated with changes in body weight over time?PARTICIPANTS: Subjects were a sample of community volunteers (n=826 women, n=218 men) taking part in a weight gain prevention project over a 3-year period.MEASURES: Body weight was measured at baseline and annually over the study period. Self-report measures of diet and exercise behavior were also measured annually.RESULTS: Among both men and women, the most consistent results were the positive association between dietary fat intake and weight gain and an inverse association between frequency of physical activity and weight gain. Individuals who weighed more both ate more and exercised less than those who weighed less. Individuals who increased their physical activity level and decreased their food intake over time were protected from weight gain compared to those who did not. Frequency of high-intensity physical activity was particularly important for both men and women. Additionally, women who consistently engaged in higher levels of moderate physical activity gained weight at a slower rate compared to women who were less active.CONCLUSIONS: Overall results indicated that both cross-sectionally and prospectively, the determinants of weight and weight change are multifactorial. Attention to exercise, fat intake and total energy intake all appear important for successful long term control of body weight.