Issues in accelerometer methodology: the role of epoch length on estimates of physical activity and relationships with health outcomes in overweight, post-menopausal women.

BACKGROUND: Current accelerometer technology allows for data collection using brief time sampling intervals (i.e., epochs). The study aims were to examine the role of epoch length on physical activity estimates and subsequent relationships with clinically-meaningful health outcomes in post-menopausal women. METHODS: Data was obtained from the Woman On the Move through Activity and Nutrition Study (n = 102). Differences in activity estimates presented as 60s and 10s epochs were evaluated using paired t-tests. Relationships with health outcomes were examined using correlational and regression analyses to evaluate differences by epoch length. RESULTS: Inactivity, moderate- and vigorous-intensity activity (MVPA) were significantly higher and light-intensity activity was significantly lower (all P < 0.001) when presented as 10s epochs. The correlation between inactivity and self-reported physical activity was stronger with 10s estimates (P < 0.03); however, the regression slopes were not significantly different. Conversely, relationships between MVPA and body weight, BMI, whole body and trunk lean and fat mass, and femoral neck bone mineral density was stronger with 60s estimates (all P < 0.05); however, regression slopes were similar. CONCLUSION: These findings suggest that although the use of a shorter time sampling interval may suggestively reduce misclassification error of physical activity estimates, associations with health outcomes did not yield strikingly different results. Additional studies are needed to further our understanding of the ways in which epoch length contributes to the ascertainment of physical activity in research studies. TRIAL REGISTRATION: Clinical Trials Identifier: NCT00023543.

Associations among walking performance, physical activity, and subclinical cardiovascular disease.

An objective measure of walking performance could have several potential applications in clinical settings. The cross-sectional relationships among long distance corridor walk (LDCW) time, physical activity, and subclinical cardiovascular disease (CVD) measures were examined before group randomization in 492 participants (mean age, 57.0+/-2.9 years) from the Women On the Move Through Activity and Nutrition (WOMAN) study, a randomized clinical trial involving postmenopausal women. Longer walk times were significantly associated with higher body mass index (P<0001), average waist circumference (P<0001), and lower levels of physical activity (P<002). The proportion of detectable coronary artery calcification and median aortic pulse wave velocity levels were significantly higher among those with slower walk times (P<002 and P<.001, respectively). Findings from the current report support the utility of the LDCW to identify women at higher risk for CVD who may be candidates for further cardiovascular testing or intensive lifestyle intervention.

The Women on the Move Through Activity and Nutrition (WOMAN) study: final 48-month results.

The Women on the Move through Activity and Nutrition (WOMAN) study was designed to test whether a nonpharmacological intervention including qualitative and quantitative dietary changes to induce weight loss and increased physical activity levels would reduce blood triglyceride levels and number of low-density lipoprotein particles (LDL-P). Such decreases in lipoproteins and other risk factors could reduce or slow progression of subclinical cardiovascular disease (CVD). Study participants were randomized to either the intervention (Lifestyle Change) or assessment (Health Education) group. Most of the intervention ended at the 30-month visit. The last 48-month examination was completed in 9/2008. There was very substantial weight loss and increased exercise during the first 30 months of the trial resulting in significant decreases in CV risk factors. Most of the intervention effect was lost through 48 months. Weight loss was 3.4 kg in Lifestyle Intervention and 0.2 kg in the Health Education at 48 months (P = 0.000). There were no significant changes at 48 months in lipid levels, blood pressure (BP), glucose, insulin, or in the subclinical measures of coronary calcium, carotid intima media thickness, or plaque. There was a significant decrease in long-distance corridor walk time in the Lifestyle vs. Health Education groups. Significant lifestyle changes can be achieved that result in decreases in CV risk factors. Whether such changes reduce CV outcomes is still untested in clinical trials of weight loss or exercise. Long-term maintenance of successful lifestyle changes, weight loss and reduced risk factors is the hurdle for lifestyle interventions attempting to prevent CV and other chronic diseases.

The impact of weight and fat mass loss and increased physical activity on physical function in overweight, postmenopausal women: results from the Women on the Move Through Activity and Nutrition study.

OBJECTIVE: The aim of this study was to determine whether changes in leisure time physical activity (LTPA) and body composition reflect concomitant changes in 400-meter walk time. METHODS: Data were collected at the baseline and 48-month visits in the Women on the Move Through Activity and Nutrition study. At baseline, participants (n = 508) were randomized to the lifestyle intervention or health education group. The lifestyle intervention focused on weight (7%-10%) and waist circumference reduction through healthy lifestyle behavior change. Change in walk time over 48 months was the primary outcome. Secondary measures included change in LTPA and body composition measures including, body weight, body mass index, waist circumference, and dual-energy x-ray absorptiometry--derived fat and lean mass. RESULTS: Increased LTPA and reductions in body weight, body mass index, waist circumference, and fat mass were associated with decreased walk time from baseline to 48 months (P < 0.01). After stratification by group, LTPA was no longer significantly related to walk time in the health education group. CONCLUSIONS: Increased LTPA and weight loss resulted in improved physical function, as measured by the 400-meter walk, in a group of overweight, postmenopausal women. These findings support the use of the 400-meter walk to evaluate progress in physical activity or weight loss programs.

Physical activity and coronary artery calcification in two cohorts of women representing early and late postmenopause.

OBJECTIVE: The aim of this study was to examine the association between physical activity (PA) and coronary artery calcification (CAC) among two cohorts of postmenopausal (PM) women representing early and late postmenopause. METHODS: The cross-sectional relationship between PA and CAC was examined in 173 younger PM women (mean age ± SD, 56.8 ± 2.9 y) from the Women on the Move Through Activity and Nutrition (WOMAN) study and 121 older PM women (mean age ± SD, 73.9 ± 3.8 y) from the Walking Women Follow-up (WWF) study who had complete PA and CAC data. PA was measured objectively using a pedometer over a 7-day period in both cohorts. CAC was assessed using electron beam tomography. Descriptive statistics were used to describe median levels of PA and CAC, as well as proportions of detectable CAC (0 vs > 0). RESULTS: Fifty-seven percent of WOMAN study participants and 74% of WWF study participants had detectable CAC. The median (interquartile range) CAC score was 1.4 (0-23.3) for participants in the WOMAN study and 38.8 (0-264.4) among WWF study participants. Median (interquartile range) step counts were 6,447 (4,823-8,722) steps per day in the WOMAN study and 5,466 (3,610-7,576) steps per day for WWF study participants. Among WWF study participants, there was a statistically significant inverse association between pedometer steps and CAC (P for trend = 0.002); no association was found among WOMAN study participants. CONCLUSIONS: Among older PM women, higher levels of PA were associated with lower CAC. However, the relationship was not observed in PM women, likely due to the lower prevalence of CAC in this age group.