Estimating physical activity from incomplete accelerometer data in field studies.
ABSTRACT The purpose of this study was to develop a data-driven approach for analyzing incomplete accelerometer data from field-base studies.
Multiple days of accelerometer data from the Stanford Girls health Enrichment Multi-site Studies (N = 294 African American girls) were summed across each minute of each day to produce a composite weekday and weekend day. Composite method estimates of physical activity were compared with those derived from methods typically described in the literature (comparison methods).
The composite method retained 99.7% and 100% of participants in weekday and weekend-day analysis, respectively, versus 84.7% to 94.2% and 28.6% to 99.0% for the comparison methods. Average wearing times for the composite method for weekday and weekend day were 99.6% and 98.6%, respectively, 91.7% to 93.9% and 82.3% to 95.4% for the comparison methods. Composite-method physical activity estimates were similar to comparison-methods estimates.
The composite method used more available accelerometer data than standard approaches, reducing the need to exclude periods within a day, entire days, and participants from analysis.
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ABSTRACT: This study examines the associations between objectively measured physical activity and cardiovascular disease (CVD) risk factors in preadolescent African American girls. We conducted a cross-sectional analysis of data from Stanford Girls Health Enrichment Multisite Studies (GEMS) trial. Physical activity was assessed for four days by using an ActiGraph accelerometer and was correlated with anthropometric measures, blood pressure, blood lipids, glucose, and insulin. Associations between physical activity and CVD risk factors were computed using by Spearman correlations. Bonferroni adjustment alpha = .003 was used to correct for multiple testing. A total of 261 girls participated, of which 208 had complete CVD risk measures (mean age 9.4 years, mean body mass index 20.7 kg/m2). Average daily physical activity and time spent in moderate-to-vigorous physical activity (MVPA) were significantly correlated with body mass index (r = -.23, P=.0008 and r = -.29, P<.0001, respectively) and insulin (r = -.27, P=.0001 and r = -.30, P<.0001, respectively) but not to other CVD factors. After adjusting for age-adjusted pubertal stage of development, the association between MVPA and insulin remained significant. Objective measures of both average daily physical activity and MVPA were inversely associated with body mass index and insulin levels in African American girls.Ethnicity & disease 01/2008; 18(4):421-6. · 0.92 Impact Factor
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ABSTRACT: This paper reviews the evidence behind the methodological decisions accelerometer users make when assessing habitual physical activity in children aged 0-5 years. The purpose of the review is to outline an evidence-guided protocol for using accelerometry in young children and to identify gaps in the evidence base where further investigation is required. Studies evaluating accelerometry methodologies in young children were reviewed in two age groups (0-2 years and 3-5 years) to examine: (i) which accelerometer should be used, (ii) where the accelerometer should be placed, (iii) which epoch should be used, (iv) how many days of monitoring are required, (v) how many minutes of monitoring per day are required, (vi) how data should be reduced, (vii) which cut-point definitions for identifying activity intensity should be used, and (viii) which physical activity outcomes should be reported and how. Critique of the available evidence provided a basis for the development of a recommended users protocol in 3-5-year olds, although several issues require further research. Because of the absence of methodological studies in children under 3 years, a protocol for the use of accelerometers in this age range could not be specified. Formative studies examining the utility, feasibility and validity of accelerometer-based physical activity assessments are required in children under 3 years of age. Recommendations for further research are outlined, based on the above findings, which, if undertaken, will enhance the accuracy of accelerometer-based assessments of habitual physical activity in young children.Journal of Science and Medicine in Sport 02/2009; 12(5):557-67. DOI:10.1016/j.jsams.2008.10.008 · 3.08 Impact Factor
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ABSTRACT: To assess the feasibility, acceptability, and potential efficacy of a school-based obesity prevention program among adolescent boys with sub-optimal cardiorespiratory fitness. In 2007, a 6-month, 2-arm parallel group, randomized controlled pilot trial was conducted in a single school setting (Sydney, Australia). Thirty-three 7th Grade boys (mean age=12.5+/-0.4 years) were randomly assigned to intervention (n=16) or active comparison group (n=17). The intervention consisted of one 60-minute curriculum session and two 20-minute lunchtime physical activity sessions per week. The active comparison group continued with their usual physical activity curriculum sessions (Friday afternoons 2-3 pm). The pilot trial's curriculum sessions were additional to Physical Education (PE) lessons. The primary outcome was BMI, and secondary outcomes included waist circumference, percentage body fat, cardiorespiratory fitness, objectively measured physical activity and small screen recreation time. Screening, recruitment and retention goals were exceeded. The majority of data were collected as planned. Implementation and attendance rates were acceptable. At follow-up, compared with boys in the active comparison group, boys in the intervention group displayed a smaller increase in BMI (adjust diff.=-0.2, 95% confidence interval [CI] -0.78, 0.39; Cohen's d=0.05); greater reductions in waist circumference (-1.65 cm [-4.67, 1.36]; d=0.15); percentage body fat (-1.69% [-4.98, 1.60]; d=0.22) and time spent in small screen recreation on weekends (-1.13 h [-5.06, 2.80]; d=0.19); and a greater increase in cardiorespiratory fitness (2.13 laps [6.22, 10.48]; d=0.16); and participation in total weekday physical activity (140.74 counts/min [-159.44, 440.92]; d=0.36). This study verified the feasibility, acceptability and potential efficacy of a multifaceted school-based intervention to prevent unhealthy weight gain among adolescent boys.Preventive Medicine 05/2009; 48(6):537-42. DOI:10.1016/j.ypmed.2009.04.007 · 2.93 Impact Factor