Abstract
PurposeThe present study aims to estimate the minimum number of accelerometer measurement days needed to estimate habitual physical activity (PA) among 6- (2010), 18- (2011) and 30- (2012) year-old participants, belonging to three population-based Brazilian birth cohorts.MethodPA was assessed by triaxial wrist-worn GENEActiv accelerometers and the present analysis is restricted to participants with at least 6 consecutive days of measurement. Accelerometer raw data were analyzed with R-package GGIR. Description of PA measures (overall PA, moderate-to-vigorous PA (MVPA), light PA (LPA)) on weekdays and weekend days were conducted, and statistical differences were tested with chi-squared and Kruskal-Wallis tests. Spearman Brown Formulae was applied to test reliability of different number of days of accelerometer use.ResultsDifferences between week and weekend days regarding LPA, MVPA and overall PA, were only observed among 30-year-olds. Higher levels of MVPA (p = 0.006) and overall PA (p<0.001) were identified on weekdays. For overall PA, to achieve a reliability coefficient >0.70, two and three days of measurement were needed in adults and children, respectively. For LPA, a reliability coefficient >0.70 was achieved with five days in 6-year-old children, three days in 18-year-old young adults, and four days in 30-year-old adults. Considering MVPA, four days would be necessary to represent a week of measurement among all cohort groups.ConclusionOur results show that four and five measurement days are needed to estimate all habitual PA constructs, for children and adults, respectively. Also, among 30-year-old adults, it is important to make efforts towards weekend days measurement.
Highlights
Physical activity (PA) has positive effect on health and quality of life of individuals and communities [1]
For overall PA, to achieve a reliability coefficient >0.70, two and three days of measurement were needed in adults and children, respectively
Our results show that four and five measurement days are needed to estimate all habitual PA constructs, for children and adults, respectively
Summary
Physical activity (PA) has positive effect on health and quality of life of individuals and communities [1]. Global PA prevalence is still low, placing PA promotion as a priority in the public health agenda and, demonstrating the need of monitoring PA at population levels [3]. The use of accelerometers for this purpose increased significantly [5], due to the capability to quantify duration, frequency and intensity of PA through acceleration signals, movement patterns and magnitude [6]. Currently available accelerometers enable large quantity of data storage, a variety of cut-off points for different PA intensities, movement pattern recognition and the possibility of more detailed analyses using the raw data [5]
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