Abstract
This study aims to determine the minimum number of days of monitoring required to reliably predict sitting/lying time, standing time, light intensity physical activity (LIPA), moderate-to-vigorous intensity physical activity (MVPA) and steps in adolescent females. 195 adolescent females (mean age = 15.7 years; SD = 0.9) participated in the study. Participants wore the activPAL activity monitor for a seven day protocol. The amount of time spent sitting/lying, standing, in LIPA and in MVPA and the number of steps per day were quantified. Spearman-Brown Prophecy formulae were used to predict the number of days of data required to achieve an intraclass correlation coefficient of both 0.7 and 0.8. For the percentage of the waking day spent sitting/lying, standing, in LIPA and in MVPA, a minimum of 9 days of accelerometer recording is required to achieve a reliability of ≥ 0.7, while a minimum of 15 days is required to achieve a reliability of ≥ 0.8. For steps, a minimum of 12 days of recording is required to achieve a reliability of ≥ 0.7, with 21 days to achieve a reliability of ≥ 0.8. Future research in adolescent females should collect a minimum of 9 days of accelerometer data to reliably estimate sitting/lying time, standing time, LIPA and MVPA, while 12 days is required to reliably estimate steps.
Highlights
The elimination of physical inactivity has the potential to reduce the incidence of major noncommunicable diseases by 6-10% [12]
Future research in adolescent females should collect a minimum of 9 days of accelerometer data to reliably estimate sitting/lying time, standing time, light intensity physical activity (LIPA) and moderate-to-vigorous physical activity (MVPA), while 12 days is required to reliably estimate steps
The findings of the present study suggest that a minimum of seven days of activPAL measurement is required to achieve a reliability coefficient of ≥0.7 for measurement of SLT, StT and LIPA, while at least 12 days of data are required for a coefficient of ≥0.8
Summary
The elimination of physical inactivity has the potential to reduce the incidence of major noncommunicable diseases by 6-10% [12]. Accurate and reliable measures of physical behaviours (including sitting/lying time (SLT), standing time (StT), light intensity physical activity (LIPA) and MVPA) in free-living environments are essential when identifying associations between specific physical behaviours and health outcomes, identifying determinants that may influence participation in physical behaviours, informing interventions that target specific physical behaviours, and evaluating the effectiveness of interventions and improving public health surveillance [28]. Reviews of the literature have highlighted the advantages and disadvantages of a wide range of field-based measures of physical activity (PA) and SB [26, 30, 31]. These reviews suggest that motion sensors, such as accelerometers, are currently the measure of choice [26, 31]
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