How many days of monitoring are needed to reliably assess SenseWear Armband outcomes in primary school-aged children?

OBJECTIVES: To identify the number of hours and days or nights of monitoring required to reliably estimate energy expenditure (EE), steps, waking sedentary time, light- (LPA), moderate- (MPA), vigorous- (VPA), moderate- to vigorous-intensity physical activity (MVPA), time in bed and total sleep time using the SenseWear Armband. DESIGN: Cross-sectional study. METHODS: One hundred and two children (50% boys) aged 8-11 years from six schools wore a SenseWear Armband (BodyMedia Inc, USA) for eight consecutive days (seven consecutive nights). Hourly increments of valid day wear time criteria were examined (days/week; 8h/day-14h/day). Intra-class correlation coefficients estimated the reliability for any individual day for each wear time criteria. The Spearman-Brown prophecy formula was used to determine the number of days/nights of monitoring needed to achieve reliability estimates of 0.7, 0.8 and 0.9. RESULTS: Fewer monitoring days were needed as the valid day criteria became more stringent. For example, at least 12h of wear time on at least 2 days was required to achieve a reliability of 0.7 for EE. In contrast, at least 8h/day on 5 days resulted in reliable estimates (0.7) for MPA, VPA and MVPA. Between 6 and 7 nights of monitoring were required to reliably estimate children's time in bed and total sleep time, respectively. CONCLUSIONS: A 7-day monitoring protocol in primary school-aged children would provide acceptable reliability for the assessment of EE, waking sedentary time, LPA, MPA, VPA, MVPA, time in bed and total sleep time, as assessed by the SenseWear Armband.