Background Accelerometers are used to objectively measure the physical activity of adults. Data on the use of accelerometers in children have been limited.
Purpose To validate a triaxial accelerometer in physical activity measurement in children and to use accelerometers to monitor daily activity level of healthy children in their natural environment.
Methods For accelerometer validation, 10 subjects (ages 9-16) performed a treadmill test using the Bruce Protocol. Activity count (counts per minute or cpm), oxygen consumption (VO2) values were collected and metabolic equivalent (MET) values were calculated. For physical activity monitoring, 14 healthy children (ages 8-14) wore an accelerometer 24 hours per day for 7 consecutive days to track minute-by-minute physical activity level. For each subject, three complete (24 hours) weekdays and two weekend days were selected for analysis.
Results In accelerometer validation, we found strong correlation between activity counts and physical exertion by METs (r = .97, p = .001). Moderate activity level of 8 METs is equivalent to an activity count of 2,000 cpm. In activity monitoring, the mean age was 11 years. Overall activity was 327 ± 24 cpm. Day time activity was 510 ± 32 cpm. Nighttime activity was 13 ± 2 cpm. The subjects were more active during the weekday than weekend (372 ± 30 cpm vs 291 ± 27 cpm, p = .04).
Conclusions Accelerometry is a valid objective measure of children's physical activity.
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