Utility of a step activity monitor for the measurement of daily ambulatory activity in children.

Objectives: To evaluate the reliability and validity of the StepWatch Activity Monitor (SAM) as a reliable and valid measurement tool for assessing ambulatory activity in able-bodied children and to assess the ambulatory activity of able-bodied children.
Design: Descriptive study.
Setting: General community.
Participants: Ninety-seven able-bodied children, aged 6 to 20 years.
Interventions: Not applicable.
Main Outcome Measures: Anthropometric parameters, calibration of a step activity monitor to ensure accuracy, and 3 days of simultaneous heart rate and step activity monitoring.
Results: The SAM had an accuracy of 99.87% compared with the observer-counted steps and was shown to be valid and reliable when compared with heart rate monitoring. The subjects in all age groups (6-10 y, 11-15 y, 16-20 y) spent most of their active time at low step rate but took the fewest steps at this rate. Although the least amount of time was spent at high step rate, it accounted for the most steps. The 6- to 10-year-old group took more total steps per day than any of the other groups. Boys spent significantly more time at high step rate than girls in all age groups (mean for boys, 66+/-4 min/d; girls, 47+/-4 min/d).
Conclusions: The SAM is an accurate, valid, and useful tool for measuring continuous, time-based step activity during real-world community activity for children and adolescents.