Performance of the ActiGraph accelerometer using a national population-based sample of youth and adults

Background: Accelerometer output may be semi-continuous or continuous in nature, which has implications on discerning non-wear and defining physical activity intensity levels. This study described field-based accelerometer performance from a surveillance sample of youth and adults. Methods: Using 2003-2006 National Health and Nutrition Examination Survey data, 4,028 youth ages 6 to 17 years and 7,931 adults age > =18 years wore an ActiGraph AM7164 accelerometer for one week, providing at least 3 days of wear for > =8 hours/day. Accelerometer performance was assessed by exploring the number of different values of accelerometer counts/minute for each participant. Results: On average, youth participants had 1381 different counts/minute over 7 days (median 1360, interquartile range 1127-1623) and adult participants had 1101 different counts/minute over 7 days (median 1085, interquartile range 874-1313). For both youth and adults, when restricting to counts/minute between 0 to 4999, every possible value (in counts/minute) occurred at least once. Conclusion: The field-based data confirmed that the accelerometer used in this study allowed for continuous counts/minute through which all but the most vigorous activities would usually occur