Key Concepts about Physical Activity Monitor Data Collection Methods

Physical Activity Monitor Data Collection

The Physical Activity Monitor component was used to assess physical activity quantified as detected motion among participants aged 6 years and older during NHANES 2003-2006. The accelerometer-based physical activity monitors captured motion during all daily activities.

Examined persons who were not wheelchair bound were asked to wear an ActiGraph Model 7164 accelerometer (ActiGraph, LLC; Pensacola, FL) for 7 days while awake. (The device records movement data continuously even when not being worn by the participant). The accelerometer records vertical acceleration, which provides an indication of physical activity intensity. Accelerometers worn at the hip primarily detect movement associated with ambulation. The accelerometer was programmed to record over 1 minute periods (epochs), providing up to 10,080 data points (7 days * 24 hours * 60 minutes) for each participant. In addition, the accelerometers had a step counter feature, which provided another objective measure of physical activity.

The accelerometer was worn on a flexible elastic waist belt over the right hip; and underneath clothing; it was not waterproof so participants were requested to remove the accelerometer before swimming or bathing. After 7 days of wear, participants returned the accelerometer by mail in a postage-paid envelope. Upon return, data were downloaded and the accelerometer was checked to determine if it was still within manufacturer’s calibration specifications. If not within calibration limits, the data were flagged as not in calibration and the accelerometer was recalibrated before being used again to collect data on another participant.

Figure 1.  NHANES Physical Activity Monitor

picture of accelerometer and accelerometer on person

Figure 1 is presented to show the scale of the device and does not reflect actual placement on the NHANES study participant.


NHANES 2011-12 physical activity monitor data are being collected with a different accelerometer device and protocol than was used during the 2003-2004 and 2005-2006 NHANES cycles. Although many of the concepts addressed in this tutorial will apply to data collected with the new device, the specifics of data analyses will differ. Analysts will need to seek updated analysis tools.



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