Accelerometer-Determined Steps per Day in US Adults

TUDOR-LOCKE, C., W. D. JOHNSON, and P. T. KATZMARZYK. Accelerometer-Determined Steps per Day in US Adults. Med. Sci. Sports Exerc., Vol. 41, No. 7, pp. 1384-1391, 2009. Introduction: The 2005-2006 National Health and Nutrition Examination Survey (NHANES) released, for the first time, the ActiGraph AM-7164 accelerometer-defined step data in addition to time in intensity (defined by activity counts). This accelerometer is known to have a lower sensitivity threshold than accepted pedometers, leading to relatively higher step estimates. Purpose: The purpose of this analysis is to provide the population- and sex-specific epidemiology of accelerometer-determined steps per day with and without censoring steps detected at the lowest end of the activity spectrum (i.e., inactivity). Methods: The analysis sample represents 3744 participants >= 20 yr who had at least one valid day (i.e., at least 10 h) of monitoring. Means (SE) for steps per day were computed using all steps (i.e., uncensored) and again after censoring those steps taken at an intensity <500 activity counts per minute (indicative of inactivity intensity). Results: On average, US adults took 9676 +/- 107 uncensored steps per day or 6540 +/- 106 censored steps per day. Conclusions: The results of this nationally representative survey indicate that US adults take approximately 10,000 uncensored accelerometer-determined steps per day, which is improbable considering other studies of free-living physical activity in the United States. Until a more valid conversion factor is ascertained for translating accelerometer and pedometer-determined steps, our use of the <500 activity count per minute threshold holds considerable merit.