Relationship between accelerometer-determined steps/day and other accelerometer outputs in US adults.

BACKGROUND The purpose of this study was to examine the relationship between 2005-2006 National Health and Nutrition Examination Survey (NHANES) accelerometer-determined steps/day and activity counts/day, and between steps/day and estimates of nonwear time (as an indicator of the unmonitored day) and time spent in sedentary behaviors as well as a range of physical activity intensities. METHODS Linear regression models were used to characterize the relationship between steps/day, activity counts/day, estimates of wear time, and intensity categories. RESULTS 1781 males (mean age = 46.5 years) and 1963 females (mean age = 47.7 years) wore accelerometers 14.0 ± SEM0.06 hours/day. The relationship between steps/day and activity counts/day was positive and strong (R2 = .87). The relationship between steps/day and time spent in sedentary behaviors was inverse and moderate (R2 = .25). Stronger and positive relationships were apparent between steps/day and time in light (R2 = .69) and moderate (R2 = .63) intensity activities. There was no discernable relationship between steps/day and time spent in low or vigorous intensity activities or with wear time. CONCLUSIONS Assessed by accelerometer, steps/day explains 87% of the variation in activity counts/day, 25% of the variation in time in sedentary behaviors, 69% of time in light intensity, and 63% of time in moderate intensity.