Important Differences in Accelerometer Cut Points for Quantifying Physical Activity in a Nested Occupational Cohort

Abstract

Background: Accurate physical activity assessment is becoming increasingly important in epidemiologic research. There is an increasing body of evidence suggesting that physical activity can prevent or reduce severity of disease. Utilizing accelerometers as an objective quantification of physical activity is a cost effective way to assess physical activity, yet there is little research on the agreement between different proposed cut points in a free-living, healthy adult population. Methods: This study investigated the correlation, sensitivity and specificity of different cut points for light, moderate, and vigorous activity in an occupational cohort of 78 participants. All participants wore the accelerometer for at least 12 hours a day for at least 5 days, including one weekend day. Results: There was a broad range of minutes of light and moderate activity and few minutes of vigorous activity. In general, correlations between free-living derived cut points were lower than those comparing laboratory derived cut points. Sensitivity and specificity values covered a broad range of values with lower sensitivity values in the light and moderate activity level categories and lowest specificity values in the light activity category. Conclusions: Cut points derived from laboratory studies are generally more congruous but may not be more accurate. There is little agreement between cut points at light and moderate levels. Consideration of the population studied should be taken into account when deciding on what set of cut points to use.