Validating measures of free-living physical activity in overweight and obese subjects using an accelerometer

Background:Free-living physical activity can be assessed with an accelerometer to estimate energy expenditure but its validity in overweight and obese subjects remains unknown.Objective:Here, we validated published prediction equations derived in a lean population with the TracmorD accelerometer (DirectLife, Philips Consumer Lifestyle, Netherlands) in a population of overweight and obese. We also explored possible improvements of new equations specifically developed in overweight and obese subjects.Design:Subjects were 11 men and 25 women (age: 41+/-7 y, BMI: 31.0+/-2.5 kg/m2). Physical activity was monitored under free-living conditions with TracmorD while total energy expenditure was measured simultaneously with doubly-labeled water. Physical activity level (PAL) and activity energy expenditure (AEE) were calculated from total energy expenditure and sleeping metabolic rate.Results:The published prediction equation explained 47% of the variance of the measured PAL (P<0.001). Physical activity level estimates were unbiased (errors [bias +/- 95%CI]: -0.02 +/- 0.28). Measured and predicted AEE/body weight were highly correlated (r2=58%, P<0.001), however the prediction model showed a significant bias of 8 kJ/kg/d or 17.4% of the average AEE/body weight. The new prediction equation of AEE/body weight developed in the obese group showed no bias.Conclusions:In conclusion, equations derived with the TracmorD allow valid assessment of PAL and AEE/body weight in overweight and obese subjects. There is evidence that estimates of AEE/body weight could be affected by gender. Equations specifically developed in overweight and obese can improve the accuracy of predictions of AEE/body weight.International Journal of Obesity accepted article preview online, 29 October 2013; doi:10.1038/ijo.2013.195.