Physical activity recognition using a wearable accelerometer New perspectives for energy expenditure assessment and health promotion

The aim of this study was to investigate the ability of a novel activity monitor designed to be minimally obtrusive in predicting free-living energy expenditure. Subjects were 18 men and 12 women (age: 41 ± 11 y, BMI: 24.4 ± 3 kg/m). The habitual physical activity was monitored for 14 days using a DirectLife tri-axial accelerometer for movement registration (TracmorD) (Philips New Wellness Solutions, Lifestyle Incubator, Netherlands). TracmorD output was expressed as activity counts per day (Cnts/d). Simultaneously, total energy expenditure (TEE) was measured in free-living conditions using doubly-labeled water. Activity energy expenditure (AEE), and the physical activity level (PAL) were determined from TEE and sleeping metabolic rate. A Multiple-linear regression model predicted 76 % of the variance in TEE, using as independent variables sleeping metabolic rate (Partial-r = 0.55, P<0.001), and Cnts/d (Partial-r = 0.21, P<0.001). The standard error of TEE estimates was 0.9 MJ/d or 7.4 % of the average TEE. A model based on body mass (Partial-r = 0.31, P<0.001) and Cnts/d (Partial-r = 0.23, P<0.001) predicted 54 % of the variance in TEE. Cnts/d were significantly and positively associated with AEE (r = 0.54, P<0.01), PAL (r = 0.68, P<0.001), and AEE corrected by body mass (r = 0.71, P<0.001). This study showed that the TracmorD is a highly accurate instrument for predicting freeliving energy expenditure. The miniaturized design did not harm the ability of the instrument in measuring physical activity and in determining outcome parameters of physical activity such as TEE, AEE, and PAL.