Physical activity level measured by doubly labeled water and accelerometry in children.

The present study investigated the use of a tri-axial accelerometer, Tracmor2, for the measurement of physical activity in children. Eleven children [age 6.9 (2.2) years, body mass 19.5 (5.3) kg and height 112.3 (14.4) cm] were studied. Total daily energy expenditure (TDEE) was measured using the doubly labeled water method over a 2-week period. In addition, basal metabolic rate (BMR) was determined by the ventilated hood system. Physical activity level (PAL) was defined as TDEE/BMR. Tracmor2 was worn during the same 2-week period throughout waking hours after which average counts per day were calculated. The average counts per day were shown to be highly correlated to PAL values measured by doubly labeled water: PAL = 1.156 x 10(-5) x Tracmor2 average counts day(-1) + 0.978 (r=0.79, P<0.01). In conclusion, Tracmor2 is a valid instrument to measure physical activity in children under free-living conditions.