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The purpose of this study was to predict energy expenditure (EE) from heart rate (HR) and activity calibrated against 24-h respiration calorimetry in 20 children. HR, oxygen consumption (V˙o 2 ), carbon dioxide production (V˙co 2 ), and EE were measured during rest, sleep, exercise, and over 24 h by room respiration calorimetry on two separate occasions. Activity was monitored by a leg vibration sensor. The calibration day ( day 1) consisted of specified behaviors categorized as inactive (lying, sitting, standing) or active (two bicycle sessions). On the validation day ( day 2), the child selected activities. Separate regression equations forV˙o 2 ,V˙co 2 , and EE for method 1 (combining awake and asleep using HR, HR 2 , and HR 3 ), method 2 (separating awake and asleep), and method 3 (separating awake into active and inactive, and combining activity and HR) were developed using the calibration data. For day 1, the errors were similar for 24-hV˙o 2 ,V˙co 2 , and EE among methods and also among HR, HR 2 , and HR 3 . The methods were validated using measured data from day 2. There were no significant differences in HR,V˙o 2 ,V˙co 2 , respiratory quotient, and EE values during rest, sleep, or over the 24 h between days 1 and 2. Applying the linear HR equations to day 2 data, the errors were the lowest with the combined HR/activity method (−2.6 ± 5.2%, −4.1 ± 5.9%, −2.9 ± 5.1% forV˙o 2 ,V˙co 2 , and EE, respectively). To demonstrate the utility of the HR/activity method, HR and activity were monitored for 24 h at home ( day 3). Free-living EE was predicted as 7,410 ± 1,326 kJ/day. In conclusion, the combination of HR and activity is an acceptable method for determining EE not only for groups of children, but for individuals.
Treuth et al. (Wed,) studied this question.