Energy expenditure by heart rate in children: an evaluation of calibration techniques

To evaluate the impact of applying seven calibration equations (CE) in the estimation of free-living total energy expenditure (TEE) over 2-3 d in seven boys (mean +/- SD age 9.4+/-0.4 yr) by the Flex heart rate (HR) method.

HR and oxygen consumption were measured simultaneously for eight activities (lying, sitting, standing, arm-reaching exercise, a stooping-and-twisting exercise, stepping, treadmill walking/running, and cycle ergometry) carried out in sequence. CE were derived from various combinations of activities. Flex HRs were identified for each CE.

There were no significant differences in TEE estimates [range (mean +/- SD); 6.65+/-0.72 to 7.27+/-0.89 MJ x d(-1)] derived from any of the CE. Mean daytime HR ranged from 86+/-4 to 122+/-15 beats x min(-1), and 82-98% of recorded daytime HR was < or = 140 beats x min(-1). As a result, within-subject CV in TEE from each of the CE ranged from 2.2% to 8.9%. Mean between-subject Flex HR ranged from 94+/-8 to 111+/-8 beats x min(-1). No significant differences were observed in corresponding TEE estimates. However, mean activity energy expenditure (AEE) ranged from 2.10+/-1.18 MJ x d(-1) (based on Flex HR 111+/-8 beats-min(-1)) to 3.55+/-1.44 MJ x d(-1) (based on Flex HR 94+/-8 beats x min(-1); NS). The corresponding estimates of resting energy expenditure (REE) were 1.89+/-0.82 MJ x d(-1) (Flex HR 111+/-8 beats-min(-1)) and 1.05+/-0.60 MJ x d(-1) (Flex HR 94+/-8 beats x min(-1)). Only the differences between the minimum and maximum estimates of REE were significant (P < 0.05).

Unduly lengthy and complex calibration procedures for the estimation of Flex HR TEE may not be justified in most cases, particularly in sedentary children.