Heart rate and physical activity to assess energy expenditure in children.

The aim of the present study was to validate assessment of oxygen consumpti on (VO2) from heart rate (HR) and physical activity (PA) electronically rec orded. Every minute, mean VO2 were validated with indirect calorimetry. We studied 25 children (12 girls, 13 boys), 12.1 +/- 0.7 years old. Measuremen ts were made during about 60 minutes while kids were supine, sitting, stand ing and walking at four intensities. Minute by minute heart rate was conver ted to VO2 and energy expenditure using 2 different functions for active an d inactive situations. A linear function (VO2 = a + beta HR) was used when counts were 7 or higher and HR higher than a prefixed point (intersection b etween the 2 line functions). A nonlinear equation (VO2 = a + beta HR3) was used in the remaining minutes. Mean predicted VO2 for every minute were si milar to measured VO2 (2 ways interaction ANOVA, p = 0.99). Mean VO2 correl ated significantly with VO2 predicted by equation (r = 0.99, p < 0.01). Hig h degree of agreement was found (Bland-Altman comparisons). Combined heart rate and physical activity predicted oxygen consumption with a precision si milar to the indirect calorimetric method.