[Heart rate and physical activity to assess energy expenditure in children]

The aim of the present study was to validate assessment of oxygen consumption (VO2) from heart rate (HR) and physical activity (PA) electronically recorded. Every minute, mean VO2 were validated with indirect calorimetry. We studied 25 children (12 girls, 13 boys), 12.1 +/- 0.7 years old. Measurements were made during about 60 minutes while kids were supine, sitting, standing and walking at four intensities. Minute by minute heart rate was converted to VO2 and energy expenditure using 2 different functions for active and 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 between the 2 line functions). A nonlinear equation (VO2 = a + beta HR3) was used in the remaining minutes. Mean predicted VO2 for every minute were similar to measured VO2 (2 ways interaction ANOVA, p = 0.99). Mean VO2 correlated significantly with VO2 predicted by equation (r = 0.99, p < 0.01). High degree of agreement was found (Bland-Altman comparisons). Combined heart rate and physical activity predicted oxygen consumption with a precision similar to the indirect calorimetric method.