A critical evaluation of energy expenditure estimates based on individual O2 consumption/heart rate curves and average daily heart rate

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Abstract
To test the applicability of indirect estimation of daily energy expenditure from average daily heart rate (HR) and individual O2-intake/heart rate (V̇O2/HR) regression lines in subjects with metabolic disorders, V̇O2/HR regression lines were determined on 2 consecutive days in 17 subjects (five healthy, five with obesity, five with untreated thyrotoxicosis, two with anorexia nervosa). Daily energy expenditure was calculated by means of the average 24 h HR. Generally, there was a high correlation coefficient for the relationship between VO2 and HR, but the slopes and intercepts varied considerably from day to day, leading to poor agreement between duplicate estimates of energy expenditures, and not infrequently to physiologically meaningless values. Further studies, comprising determination of the V̇O2/HR regression lines in three different body positions on 7 different days in one experienced test subject showed great variability of the V̇O2/HR regression lines, both in the same position and in different positions. The applied procedure seems unsuitable for metabolic studies in individual patients who engage in ordinary daily activities with low energy expenditure.