The assessment of 24-hour energy expenditure in elderly women by minute-by-minute heart rate monitoring.

Abstract

To test the suitability of minute-by-minute heart rate (HR) monitoring for estimating 24-hour total energy expenditure (TEE) in elderly women, 13 volunteers, mean (SD) age 73 +/- 3 years, participated in this study. Energy expenditure during five standardized activities, ranging from sitting quietly to walking at 3 km/h, was measured by indirect calorimetry (ventilated hood) simultaneously with HR. From these data, individual calibration curves were obtained by linear regression. The mean correlation coefficient was 0.89 +/- 0.10 (range 0.69-0.99). A group calibration curve was also calculated (r = 0.93, p < 0.02), based on the mean values of energy expenditure during standardized activities and simultaneous HR of the 13 subjects. For 3 days, minute-by-minute HR was registered continuously. The mean 24-hour HR over these days was 75.7 +/- 8.5 beats/min. In addition, activity questionnaires were used to calculate energy expenditure from time/motion data, using individual measured energy expenditure values. TEE calculated from HR using individual calibration curves (8.8 +/- 3.5 MJ/day) was only moderately correlated (r = 0.60, p < 0.001) with TEE calculated from the activity questionnaire (8.6 +/- 0.9 MJ/day). Calculated TEE using the group calibration curve was 8.1 +/- 5.2 MJ/day, which was not significantly correlated with TEE calculated from the activity questionnaire or with TEE using individual calibration curves. The mean values of TEE calculated from the three methods were not statistically significantly different. However, individual values differed markedly sometimes. Individual physical activity levels (TEE/resting metabolic rate), calculated from 24-hour HR monitoring, were unreliably high in some subjects. Minute-by-minute HR monitoring did not appear to be a valid method for predicting TEE for individuals or small groups.