THE ASSESSMENT OF 24-HOUR ENERGY-EXPENDITURE IN ELDERLY WOMEN BY MINUTE-BY-MINUTE HEART-RATE MONITORING

To test the suitability of minute-by-minute heart rate (HR) monitoring for estimating 24-hour total energy expenditure (TEE) in elderly wome n, 13 volunteers, mean (SD) age 73 +/- 3 years, participated in this s tudy. Energy expenditure during five standardized activities, ranging from sitting quietly to walking at 3 km/h, was measured by indirect ca lorimetry (ventilated hood) simultaneously with HR. From these data, i ndividual calibration curves were obtained by linear regression. The m ean correlation coefficient was 0.89 +/- 0.10 (range 0.69-0.99). A gro up calibration curve was also calculated (r = 0.93, p < 0.02), based o n 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 wa s 75.7 +/- 8.5 beats/min. In addition, activity questionnaires were us ed to calculate energy expenditure from time/motion data, using indivi dual 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 activit y questionnaire (8.6 +/- 0.9 MJ/day). Calculated TEE using the group c alibration curve was 8.1 +/- 5.2 MJ/day, which was not significantly c orrelated with TEE calculated from the activity questionnaire or with TEE using individual calibration curves. The mean values of TEE calcul ated from the three methods were not statistically significantly diffe rent. However, individual values differed markedly sometimes. Individu al physical activity levels (TEE/resting metabolic rate), calculated f rom 24-hour HR monitoring, were unreliably high in some subjects. Minu te-by-minute HR monitoring did not appear to be a valid method for pre dicting TEE for individuals or small groups.