Heart rate monitoring as a reliable tool for assessing energy expenditure in obese individuals

Previous studies have suggested the use of the FlexHR method for predicting daily energy expenditure in various populations. We investigated the stability of the relation between oxygen consumption (VO₂) and heart rate (HR) in obese subjects undergoing a fitness and weight reduction program. Eleven obese (BMI>30) healthy subjects (6 males, 5 females) were recruited from a Wellness program. Subjects performed a laboratory calibration procedure between HR and VO₂ in resting and exercising conditions, before starting the Wellness program (Stage I) and after reducing 10% of their initial body weights (BW) within 6 months (Stage II). Mean BW, BMI and % body fat were reduced by 13.1±4.4 kg, 4.2±1.4 kgm^-2 and 6.8±4.1%, respectively, for all parameters (P<0.001). Mean peak VO₂increased from 31.3±7.1 at the beginning to 37.2±7.3 mL-kg^-1 min^-1 at the end of the intervention period (P<0.01). The mean flex HR point changed from 96±14 to 86±15 beatsmin^-1 (P<0.05). There were no significant individual differences in the HR-VO ₂ prediction equations derived from the laboratory calibrations in either stage. In conclusion, the relationship between HR and VO₂ consumption remains stable during a time period of weight reduction. The use of the FlexHR method for predicting energy expenditure by heart rate monitoring is recommended for subjects undergoing a weight-reduction program. It should be taken in account, however, that an increase in aerobic capacity, in parallel to changes in body weight and composition, might cause a decrease in the flex point.