Age-related maximal heart rate: examination and refinement of prediction equations.

AIM: The aim of this study was to establish the maximal heart rate (HRmax)-age relation with minimal error rate. METHODS: The records of 28,137 participants (20,691 male and 7446 female, age range between 10 and 80 yrs) who performed a maximal stress test were used in this study. Linear regressions between HRmax and age were used for the entire sample, for the male and female samples, separately, and for each section of the gender-by-age category. The equations were then contrasted to a number of equations reported in the literature. The best fitted equations were then tested on a new sample of 2449 subjects (2091 males and 358 females) for validation purposes. RESULTS: Mean HRmax values were found to decrease at a faster rate in women than in men with age increase. The linear regression functions within each age category were found to be less reliable than the equations derived for the entire sample and for the female and male samples, respectively. The new and updated HRmax prediction equations are as follows: HRmax=208.609-0.716age and 209.273-0.804age for males and females, respectively, and 208.852-0.741age for the entire sample. Those equations along with the other four best equations for predicting HRmax were found to be correlated with the observed HRmax values (validation sample): 0.64 and 0.664 for males and females, respectively. CONCLUSION: Our equations were derived from a large data set and were found to be highly sensitive for both genders. Therefore, we propose that these new formulas, with their improved accuracy, be used in healthy active and clinical populations.

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 kg.m-2 and 6.8±4.1%, respectively, for all parameters (P<0.001). Mean peak VO2 increased 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 beats.min-1 (P<0.05). There were no significant individual differences in the HR-VO2 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.

Temporal partitioning among diurnally and nocturnally active desert spiny mice: energy and water turnover costs.

Nocturnal Acomys cahirinus and diurnally active A. russatus coexist in hot rocky deserts. Diurnal and nocturnal activity exposes them to different climatic challenges. A doubly-labelled water field study revealed no significant differences in water turnover between the species at all seasons, reflecting the adaptations of A. russatus to water conservation. In summers the energy expenditure of A. russatus tended to be higher than that of A. cahirinus. Energy requirements of A. cahirinus in winter are double than that of A. russatus, and may reflect the cost of thermoregulating during cold nights.