Evaluation of heart rate as a method for assessing moderate intensity physical activity

To further develop our understanding of the relationship between habitual physical activity and health, research studies require a method of assessment that is objective, accurate, and noninvasive. Heart rate (HR) monitoring represents a promising tool for measurement because it is a physiological parameter that correlates well with energy expenditure (EE). However, one of the limitations of HR monitoring is that training state and individual HR characteristics can affect the HR-V̇O₂ relationship. Purpose: The primary purpose of this study was to examine the relationship between HR (beats · min^-1) and V̇O₂ (mL · kg^-1.-1min^-1) during field- and laboratory-based moderate-intensity activities. In addition, we examined the validity of estimating EE from HR after adjusting for age and fitness. This was done by expressing the data as a percent of heart rate reserve (%HRR) and percent of V̇O₂ reserve (%V̇O(2R)). Methods: Sixty-one adults (18-74 yr) performed physical tasks in both a laboratory and field setting. HR and V̇O₂ were measured continuously during the 15-min tasks. Mean values over min 5-15 were used to perform linear regression analysis on HR versus V̇O₂. HR data were then used to predict EE (METs), using age-predicted HR(max) and estimated V̇O(2max). Results: The correlation between HR and V̇O₂ was r = 0.68, with HR accounting for 47% of the variability in V̇O₂. After adjusting for age and fitness level, HR was an accurate predictor of EE (r = 0.87, SEE = 0.76 METs). Conclusion: This method of analyzing HR data could allow researchers to more accurately quantify physical activity in free-living individuals.