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

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Abstract
STRATH, S. J, A. M. SWARTZ, D. R. BASSETT, JR., W. L. O’BRIEN, G. A. KING, and B. E. AINSWORTH. Evaluation of heart rate as a method for assessing moderate intensity physical activity. Med. Sci. Sports Exerc., Vol. 32, No. 9, Suppl., pp. S465–S470, 2000. 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– O2 relationship. The primary purpose of this study was to examine the relationship between HR (beats·min−1) and O2 (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 O2 reserve (% O2R). Sixty-one adults (18–74 yr) performed physical tasks in both a laboratory and field setting. HR and O2 were measured continuously during the 15-min tasks. Mean values over min 5–15 were used to perform linear regression analysis on HR versus O2. HR data were then used to predict EE (METs), using age-predicted HRmax and estimated O2max. The correlation between HR and O2 was r = 0.68, with HR accounting for 47% of the variability in O2. After adjusting for age and fitness level, HR was an accurate predictor of EE (r = 0.87, SEE = 0.76 METs). This method of analyzing HR data could allow researchers to more accurately quantify physical activity in free-living individuals.