title: Evaluation of heart rate as a method for assessing moderate intensity physical activity.
abstract: 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-VO2 relationship.
  
  
  OBJECTIVE
  The primary purpose of this study was to examine the relationship between HR (beats x min(-1)) and VO2 (mL x kg(-1 x -1) min(-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 VO2 reserve (%VO2R).
  
  
  METHODS
  Sixty-one adults (18-74 yr) performed physical tasks in both a laboratory and field setting. HR and VO2 were measured continuously during the 15-min tasks. Mean values over min 5-15 were used to perform linear regression analysis on HR versus VO2. HR data were then used to predict EE (METs), using age-predicted HRmax and estimated VO2max.
  
  
  RESULTS
  The correlation between HR and VO2 was r = 0.68, with HR accounting for 47% of the variability in VO2. After adjusting for age and fitness level, HR was an accurate predictor of EE (r = 0.87, SEE = 0.76 METs).
  
  
  CONCLUSIONS
  This method of analyzing HR data could allow researchers to more accurately quantify physical activity in free-living individuals.
authors.affiliation: Department of Exercise Science and Sport Management, University of Tennessee, Knoxville 37996, USA. sstrath@utk.edu
authors.forename: S J
authors.initials: SJ
authors.lastname: Strath
authors.forename: A M
authors.initials: AM
authors.lastname: Swartz
authors.forename: D R
authors.initials: DR
authors.lastname: Bassett
authors.forename: W L
authors.initials: WL
authors.lastname: O'Brien
authors.forename: G A
authors.initials: GA
authors.lastname: King
authors.forename: B E
authors.initials: BE
authors.lastname: Ainsworth
mesh_terms: D000328:Adult; D000368:Aged; D004734:Energy Metabolism; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D018670:Monitoring, Ambulatory; D010101:Oxygen Consumption; D010809:Physical Fitness; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity