Combined heart rate and activity improve estimates of oxygen consumption and carbon dioxide production rates

Oxygen consumption (over dotVO(2)) and carbon dioxide production (over dotVCO(2)) rates were measured by electronically recording heart rate (HR) and physical activity (PA). Mean daily over dotVO(2) and over dotVCO(2) measurements by HR and PA were validated in adults (n = 10 women and 10 men) with room calorimeters. Thirteen linear and nonlinear functions of HR alone and HR combined with PA were tested as models of 24-h over dotVO(2) and over dotVCO(2). Mean sleep over dotVO(2) and over dotVCO(2) were similar to basal metabolic rates and were accurately estimated from HR alone [respective mean errors were -0.2 +/- 0.8 (SD) and -0.4 +/- 0.6%]. The range of prediction errors for 24-h over dotVO(2) and over dotVCO(2) was smallest for a model that used PA to assign HR for each minute to separate active and inactive curves (over dotVO(2), -3.3 +/- 3.5%; over dotVCO(2), -4.6 +/- 3%). There were no significant correlations between over dotVO(2) or over dot VCO2 errors and subject age, weight, fat mass, ratio of daily to basal energy expenditure rate, or fitness. over dotVO(2), over dotVCO(2), and energy expenditure recorded for 3 free-living days were 5.6 +/- 0.9 ml . min(-1). kg(-1), 4.7 +/- 0.8 ml . min(-1). kg(-1), and 7.8 +/- 1.6 kJ/min, respectively. Combined HR and PA measured 24-h over dotVO(2) and over dot VCO2 with a precision similar to alternative methods.