Comparison of heart rate and physical activity recall with doubly labeled water in obese women. Med. Sci. Sports Exerc., Vol. 27, No. 1, pp. 126-133, 1995. Accurate methods of estimating total daily energy expenditure (TDEE) that are inexpensive and differentiate activities of varying intensities are needed in obesity research. We compared minute-by-minute heart rate (HR) monitoring and the 7-d physical activity recall (PAR) questionnaire with doubly labeled water (DLW) for the measurement of TDEE and physical activity in 14 obese women (45% +/- 4% fat, mean +/- SD) before and during 12 wk of weight reduction. TDEE was measured over 2 wk by DLW. HR monitoring was conducted for 3 d, with individual VO2/HR calibrations applied to HR data above 3 METs. PAR revealed the amount of time spent in sleep, moderate, hard, and very hard activities during 1 wk, with time spent in light activities determined by difference. Mean TDEE values, expressed as the % difference from DLW, prior to weight loss were -5.2 +/- 10.8% by HR and 3.4 +/- 14.4 by PAR, and during the diet were + 0.9 +/- 14.1% by HR and + 0.9 +/- 14.7% by PAR. Individual variability was high for both HR (-24.0 to + 25.6%) and PAR (-27.4 to + 36.2%). Energy expended in physical activity prior to weight loss were 3.97 +/- 1.23 MJ.d-1 by DLW, 3.91 +/- 0.90 by HR, and 4.79 +/- 0.95 by PAR. During weight loss, physical activity values by DLW, HR, and PAR were 4.31 +/- 1.18, 4.84 +/- 2.22, and 4.64 +/- 1.06 MJ.d-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)