COMPARATIVE-STUDY OF FLEX HEART-RATE IN COLOMBIAN CHILDREN AND IN PREGNANT, LACTATING, AND NONPREGNANT, NONLACTATING WOMEN

The heart rate (HR) value employed to separate resting and active port ions of the calibration curves used to estimate energy expenditure (EE ) from minute-by-minute HR recordings is called the flex-HR. The prese nt study has characterized it, the resting HR and the average daily HR during the awake portion of the day (12-14 h) by comparing age, gende r and nutritional status effects related to measured maximum oxygen co nsumption (V-O2 max; ml/min/kg body weight) in school-aged Colombian c hildren (145 boys and 132 girls), 6-16 years of age. The same HR varia bles have been individually measured in nutritionally normal, nonpregn ant, nonlactating (NPNL; n = 48), pregnant (n = 26), and lactating (n = 18) women, 19-43 years of age, on three occasions separarted by 3 mo nths. In general, the flex-HR followed the differences observed in res ting and average daily HRs. All three values decreased with age in chi ldren, mere higher in girls than boys, and did not exhibit differences between nutritionally normal and undernourished children. All three H Rs had a statistically significant negative relationship with V-O2 max in boys but not in girls. NPNL and lactating women showed no signific ant change in the mean values of the repeated HR measurements but exhi bited maximum individual differences of flex-HR of -56 to +42 beats/mi n. Pregnant women had higher HRs in all 3 rounds of measurement compar ed to NPNL subjects. The data support the generalization that the flex -HR method of estimating EE is appropriate in groups of subjects but n ot in individuals, and that individual calibration of subjects close t o the time of application to the making of EE measurements is an impor tant feature of its use. (C) 1997 Wileg-Liss, Inc.