Applied Physiology
Eur J Appl Physiol (1992) 65:99-103
European Journal of
and Occupational Physiology © Springer-Verlag1992
Comparison of heart rate monitoring combined with indirect calorimetry and the doubly labelled water (2H2180) method for the measurement of energy expenditure in children H. J. G. Emons, D. C. Groenenboom, K. R. Westerterp, and W. H. M. Saris
Department of Human Biology, University of Limburg, PO-Box 616, NL-6200 MD Maastricht, The Netherlands Accepted February 20, 1992
Summary. The aim of the present study was to compare data on 24-h energy expenditure (EEE4h) in nine boys and ten girls (mean age 9.3 and 8.1 years, respectively) by heart rates (f~) combined with energy expenditure obtained from a 1-day stay in an indirect calorimeter (EEoal) and a 2-week period of normal living using the doubly labelled water method (EEdtw). Individual calibration curves were derived from f~ and oxygen uptake measured during sleep (in the calorimeter), standing and walking on a treadmill. An estimation of energy expenditure based on 24-h f~ monitoring (EEIc) was made during the stay in the calorimeter and on a normal schoolday. Mean results showed an overestimation in EEIo compared to EEcal and EEdlw of 10.4% and 12.3% respectively, varying from 6.3% to 16.2°70. These results confirmed earlier observations in adults that for a group the f~ method overestimates EE24 h by about 10%. Key words: Energy expenditure - Child - Heart rate
method - Indirect calorimetry - Doubly labelled water
Of all physiological variables, heart rate (fc) is one of the easiest to measure with the least inconvenience to the subject, especially with the new developments in microelectronics. Therefore, monitoring fc has become one of the most commonly employed methods in activity studies in children (Saris 1986). There are, however, certain disadvantages in using this method of prediction: the relationship between fc and oxygen uptake (1202) is dependent upon the type of exercise and, furthermore, the relationship is less accurate at low levels of physical activity (Acheson et al. 1980; Christensen et al. 1983; Dauncey and James 1979; Washburn and Montoye 1986). These disadvantages have been established in adults. However, in children data are scarce and it is suggested that because of the relatively higher activity levels in this age group, fc monitoring could give a more accurate prediction of the energy expenditure (EE). The aim of the present study was to comparefo monitoring with the accurate indirect calorimeter and doubly labelled water method for the measurement of 24 h energy expenditure (EE24 h) in children.
Introduction
In recent years there has been a surge of interest in the triad: child - physical activity - health. A major impetus for such interest has been the increasing involvement of children in advanced level athletics. But also the relevance of physical activity in clinical paediatrics has been gaining increasing attention, be it in diagnosis, prevention, management or etiology (Bar-Or 1983). Measuring daily physical activity in children is one of the most difficult tasks for the physiologist because of the presence of contradictory aims: on the one hand it is desirable to record the normal daily movements of a child, which usually means that the child must be burdened with equipment for measuring a number of body functions. On the other hand, the child's normal daily activities should not be hindered (Saris 1986). Offprint request to: H. J. G. Emons
Methods Subjects. Healthy children between 7 and 11 years of age were re-
cruited by using posters and making personal approaches. Parents of 22 children gave their informed consent. In the course of the study it was established that it was impossible to collect data using standard procedures in the indirect calorimeter for 3 of the children (home-sickness). Therefore these children were excluded from further analysis. The study was approved by the Medical Ethics Committee of the University of Maastricht. Procedure. Body mass, height and thickness of four skinfolds
(over triceps, biceps, subscapular and suprailiac muscles) were measured. Percentage body fat was calculated according to the method of Durnin and Rahaman (1967). Three different methods were used to quantify EE24 h: 1. A 24 h stay in an indirect calorimeter (EEoa]) 2. A 14-day measurement using the doubly labelled water method (EEalw) 3. An estimation of EE based on 24 h fc monitoring (EEoc)
100
Indirect calorimeter. To m e a s u r e EE24 h accurately (error less than 2%0), 24 h measurements were carried out in an open-circuit indirect calorimeter (14m 3, ventilation rate about 40 1-min-1). Volume of the outgoing air was determined by means of a dry gas meter (Schlumberger, Dordrecht, The Netherlands) and gas analysis was made with a paramagnetic O2-analyser (Servomex, Crowborough, England) and an infrared CO2 analyser (Hartman and Braun, Frankfurt, FRG). An on-line micro computer controlled the gas sampling system and calculated EEc~a automatically according to the equation of Weir (Schoffelen et al. 1984): E (kcal) = 3.9 x 02 [1] + 1.1 x COz [1]. The calorimeter was equipped with bed, wash-stand, toilet, telephone, intercom and TV. Air temperature was maintained at 20°C during the day and at 18°C during the night. Food was offered ad libitum according to the normal diet at fixed times. To make the daily programmes as uniform as possible, activities such as board games, drawing, etc. were scheduled. Doubly labelled water. A representative sample with regard to age and body composition of 10 children (5 boys and 5 girls) was selected from the total group to study EE24 h with the EEa~wmethod (Lifson and McClintock 1966). An individually calculated dose, which was expected to give an excess of about 350 ppm 180 and about 265 ppm EH in the body water, was administered orally to these children in the evening, after collecting a baseline urine sample. Further urine samples were collected in the morning on day 1 after the first voiding and in the evening at 19 h on day 1, 7, 8, 14 and 15, respectively. Determination of the isotopic abundances of 2H and 180 was carried out with an Isotope Ratio Mass Spectrometer (Aqua Sira, VG Isogas, Middlewich, Cheshire, England). Mean EEd~w over 14 days was calculated using an estimated fixed respiratory quotient (RQ) of 0.85 ~ and the equation (Schoeller et al. 1986):
nco2 = ~
(1.01Ko-l.04KH)-0.0264r~f
where: nco~ = CO2 production rate (mol. day - 1) N = total body water (moO; Ko = elimination rate ~80; KH = elimination rate 2H; rof= correction factor for evaporative water loss. Estimated by formula r~f = 1.05 N(Ko--KH). Heart rate. The use of the f~ to estimate EE24 h was based on the assumption of a close individual linear relationship betweenf~ and I?O2 and thus also between f~ and EE (Bradfield 1971). The f~1702 regression line has been shown to be curved in its lower part up to the so-called transition point and linear in the higher ranges of 1702. In this study, two individual regression equations were determined for each subject: for quiet activities equations (f~, zqQ) were derived from f~ and I?O2 measured during sleep (in the calorimeter) and standing; for dynamic activitiesf~ and 1702 were measured during five submaximal exercise intensities on a treadmill (Quinton Cardio Exercise, Quinton Instrument CO, Seattle, USA) (fo,~qa,~). The transition point was calculated as the meanf~ during standing. The fc was measured continuously during the 24-h stay in the calorimeter and simultaneously with the measurement of EEd~w during 1 school day (0800-1900 hours) by means of a Sporttester PE 3000 (Polar Electro KY, Kempele, Finland). To obtain 24 hf~ values during the school day, f~ values of the remaining resting/ sleeping hours (1900 hours to 0800 hours) in the calorimeter were used. The 1202 was calculated from mean f~ per hour using the two individual regression equations (f~ ~q and f~ E%~ ). The EEF was calculated from VO2 using an energy eqmvalent of 20.50 J. 1~-~. •
,
,
Q
,
,
n
Error in estimation of EE by fixed RQ is 1% for each 0.01 unit RQ
Statistical analysis. Comparisons between data were made using the Student's t-test for paired and unpaired groups (c~= 0.05).
Results P h y s i c a l characteristics o f the 19 children are given in T a b l e 1. T h e g r o u p c o r r e s p o n d s well with the n a t i o n a l g r o w t h tables ( R o e d e a n d v a n W i e r i n g e n 1985). A l t h o u g h t h e r e are n o reference values a v a i l a b l e r e g a r d i n g o r g a n i z e d s p o r t s activities in T h e N e t h e r l a n d s , t h e r e were n o i n d i c a t i o n s t h a t the sports activities o f this g r o u p d i f f e r e d f r o m the n o r m . T h e m e a n d a y t i m e fc d u r i n g a s c h o o l d a y was signific a n t l y higher ( P < 0.05) c o m p a r e d to the stay in the calor i m e t e r (Table 2). N o statistical differences were o b served b e t w e e n the b o y s a n d the girls. F i g u r e 1 shows I202 p l o t t e d as a f u n c t i o n o f fc a n d the m e a n regression e q u a t i o n s (f~,EqQ a n d fo,Eqdyn) o f the 9 b o y s a n d 10 girls. F i g u r e 2 gives m e a n EE24h o f b o t h b o y s a n d girls d u r i n g the stay in the c a l o r i m e t e r , b a s e d o n EEcal a n d the f c - m e t h o d (EEcal, fc). T h e activities in the c a l o r i m e t e r consisted m a i n l y o f lying, sitting a n d s t a n d i n g . H o w e v e r , in 12 o f the 19 children fc values were m e a s u r e d a b o v e the i n d i v i d u a l t r a n s i t i o n p o i n t . Since fc, EqQ r e p r e s e n t e d the activities in the c a l o r i m e t e r , EE24 h o f all the children was also calcul a t e d using o n l y f¢,~qQ (EEcal,1~,zqQ) f o r the w h o l e m e a sured f¢-range. The EEa4h based on the two equations (EEcaI,¢c, BqQ + Eqdyn) was significantly higher ( P < 0.05) t h a n EEz4 h m e a s u r e d b y EEc~. N o significant d i f f e r e n c e was f o u n d using only fc Eq_. T h e r e were no significant differences in EE24 h b e t w e e n b o y s a n d girls. M e a n EE24h o f the selected b o y s (n = 5, m e a n age 8.4 years, b o d y m a s s 27.8 kg, b o d y fat 13.5%) a n d girls
Table 1. Characteristics of the 19 children Sex
n
Age Height Body Body Sports (year) (cm) mass fat (min.week-1) (kg) (°70)
Boys
9 mean 9.3 SD 1.4 Girls 10 mean 8.1 SD 1.3
138.8 8.8 132.3 6.0
30.9 4.3 28.2 2.6
14.2 2.2 19.9 4.0
160 104 66 31
Table 2. Mean heart rate in beats.min -1 of 19 children during a stay in a calorimeter and on a schoolday Sex
Boys Girls
n
9 10
Calorimeter (3-6 h)
Calorimeter (8-19 h)
School (8-19 h)
P*
mean
SD
mean
SD
mean
SD
75 85
9 11
93 107
9 9
107 113
10 8
Eur J Appl Physiol (1992) 65:99-103
European Journal of
and Occupational Physiology © Springer-Verlag1992
Comparison of heart rate monitoring combined with indirect calorimetry and the doubly labelled water (2H2180) method for the measurement of energy expenditure in children H. J. G. Emons, D. C. Groenenboom, K. R. Westerterp, and W. H. M. Saris
Department of Human Biology, University of Limburg, PO-Box 616, NL-6200 MD Maastricht, The Netherlands Accepted February 20, 1992
Summary. The aim of the present study was to compare data on 24-h energy expenditure (EEE4h) in nine boys and ten girls (mean age 9.3 and 8.1 years, respectively) by heart rates (f~) combined with energy expenditure obtained from a 1-day stay in an indirect calorimeter (EEoal) and a 2-week period of normal living using the doubly labelled water method (EEdtw). Individual calibration curves were derived from f~ and oxygen uptake measured during sleep (in the calorimeter), standing and walking on a treadmill. An estimation of energy expenditure based on 24-h f~ monitoring (EEIc) was made during the stay in the calorimeter and on a normal schoolday. Mean results showed an overestimation in EEIo compared to EEcal and EEdlw of 10.4% and 12.3% respectively, varying from 6.3% to 16.2°70. These results confirmed earlier observations in adults that for a group the f~ method overestimates EE24 h by about 10%. Key words: Energy expenditure - Child - Heart rate
method - Indirect calorimetry - Doubly labelled water
Of all physiological variables, heart rate (fc) is one of the easiest to measure with the least inconvenience to the subject, especially with the new developments in microelectronics. Therefore, monitoring fc has become one of the most commonly employed methods in activity studies in children (Saris 1986). There are, however, certain disadvantages in using this method of prediction: the relationship between fc and oxygen uptake (1202) is dependent upon the type of exercise and, furthermore, the relationship is less accurate at low levels of physical activity (Acheson et al. 1980; Christensen et al. 1983; Dauncey and James 1979; Washburn and Montoye 1986). These disadvantages have been established in adults. However, in children data are scarce and it is suggested that because of the relatively higher activity levels in this age group, fc monitoring could give a more accurate prediction of the energy expenditure (EE). The aim of the present study was to comparefo monitoring with the accurate indirect calorimeter and doubly labelled water method for the measurement of 24 h energy expenditure (EE24 h) in children.
Introduction
In recent years there has been a surge of interest in the triad: child - physical activity - health. A major impetus for such interest has been the increasing involvement of children in advanced level athletics. But also the relevance of physical activity in clinical paediatrics has been gaining increasing attention, be it in diagnosis, prevention, management or etiology (Bar-Or 1983). Measuring daily physical activity in children is one of the most difficult tasks for the physiologist because of the presence of contradictory aims: on the one hand it is desirable to record the normal daily movements of a child, which usually means that the child must be burdened with equipment for measuring a number of body functions. On the other hand, the child's normal daily activities should not be hindered (Saris 1986). Offprint request to: H. J. G. Emons
Methods Subjects. Healthy children between 7 and 11 years of age were re-
cruited by using posters and making personal approaches. Parents of 22 children gave their informed consent. In the course of the study it was established that it was impossible to collect data using standard procedures in the indirect calorimeter for 3 of the children (home-sickness). Therefore these children were excluded from further analysis. The study was approved by the Medical Ethics Committee of the University of Maastricht. Procedure. Body mass, height and thickness of four skinfolds
(over triceps, biceps, subscapular and suprailiac muscles) were measured. Percentage body fat was calculated according to the method of Durnin and Rahaman (1967). Three different methods were used to quantify EE24 h: 1. A 24 h stay in an indirect calorimeter (EEoa]) 2. A 14-day measurement using the doubly labelled water method (EEalw) 3. An estimation of EE based on 24 h fc monitoring (EEoc)
100
Indirect calorimeter. To m e a s u r e EE24 h accurately (error less than 2%0), 24 h measurements were carried out in an open-circuit indirect calorimeter (14m 3, ventilation rate about 40 1-min-1). Volume of the outgoing air was determined by means of a dry gas meter (Schlumberger, Dordrecht, The Netherlands) and gas analysis was made with a paramagnetic O2-analyser (Servomex, Crowborough, England) and an infrared CO2 analyser (Hartman and Braun, Frankfurt, FRG). An on-line micro computer controlled the gas sampling system and calculated EEc~a automatically according to the equation of Weir (Schoffelen et al. 1984): E (kcal) = 3.9 x 02 [1] + 1.1 x COz [1]. The calorimeter was equipped with bed, wash-stand, toilet, telephone, intercom and TV. Air temperature was maintained at 20°C during the day and at 18°C during the night. Food was offered ad libitum according to the normal diet at fixed times. To make the daily programmes as uniform as possible, activities such as board games, drawing, etc. were scheduled. Doubly labelled water. A representative sample with regard to age and body composition of 10 children (5 boys and 5 girls) was selected from the total group to study EE24 h with the EEa~wmethod (Lifson and McClintock 1966). An individually calculated dose, which was expected to give an excess of about 350 ppm 180 and about 265 ppm EH in the body water, was administered orally to these children in the evening, after collecting a baseline urine sample. Further urine samples were collected in the morning on day 1 after the first voiding and in the evening at 19 h on day 1, 7, 8, 14 and 15, respectively. Determination of the isotopic abundances of 2H and 180 was carried out with an Isotope Ratio Mass Spectrometer (Aqua Sira, VG Isogas, Middlewich, Cheshire, England). Mean EEd~w over 14 days was calculated using an estimated fixed respiratory quotient (RQ) of 0.85 ~ and the equation (Schoeller et al. 1986):
nco2 = ~
(1.01Ko-l.04KH)-0.0264r~f
where: nco~ = CO2 production rate (mol. day - 1) N = total body water (moO; Ko = elimination rate ~80; KH = elimination rate 2H; rof= correction factor for evaporative water loss. Estimated by formula r~f = 1.05 N(Ko--KH). Heart rate. The use of the f~ to estimate EE24 h was based on the assumption of a close individual linear relationship betweenf~ and I?O2 and thus also between f~ and EE (Bradfield 1971). The f~1702 regression line has been shown to be curved in its lower part up to the so-called transition point and linear in the higher ranges of 1702. In this study, two individual regression equations were determined for each subject: for quiet activities equations (f~, zqQ) were derived from f~ and I?O2 measured during sleep (in the calorimeter) and standing; for dynamic activitiesf~ and 1702 were measured during five submaximal exercise intensities on a treadmill (Quinton Cardio Exercise, Quinton Instrument CO, Seattle, USA) (fo,~qa,~). The transition point was calculated as the meanf~ during standing. The fc was measured continuously during the 24-h stay in the calorimeter and simultaneously with the measurement of EEd~w during 1 school day (0800-1900 hours) by means of a Sporttester PE 3000 (Polar Electro KY, Kempele, Finland). To obtain 24 hf~ values during the school day, f~ values of the remaining resting/ sleeping hours (1900 hours to 0800 hours) in the calorimeter were used. The 1202 was calculated from mean f~ per hour using the two individual regression equations (f~ ~q and f~ E%~ ). The EEF was calculated from VO2 using an energy eqmvalent of 20.50 J. 1~-~. •
,
,
Q
,
,
n
Error in estimation of EE by fixed RQ is 1% for each 0.01 unit RQ
Statistical analysis. Comparisons between data were made using the Student's t-test for paired and unpaired groups (c~= 0.05).
Results P h y s i c a l characteristics o f the 19 children are given in T a b l e 1. T h e g r o u p c o r r e s p o n d s well with the n a t i o n a l g r o w t h tables ( R o e d e a n d v a n W i e r i n g e n 1985). A l t h o u g h t h e r e are n o reference values a v a i l a b l e r e g a r d i n g o r g a n i z e d s p o r t s activities in T h e N e t h e r l a n d s , t h e r e were n o i n d i c a t i o n s t h a t the sports activities o f this g r o u p d i f f e r e d f r o m the n o r m . T h e m e a n d a y t i m e fc d u r i n g a s c h o o l d a y was signific a n t l y higher ( P < 0.05) c o m p a r e d to the stay in the calor i m e t e r (Table 2). N o statistical differences were o b served b e t w e e n the b o y s a n d the girls. F i g u r e 1 shows I202 p l o t t e d as a f u n c t i o n o f fc a n d the m e a n regression e q u a t i o n s (f~,EqQ a n d fo,Eqdyn) o f the 9 b o y s a n d 10 girls. F i g u r e 2 gives m e a n EE24h o f b o t h b o y s a n d girls d u r i n g the stay in the c a l o r i m e t e r , b a s e d o n EEcal a n d the f c - m e t h o d (EEcal, fc). T h e activities in the c a l o r i m e t e r consisted m a i n l y o f lying, sitting a n d s t a n d i n g . H o w e v e r , in 12 o f the 19 children fc values were m e a s u r e d a b o v e the i n d i v i d u a l t r a n s i t i o n p o i n t . Since fc, EqQ r e p r e s e n t e d the activities in the c a l o r i m e t e r , EE24 h o f all the children was also calcul a t e d using o n l y f¢,~qQ (EEcal,1~,zqQ) f o r the w h o l e m e a sured f¢-range. The EEa4h based on the two equations (EEcaI,¢c, BqQ + Eqdyn) was significantly higher ( P < 0.05) t h a n EEz4 h m e a s u r e d b y EEc~. N o significant d i f f e r e n c e was f o u n d using only fc Eq_. T h e r e were no significant differences in EE24 h b e t w e e n b o y s a n d girls. M e a n EE24h o f the selected b o y s (n = 5, m e a n age 8.4 years, b o d y m a s s 27.8 kg, b o d y fat 13.5%) a n d girls
Table 1. Characteristics of the 19 children Sex
n
Age Height Body Body Sports (year) (cm) mass fat (min.week-1) (kg) (°70)
Boys
9 mean 9.3 SD 1.4 Girls 10 mean 8.1 SD 1.3
138.8 8.8 132.3 6.0
30.9 4.3 28.2 2.6
14.2 2.2 19.9 4.0
160 104 66 31
Table 2. Mean heart rate in beats.min -1 of 19 children during a stay in a calorimeter and on a schoolday Sex
Boys Girls
n
9 10
Calorimeter (3-6 h)
Calorimeter (8-19 h)
School (8-19 h)
P*
mean
SD
mean
SD
mean
SD
75 85
9 11
93 107
9 9
107 113
10 8
