Acta Pzdiatr Scand 64: 257-263, 1975
TEMPERATURE REGULATION IN CHILDREN DURING EXERCISE R . GULLESTAD From the Institute of Work Physiology and Institute of Zoophysiology, University of Oslo, Oslo, Norwlay
ABSTRACT. Gullestad, R. (Institute of Work Physiology and Institute of Zoophysiology, University of Oslo, Oslo, Norway). Temperature regulation in children during exercise. Acta Paediatr Scand, 64:257, 1975.-Rectal and skin temperature and sweat rate were measured in eight 11-year-old boys exercising one hour on a bicycle ergometer at each of three different work loads. Rectal temperature rose according to the relative work load and reached R stendy state !eve! after 2 shorter time than had been previously observed in adult subjects. A good relationship was observed between the levelling off value of rectal temperature during work and the relative work load, but the valne of rectal temperature at rest just before the start of work affects this steady state value. The average skin temperature was kept fairly constant during exercise except on the heaviest work load (70%), during which it rose about 1°C mainly as a result of the rise in skin temperature on the arm, hand and thigh. Tenpcreture increases on skin locations in general were minimal except on the hack where the temperature decreased slightly. Sweat rate showed a close relationship to the absolute work load, and in this report the conclusion is supported that the 11-year-old boys regulate their body temperature during exercise at constant work load in the same way as do adult subjects.
KEY WORDS: temperature regulation, rectal temperature, skin temperature, sweat rate, exercise. children
During prolonged muscular exercise the deep body temperature increases to a constant level which is directly proportional to the work load performed (15, 16, 20). Using different types of work, i.e. arm work, positive and negative leg work, B. Nielsen showed that the increase in the deep body temperature was related to the oxygen uptake rather than to the work load performed ( 1 1 , 12, 13). Astrand 121) and more recently Saltin & Hermansen ( 17) observed that the constant level of the core temperature was set according to the relative work load, i.e. oxygen uptake expressed in per cent of the individuals' maximal oxygen uptake, and not to the absolute work load. However, our knowledge of temperature regulation during exercise in man, is almost entirely based on ex-
periments with adult subjects. The ai m of the present study was to measure 1 ie s in and deep body temperature during prolonged severe exercise in 1 I-year-old boys.
MATERIALS AND METHODS Eight boys, 1 0 - 1 I years of age, were selected from a group of 22 volunteers representing a school class participating in a broader longitudinal study of phy.;ical growth and development. In all classes the consent of the subject was obtained and the parents were well informed about the nature of the investigation. The subjects were given health examinations by a physician prior to their particip:ition in the project. Pertinent data describing the subjects are given in 'Table I . All work experiments were peiformed in a climate chamber at 22k 1°C ambient temperature. The air movement was 0.25 mlsec and the relative humidity varied between 35 and 55 c;. The exercise was performed on an electrically Actu Pzdiurr Scund64
158
R . Gullestad
Table 1 . Physical characteristics and physiological responses to maximal exercise on bicycle ergometer
Subject
Age
J. B . 0 . J. D.M .
II 10
E. M . H . 0. P.
10 10 II
H. W.
10 I1
s. s. s.
Height (cm)
Weight (kg)-
Resting oxygen uptake (limin)
154 153 148 149 150 138 152 141
37.5 40.3 38.6 35.2 35.2 30.6 38.2 15.0
0.19 0.25 0.22 0.23 0.21 0. I7 0.20 0.20
II
(I/min) 2.23 1.91 1.89 1.76 2.23 1.60 I.98 I .89
braked bicycle ergometer, and the pedal rate was kept at 60 rpm using a metronome. Oxygen uptake was determined with the Douglas bag method. The gas volume was measured in a spirometer and the gas analyses performed according to the method of Scholander (18). The heart rate was determined by a conventional ECGrecorder, and the blood lactate concentration was measured in samples taken from a prewarmed, clem and dry fingertip. and analysed according to the S t r ~ mmodification (19) of the colorimetric method of Barker & Summerson ( 1 ). The rectal temperature (Tr,.) was measured at three depths. i.e. 4, 8 and 12 cm from the external sphincter using copper-constantan thermocouples mounted in a 7 mm plastic tube. The average of the three measured temperatures was applied as Trp. The skin temperature was determined at 7 different locations (forehead, upper arm. hand, chest, back, leg and thigh) with a skin thermocouple. The average skin temperature (T,) was calculated according to the method described by Hardy & Du Bois (6). The temperatures were read continuously on a 24channel Speedomax recorder with adjustable zero and adjustable range ( AZAR-unit). The measurements were considered to be acctlrate to within ?O.OS"C. A calibration curve was determined for each thermocouple. Furthermore. the thermocouples for T,, were calibrated immediately after each experiment. The calibration of the skin thermocouples was checked before, in the middle and after the experimental period. Always the same curves of calibration were obtained. The total weight loss of the subjects was measured by a oalance, sensitive to ? I 0 g. The sweat secretion was calculated from the total weight loss by subtracting weight loss due to the respiratory gas exchange and the respiratory water loss. The heat production ( H ) during the experiment was calculated, according to H= M- W, where M=the metabolic energy liberation during exercise calculated from the oxygen uptake using a caloric equivalent of 4.9 kcal per litre of oxygen, and W=the external work converted to heat using the mechanic equivalent of 427 kpm per kcal. Acta Pzdiatr Scond 64
( m l h i n kg)
Highest measured heart rate (beatshin)
Highest measured lactic acid in blood (mg1100 ml)
59.5 47.2 49.0 49.1 63.4 52.3 51.8 54.0
I98 200 198 204 202 182 I96
80 61 98 56 66 113 67
Maximal oxygen uptake
PROCEDURE The subjects arrived at the laboratory on 5 different days. The first 2 days were used to estimate the relationship between oxygen uptake and work load during submaximal exercise and to determine the maximal oxygen uptake. The maximal oxygen uptake was measured on the bicycle ergometer, and in general, the method described by Hermansen & Saltin (7) was used. On the third, fourth and fifth experimental day the subjects performed I hour on the bicycle ergometer at a work load corresponding to approximately 30, 50 and 70% of the individuals' maximal oxygen uptake, respectively. The subjects came to the laboratory about nine o'clock, after having consumed a light meal 1-2 hours before. Prior to the exercise the subjects rested for at least 30 min. At the end of this period the resting oxygen uptake was determined. The rectal and skin temperatures were measured during rest and at every fifth minute during exercise. Oxygen uptake was measured twice during the 60 min work period, i.e. between the 2:.h and the 27th min and between the 50th and 52th min. Heart rate was recorded each minute, and the body weight was measured before and immediately after termination of the exercise.
RESULTS Fig. 1 shows the individual values for the rectal temperature (Tre) at different time intervals during a 60 min bicycle exercise at three different work loads representing about 30 (31-39), 50 (45-56) and 70 (61-69)% of the individuals' maximal oxygen uptake. It can be seen that T,, increased in all subjects during the first 20-40 min of the exercise period before reaching a constant level. The duration of the rise in the T,, was not
Temperature regulation in children
259
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related to the magnitude of the work load performed. It should be noted that the resting value of T,, varied considerably from one subject to another, i.e. from 36.9 t o 37.6"C. This variation markedly affected the steady state level of T,,. This was especially clear from the experiments, in which P. S. and S . S. worked twice, P. S . on a work load of 50% and S. S. on 30% (Fig. 1). The steady state value of T,, was 37.7 and 38.0"C respectively at 5096, but ATre was 0.6"C in both experiments. At 30% the values were 37.4 and 37.7"C, while ATre was 0.1 and 0.2"C. Fig. 2 clearly demonstrates for the whole material the relationship between T,, at rest and T,, a t work.
Fig. I . Rectal temperature during exer-
cise at different relative work loads.
TIME
In Fig. 3 the rectal temperature at the end of each experiment is plotted as a function of the relative work load, i.e. oxygen uptake in per cent of the individuals' maximal oxygen uptake. T,, rose with increasing work load, although considerable variations from f
"C
380
....
Y'
x
370 375 380 38.5 "C Rectal temperature (TW) 01 r e s t
Fig. 2. The relationship between rectal temperature at rest and the levelling off value during work. Arta Pzdiatr Srand 64
R . Gullestmd
260
:,>
-'
Oxygen uptake in percent of max
Oxygen uptake in percent o f rnax V g
Fig. 3. The levelling off value of rectal temperature
during exercise as a function of the relative work load. The regre4sion line y=O.?l.r+36.9 is drawn.
Vo2
Fig. 4 . The rise in rectal temperature from resting value during exercise as a function of relative work load.
The regression line y=O.21~-0.42 is drawn
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Actu Pzdiatr S c a n d 64
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60 rnm
1
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Temperature regulution in children
-1023
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20
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60 min
WORK TIME
Fig. 6. Average skin temperature during exercise at different relative work loads. Each curve represents the mean of values from eight subjects.
one subject to another were observed. Figs. 2 and 4 show that these variations were markedly reduced when the increase in body temperature was expressed as AT,,, i.e. the increase in T,, from the resting value. Regression lines were calculated and drawn in Figs. 3 and 4, but no significant difference in residual variance around the regression line was found in the two situations. Fig. 5 gives the skin temperatures a t various skin locations during exercise at the three different work loads. Each curve represents the average skin temperature of the eight subjects. It can be seen from the illustration that the skin temperature on the forehead and chest remained fairly constant during the exercise period, and also at the various work loads. On the other hand, the skin temperature of the arm, hand, thigh and leg increased and the skin temperature of the back decreased during the exercise period. Variation in the work load caused the skin temperature to differ considerably at the various skin locations. The average skin temperature (T,) is presented in Fig. 6. It shows that only the highest relative work load produced an increase in the average skin temperature.
261
Fig. 7 illustrates the relation between sweat rate and the absolute work load. The sweat rate increased almost linearly with increased work load.
DISCUSSION The results demonstrate that in I I-year-old boys the rectal temperature (Tre)rises during exercise according to the relative work load and reaches a steady state level after 2040 min of work (Fig. 1). Previous studies in adults have shown that this levelling off is accomplished after 40-50 min of work (9, 10, 14, IS) or after approximately 58 min of work (3) during exercise at constant work loads. This difference can be explained by the greater body mass of the latter subjects in relation to the boys. The equilibrium between the temperature in the different parts of the body may be reached more slowly when the mass is greater. The steady state value of T,, is depending on the relative work load (expressed in per cent of the subjects maximal oxygen uptake) (Figs. 1 and 3 ) . But the T,, at the beginning of the exercise markedly affects the steady state value of the T,,. This is clearly demonstrated by the experiments in which P. S.
I
1 ,: 1
jS
I
-~-L.
200
LOO
600
kprnimn
W O R K LOAD
Fig. 5. Skin temperatures during exercise at different relative work loads. Each curve represents the mean of values from eight subjects.
Fig. 7. Sweat rate, during one hour of exercise at different absolute work loads. The line of regression y = 0.59~-23.7 is drawn. Actu P z d i a t r
Scund 64
262
R . Gullestad
of T,, in the former subjects prior t o exercise was 0.6"C lower than that of the boys. The difference between the two mean rectale temperatures at work was found to be significant at the 0.02 level according t o a I-test applied to the data representing the two groups of subjects. In contrast to the skin temperatures (T,) of head and trunk the T, of the extremities rises during exercise (Fig. 5). According to Beveghd & Shepherd ( 2 ) and Kamon & Belding (S), blood flow through the skin of the arms increases during leg work. In the present study the Tq of upper arms rose 32°C TOTAL HEAT PRODUCTION in average at a work load of about 70%. Fig. 8. Sweat rate during one hour of exercise as a This rise probably indicates an enhanced function of total heat production. The results obtained blood flow, which causes an increase in the by B. Nielsen (13) for adult subjects and the results for the boys in the previous study are plotted. Regression heat dissipation from the arms. Iinesy=l.64x-212.67 for the former andy=1.33x-l58.96 Except from exercise a t the highest load for the latter subjects are drawn. during which the mean value of T, rose 1"C, the average skin temperature is kept fairly and S. S. performed the same work load constant (Fig. 6). In other works (4, 11, 17) twice (Fig. I). The AT,, was identical a t the the Tq is shown to decrease about 0.5"C same work load, but the levelling off value during exercise in 20-30 year old subjects of T,, was higher when the resting value working on a work load of 60-70 %. was higher. Fig. 2 demonstrates the same Assuming that the central blood temperatrend in all the work experiments. These ture is kept constant when T,, has reached observations are in agreement with the work a steady state level, this continuous rise in of Nielsen (15). T, even after 20-40 minutes' exercise on Although Figs. 3 and 4 give the impression 70 % work load, when environmental temperathat a better prediction can be given for ture, air velocity and relative humidity are ATre than for the T,, during work from rela- kept nearly constant, can be explained either tive work loads, statistical evidence does not by enhanced skin blood flow or by reduced support this point of view. In experiments sweat rate. made with subjects exercising in the chilli In Fig. 8 the sweat rate from the experiperiod of pyrogen-induced fever ( 5 ) , how- ments with the boys are presented as a funcever, exercise is accompanied with a rise in tion of heat production together with results T,,, and this ATre is equal to the T,, during obtained for adult subjects working on a no fever if the work load is equal. constant work load (13). Regression lines At the same relative work load the level were calculated for the two groups, but the of T,, during continuous exercise seems to regression coefficients of the two lines were be lower in I I-year-old boys than in 20-30- not significantly different when compared year-old subjects. In the work of Saltin & by applying the t-test to the data. Since Hermansen (17) the subjects attained a T,, the 11-year-old boys do not deviate from the of 38.I"C at a relative work load of 50% adult subjects with regard to sweat rate, compared with 37.9"C in the boys of t h e the continuous rise in Tq on the 70% work present study, even though the mean value load may indicate somewhat different periphActu Pzdrufr S c u d 64
Temperature regulation in children eral circiilation control. Sweat rate shows, as expected, a clear relationship to the absolute work load performed (Fig. 7). Although minor differences are observed, the data appear to support a conclusion that 1 1-year-old boys regulate their body temperature during exercise at constant work load in the same way as do adult subjects.
ACKNOWLEDGEMENTS The author acknowledges the assistance and cooperation of Dr L. Hermansen.
REFERENCES 1. Barker, S. B. & Summerson, W. M.: The colorimet-
ric determination of lactic acid in biological material. JBiol C h e m , 138: 535, 1941, 2 . Bevegsrd, B. S . & Shepherd, J. T.: Reaction in man of resistance and capacity vessels in forearm and hand to leg exercise. J Appl Physiol, 21: 123, 1966. 3. Clasing, D. & Laumann, U.: Das Verhalten der Korpertemperatur bei Fahrradergometerarbeit im Bereich der Ausdauergrenze ( P W Clz0).Int Z A n g e w Physiol, 26: 475, 1970. 4. Ekblom, B., Greenleaf, C . J., Greenleaf, J. E . & Hermansen, L.: Temperature regulation during exercise dehydration in man. A c t a Physiol Scand, 79: 475, 1970. 5. Grimby, G . : Exercise in man during pyrogen induced fever. Scand J Clin Lab Invest, 14:Suppl. 6 7 , 1962. 6. Hardy, J. D. & Du Bois, E . F.: The technic of measuring radiation and convection. J Nutr. 15: 461, 1938. 7 . Hermansen, L. & Saltin, B.: Oxygen uptake during maximal treadmill and bicycle exercise. J A p p l Physiol, 26: 3 I , ‘969. 8. Kamon, E. & Belding, H . S.: Dermal blood flow in the resting arm during prolonged leg exercise. J Appl Physiol, 26: 317, 1969. 9. Lind, A . R.: A physiological criterion for setting thermal environmental limits for every-day work. J Appl Physiol, 18: 5 1 , 1963.
263
10. - Physiological effects of continuous or intermittent work in the heat. J A p p ’ P h y ; i o l , 18: 57 1963. 1 1 . Nielsen, B.: Regulation of body temperature and heat dissipation at different levels of energy-and heat production in man. Acra Physiol Scand, 68: 215, 1966. 12. - Thermoregulatory responses to arm work, leg work and intermittent leg work. A c t a Physiol Scand, 72:25, 1968. 13. - Thermoregulation in rest and exercise. Acta Physiol Scand, 76: Suppl. 323, 1%9. 14. Nielsen, B. & Nielsen, M.: Body temperature during work at different environmental temperatures. Acra Physiol Scand, 56: 120, 1962. 15. Nielsen, M. : Die Regulation der Korpertemperatur bei Muskelarbeit. Skand Arch Physiol, 79: 193, 1938. 16. Robinson, S.: Physiological adjustments to heat, in L. M. Newburg (ed.): Physiology of Heat Regulation and the Science of Clothing. Saunders, Phiiadelphia 1959. 17. Saltin, B . & Hermansen, L.: Esophageal, rectal and muscle temperature during exercise. J Appl Physiol, 21: 1757, 1966. 18. Scholander, P. F.: Analyzer for accurate estimation of respiratory gases in one-half cubic centimeter samples. J Biol C h e m , 167: 235, 1947. 19. Strerm, G.: The influence of anoxia on lactate utilization in man after prolonged muscular work. Acta Physiol Scand, 17: 440, 1949. 20. Wyndham, C. H . , Bonwer, W. v. d . M., Devine, M. G. & Paterson, H. E.: Physiological responses of african laborers at various saturated air temperatures, wind velocities and rates of energy expendi5: 290. 1952. ture. J ADD/ Phvsiol. , 21. Astrand, I . : Aerobic work capacity in men and women with special reference to age. Acra Physiol Scand, 46: Suppl. 169, 1960.
..
Submitted June 5 , 1973 Accepted June 12, 1974 Laboratory of Physiology Norwegian College of Physical Education and Sport Sognsvn. 220 Oslo 8 Norway
Acra Prediatr Scand 64
TEMPERATURE REGULATION IN CHILDREN DURING EXERCISE R . GULLESTAD From the Institute of Work Physiology and Institute of Zoophysiology, University of Oslo, Oslo, Norwlay
ABSTRACT. Gullestad, R. (Institute of Work Physiology and Institute of Zoophysiology, University of Oslo, Oslo, Norway). Temperature regulation in children during exercise. Acta Paediatr Scand, 64:257, 1975.-Rectal and skin temperature and sweat rate were measured in eight 11-year-old boys exercising one hour on a bicycle ergometer at each of three different work loads. Rectal temperature rose according to the relative work load and reached R stendy state !eve! after 2 shorter time than had been previously observed in adult subjects. A good relationship was observed between the levelling off value of rectal temperature during work and the relative work load, but the valne of rectal temperature at rest just before the start of work affects this steady state value. The average skin temperature was kept fairly constant during exercise except on the heaviest work load (70%), during which it rose about 1°C mainly as a result of the rise in skin temperature on the arm, hand and thigh. Tenpcreture increases on skin locations in general were minimal except on the hack where the temperature decreased slightly. Sweat rate showed a close relationship to the absolute work load, and in this report the conclusion is supported that the 11-year-old boys regulate their body temperature during exercise at constant work load in the same way as do adult subjects.
KEY WORDS: temperature regulation, rectal temperature, skin temperature, sweat rate, exercise. children
During prolonged muscular exercise the deep body temperature increases to a constant level which is directly proportional to the work load performed (15, 16, 20). Using different types of work, i.e. arm work, positive and negative leg work, B. Nielsen showed that the increase in the deep body temperature was related to the oxygen uptake rather than to the work load performed ( 1 1 , 12, 13). Astrand 121) and more recently Saltin & Hermansen ( 17) observed that the constant level of the core temperature was set according to the relative work load, i.e. oxygen uptake expressed in per cent of the individuals' maximal oxygen uptake, and not to the absolute work load. However, our knowledge of temperature regulation during exercise in man, is almost entirely based on ex-
periments with adult subjects. The ai m of the present study was to measure 1 ie s in and deep body temperature during prolonged severe exercise in 1 I-year-old boys.
MATERIALS AND METHODS Eight boys, 1 0 - 1 I years of age, were selected from a group of 22 volunteers representing a school class participating in a broader longitudinal study of phy.;ical growth and development. In all classes the consent of the subject was obtained and the parents were well informed about the nature of the investigation. The subjects were given health examinations by a physician prior to their particip:ition in the project. Pertinent data describing the subjects are given in 'Table I . All work experiments were peiformed in a climate chamber at 22k 1°C ambient temperature. The air movement was 0.25 mlsec and the relative humidity varied between 35 and 55 c;. The exercise was performed on an electrically Actu Pzdiurr Scund64
158
R . Gullestad
Table 1 . Physical characteristics and physiological responses to maximal exercise on bicycle ergometer
Subject
Age
J. B . 0 . J. D.M .
II 10
E. M . H . 0. P.
10 10 II
H. W.
10 I1
s. s. s.
Height (cm)
Weight (kg)-
Resting oxygen uptake (limin)
154 153 148 149 150 138 152 141
37.5 40.3 38.6 35.2 35.2 30.6 38.2 15.0
0.19 0.25 0.22 0.23 0.21 0. I7 0.20 0.20
II
(I/min) 2.23 1.91 1.89 1.76 2.23 1.60 I.98 I .89
braked bicycle ergometer, and the pedal rate was kept at 60 rpm using a metronome. Oxygen uptake was determined with the Douglas bag method. The gas volume was measured in a spirometer and the gas analyses performed according to the method of Scholander (18). The heart rate was determined by a conventional ECGrecorder, and the blood lactate concentration was measured in samples taken from a prewarmed, clem and dry fingertip. and analysed according to the S t r ~ mmodification (19) of the colorimetric method of Barker & Summerson ( 1 ). The rectal temperature (Tr,.) was measured at three depths. i.e. 4, 8 and 12 cm from the external sphincter using copper-constantan thermocouples mounted in a 7 mm plastic tube. The average of the three measured temperatures was applied as Trp. The skin temperature was determined at 7 different locations (forehead, upper arm. hand, chest, back, leg and thigh) with a skin thermocouple. The average skin temperature (T,) was calculated according to the method described by Hardy & Du Bois (6). The temperatures were read continuously on a 24channel Speedomax recorder with adjustable zero and adjustable range ( AZAR-unit). The measurements were considered to be acctlrate to within ?O.OS"C. A calibration curve was determined for each thermocouple. Furthermore. the thermocouples for T,, were calibrated immediately after each experiment. The calibration of the skin thermocouples was checked before, in the middle and after the experimental period. Always the same curves of calibration were obtained. The total weight loss of the subjects was measured by a oalance, sensitive to ? I 0 g. The sweat secretion was calculated from the total weight loss by subtracting weight loss due to the respiratory gas exchange and the respiratory water loss. The heat production ( H ) during the experiment was calculated, according to H= M- W, where M=the metabolic energy liberation during exercise calculated from the oxygen uptake using a caloric equivalent of 4.9 kcal per litre of oxygen, and W=the external work converted to heat using the mechanic equivalent of 427 kpm per kcal. Acta Pzdiatr Scond 64
( m l h i n kg)
Highest measured heart rate (beatshin)
Highest measured lactic acid in blood (mg1100 ml)
59.5 47.2 49.0 49.1 63.4 52.3 51.8 54.0
I98 200 198 204 202 182 I96
80 61 98 56 66 113 67
Maximal oxygen uptake
PROCEDURE The subjects arrived at the laboratory on 5 different days. The first 2 days were used to estimate the relationship between oxygen uptake and work load during submaximal exercise and to determine the maximal oxygen uptake. The maximal oxygen uptake was measured on the bicycle ergometer, and in general, the method described by Hermansen & Saltin (7) was used. On the third, fourth and fifth experimental day the subjects performed I hour on the bicycle ergometer at a work load corresponding to approximately 30, 50 and 70% of the individuals' maximal oxygen uptake, respectively. The subjects came to the laboratory about nine o'clock, after having consumed a light meal 1-2 hours before. Prior to the exercise the subjects rested for at least 30 min. At the end of this period the resting oxygen uptake was determined. The rectal and skin temperatures were measured during rest and at every fifth minute during exercise. Oxygen uptake was measured twice during the 60 min work period, i.e. between the 2:.h and the 27th min and between the 50th and 52th min. Heart rate was recorded each minute, and the body weight was measured before and immediately after termination of the exercise.
RESULTS Fig. 1 shows the individual values for the rectal temperature (Tre) at different time intervals during a 60 min bicycle exercise at three different work loads representing about 30 (31-39), 50 (45-56) and 70 (61-69)% of the individuals' maximal oxygen uptake. It can be seen that T,, increased in all subjects during the first 20-40 min of the exercise period before reaching a constant level. The duration of the rise in the T,, was not
Temperature regulation in children
259
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related to the magnitude of the work load performed. It should be noted that the resting value of T,, varied considerably from one subject to another, i.e. from 36.9 t o 37.6"C. This variation markedly affected the steady state level of T,,. This was especially clear from the experiments, in which P. S. and S . S. worked twice, P. S . on a work load of 50% and S. S. on 30% (Fig. 1). The steady state value of T,, was 37.7 and 38.0"C respectively at 5096, but ATre was 0.6"C in both experiments. At 30% the values were 37.4 and 37.7"C, while ATre was 0.1 and 0.2"C. Fig. 2 clearly demonstrates for the whole material the relationship between T,, at rest and T,, a t work.
Fig. I . Rectal temperature during exer-
cise at different relative work loads.
TIME
In Fig. 3 the rectal temperature at the end of each experiment is plotted as a function of the relative work load, i.e. oxygen uptake in per cent of the individuals' maximal oxygen uptake. T,, rose with increasing work load, although considerable variations from f
"C
380
....
Y'
x
370 375 380 38.5 "C Rectal temperature (TW) 01 r e s t
Fig. 2. The relationship between rectal temperature at rest and the levelling off value during work. Arta Pzdiatr Srand 64
R . Gullestmd
260
:,>
-'
Oxygen uptake in percent of max
Oxygen uptake in percent o f rnax V g
Fig. 3. The levelling off value of rectal temperature
during exercise as a function of the relative work load. The regre4sion line y=O.?l.r+36.9 is drawn.
Vo2
Fig. 4 . The rise in rectal temperature from resting value during exercise as a function of relative work load.
The regression line y=O.21~-0.42 is drawn
F
=33O0I
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Actu Pzdiatr S c a n d 64
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Temperature regulution in children
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Fig. 6. Average skin temperature during exercise at different relative work loads. Each curve represents the mean of values from eight subjects.
one subject to another were observed. Figs. 2 and 4 show that these variations were markedly reduced when the increase in body temperature was expressed as AT,,, i.e. the increase in T,, from the resting value. Regression lines were calculated and drawn in Figs. 3 and 4, but no significant difference in residual variance around the regression line was found in the two situations. Fig. 5 gives the skin temperatures a t various skin locations during exercise at the three different work loads. Each curve represents the average skin temperature of the eight subjects. It can be seen from the illustration that the skin temperature on the forehead and chest remained fairly constant during the exercise period, and also at the various work loads. On the other hand, the skin temperature of the arm, hand, thigh and leg increased and the skin temperature of the back decreased during the exercise period. Variation in the work load caused the skin temperature to differ considerably at the various skin locations. The average skin temperature (T,) is presented in Fig. 6. It shows that only the highest relative work load produced an increase in the average skin temperature.
261
Fig. 7 illustrates the relation between sweat rate and the absolute work load. The sweat rate increased almost linearly with increased work load.
DISCUSSION The results demonstrate that in I I-year-old boys the rectal temperature (Tre)rises during exercise according to the relative work load and reaches a steady state level after 2040 min of work (Fig. 1). Previous studies in adults have shown that this levelling off is accomplished after 40-50 min of work (9, 10, 14, IS) or after approximately 58 min of work (3) during exercise at constant work loads. This difference can be explained by the greater body mass of the latter subjects in relation to the boys. The equilibrium between the temperature in the different parts of the body may be reached more slowly when the mass is greater. The steady state value of T,, is depending on the relative work load (expressed in per cent of the subjects maximal oxygen uptake) (Figs. 1 and 3 ) . But the T,, at the beginning of the exercise markedly affects the steady state value of the T,,. This is clearly demonstrated by the experiments in which P. S.
I
1 ,: 1
jS
I
-~-L.
200
LOO
600
kprnimn
W O R K LOAD
Fig. 5. Skin temperatures during exercise at different relative work loads. Each curve represents the mean of values from eight subjects.
Fig. 7. Sweat rate, during one hour of exercise at different absolute work loads. The line of regression y = 0.59~-23.7 is drawn. Actu P z d i a t r
Scund 64
262
R . Gullestad
of T,, in the former subjects prior t o exercise was 0.6"C lower than that of the boys. The difference between the two mean rectale temperatures at work was found to be significant at the 0.02 level according t o a I-test applied to the data representing the two groups of subjects. In contrast to the skin temperatures (T,) of head and trunk the T, of the extremities rises during exercise (Fig. 5). According to Beveghd & Shepherd ( 2 ) and Kamon & Belding (S), blood flow through the skin of the arms increases during leg work. In the present study the Tq of upper arms rose 32°C TOTAL HEAT PRODUCTION in average at a work load of about 70%. Fig. 8. Sweat rate during one hour of exercise as a This rise probably indicates an enhanced function of total heat production. The results obtained blood flow, which causes an increase in the by B. Nielsen (13) for adult subjects and the results for the boys in the previous study are plotted. Regression heat dissipation from the arms. Iinesy=l.64x-212.67 for the former andy=1.33x-l58.96 Except from exercise a t the highest load for the latter subjects are drawn. during which the mean value of T, rose 1"C, the average skin temperature is kept fairly and S. S. performed the same work load constant (Fig. 6). In other works (4, 11, 17) twice (Fig. I). The AT,, was identical a t the the Tq is shown to decrease about 0.5"C same work load, but the levelling off value during exercise in 20-30 year old subjects of T,, was higher when the resting value working on a work load of 60-70 %. was higher. Fig. 2 demonstrates the same Assuming that the central blood temperatrend in all the work experiments. These ture is kept constant when T,, has reached observations are in agreement with the work a steady state level, this continuous rise in of Nielsen (15). T, even after 20-40 minutes' exercise on Although Figs. 3 and 4 give the impression 70 % work load, when environmental temperathat a better prediction can be given for ture, air velocity and relative humidity are ATre than for the T,, during work from rela- kept nearly constant, can be explained either tive work loads, statistical evidence does not by enhanced skin blood flow or by reduced support this point of view. In experiments sweat rate. made with subjects exercising in the chilli In Fig. 8 the sweat rate from the experiperiod of pyrogen-induced fever ( 5 ) , how- ments with the boys are presented as a funcever, exercise is accompanied with a rise in tion of heat production together with results T,,, and this ATre is equal to the T,, during obtained for adult subjects working on a no fever if the work load is equal. constant work load (13). Regression lines At the same relative work load the level were calculated for the two groups, but the of T,, during continuous exercise seems to regression coefficients of the two lines were be lower in I I-year-old boys than in 20-30- not significantly different when compared year-old subjects. In the work of Saltin & by applying the t-test to the data. Since Hermansen (17) the subjects attained a T,, the 11-year-old boys do not deviate from the of 38.I"C at a relative work load of 50% adult subjects with regard to sweat rate, compared with 37.9"C in the boys of t h e the continuous rise in Tq on the 70% work present study, even though the mean value load may indicate somewhat different periphActu Pzdrufr S c u d 64
Temperature regulation in children eral circiilation control. Sweat rate shows, as expected, a clear relationship to the absolute work load performed (Fig. 7). Although minor differences are observed, the data appear to support a conclusion that 1 1-year-old boys regulate their body temperature during exercise at constant work load in the same way as do adult subjects.
ACKNOWLEDGEMENTS The author acknowledges the assistance and cooperation of Dr L. Hermansen.
REFERENCES 1. Barker, S. B. & Summerson, W. M.: The colorimet-
ric determination of lactic acid in biological material. JBiol C h e m , 138: 535, 1941, 2 . Bevegsrd, B. S . & Shepherd, J. T.: Reaction in man of resistance and capacity vessels in forearm and hand to leg exercise. J Appl Physiol, 21: 123, 1966. 3. Clasing, D. & Laumann, U.: Das Verhalten der Korpertemperatur bei Fahrradergometerarbeit im Bereich der Ausdauergrenze ( P W Clz0).Int Z A n g e w Physiol, 26: 475, 1970. 4. Ekblom, B., Greenleaf, C . J., Greenleaf, J. E . & Hermansen, L.: Temperature regulation during exercise dehydration in man. A c t a Physiol Scand, 79: 475, 1970. 5. Grimby, G . : Exercise in man during pyrogen induced fever. Scand J Clin Lab Invest, 14:Suppl. 6 7 , 1962. 6. Hardy, J. D. & Du Bois, E . F.: The technic of measuring radiation and convection. J Nutr. 15: 461, 1938. 7 . Hermansen, L. & Saltin, B.: Oxygen uptake during maximal treadmill and bicycle exercise. J A p p l Physiol, 26: 3 I , ‘969. 8. Kamon, E. & Belding, H . S.: Dermal blood flow in the resting arm during prolonged leg exercise. J Appl Physiol, 26: 317, 1969. 9. Lind, A . R.: A physiological criterion for setting thermal environmental limits for every-day work. J Appl Physiol, 18: 5 1 , 1963.
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10. - Physiological effects of continuous or intermittent work in the heat. J A p p ’ P h y ; i o l , 18: 57 1963. 1 1 . Nielsen, B.: Regulation of body temperature and heat dissipation at different levels of energy-and heat production in man. Acra Physiol Scand, 68: 215, 1966. 12. - Thermoregulatory responses to arm work, leg work and intermittent leg work. A c t a Physiol Scand, 72:25, 1968. 13. - Thermoregulation in rest and exercise. Acta Physiol Scand, 76: Suppl. 323, 1%9. 14. Nielsen, B. & Nielsen, M.: Body temperature during work at different environmental temperatures. Acra Physiol Scand, 56: 120, 1962. 15. Nielsen, M. : Die Regulation der Korpertemperatur bei Muskelarbeit. Skand Arch Physiol, 79: 193, 1938. 16. Robinson, S.: Physiological adjustments to heat, in L. M. Newburg (ed.): Physiology of Heat Regulation and the Science of Clothing. Saunders, Phiiadelphia 1959. 17. Saltin, B . & Hermansen, L.: Esophageal, rectal and muscle temperature during exercise. J Appl Physiol, 21: 1757, 1966. 18. Scholander, P. F.: Analyzer for accurate estimation of respiratory gases in one-half cubic centimeter samples. J Biol C h e m , 167: 235, 1947. 19. Strerm, G.: The influence of anoxia on lactate utilization in man after prolonged muscular work. Acta Physiol Scand, 17: 440, 1949. 20. Wyndham, C. H . , Bonwer, W. v. d . M., Devine, M. G. & Paterson, H. E.: Physiological responses of african laborers at various saturated air temperatures, wind velocities and rates of energy expendi5: 290. 1952. ture. J ADD/ Phvsiol. , 21. Astrand, I . : Aerobic work capacity in men and women with special reference to age. Acra Physiol Scand, 46: Suppl. 169, 1960.
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Submitted June 5 , 1973 Accepted June 12, 1974 Laboratory of Physiology Norwegian College of Physical Education and Sport Sognsvn. 220 Oslo 8 Norway
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