European Journal of
Europ. J. appl. Physiol. 37, 129-136 (1977)
Applied
Physiology
and Occupational Physiology 9 by Springer-Verlag1977
Influence of Water Temperature on Thermal, Circulatory and Respiratory Responses to Muscular Work F. Pirnay, R. Deroanne, and J. M. Petit Institut E. Malvoz, Province de Li+ge, M+decine et Hygi+ne Sociales, Universit~ de Li+ge, 4, Quai du Barbou, B-4020 Li6ge, Belgium
Summary. Different muscular exercises have been executed on a bicycle ergometer during immersion in water, the temperature of which varied between 20 and 40 ~ C. During submaximal works, 02 consumption was not modified by the temperature of the water. On the other hand, body temperatures (rectal and muscular) are clearly influenced by environment. The temperature of the quadriceps varies from 37.7-38.5 ~ C when the bath temperature rises from 2 0 - 4 0 ~ C during the same work intensity corresponding to 1/3 of the individual maximal work capacity. The rectal temperature was always lower about 0.5 ~ C. Ventilation and heart rate underwent modifications which were significantly accentuated in hot water. Maximal 02 consumption does not reach its highest level in cold water. The low muscular temperature observed in these conditions seems to limit the aerobic metabolism and the working of the muscles. Maximal O 2 consumption then rises in parallel with the increase in bath temperature and in body temperatures. In very hot water however (40 ~ C), when rectal temperature rises unduly, the circulatory demand linked to thermolysis becomes excessive, and maximal 02 consumption decreases. Key words: Submaximum and maximum exercise - Water immersion - Temperature. Since a paper published by Nielsen (1938) he has generally been admitted that the rise of central temperature during muscular work is proportional to work intensity, and independent of the environmental thermal conditions when air temperature remains within a range of 5 - 3 0 ~ C. Such an indifference of rectal temperature to environment, during exercise, seems to be confirmed by the later works of Wyndham et al. (1952), as well as those of Nielsen and Nielsen (1962). Some restrictions should be made however. Stromme et al. (1963) show that rectal temperature may decrease in a cold environment if work intensity is low. Inversely, it rises in a hot environment if mechanical work is intense (Wyndham et al., 1952; Lind, 1963). The extent of the indifference area of rectal temperature to
130
F. Pirnay et al.
environment m a y thus vary according to work intensity. On the other hand, the temperature reached during exercise depends on the training of the subject (Saltin and Hermansen, 1966), and is modified after acclimatation ( W y n d h a m et al., 1966; Davies et al., 1971). Then, for Kitzing et al. (1968), as for Candas et al. (1973), the core temperature related to the intensity of work is also influenced, but to a lesser degree, by the environmental conditions. The evolution of body temperature can be less well studied when muscular exercise is performed during water immersion (Craig and Dvorak, 1968). Water temperature is likely to modify behaviour during effort. In fact, the processes involved in thermal regulation are solicited to varying degrees and m a y interfere with the reactions to exercise. Thus, the circulatory function responds to a twofold requirement, both by muscular exercise to ensure the transport of 02 to working muscles, and by thermal regulation to convey the calories. Mechanical performances m a y also depend on water temperature. According to some authors, maximal oxygen consumption is limited by the cardiovascular transport of this gas (Mitchell et al., 1958; Stenberg et al., 1967; Ouellet et al., 1969). But the blood flow required by thermal regulation might become competitive and reduce the irrigation of the working muscles. According to some other authors, muscular performances are limited by the chemical production of energy within muscular cells (Doll et al., 1968; Kaijser, 1970). By varying the temperature of contracting muscles, the speed of biochemical reactions m a y be modified, thereby inducing a simultaneous change in the maximal muscular aerobic metabolism. The purpose of this investigation is to study the influence of water temperature on responses to muscular work during immersion: during sub-maximal effort by examining circulatory, respiratory and thermal changes; during maximal effort, by analysing the evolution of maximal 02 consumption.
Methods Five medical students volunteered for this study. Their height was 174.6 cm (+ 2.1 cm), and their weight 68.2 kg (+ 3.2 kg). The muscular exercise consisted in pedalling on a bicycle ergometer (Monark). The ergometer and subject, except for his head, were immersed in water, the temperature of which was modified from 20--40~ C. Two sub-maximal efforts corresponding approximately to 1/3 and 2/3of the individual maximal work capacity were performed, on different days, during 15 min. Maximal exercise is the work that exhausts the subject within 2 or 3 min. It was preceded by a 15 min sub-maximal effort, intended to afford a better distinction between experimental conditions and body temperatures. Individual intensities were determined according to the results of earlier tests. Oxygen consumption was measured according to the Douglas bag method. The volume of expired air was measured with Tissot's gasometer and the analysis of oxygen was done by the paramagnetic method (Servomex). The heart rate was measured from the recording of a thoracic derivation of the ECG, according to the method of Deroanne et al. (1974). Continuous measurement of the rectal temperature was effected by a thermocouple probe (Ellab) connected to an electromanometer (Electrolaboratoriet). The muscular temperature was measured at the end of each sub-maximal and maximal performance by a thermoeouple, implanted 4-5 cm deep into the lateral part of the quadriceps, as recommended by Saltin (1968).
Muscular Work in Water
131
Results Sub-Maximal Exercises Figure 1 shows the average (+ S.D.) results obtained during the two submaximal exercises. 02 consumption showed no clear or significant difference related to water temperature, which is consistent with the findings of Costill (1967) and of Craig and Froehlich (1968). But body temperatures are clearly influenced by environment; when the bath temperature was maintained between 25 and 30 ~ C, muscular and rectal temperatures corresponded to the values observed in the air during an exercise of same intensity (Saltin and Hermansen, 1966). In warmer baths, metabolic heat expenditure was no longer possible, and body hyperthermia set in. For a work corresponding to 50% of the individual maximum, rectal temperature then reached 38.8 ~ C. Inversely, 20 ~ C cold water accelerates heat exchanges between body and bath. Rectal temperature was always lower in these conditions and reached 37.4 ~ C for the same work intensity. It should be noted that the thermal balance remained positive and that the core temperature was higher than in a resting condition. The temperature inside working muscles depends mainly on the intensity of the contractions, but also appears to be influenced by environment. It is always higher than the rectal temperature. The difference was about 0.5 ~ C, increasing with cold
Q
Q
9O2
2.5
2"0 tl.5 [srp~ 1.0 { { 150Heart Rate 140- b/rain T 130120110!001 9 Muscle 40] "C o Recta[ Temp.
T T
!~
38
371 '~ 'o 36J Water
2%
2'5
20
Temp (oC)
2s
Fig. 1. Parameters measured during two submaximal exercises in water at different temperatures
132
F. Pirnay et al.
and decreasing in warm water. Any modification of bath temperature and of core temperature caused reactions in relation with thermal regulation, expecially in a hot environment. Ventilation increased slightly, since it changed from 24.7-27.21 or from 40.6-50.21/min during the two intensities of the studied work. Circulatory changes were far more marked. The heart rate strongly increased in warm water. During the lightest exercise, it varied between 102 and 132.4 beats/rain when the temperature of the water was increased from 2 0 - 4 0 ~ C; it rose from 131.1-150.8 beats/min in the same conditions when the intensity of exercise corresponds to 50% of the maximum.
Maximal Exercises Figure 2 shows results (means and the standard deviations) of the parameters measured during maximal exercise; muscular temperature then averaged 39.9 ~ C in lukewarm water. It was definitely lower in 20 ~ C water as it only reached 38 ~ C; it was strongly increased in 40 ~ C water, where it reached 40.2 ~ C. The modification due to environment thus gave a maximal difference of 2.2 ~ C. The difference between muscular and rectal temperature was greater during maximal work. It was close to 1~ C and was due to the short duration of the performance. Metabolic heat had no time to spread uniformly in the whole body.
4.0 s 3't3.5 7 [STPD(min 3.2 HeartRate
170 ~
9 Muscle 40] o Rectal Temp. 391oc
{
{
I
37 36
Water Temp.(~ 2'0
2's
is
Fig. 2. Parameters measured during maximal exercise in water at different temperatures
Muscular Work in Water
133
The maximal 02 consumption varied with the bath temperature. In cold water (20 ~ C) the aerobic capacity was low for all subjects. Muscular temperature was then comparatively low too. When the bath temperature rose, maximal O5 consumption initially showed a significant increase. Then, between 25 and 35 ~ C, the rise was very moderate and the variation of individual results means that the observed changes were hardly significant. In very warm water (40 ~ C), maximal 02 consumption no longer increased. On the contrary, it decreased for all subjects despite a higher muscular temperature. This decrease was accompanied by a strong rise of rectal temperature, which then reached 39 ~ C, and a strong acceleration of the heart rate (201.4 beats/rain).
Discussion
The mechanisms of thermal regulation are disturbed when the body is immersed in water. Heat exchanges with the fluid are significantly accelerated because of the higher thermal conductivity of water, which is 25 times higher than that of air. Due to its great caloric capacity, water also enhances exchanges because it can thus rapidly take up or release great quantities of heat. Body temperatures are therefore far more influenced by environment than they are in the air. Muscular temperature, however, mainly depends on the intensity of the contractions. It rises right from the beginning of work (as demonstrated by Buchtal et ai., 1944), and remains level after 10-15 min of exercise (Saitin et al., 1968). Core temperature always rises during muscular work, even in cold water. Pugh et al. (1960) observed that the thermal balance remains possible, even in much colder water during swimming sports, such as cross-Channel competitions. To ensure the expenditure of the great amount of calories produced by metabolism during muscular work, the water temperature has to be lowered, especially as work intensity increases. The indifferent temperature of a bath, set at 36 ~ C when the subject is at rest, thus drops to 31 ~ C when the metabolism is trebled (Craig and Dvorak, 1968). For the same reason, the temperature of competition swimming pools never exceeds 2 5 - 2 6 ~ C (Costill, 1967). In fact, if the defense mechanisms against cold remain effectual in water, the thermal balance becomes impossible in warm water. In point of fact, these conditions suppress the most effective means of dissipating heat in warm and dry air, i.e. evaporation of sweat. Therefore, in warm water, the calories produced by muscular work accumulate in the organism and cause the body temperatures to rise. The contact of warm water with the skin, as well as central hyperthermia, contribute to the stimulation of the thermosensitive nerve centres of the anterior hypothalamus. In this way, thermolysis reactions set in, but they are ineffectual however, and are even harmful in warm water. Tachycardia is one of these reactions. The additional increase in heart rate exceeds 20 beats/min in 40 ~ C warm water, which shows the importance of stimulation due to thermal regulation. Exertion in warm water is uncomfortable, due to tachycardia, facial sweating, headache and muscular asthenia. The performance is also reduced in warm water, as shown by the decrease of maximal 02 consumption. Circulatory and cardiac limitations can be observed. Too high a blood flow is required by the transport of calories. Since heart rates have
134
F. Pirnay et al.
reached their maximal value, the circulatory demands of thermolysys lessen the blood and oxygen flow in working muscules. Such a decrease in maximal 02 consumption in a hot environment was observed in air, namely by Rowell et al. (1965), Craig and Froehlich (1968), Klausen et al. (1967), Pirnay et al. (1970). Whereas Costill (1967) did not observe any influence of water temperature on the aerobic capacity in maximal exercise during immersion. However, the experimental conditions of this author differ from ours in that the exercise consisted in in situ swimming against resistance, and its duration limited to 3 rain. Induced no concomitant variation of rectal temperature. The importance of body hyperthermia, however, has been well demonstrated by Craig and Froehlich (1968), and by Pirnay et al. (1970). It explains the discrepancy between the observations quoted and the investigation. On the other hand, we have also tried to find out how far muscular temperature influences maximal aerobic metabolism. But one must not forget that such variations in temperature are obtained simultaneously with other general physiological modifications, especially heart rate and rectal temperature. The results are difficult to interpret, owing to the simultaneous occurrence of such phenomena and to the slight variations in muscular temperature. However, comparing the evolution of muscular temperature with the simultaneous evolution of 02 consumption (Fig. 3), suggests a relation between the two phenomena in cold and medium temperatures. Maximal 02 consumption follows an increasing line which is parallel to that of muscular temperature. This increase in metabolism is approximately 10% for a rise in temperature of 1~ C. In cold water, maximal 02 consumption does not reach its highest point. The muscular temperature measured at that time is comparatively low. It can be accepted that the speed of oxidative biochemical reactions is then reduced and that the working of the muscles is limited. Kaijser (1970) measured, in similar cooling conditions, a higher saturation of venous blood compared with that observed in normal
4.0"
3.5
1 3~, '
MUSCLE
TEMPERATURE ( ~ 39 '
4'0
Fig. 3. Evolution of maximal 02 consumption in relation to temperature of the quadriceps during maximal performances on a bicycle ergometer, during water immersion at different temperatures
Muscular Work in Water
135
conditions. Besides M c A r d l e et al. (19 76) observed that the cardiac output remained unchanged in cold water. The diminution of heart rate is then c o m p e n s a t e d b y an increment o f the stroke volume. These results are an argument against an eventual circulatory deficit in cold water, and support an argument for a biochemical limitation of O2 consumption during the muscular contractions in our experiences. However, in other conditions, the immersion in cold water can increase muscular performance and accelerate the recovery ( N u k a d a and Miiller, 1955). These authors observed indeed a lengthening o f the leg-work when these are immersed in water at 10 ~ C. However the m a x i m u m 02 uptake was not measured. F o r high temperatures, the evolution of the maximal Oz consumption is no longer parallel with the muscle temperature. On the contrary, maximal 0 2 consumption drops, despite a rise in muscular temperature. This decrease m a y be explained by a circulatory limitation which occurs gradually, owing to the competitive dem a n d s o f thermolysis. The very high heart rates measured at this time, evidence an extremely strong cardiocirculatory demand. The aerobic power therefore appears to reach its maximal value when a high temperature in the muscles allows a high supply of chemical energy, although the d e m a n d s related to thermolysis have not yet started to exert their circulatory competitive and limitative effects.
References Buchtal, F., Honcke, P., Lindhard, J.: Temperature measurements in human muscles in situ at rest and during muscular work. Acta physiol, scand. 8, 230-258 (1944) Candas, V., Vogt, J. J., Libert, J. P.: Evolution des temp+ratures rectales et cutan6es lors de l'exercice musculaire effectu+ darts des temp+ratures flair comprises entre 10 et 30~ C. Arch. Sci. Physiol. 27, A239-A246 (1973) Costill, D. L.: Effects of water temperature on aerobic working capacity. Res. Quart. J. 39, 67-73 (1967) Costill, D. L., Cahill, P. J., Eddy, D.: Metabolic responses to submaximal exercise in three water temperatures. J. appl. Physiol. 24, 628-632 (1967) Craig, A. B. Jr., Dvorak, M.: Thermal regulation of man exercising during water immersion. J. appl. Physiol. 25, 28--35 (1968) Craig, F. N., Froehlich, H. L.: Endurance of preheated men in exhausting work. J. appl. Physiol. 24~ 636--639 (1968) Davies, C. T. M., Barnes, C., Sargeant, A. J.: Body temperature in exercise. Int. Z. angew. Physiol. 30, 10--19 (1971) Deroanne, R., Leloup, M., Pirnay, F., Petit, J. M.: Telemetry and training control of swimmers. In: Biotelemetry II, Proceedings of the Second International Symposium on Biotelemetry, pp. 103-105. Basel: Karger 1974 Doll, E., Keul, J., Maiwald, C.: Oxygen tension and acido-base equilibria in venous blood of working muscle. Amer. J. Physiol. 215, 23--29 (1968) Kaijser, L.: Limiting factors of aerobic muscle performance. Acta physiol, scand. 346, 1-96 (1970) Kitzing, J., Behling, K., Bleichert, A., Scarperi, M., Scarperi, S.: Antriebe und effektorische Mal3nahmen der Thermoregulation bei Ruhe und w~hrend k6rperlicher Arbeit. Int. Z. angew. Physiol. 30, 119-131 (1972) Klausen, K., Dill, D. B., Phillips, E. E., McGregor, D.: Metabolic reactions to work in the desert. J. appl. Physiol. 22, 292--296 (1967) Lind, A. R.: A physiological criterion for setting thermal environmental limits for every day work. J. appl. Physiol. 18, 51-56 (1963)
136
F. Pirnay et al.
McArdle, W. D., Magel, J. R., Lesmes, G. R., Pechar, G. S.: Metabolic and cardiovascular adjustement to work in air and water at 18, 25 and 33~ C. J. appl. Physiol. 40, 85-90 (1976) Mitchell, J. H., Sproule, B. J., Chapman, C. B.: The physiological meaning of the maximal oxygen intake test. J. clin. Invest. 37, 538-547 (1958) Nielsen, B., Nielsen, M.: Body temperature during work at different environmental temperatures. Acta physiol, scand. 56, 120-129 (1962) Nielsen, M.: Die Regulation der KSrpertemperatur bei Muskelarbeit. Skand. Arch. Physiol. 79, 193-230 (1938) Nukada, A., Mfiller, E. A.: Hauttemperatur und Leistungsfiihigkeit in Extremit~iten bei dynamischer Arbeit. Int. Z. angew. Physiol. 16, 61-73 (1955) Ouellet, Y., Poh, S. C., Beckalde, M. R.: Circulatory factors limiting maximal aerobic exercise capacity. J. appl. Physiol. 27, 874-880 (1969) Pirnay, F., Deroanne, R., Petit, J. M.: Maximal oxygen consumption in a hot environment. J. appl. Physiol. 28, 642-645 (1970) Pugh, L. G., Edholm, O. G., Fox, R. H., Wolff, H. S., Hervey, G. R., Hammond, W. H., Tanner, J. M., Whitehouse, R. H.: A physiological study of channel swimming. Clin. Sci. 19, 257-273 (1960) Saltin, B., Hermansen, L.: Esophageal, rectal and muscle temperatures during exercise. J. appl. Physiol. 21, 1757-1762 (1966) Saltin, B., Gagge, A. P., Stolwijk, J. A. J.: Muscle temperature during submaximal exercise in man. J. appl. Physiol. 25, 679-688 (1968) Stenberg, J.,/kstrand, P. O., Ekblom, B., Royce, J., Saltin, B.: Hemodynamic response to work with different muscle groups, sitting and supine. J. appl. Physiol. 22, 61-70 (1967) Stromme, S., Lange Andersen, K., Elsner, R. W.: Metabolic and thermal responses to muscular exertion in the cold. J. appl. Physiol. 18~ 756-763 (1963) Wyndham, C. H., Bouwer, W. D., Devine, M. G., Patterson, H. E.: Physiological responses of African laborers at various saturated air temperatures, wind velocities and rates of energy expenditure. J. appl. Physiol. 5, 290-298 (1952) Wyndham, C. H., Strydom, N. B., Williams, G. G., Morrisson, J. F., Bredell, G. A. G.: The heat reactions of Bantu males in various states of acclimatization. Int. Z. angew. Physiol. 23, 79-92 (1966)
Accepted February 14, 1977
Europ. J. appl. Physiol. 37, 129-136 (1977)
Applied
Physiology
and Occupational Physiology 9 by Springer-Verlag1977
Influence of Water Temperature on Thermal, Circulatory and Respiratory Responses to Muscular Work F. Pirnay, R. Deroanne, and J. M. Petit Institut E. Malvoz, Province de Li+ge, M+decine et Hygi+ne Sociales, Universit~ de Li+ge, 4, Quai du Barbou, B-4020 Li6ge, Belgium
Summary. Different muscular exercises have been executed on a bicycle ergometer during immersion in water, the temperature of which varied between 20 and 40 ~ C. During submaximal works, 02 consumption was not modified by the temperature of the water. On the other hand, body temperatures (rectal and muscular) are clearly influenced by environment. The temperature of the quadriceps varies from 37.7-38.5 ~ C when the bath temperature rises from 2 0 - 4 0 ~ C during the same work intensity corresponding to 1/3 of the individual maximal work capacity. The rectal temperature was always lower about 0.5 ~ C. Ventilation and heart rate underwent modifications which were significantly accentuated in hot water. Maximal 02 consumption does not reach its highest level in cold water. The low muscular temperature observed in these conditions seems to limit the aerobic metabolism and the working of the muscles. Maximal O 2 consumption then rises in parallel with the increase in bath temperature and in body temperatures. In very hot water however (40 ~ C), when rectal temperature rises unduly, the circulatory demand linked to thermolysis becomes excessive, and maximal 02 consumption decreases. Key words: Submaximum and maximum exercise - Water immersion - Temperature. Since a paper published by Nielsen (1938) he has generally been admitted that the rise of central temperature during muscular work is proportional to work intensity, and independent of the environmental thermal conditions when air temperature remains within a range of 5 - 3 0 ~ C. Such an indifference of rectal temperature to environment, during exercise, seems to be confirmed by the later works of Wyndham et al. (1952), as well as those of Nielsen and Nielsen (1962). Some restrictions should be made however. Stromme et al. (1963) show that rectal temperature may decrease in a cold environment if work intensity is low. Inversely, it rises in a hot environment if mechanical work is intense (Wyndham et al., 1952; Lind, 1963). The extent of the indifference area of rectal temperature to
130
F. Pirnay et al.
environment m a y thus vary according to work intensity. On the other hand, the temperature reached during exercise depends on the training of the subject (Saltin and Hermansen, 1966), and is modified after acclimatation ( W y n d h a m et al., 1966; Davies et al., 1971). Then, for Kitzing et al. (1968), as for Candas et al. (1973), the core temperature related to the intensity of work is also influenced, but to a lesser degree, by the environmental conditions. The evolution of body temperature can be less well studied when muscular exercise is performed during water immersion (Craig and Dvorak, 1968). Water temperature is likely to modify behaviour during effort. In fact, the processes involved in thermal regulation are solicited to varying degrees and m a y interfere with the reactions to exercise. Thus, the circulatory function responds to a twofold requirement, both by muscular exercise to ensure the transport of 02 to working muscles, and by thermal regulation to convey the calories. Mechanical performances m a y also depend on water temperature. According to some authors, maximal oxygen consumption is limited by the cardiovascular transport of this gas (Mitchell et al., 1958; Stenberg et al., 1967; Ouellet et al., 1969). But the blood flow required by thermal regulation might become competitive and reduce the irrigation of the working muscles. According to some other authors, muscular performances are limited by the chemical production of energy within muscular cells (Doll et al., 1968; Kaijser, 1970). By varying the temperature of contracting muscles, the speed of biochemical reactions m a y be modified, thereby inducing a simultaneous change in the maximal muscular aerobic metabolism. The purpose of this investigation is to study the influence of water temperature on responses to muscular work during immersion: during sub-maximal effort by examining circulatory, respiratory and thermal changes; during maximal effort, by analysing the evolution of maximal 02 consumption.
Methods Five medical students volunteered for this study. Their height was 174.6 cm (+ 2.1 cm), and their weight 68.2 kg (+ 3.2 kg). The muscular exercise consisted in pedalling on a bicycle ergometer (Monark). The ergometer and subject, except for his head, were immersed in water, the temperature of which was modified from 20--40~ C. Two sub-maximal efforts corresponding approximately to 1/3 and 2/3of the individual maximal work capacity were performed, on different days, during 15 min. Maximal exercise is the work that exhausts the subject within 2 or 3 min. It was preceded by a 15 min sub-maximal effort, intended to afford a better distinction between experimental conditions and body temperatures. Individual intensities were determined according to the results of earlier tests. Oxygen consumption was measured according to the Douglas bag method. The volume of expired air was measured with Tissot's gasometer and the analysis of oxygen was done by the paramagnetic method (Servomex). The heart rate was measured from the recording of a thoracic derivation of the ECG, according to the method of Deroanne et al. (1974). Continuous measurement of the rectal temperature was effected by a thermocouple probe (Ellab) connected to an electromanometer (Electrolaboratoriet). The muscular temperature was measured at the end of each sub-maximal and maximal performance by a thermoeouple, implanted 4-5 cm deep into the lateral part of the quadriceps, as recommended by Saltin (1968).
Muscular Work in Water
131
Results Sub-Maximal Exercises Figure 1 shows the average (+ S.D.) results obtained during the two submaximal exercises. 02 consumption showed no clear or significant difference related to water temperature, which is consistent with the findings of Costill (1967) and of Craig and Froehlich (1968). But body temperatures are clearly influenced by environment; when the bath temperature was maintained between 25 and 30 ~ C, muscular and rectal temperatures corresponded to the values observed in the air during an exercise of same intensity (Saltin and Hermansen, 1966). In warmer baths, metabolic heat expenditure was no longer possible, and body hyperthermia set in. For a work corresponding to 50% of the individual maximum, rectal temperature then reached 38.8 ~ C. Inversely, 20 ~ C cold water accelerates heat exchanges between body and bath. Rectal temperature was always lower in these conditions and reached 37.4 ~ C for the same work intensity. It should be noted that the thermal balance remained positive and that the core temperature was higher than in a resting condition. The temperature inside working muscles depends mainly on the intensity of the contractions, but also appears to be influenced by environment. It is always higher than the rectal temperature. The difference was about 0.5 ~ C, increasing with cold
Q
Q
9O2
2.5
2"0 tl.5 [srp~ 1.0 { { 150Heart Rate 140- b/rain T 130120110!001 9 Muscle 40] "C o Recta[ Temp.
T T
!~
38
371 '~ 'o 36J Water
2%
2'5
20
Temp (oC)
2s
Fig. 1. Parameters measured during two submaximal exercises in water at different temperatures
132
F. Pirnay et al.
and decreasing in warm water. Any modification of bath temperature and of core temperature caused reactions in relation with thermal regulation, expecially in a hot environment. Ventilation increased slightly, since it changed from 24.7-27.21 or from 40.6-50.21/min during the two intensities of the studied work. Circulatory changes were far more marked. The heart rate strongly increased in warm water. During the lightest exercise, it varied between 102 and 132.4 beats/rain when the temperature of the water was increased from 2 0 - 4 0 ~ C; it rose from 131.1-150.8 beats/min in the same conditions when the intensity of exercise corresponds to 50% of the maximum.
Maximal Exercises Figure 2 shows results (means and the standard deviations) of the parameters measured during maximal exercise; muscular temperature then averaged 39.9 ~ C in lukewarm water. It was definitely lower in 20 ~ C water as it only reached 38 ~ C; it was strongly increased in 40 ~ C water, where it reached 40.2 ~ C. The modification due to environment thus gave a maximal difference of 2.2 ~ C. The difference between muscular and rectal temperature was greater during maximal work. It was close to 1~ C and was due to the short duration of the performance. Metabolic heat had no time to spread uniformly in the whole body.
4.0 s 3't3.5 7 [STPD(min 3.2 HeartRate
170 ~
9 Muscle 40] o Rectal Temp. 391oc
{
{
I
37 36
Water Temp.(~ 2'0
2's
is
Fig. 2. Parameters measured during maximal exercise in water at different temperatures
Muscular Work in Water
133
The maximal 02 consumption varied with the bath temperature. In cold water (20 ~ C) the aerobic capacity was low for all subjects. Muscular temperature was then comparatively low too. When the bath temperature rose, maximal O5 consumption initially showed a significant increase. Then, between 25 and 35 ~ C, the rise was very moderate and the variation of individual results means that the observed changes were hardly significant. In very warm water (40 ~ C), maximal 02 consumption no longer increased. On the contrary, it decreased for all subjects despite a higher muscular temperature. This decrease was accompanied by a strong rise of rectal temperature, which then reached 39 ~ C, and a strong acceleration of the heart rate (201.4 beats/rain).
Discussion
The mechanisms of thermal regulation are disturbed when the body is immersed in water. Heat exchanges with the fluid are significantly accelerated because of the higher thermal conductivity of water, which is 25 times higher than that of air. Due to its great caloric capacity, water also enhances exchanges because it can thus rapidly take up or release great quantities of heat. Body temperatures are therefore far more influenced by environment than they are in the air. Muscular temperature, however, mainly depends on the intensity of the contractions. It rises right from the beginning of work (as demonstrated by Buchtal et ai., 1944), and remains level after 10-15 min of exercise (Saitin et al., 1968). Core temperature always rises during muscular work, even in cold water. Pugh et al. (1960) observed that the thermal balance remains possible, even in much colder water during swimming sports, such as cross-Channel competitions. To ensure the expenditure of the great amount of calories produced by metabolism during muscular work, the water temperature has to be lowered, especially as work intensity increases. The indifferent temperature of a bath, set at 36 ~ C when the subject is at rest, thus drops to 31 ~ C when the metabolism is trebled (Craig and Dvorak, 1968). For the same reason, the temperature of competition swimming pools never exceeds 2 5 - 2 6 ~ C (Costill, 1967). In fact, if the defense mechanisms against cold remain effectual in water, the thermal balance becomes impossible in warm water. In point of fact, these conditions suppress the most effective means of dissipating heat in warm and dry air, i.e. evaporation of sweat. Therefore, in warm water, the calories produced by muscular work accumulate in the organism and cause the body temperatures to rise. The contact of warm water with the skin, as well as central hyperthermia, contribute to the stimulation of the thermosensitive nerve centres of the anterior hypothalamus. In this way, thermolysis reactions set in, but they are ineffectual however, and are even harmful in warm water. Tachycardia is one of these reactions. The additional increase in heart rate exceeds 20 beats/min in 40 ~ C warm water, which shows the importance of stimulation due to thermal regulation. Exertion in warm water is uncomfortable, due to tachycardia, facial sweating, headache and muscular asthenia. The performance is also reduced in warm water, as shown by the decrease of maximal 02 consumption. Circulatory and cardiac limitations can be observed. Too high a blood flow is required by the transport of calories. Since heart rates have
134
F. Pirnay et al.
reached their maximal value, the circulatory demands of thermolysys lessen the blood and oxygen flow in working muscules. Such a decrease in maximal 02 consumption in a hot environment was observed in air, namely by Rowell et al. (1965), Craig and Froehlich (1968), Klausen et al. (1967), Pirnay et al. (1970). Whereas Costill (1967) did not observe any influence of water temperature on the aerobic capacity in maximal exercise during immersion. However, the experimental conditions of this author differ from ours in that the exercise consisted in in situ swimming against resistance, and its duration limited to 3 rain. Induced no concomitant variation of rectal temperature. The importance of body hyperthermia, however, has been well demonstrated by Craig and Froehlich (1968), and by Pirnay et al. (1970). It explains the discrepancy between the observations quoted and the investigation. On the other hand, we have also tried to find out how far muscular temperature influences maximal aerobic metabolism. But one must not forget that such variations in temperature are obtained simultaneously with other general physiological modifications, especially heart rate and rectal temperature. The results are difficult to interpret, owing to the simultaneous occurrence of such phenomena and to the slight variations in muscular temperature. However, comparing the evolution of muscular temperature with the simultaneous evolution of 02 consumption (Fig. 3), suggests a relation between the two phenomena in cold and medium temperatures. Maximal 02 consumption follows an increasing line which is parallel to that of muscular temperature. This increase in metabolism is approximately 10% for a rise in temperature of 1~ C. In cold water, maximal 02 consumption does not reach its highest point. The muscular temperature measured at that time is comparatively low. It can be accepted that the speed of oxidative biochemical reactions is then reduced and that the working of the muscles is limited. Kaijser (1970) measured, in similar cooling conditions, a higher saturation of venous blood compared with that observed in normal
4.0"
3.5
1 3~, '
MUSCLE
TEMPERATURE ( ~ 39 '
4'0
Fig. 3. Evolution of maximal 02 consumption in relation to temperature of the quadriceps during maximal performances on a bicycle ergometer, during water immersion at different temperatures
Muscular Work in Water
135
conditions. Besides M c A r d l e et al. (19 76) observed that the cardiac output remained unchanged in cold water. The diminution of heart rate is then c o m p e n s a t e d b y an increment o f the stroke volume. These results are an argument against an eventual circulatory deficit in cold water, and support an argument for a biochemical limitation of O2 consumption during the muscular contractions in our experiences. However, in other conditions, the immersion in cold water can increase muscular performance and accelerate the recovery ( N u k a d a and Miiller, 1955). These authors observed indeed a lengthening o f the leg-work when these are immersed in water at 10 ~ C. However the m a x i m u m 02 uptake was not measured. F o r high temperatures, the evolution of the maximal Oz consumption is no longer parallel with the muscle temperature. On the contrary, maximal 0 2 consumption drops, despite a rise in muscular temperature. This decrease m a y be explained by a circulatory limitation which occurs gradually, owing to the competitive dem a n d s o f thermolysis. The very high heart rates measured at this time, evidence an extremely strong cardiocirculatory demand. The aerobic power therefore appears to reach its maximal value when a high temperature in the muscles allows a high supply of chemical energy, although the d e m a n d s related to thermolysis have not yet started to exert their circulatory competitive and limitative effects.
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Accepted February 14, 1977
