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Is sweat rate during steady state exercise related to maximum oxygen uptake?
ARTICLE IN PRESS
Journal of Thermal Biology 31 (2006) 521–525 www.elsevier.com/locate/jtherbio
Is sweat rate during steady state exercise related to maximum oxygen uptake? F.T. Amorim, A.C. Vimieiro-Gomes, C.A. Machado-Moreira, F.C. Magalha˜es, M.S. Rosa, L.S. Prado, L.O.C. Rodrigues Laborato´rio de Fisiologia do Exercı´cio, Escola de Educac- a˜o Fı´sica, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais, Av. Presidente Carlos Luz, 4664 Campus Pampulha, 31.310-250 Belo Horizonte, Minas Gerais, Brazil Received 14 March 2006; accepted 23 May 2006
Abstract The purpose of this study was to investigate whether whole-body sweat rate induced by exercise (SRex) at the same oxygen uptake _ 2peak Þ). A secondary purpose was to examine the could be correlated with individual maximum oxygen uptake (peak oxygen uptake ðVO _ 2peak relationship between SRex and local sweat rate induced by pilocarpine on the forearm at rest (SRpilo). Nine healthy young males (VO 1 1 1 1 55.2 (12.3) mL min kg , mean (SD); 43.3–76.1 mL min kg , range), acclimatized to a tropical climate had their sweating stimulated in two situations: (1) exercise-induced whole-body sweat by 120 min of cycling exercise at a constant submaximal oxygen uptake of 1.65 L min1 or (2) pilocarpine-induced sweat on the right forearm with 0.5% pilocarpine hydrochloride (1.5 mA, 5 min) at rest. The SRex _ 2peak (r ¼ 0:53, p ¼ 0:14). In addition, there was not correlation between SRex (0.38 (0.03) mg cm2 min1) was not correlated with VO and SRpilo (0.36 (0.20) mg cm2 min1) (r ¼ 0:23, p ¼ 0:57). These results suggest that whole-body sweat rate during exercise at the same _ 2peak . Furthermore, the eccrine sweat gland does not respond similarly for oxygen uptake in a temperate environment is not related to VO local pilocarpine or exercise stimuli. r 2006 Elsevier Ltd. All rights reserved. Keywords: Sweat rate; Maximum oxygen uptake; Exercise; Pilocarpine; Thermoregulation
1. Introduction The evaporation of sweat secreted by eccrine sweat glands during exercise is an important way to dissipate heat and to control body temperature. The ability to produce sweat is affected by heat acclimation (Robison et al., 1943; Nadel et al., 1974; Patterson et al., 2004), hydration status (Candas et al., 1988), age (Anderson and Kenney, 1987), gender (Buono and Sjoholm, 1988), and physical training (Nadel et al., 1974; Sato and Sato, 1983; Buono and Sjoholm, 1988; Buono et al., 1991). Heat acclimation and physical training probably promote local adaptations on eccrine sweat glands, such as increased size, capacity and cholinergic sensitivity (Sato and Sato, 1983; Sato et al., 1990). Corresponding author. Tel./fax: +55 31 3499 2325.
E-mail address: [email protected] (L.O.C. Rodrigues). 0306-4565/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jtherbio.2006.05.006
Previous researches demonstrated that local adaptations of eccrine sweat gland could be observed using in vivo or in vitro stimulation through pharmacological induction (pilocarpine or methacholine) (Sato and Sato, 1983; Buono and Sjoholm, 1988; Sato et al., 1990; Buono et al., 1991; Kondo et al., 1999). Buono and Sjoholm (1988) reported that trained men and women had greater local sweat rates after pilocarpine stimulation compared to sedentary men and women at rest. Sato and Sato (1983) also showed that eccrine sweat glands of individuals assumed as poor sweaters exhibited smaller size, lower activity and decreased cholinergic sensitivity than the glands of physically fit individuals. Buono et al. (1991) observed a significant correlation between whole-body sweat rate induced by steady state _ 2 max Þ in exercise (SRex) and maximum oxygen uptake ðVO trained and untrained subjects. They also verified a significant correlation between SRex and sweat rate induced on the forearm by pilocarpine at rest (SRpilo). The authors
ARTICLE IN PRESS F.T. Amorim et al. / Journal of Thermal Biology 31 (2006) 521–525
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suggested that endurance training probably resulted in increases in the sweating capacity of the sweat gland itself, and that SRpilo could serve as an index of whole-body sweat rate during non-resting thermoregulatory stress, such as steady state exercise. However, that study measured _ 2 max in two groups with different SRex using 70% of the VO _ VO2 max (trained and untrained), which resulted in different oxygen uptake and heat production. Therefore, the main purpose of the present study was to determine whether whole-body sweat rate produced by exercise at the same oxygen uptake correlate with _ 2peak Þ). maximum oxygen uptake (peak oxygen uptake ðVO A secondary purpose was to evaluate the relationship between whole-body sweat rate induced by exercise and local sweat rate induced by iontophoresis with pilocarpine at rest. Our hypotheses were that whole-body sweat rate _ 2peak , and during exercise should not be correlated with VO local sweat rate induced by pilocarpine should not be correlated with whole-body sweat rate during exercise.
_ 2peak was measured. On the second day, sweat was day, VO pharmacologically induced at rest and it was followed by 120 min of exercise. The trials were carried out in an airconditioned controlled room (Consul AirMaster 7500, Sa˜o Paulo, SP, Brazil), in a temperate environment (22 (1) 1C dry bulb, 17 (1) 1C wet bulb, 64 (6)% relative humidity and wind speed less than 0.1 m s1). Data collection occurred from May to July, in a tropical region of South Hemisphere. Subjects were advised to refrain from caffeine, alcoholic beverages and strenuous physical activity on the day before each trial, and to sleep at least 8 h during the night prior the trials. The subjects were instructed to drink 500 mL of water 2 h before they arrived in the laboratory. This procedure was designed to ensure an euhydrated status, which was verified by the measurement of urine specific gravity before trials (JSCP-Uridens, Sa˜o Paulo, SP, Brazil), and it was always lower than 1.030 (Armstrong et al., 1994). During the experiments, the volunteers wore shorts, socks and sport shoes.
2. Methods 2.3. Peak oxygen uptake measurement This study was approved by the Research and Ethics Committee of the Federal University of Minas Gerais (no. 023/2003). All procedures were performed according to the resolution 196 of the National Health Council (1996) on scientific research involving humans. Prior to participation, each subject was informed regarding the procedures, and written consent was obtained. 2.1. Subjects Nine healthy young males who were acclimatized to a tropical region in the southern hemisphere (19.51S and 431W) volunteered for this study. Their fitness levels varied as some subjects were sedentary and others were well trained. The physical characteristics of the volunteers (age, height, weight, the sum (SSK ) of biceps, triceps, subscapular, pectoral, midaxilla, suprailiac, abdominal, midthigh and medial calf skinfold thicknesses (Skinfold Caliper, Lange, Santa Cruz, CA, USA), and body surface area (AD) (Dubois and Dubois, 1916)) are shown in Table 1. 2.2. Experimental procedures The study was performed on two different days at the same time of the day, separated by at least 48 h. On the first
_ 2peak was measured during a maximal graded exercise VO test, using a calibrated mechanically braked cycle ergometer (Monark, 824E, Varberg, Sweden). Expired vo_ 2 Þ, carbon dioxide production lume, oxygen uptake ðVO and respiratory exchange ratio were measured every 30 s using open circuit spirometry, which was calibrated before each test (Medgraphics, VO-2000, Ann Arbor, Michigan, USA). 2.4. Pharmacological and exercise induction of sweat Sweat at rest was induced by pilocarpine through iontophoresis on the middle region of the flexor area of the right forearm, close to the antecubital fosse (non glabrous skin) (Buono and Sjoholm, 1988; Buono et al., 1991). Pilocarpine hydrochloride solution (5 mL, 0.5%, Galena Quı´ mica e Farmaceˆutica, Campinas, SP, Brazil) was applied through the skin using an electrical current of 1.5 mA (60 mA cm2) for 5 min, as described by Gibson and Cooke (1959) and Buono and Sjoholm, 1988; Buono et al. (1991). In sequence, a filter paper (16 cm2; 250 g m2, J. Prolab, S.J. dos Pinhais, Pr, Brazil) was attached at the stimulated area during 15 min. To avoid sweat evaporation, the filter paper was covered with a 64 cm2 plastic fixed
Table 1 Physical and physiological characteristics of subjects
Mean SD Range
Age (years)
Height (cm)
Weight (kg)
BSA (m2)
SSK (mm)
_ 2peak (mL min1 kg1) VO
22 3 19–29
176 6 164–183
67.3 7.9 56.4–80.0
1.82 0.09 1.72–1.97
67 23 39–115
55.2 12.3 43.3–76.1
_ 2peak : Peak oxygen uptake. Values are means SD. BSA: body surface area. SSK : skin folds. VO
ARTICLE IN PRESS F.T. Amorim et al. / Journal of Thermal Biology 31 (2006) 521–525
0.7
y = 0.459 - 0.0015x r = -0.53 p = 0.14
SRexe (mg.cm-2.min-1)
0.6 0.5 0.4 0.3 0.2 0.1 0.0 0
40
45
50
0.7
y = 0.007x - 0.032
0.6
r = 0.43
The present study did not observe a significant correla_ 2peak tion between SRex during steady state exercise and VO (Fig. 1), as hypothesized. Moreover, our data showed a narrow range of SRex although the volunteers exhibited a _ 2peak . These results suggest that the wide range VO improved ability to produce sweat induced by physical training on eccrine sweat glands is not necessarily
65
70
75
80
p = 0.25 0.5 0.4 0.3 0.2 0.1 0.0 0
40
45
50
55
VO2peak
60
65
70
75
80
(mL.kg-1.min-1)
_ 2peak and SRpilo. Fig. 2. Non-significant correlation between VO
0.7
y = 0.364x - 0.039 r = 0.23 p = 0.55
0.6 SRexe (mg.cm-2.min-1)
4. Discussion
60
_ 2peak and SRex. Fig. 1. Non-significant correlation between VO
3. Results All subjects completed 120 min of exercise at 112 (9) W, which required 1.64 (0.12) L O2 min1, as previously planned. There was not significant correlation between _ 2peak ðp ¼ 0:14Þ (Fig. 1). Figs. 2 and 3 show a SRex and VO _ 2peak , and non significant correlation between SRpilo and VO SRpilo and SRex (p ¼ 0:25 and 0.55, respectively). The mean value SRex (0.38 (0.03) mg cm2 min1) was not different from the mean value of SRpilo (0.36 (0.20) mg cm2 min1) ðp ¼ 0:85Þ (Fig. 4). However, SRex ranged from 0.33 to 0.42 mg cm2 min1 and SRpilo ranged from 0.11 to 0.66 mg cm2 min1.
55
VO2peak (mL.kg-1.min-1)
SRpilo (mg.cm-2.min-1)
to skin with impermeable adhesive tape. The sweat rate was calculated by weighting (Mettler Toledo AB 204 analytical scale, Columbus, OH, USA) the filter paper before and after sweat induction in an airtight plastic bag, and then divided by the time of sweat collection and the area of the filter paper (mg cm2 min1). After the procedures above, the subjects emptied their bladders, and they had their body weight measured (Filizola MF-100 scale, precision of 0.02 kg, Sa˜o Paulo, SP, Brazil). Then, each subject cycled for 120 min at a constant oxygen uptake of 1.65 L min1, which represented _ 2peak . This metabolic rate was 36 to 61% of subject’s VO selected to guarantee that the lesser fit subject could finish the entire exercise protocol. Water (18–21 1C) was ingested each 15 min at a volume to match sweat rate, as previously _ 2 was measured every calculated (Ribeiro et al., 2004). VO 30 s during the last 15 min of each 30 min interval using the method described above. Whole-body sweat rate (mg cm2 min1) was assumed as been equivalent to the difference between weight before and after exercise, corrected for the water ingested and urine volume, divided by the time (min) between weighting, and AD. No corrections were made for respiratory water output, substrate consumption and insensible perspiration, and all of these variables were assumed as minimal during the experimental protocol. Pearson’s correlation coefficients were calculated between whole-body sweat rate during exercise and peak oxygen uptake; the pilocarpine induced sweat rate at rest and whole-body sweat rate during exercise; the pilocarpine induced sweat rate at rest and peak oxygen uptake. Comparisons between means were made using paired t-Test. Significance was established at ao0:05.
523
0.5 0.4 0.3 0.2 0.1 0.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
SRpilo (mg.cm-2.min-1) Fig. 3. Non-significant correlations between SRpilo and SRex.
0.7
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0.7
SR (mg.cm-2.min-1)
0.6 0.5 0.4 0.3 0.2 0.1 0.0
SRexe
SRpilo
Fig. 4. Sweat rate during pilocarpine test and steady state exercise ðp ¼ 0:57Þ.
expressed during a prolonged exercise with constant oxygen uptake in a temperate environment. Traditionally sweat rate during exercise has been _ 2 max using compared among individuals with different VO exercise at the same relative maximum oxygen uptake, which provides disproportional heat production but similar increase on core temperature (Saltin and Hermassen, 1966; Greenleaf et al., 1972; Anderson and Kenney, 1987; Buono and Sjoholm, 1988). Following this approach, Buono et al. (1991) observed a significant correlation between SRex and _ 2 max during 30 min of exercise, at 70% of VO _ 2 max , in VO trained and untrained subjects. However, the significant correlation found on that study could be due to markedly differences in metabolic heat production during exercise between groups, although final core temperature was not _ 2 max different. Hence, the workload was proportional to VO and the sweat rate was proportional to the workloads, as previously demonstrated by Saltin and Hermassen (1966). In the present study, exercise work rate was adjusted _ 2 between subjects during the trial to match similar VO 1 (1.64 (0.12) L O2 min ). This procedure induced both similar heat production and SRex in a group with _ 2peak . considerably different VO Previous investigations have also showed a constant sweat rate when external work rate was similar between trained and non-trained subjects (Shvartz et al., 1977; Araki et al., 1981; Yamauchi et al., 1997). In addition, Shapiro et al. (1982) demonstrated that sweat rate could be predicted (within 720%) with exercise work rate, environmental conditions, and clothes without any physiological measurements. On the other hand, Greenhaff (1989) reported that sweat rate during 1 h of cycling at constant _ 2 max . work rate (140 W) correlated to the subjects’ VO However, that study expressed total sweat rate without correcting for body surface area, which could explain the discrepancy between Greenhaff’s (1989) results and the results of the present study. In the present study, SRex was corrected for body surface area and it was not related _ 2peak . to VO
The current study also showed that SRex and SRpilo were not correlated (Fig. 3). This result shows that the eccrine sweat glands are activated by different ways during pilocarpine or exercise stimuli and it is in agreement with literature (Johnson and Spaulding, 1974). During the pharmacological stimulation at rest, pilocarpine was directly applied to the skin surface through an electrical current, which resulted in a local stimulation of cholinergic muscarinic receptors to produce sweat; however, when eccrine sweat glands were stimulated by exercise, they were activated via central autonomic nervous system stimulating the postganglionic cholinergic nerve fibers. Furthermore, during exercise sweating was modulated by central and peripheral thermoreceptors, metaboreceptors and mechanoreceptors (Gisolfi and Robinson, 1970; Nadel et al., 1971a, b; Kondo et al., 1999) and also modified by circulating hormones, such as noradrenaline, adrenaline, vasoactives peptides and plasma osmolality (Ohara et al., 1984; Yamazaki et al., 1994; Eiken and Mekjavic, 2004). Besides, the local skin conditions (temperature, humidity) were also modulators of sweat production. We speculate that the different modulators could explain the absence of correlation between sweat rates induced by pilocarpine at rest and during exercise at constant oxygen uptake. In our previous study, we observed a correlation between SRpilo and whole-body sweat rate induced by graded exercise until exhaustion (Vimieiro-Gomes et al., 2005). It is interesting to note that during both types of exercise (graded and constant work rate) the eccrine sweat glands were stimulated by central nervous system. It is probable that thermal factors had a more important role on sweat production during prolonged submaximal exercise than during graded exercise until exhaustion (Yamazaki et al., 1994), differentiating the results of the studies. It was also observed that the SRpilo did not correlate _ 2peak (Fig. 2). This result is not in significantly with VO agreement with previous studies, which demonstrated that sweating response induced pharmacologically could be associated to physical training or fitness (Buono and Sjoholm, 1988; Buono et al., 1991; Sato and Sato, 1983). We speculate that our results could have been affected by the sample size and by possible individual’s variation in pilocarpine sensitivity and heat acclimatization status. Our volunteers were born and resided in a tropical region that probably induced increases in eccrine sweat rate as demonstrated by Wyndham et al. (1964) and Wyndham (1967). The studies that found a significant correlation _ 2 max had volunteers from temperate between SRpilo and VO and cold climates. Our study was carried out during the tropical coolest months of the year but it probably had not changed the volunteer’s heat acclimatization status, because environmental temperature variation among tropical seasons is minimal compared to that in cold climates regions. Furthermore, individuals living in temperate climates and enrolled in physical training are exposed to cross heat acclimatization (Nadel et al., 1974), and consequently the sweat rate induced by pilocarpine can
ARTICLE IN PRESS F.T. Amorim et al. / Journal of Thermal Biology 31 (2006) 521–525
_ 2 max (Buono and Sjoholm, 1988; be proportional to VO Buono et al., 1991). It is possible that in our volunteers, who were heat acclimatized to the tropics, increased SRpilo _ 2 max ) due to physical training (or improvement in the VO was not so evident. In conclusion, whole-body sweat rate during steady state exercise in a temperate environment exercise was not _ 2peak , suggesting that sweating was more correlated to VO _ 2peak in closely related to exercise oxygen uptake than VO individuals heat acclimatized to the tropics. Acknowledgements The authors gratefully acknowledge Professor Suzanne Schneider and Paulette Yamada (University of New Mexico, USA) and Professor Nigel Anthony Southworth Taylor (University of Wollongong, Australia) for their useful suggestions about the paper and also the colleagues Samuel Penna Wanner, Juliana Bohnen Guimara˜es from the Laborato´rio de Fisiologia do Exercı´ cio (Universidade Federal de Minas Gerais). The study was supported by CAPES and CNPq. References Anderson, R.K., Kenney, W.L., 1987. Effect of age on heat-activated sweat gland density and flow during exercise in dry heat. J. Appl. Physiol. 63, 1089–1094. Araki, T., Matsushita, K., Umeno, K., Tsujino, A., Toda, Y., 1981. Effect of physical training on exercise-induced sweating in women. J. Appl. Physiol. 51, 1526–1532. Armstrong, L.E., Maresh, C.M., Castellani, J.W., Bergeron, M.F., Kenefick, R.W., LaGasse, K.E., Riebe, D., 1994. Urinary indices of hydration status. Int. J. Sports Nutr. 4, 265–279. Buono, M.J., Sjoholm, N.T., 1988. Effect of physical training on peripheral sweat production. J. Appl. Physiol. 65, 811–814. Buono, M.J., White, C., Connolly, KP., 1991. Pilocarpine-induced sweat rate at rest versus whole body sweat rate during exercise. J. Appl. Sport Sci. Res. 5, 82–86. Candas, V., Libert, J.P., Brandenberger, G., Sagot, J.C., Kahn, J.M., 1988. Thermal and circulatory responses during prolonged exercise at different levels of hydration. J. Physiol. (Paris) 83 (1), 11–18. Dubois, D., Dubois, E.F., 1916. A formula to estimate the approximate surface area if height and weight be known. Arch. Inter Med. 17, 831–836. Eiken, O., Mekjavic, I.B., 2004. Ischaemia in working muscles potentiates the exercise-induced sweating response in man. Acta Physiol. Scand 181, 305–311. Gibson, L.E., Cooke, R.E., 1959. A test for concentration of electrolytes in sweat in cystic fibrosis of the pancreas utilizing pilocarpine by iontophoresis. Pediatrics 23, 545–549. Gisolfi, C., Robinson, S., 1970. Central and peripheral stimuli regulating sweating during intermittent work in men. J. Appl. Physiol. 29, 761–768. Greenhaff, P.L., 1989. Cardiovascular fitness and thermoregulation during prolonged exercise in man. Braz. J. Sport Med. 23, 109–114.
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Greenleaf, J.E., Castle, B.L., Ruff, W.K., 1972. Maximal oxygen uptake, sweating and tolerance to exercise in the heat. Int. J. Biometeor. 16, 375–387. Johnson, R.H., Spaulding, J.M., 1974. Disorders of the autonomic nervous system. Chapter 10. Sweating. Contemp. Neurol Ser. 11, 179–198. Kondo, N., Tominaga, M., Shibasaki, M., Aoki, K., Koga, S., Nishiyasu, T., 1999. Modulation of the thermoregulatory sweating response to mild hyperthermia during activation of the muscle metaboreflex in humans. J. Physiol. 515, 591–598. Nadel, E.R., Bullard, R.W., Stolwijk, J.A.J., 1971a. Importance of skin temperature in the regulation of sweating. J. Appl. Physiol. 31, 80–87. Nadel, E.R., Mitchell, J.W., Saltin, B., Stolwijk, J.A.J., 1971b. Peripheral modifications to the central drive for sweating. J. Appl. Physiol. 31, 828–833. Nadel, E.R., Pandolf, K.B., Roberts, M.F., Stolwijk, J.A.J., 1974. Mechanisms of thermal acclimation to exercise and heat. J. Appl. Physiol. 37, 515–520. Ohara, K., Morita, Y., Okuda, N., 1984. Significance of adrenergic transmission in thermal sweating in man. J. Therm. Biol. 9, 127–132. Patterson, M.J., Stocks, J.M., Taylor, N.A., 2004. Humid heat acclimation does not elicit a preferential sweat redistribution toward the limbs. Am. J. Physiol. Regul. Integr. Comp. Physiol. 286, R512–R518. Ribeiro, G.A., Rodrigues, L.O., Moreira, M.C., Silami-Garcia, E., Pascoa, M.R., Camargos, F.F., 2004. Thermoregulation in hypertensive men exercising in the heat with water ingestion. Braz. J. Med. Biol. Res. 37, 409–417. Robinson, S., Turrell, E.S., Belding, H.S., Horvath, S.M., 1943. Rapid acclimatization to work in hot climates. Am. J. Physiol. 140, 168–176. Saltin, B., Hermassen, L., 1966. Esophageal, rectal, and muscle temperature during exercise. J. Appl. Physiol. 21, 1757–1762. Sato, K., Sato, F., 1983. Individual variations in structure and function of human eccrine sweat gland. Am. J. Physiol. 245, R203–R208. Sato, F., Owen, M., Matthes, R., Sato, K., Gisolfi, C.V., 1990. Functional and morphological changes in the eccrine sweat gland with heat acclimation. J. Appl. Physiol. 69, 232–236. Shapiro, Y., Pandolf, K.B., Goldman, R.F., 1982. Predicting sweat loss response to exercise, environment and clothing. Eur. J. Appl. Physiol. 48, 83–96. Shvartz, E., Shapiro, Y., Magazanik, A., Meroz, A., Birnfield, H., Metchtinger, A., Shibolet, S., 1977. Heat acclimation, physical fitness, and responses to exercise in temperate and hot environments. J. Appl. Physiol. 43, 678–683. Vimieiro-Gomes, A.C., Magalhaes, F.C., Amorim, F.T., MachadoMoreira, C.A., Rosa, M.S., Lima, N.R., Rodrigues, L.O., 2005. Comparison of sweat rate during graded exercise and the local rate induced by pilocarpine. Braz. J. Med. Biol. Res. 38, 1133–1139. Wyndham, C.H., Strydom, N.B., Munro, A., MacPherson, R.K., Metz, B., Schaff, G., Schieber, J., 1964. Heat reaction of Caucasians in temperate, in hot, dry, and in hot, humid climates. J. Appl. Physiol. 19, 607–612. Wyndham, C.H., 1967. Effects of acclimatization on the sweat rate-rectal temperature relationship. J. Appl. Physiol. 22, 27–30. Yamauchi, M., Matsumoto, T., Ohwatari, N., Kosaka, M., 1997. Sweating economy by graded control in well-trained athletes. Pflugers Arch. Eur. J. Physiol. 433, 675–678. Yamazaki, F., Sone, R., Ikegami, H., 1994. Responses of sweating and body temperature to sinusoidal exercise. J. Appl. Physiol. 76, 2541–2545.
Journal of Thermal Biology 31 (2006) 521–525 www.elsevier.com/locate/jtherbio
Is sweat rate during steady state exercise related to maximum oxygen uptake? F.T. Amorim, A.C. Vimieiro-Gomes, C.A. Machado-Moreira, F.C. Magalha˜es, M.S. Rosa, L.S. Prado, L.O.C. Rodrigues Laborato´rio de Fisiologia do Exercı´cio, Escola de Educac- a˜o Fı´sica, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais, Av. Presidente Carlos Luz, 4664 Campus Pampulha, 31.310-250 Belo Horizonte, Minas Gerais, Brazil Received 14 March 2006; accepted 23 May 2006
Abstract The purpose of this study was to investigate whether whole-body sweat rate induced by exercise (SRex) at the same oxygen uptake _ 2peak Þ). A secondary purpose was to examine the could be correlated with individual maximum oxygen uptake (peak oxygen uptake ðVO _ 2peak relationship between SRex and local sweat rate induced by pilocarpine on the forearm at rest (SRpilo). Nine healthy young males (VO 1 1 1 1 55.2 (12.3) mL min kg , mean (SD); 43.3–76.1 mL min kg , range), acclimatized to a tropical climate had their sweating stimulated in two situations: (1) exercise-induced whole-body sweat by 120 min of cycling exercise at a constant submaximal oxygen uptake of 1.65 L min1 or (2) pilocarpine-induced sweat on the right forearm with 0.5% pilocarpine hydrochloride (1.5 mA, 5 min) at rest. The SRex _ 2peak (r ¼ 0:53, p ¼ 0:14). In addition, there was not correlation between SRex (0.38 (0.03) mg cm2 min1) was not correlated with VO and SRpilo (0.36 (0.20) mg cm2 min1) (r ¼ 0:23, p ¼ 0:57). These results suggest that whole-body sweat rate during exercise at the same _ 2peak . Furthermore, the eccrine sweat gland does not respond similarly for oxygen uptake in a temperate environment is not related to VO local pilocarpine or exercise stimuli. r 2006 Elsevier Ltd. All rights reserved. Keywords: Sweat rate; Maximum oxygen uptake; Exercise; Pilocarpine; Thermoregulation
1. Introduction The evaporation of sweat secreted by eccrine sweat glands during exercise is an important way to dissipate heat and to control body temperature. The ability to produce sweat is affected by heat acclimation (Robison et al., 1943; Nadel et al., 1974; Patterson et al., 2004), hydration status (Candas et al., 1988), age (Anderson and Kenney, 1987), gender (Buono and Sjoholm, 1988), and physical training (Nadel et al., 1974; Sato and Sato, 1983; Buono and Sjoholm, 1988; Buono et al., 1991). Heat acclimation and physical training probably promote local adaptations on eccrine sweat glands, such as increased size, capacity and cholinergic sensitivity (Sato and Sato, 1983; Sato et al., 1990). Corresponding author. Tel./fax: +55 31 3499 2325.
E-mail address: [email protected] (L.O.C. Rodrigues). 0306-4565/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jtherbio.2006.05.006
Previous researches demonstrated that local adaptations of eccrine sweat gland could be observed using in vivo or in vitro stimulation through pharmacological induction (pilocarpine or methacholine) (Sato and Sato, 1983; Buono and Sjoholm, 1988; Sato et al., 1990; Buono et al., 1991; Kondo et al., 1999). Buono and Sjoholm (1988) reported that trained men and women had greater local sweat rates after pilocarpine stimulation compared to sedentary men and women at rest. Sato and Sato (1983) also showed that eccrine sweat glands of individuals assumed as poor sweaters exhibited smaller size, lower activity and decreased cholinergic sensitivity than the glands of physically fit individuals. Buono et al. (1991) observed a significant correlation between whole-body sweat rate induced by steady state _ 2 max Þ in exercise (SRex) and maximum oxygen uptake ðVO trained and untrained subjects. They also verified a significant correlation between SRex and sweat rate induced on the forearm by pilocarpine at rest (SRpilo). The authors
ARTICLE IN PRESS F.T. Amorim et al. / Journal of Thermal Biology 31 (2006) 521–525
522
suggested that endurance training probably resulted in increases in the sweating capacity of the sweat gland itself, and that SRpilo could serve as an index of whole-body sweat rate during non-resting thermoregulatory stress, such as steady state exercise. However, that study measured _ 2 max in two groups with different SRex using 70% of the VO _ VO2 max (trained and untrained), which resulted in different oxygen uptake and heat production. Therefore, the main purpose of the present study was to determine whether whole-body sweat rate produced by exercise at the same oxygen uptake correlate with _ 2peak Þ). maximum oxygen uptake (peak oxygen uptake ðVO A secondary purpose was to evaluate the relationship between whole-body sweat rate induced by exercise and local sweat rate induced by iontophoresis with pilocarpine at rest. Our hypotheses were that whole-body sweat rate _ 2peak , and during exercise should not be correlated with VO local sweat rate induced by pilocarpine should not be correlated with whole-body sweat rate during exercise.
_ 2peak was measured. On the second day, sweat was day, VO pharmacologically induced at rest and it was followed by 120 min of exercise. The trials were carried out in an airconditioned controlled room (Consul AirMaster 7500, Sa˜o Paulo, SP, Brazil), in a temperate environment (22 (1) 1C dry bulb, 17 (1) 1C wet bulb, 64 (6)% relative humidity and wind speed less than 0.1 m s1). Data collection occurred from May to July, in a tropical region of South Hemisphere. Subjects were advised to refrain from caffeine, alcoholic beverages and strenuous physical activity on the day before each trial, and to sleep at least 8 h during the night prior the trials. The subjects were instructed to drink 500 mL of water 2 h before they arrived in the laboratory. This procedure was designed to ensure an euhydrated status, which was verified by the measurement of urine specific gravity before trials (JSCP-Uridens, Sa˜o Paulo, SP, Brazil), and it was always lower than 1.030 (Armstrong et al., 1994). During the experiments, the volunteers wore shorts, socks and sport shoes.
2. Methods 2.3. Peak oxygen uptake measurement This study was approved by the Research and Ethics Committee of the Federal University of Minas Gerais (no. 023/2003). All procedures were performed according to the resolution 196 of the National Health Council (1996) on scientific research involving humans. Prior to participation, each subject was informed regarding the procedures, and written consent was obtained. 2.1. Subjects Nine healthy young males who were acclimatized to a tropical region in the southern hemisphere (19.51S and 431W) volunteered for this study. Their fitness levels varied as some subjects were sedentary and others were well trained. The physical characteristics of the volunteers (age, height, weight, the sum (SSK ) of biceps, triceps, subscapular, pectoral, midaxilla, suprailiac, abdominal, midthigh and medial calf skinfold thicknesses (Skinfold Caliper, Lange, Santa Cruz, CA, USA), and body surface area (AD) (Dubois and Dubois, 1916)) are shown in Table 1. 2.2. Experimental procedures The study was performed on two different days at the same time of the day, separated by at least 48 h. On the first
_ 2peak was measured during a maximal graded exercise VO test, using a calibrated mechanically braked cycle ergometer (Monark, 824E, Varberg, Sweden). Expired vo_ 2 Þ, carbon dioxide production lume, oxygen uptake ðVO and respiratory exchange ratio were measured every 30 s using open circuit spirometry, which was calibrated before each test (Medgraphics, VO-2000, Ann Arbor, Michigan, USA). 2.4. Pharmacological and exercise induction of sweat Sweat at rest was induced by pilocarpine through iontophoresis on the middle region of the flexor area of the right forearm, close to the antecubital fosse (non glabrous skin) (Buono and Sjoholm, 1988; Buono et al., 1991). Pilocarpine hydrochloride solution (5 mL, 0.5%, Galena Quı´ mica e Farmaceˆutica, Campinas, SP, Brazil) was applied through the skin using an electrical current of 1.5 mA (60 mA cm2) for 5 min, as described by Gibson and Cooke (1959) and Buono and Sjoholm, 1988; Buono et al. (1991). In sequence, a filter paper (16 cm2; 250 g m2, J. Prolab, S.J. dos Pinhais, Pr, Brazil) was attached at the stimulated area during 15 min. To avoid sweat evaporation, the filter paper was covered with a 64 cm2 plastic fixed
Table 1 Physical and physiological characteristics of subjects
Mean SD Range
Age (years)
Height (cm)
Weight (kg)
BSA (m2)
SSK (mm)
_ 2peak (mL min1 kg1) VO
22 3 19–29
176 6 164–183
67.3 7.9 56.4–80.0
1.82 0.09 1.72–1.97
67 23 39–115
55.2 12.3 43.3–76.1
_ 2peak : Peak oxygen uptake. Values are means SD. BSA: body surface area. SSK : skin folds. VO
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0.7
y = 0.459 - 0.0015x r = -0.53 p = 0.14
SRexe (mg.cm-2.min-1)
0.6 0.5 0.4 0.3 0.2 0.1 0.0 0
40
45
50
0.7
y = 0.007x - 0.032
0.6
r = 0.43
The present study did not observe a significant correla_ 2peak tion between SRex during steady state exercise and VO (Fig. 1), as hypothesized. Moreover, our data showed a narrow range of SRex although the volunteers exhibited a _ 2peak . These results suggest that the wide range VO improved ability to produce sweat induced by physical training on eccrine sweat glands is not necessarily
65
70
75
80
p = 0.25 0.5 0.4 0.3 0.2 0.1 0.0 0
40
45
50
55
VO2peak
60
65
70
75
80
(mL.kg-1.min-1)
_ 2peak and SRpilo. Fig. 2. Non-significant correlation between VO
0.7
y = 0.364x - 0.039 r = 0.23 p = 0.55
0.6 SRexe (mg.cm-2.min-1)
4. Discussion
60
_ 2peak and SRex. Fig. 1. Non-significant correlation between VO
3. Results All subjects completed 120 min of exercise at 112 (9) W, which required 1.64 (0.12) L O2 min1, as previously planned. There was not significant correlation between _ 2peak ðp ¼ 0:14Þ (Fig. 1). Figs. 2 and 3 show a SRex and VO _ 2peak , and non significant correlation between SRpilo and VO SRpilo and SRex (p ¼ 0:25 and 0.55, respectively). The mean value SRex (0.38 (0.03) mg cm2 min1) was not different from the mean value of SRpilo (0.36 (0.20) mg cm2 min1) ðp ¼ 0:85Þ (Fig. 4). However, SRex ranged from 0.33 to 0.42 mg cm2 min1 and SRpilo ranged from 0.11 to 0.66 mg cm2 min1.
55
VO2peak (mL.kg-1.min-1)
SRpilo (mg.cm-2.min-1)
to skin with impermeable adhesive tape. The sweat rate was calculated by weighting (Mettler Toledo AB 204 analytical scale, Columbus, OH, USA) the filter paper before and after sweat induction in an airtight plastic bag, and then divided by the time of sweat collection and the area of the filter paper (mg cm2 min1). After the procedures above, the subjects emptied their bladders, and they had their body weight measured (Filizola MF-100 scale, precision of 0.02 kg, Sa˜o Paulo, SP, Brazil). Then, each subject cycled for 120 min at a constant oxygen uptake of 1.65 L min1, which represented _ 2peak . This metabolic rate was 36 to 61% of subject’s VO selected to guarantee that the lesser fit subject could finish the entire exercise protocol. Water (18–21 1C) was ingested each 15 min at a volume to match sweat rate, as previously _ 2 was measured every calculated (Ribeiro et al., 2004). VO 30 s during the last 15 min of each 30 min interval using the method described above. Whole-body sweat rate (mg cm2 min1) was assumed as been equivalent to the difference between weight before and after exercise, corrected for the water ingested and urine volume, divided by the time (min) between weighting, and AD. No corrections were made for respiratory water output, substrate consumption and insensible perspiration, and all of these variables were assumed as minimal during the experimental protocol. Pearson’s correlation coefficients were calculated between whole-body sweat rate during exercise and peak oxygen uptake; the pilocarpine induced sweat rate at rest and whole-body sweat rate during exercise; the pilocarpine induced sweat rate at rest and peak oxygen uptake. Comparisons between means were made using paired t-Test. Significance was established at ao0:05.
523
0.5 0.4 0.3 0.2 0.1 0.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
SRpilo (mg.cm-2.min-1) Fig. 3. Non-significant correlations between SRpilo and SRex.
0.7
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524
0.7
SR (mg.cm-2.min-1)
0.6 0.5 0.4 0.3 0.2 0.1 0.0
SRexe
SRpilo
Fig. 4. Sweat rate during pilocarpine test and steady state exercise ðp ¼ 0:57Þ.
expressed during a prolonged exercise with constant oxygen uptake in a temperate environment. Traditionally sweat rate during exercise has been _ 2 max using compared among individuals with different VO exercise at the same relative maximum oxygen uptake, which provides disproportional heat production but similar increase on core temperature (Saltin and Hermassen, 1966; Greenleaf et al., 1972; Anderson and Kenney, 1987; Buono and Sjoholm, 1988). Following this approach, Buono et al. (1991) observed a significant correlation between SRex and _ 2 max during 30 min of exercise, at 70% of VO _ 2 max , in VO trained and untrained subjects. However, the significant correlation found on that study could be due to markedly differences in metabolic heat production during exercise between groups, although final core temperature was not _ 2 max different. Hence, the workload was proportional to VO and the sweat rate was proportional to the workloads, as previously demonstrated by Saltin and Hermassen (1966). In the present study, exercise work rate was adjusted _ 2 between subjects during the trial to match similar VO 1 (1.64 (0.12) L O2 min ). This procedure induced both similar heat production and SRex in a group with _ 2peak . considerably different VO Previous investigations have also showed a constant sweat rate when external work rate was similar between trained and non-trained subjects (Shvartz et al., 1977; Araki et al., 1981; Yamauchi et al., 1997). In addition, Shapiro et al. (1982) demonstrated that sweat rate could be predicted (within 720%) with exercise work rate, environmental conditions, and clothes without any physiological measurements. On the other hand, Greenhaff (1989) reported that sweat rate during 1 h of cycling at constant _ 2 max . work rate (140 W) correlated to the subjects’ VO However, that study expressed total sweat rate without correcting for body surface area, which could explain the discrepancy between Greenhaff’s (1989) results and the results of the present study. In the present study, SRex was corrected for body surface area and it was not related _ 2peak . to VO
The current study also showed that SRex and SRpilo were not correlated (Fig. 3). This result shows that the eccrine sweat glands are activated by different ways during pilocarpine or exercise stimuli and it is in agreement with literature (Johnson and Spaulding, 1974). During the pharmacological stimulation at rest, pilocarpine was directly applied to the skin surface through an electrical current, which resulted in a local stimulation of cholinergic muscarinic receptors to produce sweat; however, when eccrine sweat glands were stimulated by exercise, they were activated via central autonomic nervous system stimulating the postganglionic cholinergic nerve fibers. Furthermore, during exercise sweating was modulated by central and peripheral thermoreceptors, metaboreceptors and mechanoreceptors (Gisolfi and Robinson, 1970; Nadel et al., 1971a, b; Kondo et al., 1999) and also modified by circulating hormones, such as noradrenaline, adrenaline, vasoactives peptides and plasma osmolality (Ohara et al., 1984; Yamazaki et al., 1994; Eiken and Mekjavic, 2004). Besides, the local skin conditions (temperature, humidity) were also modulators of sweat production. We speculate that the different modulators could explain the absence of correlation between sweat rates induced by pilocarpine at rest and during exercise at constant oxygen uptake. In our previous study, we observed a correlation between SRpilo and whole-body sweat rate induced by graded exercise until exhaustion (Vimieiro-Gomes et al., 2005). It is interesting to note that during both types of exercise (graded and constant work rate) the eccrine sweat glands were stimulated by central nervous system. It is probable that thermal factors had a more important role on sweat production during prolonged submaximal exercise than during graded exercise until exhaustion (Yamazaki et al., 1994), differentiating the results of the studies. It was also observed that the SRpilo did not correlate _ 2peak (Fig. 2). This result is not in significantly with VO agreement with previous studies, which demonstrated that sweating response induced pharmacologically could be associated to physical training or fitness (Buono and Sjoholm, 1988; Buono et al., 1991; Sato and Sato, 1983). We speculate that our results could have been affected by the sample size and by possible individual’s variation in pilocarpine sensitivity and heat acclimatization status. Our volunteers were born and resided in a tropical region that probably induced increases in eccrine sweat rate as demonstrated by Wyndham et al. (1964) and Wyndham (1967). The studies that found a significant correlation _ 2 max had volunteers from temperate between SRpilo and VO and cold climates. Our study was carried out during the tropical coolest months of the year but it probably had not changed the volunteer’s heat acclimatization status, because environmental temperature variation among tropical seasons is minimal compared to that in cold climates regions. Furthermore, individuals living in temperate climates and enrolled in physical training are exposed to cross heat acclimatization (Nadel et al., 1974), and consequently the sweat rate induced by pilocarpine can
ARTICLE IN PRESS F.T. Amorim et al. / Journal of Thermal Biology 31 (2006) 521–525
_ 2 max (Buono and Sjoholm, 1988; be proportional to VO Buono et al., 1991). It is possible that in our volunteers, who were heat acclimatized to the tropics, increased SRpilo _ 2 max ) due to physical training (or improvement in the VO was not so evident. In conclusion, whole-body sweat rate during steady state exercise in a temperate environment exercise was not _ 2peak , suggesting that sweating was more correlated to VO _ 2peak in closely related to exercise oxygen uptake than VO individuals heat acclimatized to the tropics. Acknowledgements The authors gratefully acknowledge Professor Suzanne Schneider and Paulette Yamada (University of New Mexico, USA) and Professor Nigel Anthony Southworth Taylor (University of Wollongong, Australia) for their useful suggestions about the paper and also the colleagues Samuel Penna Wanner, Juliana Bohnen Guimara˜es from the Laborato´rio de Fisiologia do Exercı´ cio (Universidade Federal de Minas Gerais). The study was supported by CAPES and CNPq. References Anderson, R.K., Kenney, W.L., 1987. Effect of age on heat-activated sweat gland density and flow during exercise in dry heat. J. Appl. Physiol. 63, 1089–1094. Araki, T., Matsushita, K., Umeno, K., Tsujino, A., Toda, Y., 1981. Effect of physical training on exercise-induced sweating in women. J. Appl. Physiol. 51, 1526–1532. Armstrong, L.E., Maresh, C.M., Castellani, J.W., Bergeron, M.F., Kenefick, R.W., LaGasse, K.E., Riebe, D., 1994. Urinary indices of hydration status. Int. J. Sports Nutr. 4, 265–279. Buono, M.J., Sjoholm, N.T., 1988. Effect of physical training on peripheral sweat production. J. Appl. Physiol. 65, 811–814. Buono, M.J., White, C., Connolly, KP., 1991. Pilocarpine-induced sweat rate at rest versus whole body sweat rate during exercise. J. Appl. Sport Sci. Res. 5, 82–86. Candas, V., Libert, J.P., Brandenberger, G., Sagot, J.C., Kahn, J.M., 1988. Thermal and circulatory responses during prolonged exercise at different levels of hydration. J. Physiol. (Paris) 83 (1), 11–18. Dubois, D., Dubois, E.F., 1916. A formula to estimate the approximate surface area if height and weight be known. Arch. Inter Med. 17, 831–836. Eiken, O., Mekjavic, I.B., 2004. Ischaemia in working muscles potentiates the exercise-induced sweating response in man. Acta Physiol. Scand 181, 305–311. Gibson, L.E., Cooke, R.E., 1959. A test for concentration of electrolytes in sweat in cystic fibrosis of the pancreas utilizing pilocarpine by iontophoresis. Pediatrics 23, 545–549. Gisolfi, C., Robinson, S., 1970. Central and peripheral stimuli regulating sweating during intermittent work in men. J. Appl. Physiol. 29, 761–768. Greenhaff, P.L., 1989. Cardiovascular fitness and thermoregulation during prolonged exercise in man. Braz. J. Sport Med. 23, 109–114.
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