Sweat Rate and Electrolyte Concentration in Swimmers, Runners, and Nonathletes

Abstract

Because swimmers train in an aquatic environment, they probably do not need to sweat as much as runners who train on land and, therefore, should not develop the same magnitude of sweating adaptations.
To compare sweat rate and electrolyte concentration in swimmers, runners and nonathletes.
Ten swimmers (22.9 ± 3.1 years old), 10 runners (25 ± 2.9 y) and 10 nonathletes (26.5 ± 2.2 y) cycled in the heat (32 degrees Celsius and 40% relative humidity) for 30 min at similar intensity relative to their maximal cycle test. Sweat volume was calculated from the difference of their body mass before and after cycling, since they were not allowed to drink. Sweat was collected from the scapula using absorbent patch placed on the skin that was cleaned with distilled water. After cycling, the patch was transferred to syringe and the sample was obtained when squeezing it to a tube. Concentration of sodium ([Na+]), chloride ([Cl-]) and potassium ([K+]) were analyzed using an ion selector analyzer.
The sweat volume, in liters, of swimmers (0.9 ± 0.3) was lower (P < .05) than that of runners (1.5 ± 0.2) and similar to that of nonathletes (0.6 ± 0.2). [Na+] and [Cl-], in mmol x L(-1), of swimmers (65.4 ± 5.5 and 61.2 ± 81), and nonathletes (67.3 ± 8.5 and 58.3 ± 9.6) were higher (P < .05) than those of runners (45.2 ± 7.5 and 38.9 ± 8.3). [K+] was similar among groups.
The lower sweat volume and higher sweat [Na+] and [Cl-] of swimmers, as compared with runners, indicate that training in the water does not cause the same magnitude of sweating adaptations.

Full text

359
International Journal of Sports Physiology and Performance, 2010, 5, 359-366
© Human Kinetics, Inc.
The authors are with Escola de Educação Física, Universidade Federal do Rio Grande do Sul, Porto
Alegre, RS, Brasil.
Sweat Rate and Electrolyte Concentration
in Swimmers, Runners, and Nonathletes
Simone D. Henkin, Paulo L. Sehl, and Flavia Meyer
Because swimmers train in an aquatic environment, they probably do not need
to sweat as much as runners who train on land and, therefore, should not develop
the same magnitude of sweating adaptations. Purpose: To compare sweat rate
and electrolyte concentration in swimmers, runners and nonathletes. Methods:
Ten swimmers (22.9 ± 3.1 years old), 10 runners (25 ± 2.9 y) and 10 nonathletes
(26.5 ± 2.2 y) cycled in the heat (32°C and 40% relative humidity) for 30 min at
similar intensity relative to their maximal cycle test. Sweat volume was calculated
from the difference of their body mass before and after cycling, since they were
not allowed to drink. Sweat was collected from the scapula using absorbent patch
placed on the skin that was cleaned with distilled water. After cycling, the patch
was transferred to syringe and the sample was obtained when squeezing it to a
tube. Concentration of sodium ([Na+]), chloride ([Cl–]) and potassium ([K+]) were
analyzed using an ion selector analyzer. Results: The sweat volume, in liters, of
swimmers (0.9 ± 0.3) was lower (P < .05) than that of runners (1.5 ± 0.2) and similar
to that of nonathletes (0.6 ± 0.2). [Na+] and [Cl–], in mmol⋅L−1, of swimmers (65.4
± 5.5 and 61.2 ± 81), and nonathletes (67.3 ± 8.5 and 58.3 ± 9.6) were higher (P
< .05) than those of runners (45.2 ± 7.5 and 38.9 ± 8.3). [K+] was similar among
groups. Conclusions: The lower sweat volume and higher sweat [Na+] and [Cl–]
of swimmers, as compared with runners, indicate that training in the water does
not cause the same magnitude of sweating adaptations.
Keywords: sweat glands, sweat ion concentration, acclimatization, exercise in
the heat
Aerobic training may change sweating responses as it was shown that overall
trained men have a greater sweat rate compared with untrained men.1 The heat
acclimatization process due to repeated heat exposure while living under heat stress2
also indicates increase in sweat rate and change in sweat electrolyte concentration,
mainly a decrease in sweat [Na+].3,4 Thus, the combination of aerobic training and
heat acclimatization could probably optimize these sweat adaptations of runners.
There are few studies on sweating responses of swimmers, and they all took
place in the swimming pool.5–8 Swimmer athletes, even training aerobically, may
not develop the same degree of sweat adaptations as runners. This is because swim-

360 Henkin, Sehl, and Meyer
mers exercise in the water, which helps dissipate the body heat production through
convection and conduction.9,10 The facilitated body heat removal may reduce the
need to sweat during swimming and thus attenuate those sweat adaptations that were
shown in runners. Such differences in sweating responses could be demonstrated
by using a study design in which swimmers and runners exercise outside the water,
under similar environmental and exercise conditions.
We are unaware of any study that examined sweat rate and sweat electrolyte
concentrations of swimmers in comparison with other athletes outside the water.
We hypothesized that, as untrained individuals, swimmers present a lower sweat
rate and a higher sweat [Na+] than runners when they exercise out of water under
similar environmental and exercise conditions. If indeed the aquatic training spare
sweating adaptations, swimmers may be at thermoregulatory disadvantages if they
occasionally exercise out of water for a long time in the heat. Knowledge of such
responses may have another practical implication regarding hydration needs. There-
fore, the purpose of this study was to compare the sweat rate and sweat electrolyte
concentration in swimmers, runners and nonathletes.
Methods
Subjects
Ten endurance runners, 10 endurance swimmers and 10 nonathletes, all males,
gave written informed consent to participate in this study which was approved by
the Ethical Committee of the Universidade Federal do Rio Grande do Sul. At the
time of the experiment, runners and swimmers had been training in their respective
sports for at least 5 y until the month before testing. For the swimmers, we chose
those who competed distances of 400 and 800 m, and trained in the pool about 35
km per week. The runners competed 10 and 20 km and trained outdoors, about 92
km per week. Basically, runners and swimmers were training in their respective
dry-land and aquatic environments for about 2 h, 5 d per week, and at the time of
the experiment using their routine exercise intensity for a noncompetitive period.
The nonathlete group was active, practicing weight training three times a week
but had not been participating in any kind of competitive or systematic training for
the last 6 mo before the experiment. None of the subjects were taking medications
or were smokers.
All subjects were living in similar environmental conditions (South Brazil)
and experiments took place during late winter, when the air temperature ranged
from 16°C to 24°C. Athletes were therefore at similar training seasons, and run-
ners wore shorts and T-shirts while training. Subjects came rst for the screening
session and later for the experimental session.
Screening Session
Subjects came to the laboratory to evaluate physical characteristics (age, height,
weight and sum of skinfolds) and maximal oxygen uptake (VO2max) to standardize
exercise intensity for the experimental session. VO2max was measured using online,
breath-by-breath, open-circuit spirometry (O2 and CO2 analyzer Medgraphics model
CPX/D) on a cycle ergometer (Cybex, The Bike) using a progressive protocol.11

Sweat Responses in Swimmers 361
Subjects cycled for 3 min at a self-selected pace at an initial load of 50 W, and
then the load was increased by 25 W each minute. During the test, subjects were
instructed to cycle at a rate ≥ 60 rpm. Heart rate (HR; Polar, S610, Polar Electro
Oy, Finland) was monitored continuously. Subjects were given verbal encourage-
ment throughout the test, which ended when they were unable to maintain the
rhythm or when HR exceeded 200 bpm. The second ventilatory threshold was set
using increases of O2 and CO2 ventilatory equivalent (VE⋅VO2
–1 and VE⋅VCO2
–1).
Subjects were instructed to drink 500 mL of water 2 h before the next session
(experimental)12 and to refrain from caffeine and alcoholic beverages as well as
physical activities the prior 24 h.
Experimental Session
On arrival at the laboratory, we conrmed that subjects had followed the instruc-
tions, and we then assumed they were euhydrated. Afterward, subjects emptied
their bladder, and their body weight was assessed (Fillizola) wearing only shorts.
At the site of sweat collection, the skin was cleaned with distilled water. A
gauze patch (Tegaderm 3582, 3M) was attached to the right side of the scapula
(approx. 7 cm lateral from the vertebral column) to absorb the local sweat as
described by Patterson et al.13 Before attaching the patch, the site was washed with
distilled water and dried with sterilized gauze to avoid contamination. Following
cycling, as described bellow, the patch was removed with tweezers (cleansed with
distilled water) and placed into a disposable syringe that was squeezed into a tube
(Eppendorf) to obtain the sweat sample for later analysis.
Wearing only shorts, subjects cycled on a friction-braked ergometer (Ergo Fit
167, Spain, 5 W). They cycled for 30 min and the power output was calculated to
be approximately 10% below the second ventilatory threshold from their individual
VO2max measured in the screening session, The corresponding means ± SD (in
watts) were 125 ± 26.8 for swimmers, 171 ± 10.3 for runners and 91.7 ± 14.4 for
nonathletes. Heart rate (Polar, S610, Polar Electro Oy, Finland) was monitored
throughout the exercise session, corresponding to 65 to 75% of maximal HR. Sub-
jects cycled in the heat of an environmental chamber (Russels, 3.63 m wide × 2.39 m
high × 3.81 m deep) with an air temperature of 32°C and relative humidity of 40%.
After cycling, each subject toweled dry, voided, and the body mass was recorded
again with subjects wearing a dry short.
Sweat Analyses and Calculations
Sweat was analyzed for [Na+], [Cl–], and [K+] using an ion selector analyzer (AVL,
9180, Roche), in duplicate. We considered the mean value since results were similar
within samples.
Body mass loss was determined by change in body mass. This difference
between pre- and postexercise body mass represented the 30-min sweat volume,
since subjects did not drink any uid during cycling. We corrected to 1 h (by mul-
tiplying by 2) and also divided by the body mass and minutes to express the sweat
rate in mL⋅kg−1⋅min−1.
The amount of sodium loss was calculated by multiplying the sweat electrolyte
concentration obtaining from sample of the scapula by the total sweat volume.

362 Henkin, Sehl, and Meyer
Statistical Analysis
Data were tested for normality of distribution and are presented as mean ± SD. To
compare the variables among groups, analysis of variance (ANOVA) with Tukey
post hoc test were used. Differences were considered signicant when P < .05.
Data were analyzed using SPSS 13.0.
Results
As shown in Table 1, the three groups were similar in height, body mass, and sum
of skinfolds, but they were different in VO2max. Runners had the highest VO2max.
Mean (± SD) HR over the 30-min cycling session was lower in nonathletes
(127 ± 3 bpm) than in runners (154 ± 11 bpm) and swimmers (162 ± 8 bpm). Swim-
mers’ sweat rates (absolute and relative body mass) were lower than runners’ and
similar to nonathletes’ (Table 2). As a result, runners lost signicantly more body
mass than swimmers and nonathletes. Considering the body mass measured just
before exercise, the loss in kilograms and the respective percentage dehydration
were 0.46 ± 0.1 and 0.61 ± 0.17 in swimmers, 0.73 ± 0.1 and 0.98 ± 0.17 in run-
ners, and 0.27± 0.1 and 0.33 ± 0.12 in nonathletes.
As shown in Table 2, sweat [Na+] and [Cl–] in swimmers and nonathletes were
higher than in runners. Sweat [K+] was similar across the three groups. Estimated
Table 1 Physical and physiological characteristics of runners,
swimmers, and nonathletes
Age
(years)
Height
(cm)
Body mass
(kg)
∑
of nine
skinfolds* (mm)
VO
2
max
(mL
·
kg
−1·
min
−1
)
Swimmers 22.9 ± 3.1 178 ± 5.8 75 ± 10.0 116 ± 44.8 54.2 ± 5.7 b
Runners 25.4 ± 2.9 178 ± 5.8 74 ± 7.8 106 ± 19.8 60.5 ± 5.8 a
Nonathletes 26.5 ± 2.4 176 ± 5.6 80 ± 11.8 131 ± 39.5 45.2 ± 2.9 c
* Triceps, biceps, chest, axilla, iliac crest, subscapular, abdominal, front thigh, and medial calf. Data
are mean ± SD.
a Greater than in swimmers and nonathletes, P < .001. b Greater than in nonathletes, lower than in run-
ners, P < .001. c Lower than in swimmers and runners.
Table 2 Sweat rate (L·h–1 and mL·kg−1·min−1) and electrolyte
concentration (mmol·L−1) in swimmers, runners, and nonathletes
Sweat rate Electrolyte concentration
L
·
h
−1
mL
·
kg
−1·
min
−1
Na
+
Cl
–
K
+
Swimmers 0.9 ± 0.3 0.20 ± 0.57 65.4 ± 5.5 b61.2 ± 8.1 b3.7 ± 0.3
Runners 1.5 ± 0.2 a0.33 ± 0.06 a45.2 ± 7.5 38.9 ± 8.3 3.8 ± 0.4
Nonathletes 0.6 ± 0.2 0.11 ± 0.04 67.3 ± 8.5 b58.3 ± 9.6 b4.4 ±1.1
Data are mean ± SD. a Greater than in swimmers and nonathletes (P < .05). b Greater than in runners
(P < .05).

Sweat Responses in Swimmers 363
sweat sodium loss (in mmol⋅kg–1⋅h–1) of swimmers (0.79 ± 0.24) was similar to
that of runners (0.88 ± 0.18), and higher than that of nonathletes (0.44 ± 0.14).
Discussion
The main ndings of the current study were that, when exercising out of water,
swimmers and nonathletes did not sweat as much as runners; and their sweat [Na+]
and [Cl–] were higher than those of runners, conrming our hypothesis. These
ndings indicate that sweat responses are dependent on the training environment
(land vs water). The aquatic environment may facilitate body heat transfer through
conduction and convection, limiting sweating. We purposely used an environmental
condition to stimulate swimmers to sweat out of their usual training environment
(on land). Further, this design enabled us to compare sweating responses among
swimmers, runners and nonathletes under similar exercise conditions. On the other
hand, more studies are necessary to explain the mechanisms of the observed ndings.
Some studies5–8 have investigated the thermoregulatory responses of swimmers
and runners in the water, making it impossible to compare these with the responses
of our study. Swimmers’ sweat rate in the current study (0.9 L⋅h–1) was greater than
that previously reported for swimmers in the literature (0.4 L⋅h–1 and 0.7 L⋅h–1).5,8
The estimated mean sweat volume per hour (1.5 L⋅h–1) in runners in the current
study was similar to previously reported values for runners under similar exercise
conditions.14,15
In agreement with the current study, swimmers showed a lower sweating
rate during heat stress. It has been reported that swimmers have a reduced sweat
rate.5–7 This lower sweating rate in water-trained individuals may be explained by
the fact that swimmers do not experience marked daily increases in core or skin
temperature because of the increased heat transfer characteristics of the water envi-
ronment (increases that have been reported to be necessary to initiate sweating).16
The lower sweat rate in swimmers has also been attributed to an inhibition in the
sweat gland activity due to training in the water.17 This may cause a depression in
sweat response which was named as chronic hidromeiosis.18
Sweat rate in athletes is markedly higher than in sedentary subjects.19–21 In this
study, however, the sweat rate in swimmers was not higher than in nonathletes,
which is in disagreement with earlier studies.22 The similar sweat rates found in
swimmers and nonathletes might be due to the relative low degree of thermal stress
that induces sweating. At low levels of thermal stress, it may be difcult to nd
a difference in sweat rate between groups due to the lower sweating rate of the
limbs.7 Such differences could become clearer with an increase in the stimulus to
sweat at higher levels of thermal stress and sweating.
Aerobic conditioning and heat acclimatization are factors that affect sweat rate
induced by exercise.1,3,4 They could explain a higher sweat rate in runners as they
presented a greater VO2max. A high level of cardiorespiratory tness is associated
with an improved exercise-heat tolerance including increases in sweat rate.20 It is
known that endurance training in high air temperate conditions with signicant
increases of VO2max contributes to heat acclimatization.22 For example, Piwonka
et al19 reported that trained distance runners showed a decreased physiological
strain compared with untrained individuals during exercise-heat stress. In addition,
because runners train in conditions that facilitate heat gain, they develop a greater

364 Henkin, Sehl, and Meyer
evaporative heat capacity that is more efcient than convection in an air environ-
ment. In the current study, although all athletes were competitive, relative VO2max
was about 10% higher in runners than in swimmers. In this case, we do not know
how much the VO2max affected the results; but it could explain them only partially,
since the relative sweat rate was about 40% higher in runners than in swimmers.
VO2 was not measured during exercise; but subjects’ workload was individually
estimated at the same relative intensity from their maximal.
Body size also affects the sweat rate during exercise;15 however, the three
groups assessed here were similar in height, weight, and sum of skinfolds. Thus,
differences in body mass could not account for the greater sweat rate in runners.
The density of heat-activated sweat glands is also associated with a greater
sweat rate.20,23,24 Ogawa et al25 observed that the number of heat-activated sweat
glands, which may be indicative of sudomotor neural activity, increased after heat
acclimatization, suggesting that heat acclimatization may alter central modulation of
the sweating response. In the current study, to avoid variations of heat acclimatiza-
tion, all subjects were tested at the same time of the year (late winter). Nevertheless,
we cannot guarantee that all subjects were equally acclimatized.
Another factor is that the sweating threshold at a given core temperature may
be decreased by training and acclimatization.26 We did not measure this relation to
determine how much it affected the sweat rate among groups. It is possible that a
delayed onset of sweating in swimmers and nonathletes could have underestimated
their sweat rate over the 30 min cycling. We used a relatively short exercise in the
heat protocol (30 min at 32°C, 40% relative humidity), but it was sufcient to show
some differences in sweating volumes and to obtain samples for electrolyte analyses.
The novel data of the current study concern the sweat electrolyte concentration
in swimmers. Sweat [Na+] and [Cl–] were higher in swimmers and nonathletes.
Sweat [Na+] and [Cl–] have decreased with heat acclimatization even for a given
increase in sweating rate.4,27 Thus, although heat-acclimatized individuals sweat
more—as observed in the greater sweat rate in runners—there is lower [Na+] and
[Cl–] in that sweat.23 Another signicant nding was that sweat Na+ loss was higher
in swimmers and runners than in nonathletes. This was due to the somewhat higher
sweat [Na+] in swimmers despite their lower sweat rate as compared with runners.
One limitation of the current study was that sweat was collected from one region
only (scapula). The sweat electrolyte concentration may vary at different sites, and
sweating distribution across the limbs and trunk changes with acclimatization.28
Future studies should evaluate sweat electrolyte loss using an estimation of dif-
ferent body areas.
Conclusions and Practical Applications
Swimmers as well as the nonathletic group did not sweat as much as runners; neither
did they have a lower NaCl sweat concentration. These sweating responses induced
by a 30-min cycling in the heat, out of the water, suggest that sweating adaptations
may be inuenced by the sport training environment. This lower sweat rate of
swimmers, in relation to runners, may represent a thermoregulatory disadvantage
and they, just like nonathletes, may need special care to avoid hyperthermia and
other heat-related disorders if they start running or training in a warm environment
out of the water. More experimental studies, including measurements such as core

Sweat Responses in Swimmers 365
temperature, sweating threshold and heat-activated sweat glands could clarify such
ndings. Another practical implication is related to the uid intake needs. The usual
volume, but not the amount of sodium, recommended for a swimmer to maintain
euhydration may be lower than that of a runner athlete.
Acknowledgments
The authors are grateful to the subjects who participated in this study and the technical
assistance of Marcio M. Silveira.
References
1. Buono MJ, Sjoholm NT. Effect of Physical training on peripheral sweat production. J
Appl Physiol. 1988;65:811–814.
2. Armstrong LE, Maresh CM. The induction and decay of heat acclimatization in trained
athletes. Sports Med. 1991;12:302–312.
3. Chinevere TD, Keneck RW, Cheuvront SN, Lukasky HC, Sawka MN. Effect of heat
acclimation on sweat minerals. Med Sci Sports Exerc. 2008;40:886–891.
4. Allan JR, Wilson CG. Inuence of acclimatization on sweat sodium concentration. J
Appl Physiol. 1971;30:708–712.
5. McMurray RG, Horvath SM. Thermoregulation in swimmers and runners. J Appl
Physiol. 1979;46:1086–1092.
6. Avellini RA, Shapiro Y, Fortney SM, Wenger CB, Pandolf KB. Effects on heat tolerance
of physical training in water and on land. J Appl Physiol. 1982;53:1291–1298.
7. Kondo N, Nishiyasu T, Ikegami H. The sweating responses of athletes trained on land
and in water. Jpn J Physiol. 1995;45:571–581.
8. Soler R, Echegaray M, Rivera M. Thermal responses and body uid balance of competi-
tive male swimmers during a training session. J Strength Cond Res. 2003;17:362–367.
9. Nielsen B, Davies CT. Temperature regulation during exercises in water and air. Physi-
ologica Scandinavica. 1976;4:500–508.
10. Higham DG, Naughton GA, Burt LA, Shi X. Comparison of uid balance between
competitive swimmers and less active adolescents. Int J Sport Nutr Exerc Metab.
2008;19:259–274.
11. Lucia A, Hoyos J, Perez M, Chicharro JL. Heart rate and performance parameters in
elite cyclists: a longitudinal study. Med Sci Sports Exerc. 2000;32:1777–1782.
12. American College of Sports Medicine. Position stand on exercise and uid replacement.
Med Sci Sports Exerc. 2007;39(1):377–390.
13. Patterson MJ, Gallloway SDR, Nimmo MA. Variations in regional sweat composition
in normal human males. Exp Physiol. 2000;85:869–875.
14. Millard-Stafford ML, Sparling PB, Rosskopf LB, Snow TK, DiCarlo LJ, Hinson BT.
Fluid intake in male and female runners during a 40 km run in the heat. J Sports Sci.
1995;13:257–263.
15. Godek SF, Bartolozzi AR, Godek JJ. Sweat rate and uid turnover in American foot-
ball players compared with runners in a hot and humid environment. Br J Sports Med.
2005;39:205–211.
16. Nadel E, Fortney SM, Wenger CB. Effect of hydration state on circulatory and thermal
regulations. J Appl Physiol. 1980;49:715–721.
17. Nadel ER, Pandolf KB, Roberts MF, Stolwijk JAJ. Mechanisms of thermal acclimation
to exercise and heat. J Appl Physiol. 1974;37:515–520.
18. Brown W, Sargent F. Hidromeiosis. Arch Environ Health. 1965;11:442–453.
19. Piwonka RW, Robinson S, Gay VL, Manalis RS. Acclimatization of men to heat by
training. J Appl Physiol. 1965;20:379–384.

366 Henkin, Sehl, and Meyer
20. McLellan TM. The importance of aerobic tness in determining tolerance to uncom-
pensable heat stress. Comp Biochem Physiol Part. 2001;128:691–700.
21. Maughan R, Shirreffs S. Exercise in the heat: challenges and opportunities. J Sports
Sci. 2004;22:917–927.
22. Henane R, Flandrois R, Charbonnier JD. Increase in sweating sensitivity by endurance
conditioning in man. J Appl Physiol. 1997;43:822–828.
23. Shibasaki M, Thad E, Crandall C. Neural control and mechanisms of eccrine sweating
during heat stress and exercise. J Appl Physiol. 2006;100:1692–1701.
24. Sato K, Sato F. Individual variations in structure and function of human eccrine sweat
gland. Am J Physiol Regul Integr Comp Physiol. 1983;245(2):203–208.
25. Ogawa T, Ohnishi N, Yamashita Y, Sugenoya J, Asayama M, Miyagawa T. Effect of
facial cooling during heat acclimation process on adaptive changes in sweating activity.
Jpn J Physiol. 1988;38:479–490.
26. Roberts MF, Wenger CB. Stolwijk, Nadel ER. Skin blood ow and sweating changes
following exercise training and heat acclimation. J Appl Physiol. 1977;43:133–137.
27. Kirby CR, Convertino VA. Plasma aldosterone and sweat sodium concentrations after
exercise and heat acclimatization. J Appl Physiol. 1986;61:967–997.
28. Coyle EF. Physical activity as a metabolic stressor. Am J Clin Nutr. 2000;72:512S–520S.