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Pre-game hydration status, sweat loss, and fluid intake
in elite Brazilian young male soccer players during
competition
a
b
a
c
Rafael P. Da Silva , Toby Mündel , Antonio J. Natali , Mauricio G. Bara Filho , Rita C.
d
c
a
a
G. Alfenas , Jorge R. P. Lima , Felipe G. Belfort , Priscila R. N. R. Lopes & João C. B.
Marins
a
a
Department of Physical Education, Federal University of Viçosa, Viçosa, Brazil
b
School of Sport and Exercise, Massey University, Palmerston North, New Zealand
c
School of Sports and Physical Education, Federal University of Juiz de Fora, Juiz de Fora,
Brazil
d
Department of Nutrition and Health, Federal University of Viçosa, Viçosa, Brazil
Available online: 23 Nov 2011
To cite this article: Rafael P. Da Silva, Toby Mündel, Antonio J. Natali, Mauricio G. Bara Filho, Rita C. G. Alfenas, Jorge R. P.
Lima, Felipe G. Belfort, Priscila R. N. R. Lopes & João C. B. Marins (2012): Pre-game hydration status, sweat loss, and fluid
intake in elite Brazilian young male soccer players during competition, Journal of Sports Sciences, 30:1, 37-42
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Journal of Sports Sciences, January 2012; 30(1): 37–42
Pre-game hydration status, sweat loss, and fluid intake in elite Brazilian
young male soccer players during competition
RAFAEL P. DA SILVA1, TOBY MÜNDEL2, ANTONIO J. NATALI1,
MAURICIO G. BARA FILHO3, RITA C. G. ALFENAS4, JORGE R. P. LIMA3,
FELIPE G. BELFORT1, PRISCILA R. N. R. LOPES1, & JOÃO C. B. MARINS1
1
Department of Physical Education, Federal University of Viçosa, Viçosa, Brazil, 2School of Sport and Exercise, Massey
University, Palmerston North, New Zealand, 3School of Sports and Physical Education, Federal University of Juiz de Fora,
Juiz de Fora, Brazil, 4Department of Nutrition and Health, Federal University of Viçosa, Viçosa, Brazil
Downloaded by [INAOE] at 05:17 21 December 2011
(Accepted 12 September 2011)
Abstract
In this study, we assessed the pre-game hydration status and fluid balance of elite young soccer players competing in a match
played in the heat (temperature 31.0 + 2.08C, relative humidity 48.0 + 5.0%) for an official Brazilian soccer competition.
Fluid intake was measured during the match, as were urine specific gravity and body mass before and after the game to
estimate hydration status. Data were obtained from 15 male players (age 17.0 + 0.6 years, height 1.78 + 0.06 m, mass
65.3 + 3.8 kg); however, data are only analysed for 10 players who completed the full game. The mean (+s) sweat loss of
players amounted to 2.24 + 0.63 L, and mean fluid intake was 1.12 + 0.39 L. Pre-game urine specific gravity was
1.021 + 0.004, ranging from 1.010 to 1.025. There was no significant correlation between sweat loss and fluid intake
(r ¼ 0.504, P ¼ 0.137) or between urine specific gravity and fluid intake (r ¼ 70.276, P ¼ 0.440). We conclude that young,
native tropical soccer players started the match hypohydrated and replaced about 50% of the sweat lost. Thus, effective
strategies to improve fluid replacement are needed for players competing in the heat.
Keywords: Dehydration, fluid balance, sweating, junior athletes, soccer
Introduction
Soccer is a team sport that requires frequent fluctuation between high and low exercise intensities, where
the high work rates and extended nature of the game
lead to elevations in body temperature(s) and the
initiation of a sweating response (Bangsbo, Mohr, &
Krustrup, 2006). Several reports in the literature
have shown that fluid loss in adult soccer players can
be substantial (Kurdak et al., 2010; Maughan,
Watson, Evans, Broad, & Shirreffs, 2007; Shirreffs
et al., 2005), and even mild dehydration may have
adverse effects on a number of physiological and
cognitive functions that are important for components of soccer performance (Edwards et al., 2007).
Sweat loss is influenced both by exogenous factors,
such as environmental conditions and clothing type,
and by endogenous factors, such as metabolic rate
(Sawka et al., 2007). While the rate of energy
expenditure by soccer players depends on many
independent factors, including chronological age,
biological maturity, training age, morphology, and
anthropometry (Le Gall, Carling, Williams, & Reilly,
2010), sweat loss may be different between soccer
players engaged in distinct age categories. Although
there are some data on fluid balance in soccer
players, most relate to adult players during training
in cool environments, with limited data on professional young soccer players competing in warmer
environments.
Players would normally be expected to ingest
fluids during training or match-play, and both water
and carbohydrate-electrolyte drinks are widely used.
However, unlike most sports, soccer provides few
opportunities to drink because of limited access to
fluids and the absence of breaks during a match
(Edwards & Clark, 2006). Fluid losses of 1–2% of
body mass are typical in adult soccer athletes across
most environmental conditions (Shirreffs, Sawka, &
Stone, 2006), and the amount of fluid intake during
games rarely matches the fluid lost, often resulting in
voluntary dehydration (Maughan et al., 2007).
Correspondence: R. P. da Silva, Department of Physical Education, Federal University of Viçosa, Viçosa/MG, Brazil. E-mail: [email protected]
ISSN 0264-0414 print/ISSN 1466-447X online Ó 2012 Taylor & Francis
http://dx.doi.org/10.1080/02640414.2011.623711
Downloaded by [INAOE] at 05:17 21 December 2011
38
R. P. da Silva et al.
In competitive match-play, the players are under
constant emotional and psychological stress, which
could influence their motivational behaviour on the
field. Such factors may affect elements of self-pacing
that determine variables such as distance covered,
energy expenditure, and hence fluid balance (Harley
et al., 2010). However, limited data are available on
professional young soccer players during official
competition match-play where habitual hydration
regimes were maintained. Furthermore, it has been
reported that a great proportion of soccer players
start a match in a hypohydrated state (AragónVargas, Moncada-Jiménez, Hernándes-Elizondo,
Barrenechea, & Monde-Alvarado, 2009; Maughan
et al., 2007). However, the extent of this pre-game
hypohydration in young soccer players requires
further investigation.
The majority of studies have examined thermoregulatory responses of soccer players in non-tropical
natives and limited data are available on fluid balance
in young, tropical native soccer players practising in
their natural environment. Tropical natives present a
more efficient thermoregulatory system with reduced
heat strain and increased tolerance to exercise in hot
environments compared with non-tropical natives
(Hori, 1995; Magalhães et al., 2010; Nguyen &
Tokura, 2003). Recently, Silva et al. (2011) investigated tropical natives and reported a significant
relationship between fluid intake and estimated
sweat loss of young soccer players during training,
while Aragón-Vargas et al. (2009) observed that
tropical adult soccer players who report for competition with the highest urine specific gravity are likely
to drink more during the match. It remains to be
determined, however, whether tropical young
soccer players respond similarly during official
match-play.
The aim of the present study, therefore, was to
assess the fluid losses and fluid intake of elite
Brazilian youth soccer players during official
match-play for the classification phase of a Brazilian
soccer competition. We also assessed pre-game
hydration status and its relationship with the volume
of sweat loss and the fluid consumed by players.
Methods
Participants
Fifteen adolescent male soccer players agreed to
participate in the study. They were the team
members and substitutes of a first division Brazilian
professional soccer club who took part in a competitive match. All players and parents gave written
informed consent and the study was approved by the
Institutional Ethics Committee. The players’ physical characteristics were as follow: age 17.0 + 0.6
years, height 1.78 + 0.06 m, and body mass
65.3 + 3.8 kg.
Experimental design
All measurements were made during the last game of
the classification phase of an under-17 Brazilian
soccer competition. The game, which consisted of
two 40-min periods and a 15-min half-time interval,
was played in the morning (11:30 h kick-off). The
temperature at the time of the match was approximately 31.0 + 2.08C with relative humidity (RH) of
48.0 + 5.0% measured by a wet bulb globe temperature (WBGT) monitor (TGM 100, Homis1,
Brazil). Heat stress (WBGT measured every 15 min)
was 29.3 + 2.38C (range 28.6–32.08C). Data for the
pre-game urine and thirst sensation measurements of
all participants are included, but all other data
relating to players who did not complete the full
match are excluded. Complete data are therefore
available for 10 players who completed the full 80
min of play (one player was expelled 5 min into the
game) and four substitutes, none of whom played.
Efforts were made to minimally alter the typical
behaviour of the athletes, so no change to the athletes’
routine was made before they arrived at the stadium
for competition. This included instructing athletes to
maintain their usual pre-match diet and hydration
practices and the measurements made once at the
stadium were both fast and efficient so as not to
impact on their pre-match routine. Approximately 1
h before the game all players, including substitutes,
reported to the dressing room of the stadium after
following their normal pre-game routine. Athletes
were instructed to empty their bladders as completely
as possible and defecate if necessary. Each participant
provided a urine sample and was weighed nude on a
digital scale accurate to 0.01 kg (Soehnle1, Spain).
Pre-game urine specific gravity was assessed within
30 min of collection using a clinical handheld
refractometer (model A300; ATAGO Co., Tokyo,
Japan) that was calibrated with distilled water before
the start of the tests and reviewed periodically
between samples. The same individual measured all
urine samples, which were discarded immediately
after assessment. The participants also responded
verbally to a survey enquiring about pre-game thirst
sensation using a 9-point scale (Engell et al., 1987)
ranging from 1 (‘‘not thirsty’’) to 9 (‘‘very thirsty’’).
Thereafter, players and substitutes changed into
playing kit (standardized to all athletes: T-shirt,
shorts, socks, and shoes), received an individual
opaque bottle labelled with the player’s name, and
performed the warm-up on the field for about 15 min
before returning to the dressing room approximately
5 min before kick-off. The bottles contained water,
as this was normally available to the players during
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Fluid balance of soccer players during competition
the match. They were allowed to consume water ad
libitum but drinking only from the bottles provided
and not spitting any of the fluid out or using the fluid
to rinse their faces. During match-play the players
and substitutes had free access to the bottles that
were positioned at a specific location off the field of
play, reproducing habitual athletes’ behaviour. Individual drink bottles were weighed before being
provided to the volunteers and at every refilling using
a digital scale (Plenna, MSI Inc., USA; + 0.01 g).
All participants were constantly observed by their
own support staff and by the researchers before and
during the match to ensure compliance. To reduce
potential bias, limited explanations were provided to
the participants about fluid intake behaviour. They
were informed that measurements of their sensory,
subjective, and physiological parameters of fluid
replacement would be made, but were unaware that
their fluid consumption was measured and were
blind to the purpose of the study. Participants were
also instructed by the coaching staff to ingest 400 mL
of a 6% carbohydrate-electrolyte drink over the
course of the game, as well as 200 mL 30 min before
the match and an additional 200 mL at half-time;
this was in keeping with usual match-day routine/
instruction. The athletes were instructed to collect
any urine passed during the game in containers
provided so that this could be taken into account in
the calculation of sweat loss from the measured
changes in body mass. None of the players passed
urine in the period between baseline measurement of
body mass and the start of the match. Two of the 10
players involved in the game and one substitute
passed urine at half-time. Substitutes warmed up
with players before the game, and then stood on the
corner line during the game performing minimal
activities directed by coaching staff aimed at keeping
them warmed up. None of the participants changed
their clothing during the course of the game.
At the end of the match, all bottles were
immediately collected and weighed, and the athletes
were not allowed to drink anything else until the
measurement of their post-game body mass. Any
excess of sweat was then towelled off and the players
were weighed as before the game. Participants were
asked to empty their bladder as fully as possible and
to collect the entire volume in a container provided,
which was used to assess post-game urine specific
gravity and urine volume. Water palatability was
reported after the match using a 10-point hedoniccategory scale (Peryam & Pilgrim, 1957) ranging
from 1 (‘‘dislike extremely’’) to 10 (‘‘like extremely’’)
as well as thirst sensation as before the game. Sweat
loss was estimated using the change in body mass,
corrected for any urine loss and the volume of fluid
consumed. The relatively small changes in body
mass due to substrate oxidation and other sources of
39
water loss (primarily evaporative loss from the lungs)
were ignored (Maughan & Shirreffs, 2010).
Statistical analysis
The data were tested for normality of distribution
and are presented as means + standard deviations
(s), minimum and maximum values (range). Pearson
correlation coefficients were generated to determine
whether there was a relationship between variables
such as urine specific gravity, thirst sensation, fluid
intake, and sweat loss. A paired t-test was performed
to evaluate the effects of time (pre or post measurement) on urine specific gravity, body mass, and thirst
sensation. Data analyses were conducted with SPSS
(version 14.0; SPSS Inc., Chicago, IL). Statistical
significance was set at P 5 0.05.
Results
The body mass loss, fluid intake, sweat loss, and
urine output data of the players who completed the
game (n ¼ 10) and substitutes (n ¼ 4) are shown in
Table I. There was no significant relationship
between the total volume of sweat lost during the
match and the volume of fluid ingested (r ¼ 0.504,
P ¼ 0.137; n ¼ 10) (Figure 1).
The pre-game urine specific gravity of all participants (n ¼ 15) was 1.021 + 0.004 (range 1.010–
1.025). The pre-game urine specific gravity
(1.020 + 0.004; range 1.010–1.025) of the players
who completed the game (n ¼ 10) was significantly
different (P 5 0.05) from the post-game urine specific
gravity (1.016 + 0.004; range 1.007–1.018). There
was no statistically significant relationship between
pre-game urine specific gravity and the volume of fluid
consumed (r ¼ 70.276, P ¼ 0.440; n ¼ 10) (Figure 2).
The pre-game thirst sensation of all participants
(n ¼ 15) was 4.2 + 1.6 (range 1–7). There was no
significant difference (P 4 0.05) in thirst sensation
of the 10 players who completed the game before
(4.0 + 1.5, range 1–6) and after (4.4 + 2.5, range
1–8) the match. Pre-game thirst sensation was not
correlated to pre-game urine specific gravity
(r ¼ 70.0868, P ¼ 0.768, n ¼ 15) or total volume
ingested (r ¼ 0.0871, P ¼ 0.767, n ¼ 10). The
mean value of drink palatability was 8.3 + 0.94
(range 7–9).
Discussion
This is the first study to report data on fluid balance
of Brazilian youth soccer players during an official
match where habitual hydration regimes were maintained. We observed that all the players lost weight
during the game (P 5 0.001) and the volume of fluid
consumed rarely matched fluid lost (only two players
40
R. P. da Silva et al.
Table I. Changes in body mass (BM), fluid intake, estimated sweat loss, and urine output for the players who completed the game (n ¼ 10)
and the substitutes (n ¼ 4).
Variable
Players (n ¼ 10)
Range
Substitutes (n ¼ 4)
Range
Pre BM (kg)
Post BM (kg)
Mass loss (kg)
Mass loss (%)
Fluid intake (L)
Sweat loss (L)
Urine output (L)
65.79 + 4.43
64.71 + 4.20*
1.08 + 0.55
1.62 + 0.78
1.12 + 0.39
2.24 + 0.63
0.12 + 0.10
61.30–76.20
60.60–74.50
0.40–2.10
0.59–3.15
0.47–1.76
1.48–3.25
0.0–0.29
64.02 + 1.75
63.85 + 1.71
0.17 + 0.04
0.27 + 0.06
0.55 + 0.10
0.60 + 0.12
0.25 + 0.10
61.90–65.70
61.80–65.50
0.10–0.20
0.16–0.31
0.40–0.70
0.34–0.71
0.11–0.32
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*Significantly different from pre BM (P 5 0.001).
Figure 1. The relationship between the volume of sweat lost and
the volume of fluid ingested by the players (n ¼ 10) during the
match.
Figure 2. The relationship between pre-game urine specific gravity
and total volume ingested during the match by the players
(n ¼ 10).
and the substitutes ingested sufficient drink to limit
body mass loss to less than 1% of the pre-game body
mass). The weight loss varied widely between players
ranging from minimal (0.40 kg; 0.59%) to substantial (2.10 kg; 3.15%) with mean values of
1.08 + 0.55 kg (1.62 + 0.78%). These values are in
line with that reported by Edwards and Clark (2006)
in recreational adult soccer players (1.6%; temperature 168C and 47% relative humidity) and by Veale
and Pearce (2009) in Australian adolescent soccer
players (1.53 kg; range 0–3 kg) during soccer matchplay (WBGT 20.1–31.48C and 42–66% relative
humidity). The mean volume of sweat lost by players
in the present study was more than 2 L (range 1.48–
3.25 L). This is not to say that all sweat losses
occurred only during playing time (80 min), as
players were sweating at different rates during nonplaying time (warm-up, half-time break, and immediately after the game). Although tropical natives
have a more efficient thermoregulatory system,
requiring less sweat production and evaporation for
temperature control (4dry heat exchange) (Hori,
1995; Magalhães et al., 2010), the hot weather in the
current study may have been a major influence on
the sweating response. It is worth noting that the
values of sweat loss in this study are higher than the
volume of 1.68 + 0.40 L reported by Maughan et al.
(2007) when non-tropical adults were evaluated
during a regular soccer match of 90 min duration.
However, the weather at the time of the match in the
study cited above (approximately 88C) was much
cooler than the weather in the present study (WBGT
29.38C). Indeed, Kurdak et al. (2010) reported a
greater sweat loss volume (3.1 L) when adult soccer
athletes played in a warm environment (34.38C).
All players in the present study drank water and a
carbohydrate-electrolyte drink. Players consumed
between 0.47 L and 1.76 L, and the percentage of
replaced sweat loss was *50% (1.12 + 0.39 L).
However, it is noteworthy that the ingestion of 400
mL of carbohydrate-electrolyte drink was recommended by the coaching staff and was not consumed
voluntarily. Studies have consistently reported that
soccer players do not ingest enough fluid to replace the
fluid lost during training or competition (AragónVargas et al., 2009; Shirreffs et al., 2006; Silva et al.,
2011). There is further evidence of this when players
practise activities in the heat (Kurdak et al., 2010; Silva
et al., 2011). Various factors influence fluid replacement by players in team sports like soccer, including
provision of individual bottles, proximity to bottles,
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Fluid balance of soccer players during competition
drink palatability, duration and number of opportunities to drink (Broad, Burke, Cox, Heeley, & Riley,
1996). In the present study, however, the mean value
of water palatability was of 8.3 + 0.94 (range 7–9) and
players had unlimited access to fluid and individual
bottles provided. Given these factors, a distinct
possibility exists that players in our study ingested
fluid that corresponded to half of the mean sweat loss
due to the nature of the game in which they have few
opportunities to drink. We made no record of when
the fluid was consumed. There were concerns about
influencing the normal drinking behaviour of the
players if the bottles were weighed at the times
necessary to obtain this information. However, we
observed that some water was consumed before kickoff, some at the half-time interval, and very few players
consumed water during the game itself. The fluid
intake by the substitutes (0.40–0.70 L) was enough to
match their sweat loss (0.34–0.71 L). The pre-game
warm-up and a constant pattern of soccer-specific
activities over the game might have contributed to
some sweat loss (0.60 + 0.12 L) that was easily
replaced due to the players’ proximity and constant
access to the drinks bottles.
There was no significant relationship between the
sweat lost and the fluid ingested by the players,
despite a more than trivial association (r ¼ 0.5),
perhaps confounded by a relatively small sample
size. Studies to date have also not found such a
relationship in adult soccer players (Maughan,
Shirreffs, Merson, & Horswill, 2005). Silva et al.
(2011) investigated young Brazilian soccer players
during training and observed a significant relationship between fluid intake and estimated sweat loss.
In that study, however, the coaching staff scheduled
regular breaks in activities to allow the players to
consume the fluid ad libitum and players had much
more opportunity to drink than the athletes in the
present study. Replication of the current design with
a greater number of participants might provide
increased power and further enhance our ability to
achieve statistical significance.
Studies that have measured the hydration status of
athletes in a free-living situation before exercise have
observed that they typically start the exercise
dehydrated (Bergeron, Waller, & Marinik, 2006;
Osterberg, Horswill, & Baker, 2009; Silva et al.,
2010). Data regarding pre-game hydration status of
adult soccer players are similar (Aragón-Vargas et al.,
2009; Decher et al., 2008; Maughan et al., 2005). In
the present study, we classified as dehydrated the
individuals with urine specific gravity above 1.020, as
suggested by the National Athletic Trainers’
Association for trained athletes (Casa et al., 2000).
Mean values of pre-game urine specific gravity
(1.021 + 0.004) suggest that the young players were
at the lower limit for significant dehydration.
41
Individual analyses make it clear that not all
players were well hydrated before the match (10
of 15 athletes had pre-game urine specific gravity
greater than 1.020) in spite of the game being
played late in the morning, thereby affording ample
opportunity for fluid intake in the hours beforehand. Decher et al. (2008) also observed that urine
specific gravity remained consistently high in active
youths participating in a 4-day sports camp (soccer
and American football). However, in the current
study, none of the players presented with urine
specific gravity greater than 1.020 after the match.
Nevertheless, this may not necessarily be interpreted as displaying better hydration during the
game, as players still developed mild dehydration
(1.62 + 0.78% of body mass) by the end of the
match.
When total fluid intake during the game was
correlated with the pre-game urine specific gravity
and thirst sensation, no significant relationship was
observed. This is in contrast to a previous report in
which the volume of fluid ingested by adult tropical
players in a match (WBGT 31.98C) was significantly
related to the pre-game urine specific gravity (Aragón-Vargas et al., 2009). This association, however,
was influenced by an outlier, and other studies have
also not found any relationship (Bergeron et al.,
2006; Osterberg et al., 2009). The reason we failed to
find an association among pre-game urine specific
gravity, thirst sensation, and fluid intake is not clear,
although factors regarding the thirst mechanism may
be responsible. The sensation of thirst typically lags
behind the fluid deficit, and dehydration may reach
2–3% of body mass before an increase in plasma
osmolality stimulates the thirst mechanism (Greenleaf, 1992).
Conclusion
Sweat loss and fluid deficits can be high (up to 3% of
body mass) in tropical young soccer players taking
part in a match played in the heat. The mean fluid
intake was about half of the mean sweat loss,
indicating that under official match-play conditions,
fluid replacement remains a challenge for certain
athletes, and a more effective strategy of fluid
replacement is required for players competing in the
heat. We conclude that it is worthwhile to educate
young soccer players about the importance of pregame hydration since several athletes were hypohydrated before kick-off.
Acknowledgements
We would like to thank FAPEMIG for providing the
necessary funding and all volunteers and researchers
involved who made this study possible.
42
R. P. da Silva et al.
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