Original Article

Hydration and sweating responses to hot-weatherfootball competition

S. S. Kurdak1, S. M. Shirres2, R. J. Maughan2, K. T. Ozgunen1, C. Zeren1, S. Korkmaz1, Z. Yazici1, G. Ersoz3,

M. S. Binnet4, J. Dvorak5

1Department of Physiology, Division of Sports Physiology, Cukurova University, Balcali, Adana, Turkey, 2School of Sport, Exercise& Health Sciences, Loughborough University, Loughborough, UK, 3College of Physical Education & Sports, Ankara University,Ankara, Turkey, 4Ibn-i Sina Hospital, Ankara University School of Medicine, Ankara, Turkey, 5Schulthess Clinic, F-MARC, Zurich,SwitzerlandCorresponding author: Dr Susan M. Shirres, School of Sport, Exercise & Health Sciences, Loughborough University,Loughborough LE11 3TU, UK. Tel: 144 1509 226332, E-mail: s.shirres@lboro.ac.uk

Accepted for publication 29 April 2010

During a football match played in warm (34.3 0.6 1C),humid (64 2%rh) conditions, 22 male players had theirpre-match hydration status, body mass change, sweat lossand drinking behavior assessed. Pre-match urine specicgravity (1.012 0.006) suggested that all but three playerscommenced the match euhydrated. Players lost 3.1 0.6 Lof sweat and 45 9mmol of sodium during the 90-minmatch and replaced 55 19% of their sweat losses andhence by the end of the game were 2.2 0.9% lighter. Thewater volume consumed during the game was highly variable(1653 487mL; 7412387mL) but there was a strongerrelationship between the estimated pre-game hydration

status and water volume consumed, than between sweatrate and water volume consumed. In a second match, withthe same players 2 weeks later in 34.4 0.6 1C,65 3%rh, 11 players had a sports drink available tothem before and during the match in addition to water.Total drink volume consumed during the match was thesame, but approximately half the volume was consumed assports drink. The results indicate that substantial sweatwater and electrolyte losses can occur during match play inhot conditions and a substantial water and sodium decitcan occur in many players even when water or sports drink isfreely available.

Exercise in the heat adds thermal stress to the bodyand it typically responds by sweating in an attemptto control body temperature. This, however, has thepotential to disrupt body water and electrolytebalance. It is known that substantial body tempera-ture increases can occur during football match play(Rico-Sanz et al., 1996; Mohr et al., 2004; Edwards& Clark, 2006) and that signicant sweat volumeand electrolyte losses can occur in football playersduring training and match play (Maughan et al.,2004, 2005, 2007; Shirres et al., 2005; Shirres &Maughan, 2008). These losses can be highly variablebetween individuals even when performing the sameexercise at the same time in the same conditions(Shirres et al., 2006). Also, at present, there are farmore data available from training scenarios thanfrom match situations and indeed there are currentlyno data in the scientic literature describing thesweating and body-temperature responses of foot-ball players playing competitive matches in a warmenvironment. This, therefore, was the aim of thispresent study.

Materials and methods

Data were collected before and during two of three competitivefootball matches played in the summer of 2008. Twenty-twoplayers (age 20 2 years, height 176 2 cm, mass 68 7kg)played in the matches, which occurred outdoors, at the sametime in the afternoon, in July in the southern Turkish city ofAdana. The matches were FIFA-regulation 90-min matches.The environmental conditions during the matches are shown inTable 1. Before undertaking any data collection, ethics com-mittee approval was obtained from Cukurova University andall subjects gave their written informed consent to participation.

Approximately 5 h before the start of the match, the playersswallowed an ingestible temperature pill (VitalSense

s

, MiniMitter Co. Inc., Bend, Oregon, USA). Subjects ate a standar-dized pre-match meal of sandwiches 3 h before the start of thematches. This meal was the same before both matches. Onarrival at the match venue, approximately 45min before thestart of the match, players were asked to empty their bladderas fully as possible and keep a 20mL sample in a containerprovided to them. The specic gravity of this sample wasdetermined by refractometry (Atago, Tokyo, Japan) and wasused to estimate the pre-match hydration status (Shirres,2003; Sawka et al., 2007).

Over a 15-min period from 30 to 15min before the startof the match, all players were weighed to the nearest 20 g

Scand J Med Sci Sports 2010: 20(Suppl. 3): 133139 & 2010 John Wiley & Sons A/S

doi: 10.1111/j.1600-0838.2010.01218.x

133

on an electronic balance (Kurdaklar Scale, Adana, Turkey)when wearing only their underwear. Then during the rstmatch only, immediately after being weighed, players wereprepared for sweat sample collection as described pre-viously (Maughan et al., 2007; Maughan & Shirres,2008). Briey, players had absorbent patches (Tegaderm1-pad, 3M, Loughborough, UK) placed on four locations:their forearm, thigh, chest and back, all on the right side oftheir body. Before sticking the patches to the skin, thelocations were washed thoroughly with deionized water anddried with electrolyte-free gauze. These patches remained inplace for the warm-up and rst half of the match. As soonas the referee stopped the match for the half-time break,players had patches removed with electrolyte-free forcepsand each patch was placed in an electrolyte-free container,which was sealed immediately after the patch was placedwithin it.

Within the last 15min before the game, players were ttedwith a heart rate monitor combined with a global positionalsystem receiver (Forerunner 305, Garmin, Southampton, UK)that were worn during the match, using the same methods andprocedures as reported in an accompanying paper (Ozgunenet al., 2010).

On completion of the 90-min matches, players werereweighed on the same balance as their pre-match mass wasdetermined, again wearing only their underwear. This wascompleted within 15min of the end of the match: playerswere not allowed to eat or drink until after they had beenweighed.

During the rst match, all players had access to drinkingwater. During the second match, one team (Team W) hadaccess to drinking water only while the other team (Team SD)had access to both drinking water and a commercially avail-able sports drink (Powerade, Coca Cola, Istanbul, Turkey).All bottles were individually numbered and players only drankfrom bottles assigned to them. During the rst match, drink-ing was neither encouraged nor discouraged before and duringthe match and players were left to behave as they wished withregard to drinking. During the second match, the players whowere provided with the sports drink in addition to water wereinformed that there were limitless quantities and they coulddrink freely and have as much as they wished. In bothmatches, sponges and non-drinking water were provided bythe pitch side for players who wanted to pour water overthemselves during the match. All drink bottles were weighedon electric scales (LS2000, Ohaus, Leicester, UK), measuringto the nearest 1 g, before and at the end of the match todetermine the volume consumed by each player. A volume of1mL of water/sports drink was assumed to weigh 1 g for thepurposes of this study.

Some players wanted to urinate after the rst body massmeasurement and before the second measurement were made.These players were allowed to do so but were asked to collectthe entire volume in a container provided. The mass of thiswas determined on electric scales (LS2000, Ohaus) measuringto the nearest 1 g, assuming 1mL of urine weighed 1 g, and thepost-exercise body mass measurement was corrected to takethis mass into account.

From the rst match, the volume of sweat collected in eachpatch was determined gravimetrically on electric scales(AC100, Mettler, Zurich, Switzerland) measuring to the near-est 0.0001 g. The mass of the patch and container into which itwas placed was determined previously and the sweat volumewas determined by assuming 1mL of sweat weighed 1 g whenthe storage tube and its contents were reweighed. The sweatcollected was analyzed for sodium (Na1) and potassium (K1)concentrations by ame photometry (Corning, 410C, Sher-wood Scientic, Cambridge, UK).

Statistical analysis

Data were tested for normality of distribution by the Kolmo-grovSmirnov and ShapiroWilk tests, for skewness andkurtosis by looking at the ratio of the mean of the relevantvalue to its standard error and for homogeneity of variance.Relationships between parameters were investigated by Pear-son correlations. Comparisons between paired data were madeusing the paired t-test; comparisons between data fromdierent subjects were by the unpaired t-test. All statisticalanalyses were performed using SPSS v 16. Data are presentedas mean SD and, when of interest, the range of data is givenin square parentheses.

Results

The pre-match urine specic gravity data (Table 2)indicated that players, on average, started the matchesin a euhydrated condition (o1.020; Sawka et al.,2007). However, examination of the individual dataindicated that three players in the rst match and twodierent players in the second match presented withpre-match urine specic gravities41.020, which maybe indicative of a hypohydrated condition.In all four game halves, the players of Team W

always covered the same distance as the players inTeam SD (P40.250) averaging 4158 386m perhalf. In the rst match, there was no dierence inthe distance covered in each of the two halves byeither team (P40.09) but in the second match,players in both teams covered a greater distance inthe second half (4298 363m) than in the rst half(3913 284m) (Po0.013).The intestinal temperatures recorded before, dur-

ing and at half time of each match are shown inFig. 1. The temperature increased over the durationof the rst half, then decreased over the half timebreak and the rst part of the second half beforeincreasing again over the second half of the match.The highest temperature recorded in the rst matchwas at half time in one player of Team W and at the35th minute of the second half in another player ofTeamW and was 40.6 1C in both cases. In the secondmatch, the highest temperature recorded was 40.3 1Cand this was recoded in two players of TeamW at the20th minute of the rst half.A summary of the data collected before, during

and after each match is shown in Table 2. Therewas no dierence in any of the measured parametersbetween the two teams in the rst match (P40.437).

Table 1. Environmental conditions of temperatures (1C) and relativehumidity (%) during the matches

Match 1 Match 2

Temperature (1C) 34.3 0.6 34.4 0.6Relative humidity (%) 64 2 65 3Heat index apparent temperature (1C) 45 2 46 2

Data are presented as mean SD.

Kurdak et al.

134

There were also no dierences in any of the measuredparameters between the two matches for Team Wwho had only water available to them before andduring each match (P40.284). However, the pre-match urine specic gravity for Team SD was sig-nicantly lower before their second match than it wasbefore the rst match (P5 0.030) and it was alsolower than that of Team W before the second match(P5 0.007).In neither match was there a relationship between

the pre-match urine specic gravity and the bodymass loss over the course of the matches (Fig. 2), butthere was a signicant correlation between pre-matchurine specic gravity and the drink volume consumedduring the matches (Fig. 3). The relationship betweensweat rate and drink volume consumed was notsignicant (Fig. 4).In the second match, when 11 players in one team

had both the sports drink and water available tothem, they consumed the same volume (1347 411mL) as they had done in the rst match(1474 423mL; P5 0.294) when only water wasavailable to them. On average, they consumed equalamounts of water (0.8 0.5 L) and sports drink(0.5 0.3 L) during this match (P5 0.197). How-ever, one individual (the goalkeeper) consumedonly plain water during the match.

Discussion

The results of this study indicate that substantialsweat water and electrolyte losses can occur duringmatch play in hot conditions. These sweat water andelectrolyte losses are similar to those reported pre-viously for elite professional players training in hotenvironments (Shirres et al., 2006); e.g. in 26 maleprofessional players, training for 90min when theenvironment was 32 3 1C, 20 5% rh and wetbulb globe temperature was 22 2 1C, the estimatedsweat volume lost was 2193 365mL (16723138mL) (Shirres et al., 2005). Further, eventhough water was freely available to players duringthe rst match, many players developed a signicantdegree of hypohydration. Indeed, 16 of the 22 playerslost42% of their body weight over the course of thematch and on average 55 19% of the sweat volumelosses were replaced by drinking over the course ofthe match. At the extremes, one player drank avolume of water greater than his sweat loss, consum-ing approximately 200mL more than the estimatedsweat volume, and one player drank almost 3 L lessthan his sweat loss. Fluid intake across both gamesranged from 738 to 2387mL, with a mean intake of1544mL. This is substantially higher than the mean( SD) intake of 0.84 0.47L reported for playersin a competitive game played in a cool environment(Maughan et al., 2007).Ta

ble2.

Bod

ymassandbo

dymassloss,drink,

urineandsw

eatvolumes,pre-match

urine-specificgravity

and(w

here

collected)sw

eatsodium

andpo

tassium

concentrationandestim

ated

losses

Match

1Match

2

Team

WTeam

SD

Team

WTeam

SD

Pre-m

atch

body

mass(kg)

70.66

7.41

[50.16

78.70

]65

.91

4.79

[59.70

73.50

]71

.36

8.40

[49.72

80.26

]66

.52

4.94

[60.10

73.78

]Post-match

body

mass(kg)

69.29

7.01

[50.28

77.60

]64

.26

4.59

[57.62

70.58

]69

.76

7.94

[49.52

79.08

]64

.80

4.71

[58.62

71.70

]Bod

ymassloss

(kg)

1.37

0.62

[gainof

0.12

1.96loss]

1.65

0.67

[0.20

2.92

]1.60

0.66

[0.20

2.22

]1.71

0.66

[0.04

2.52

]Bod

ymassloss

(%)

1.88

0.89

[gainof

0.24

2.89loss]

2.49

0.94

[0.30

3.97

]2.19

0.86

[0.40

3.04

]2.56

0.93

[0.06

3.47

]Drink

volumeconsum

ed(m

L)18

32

499[741

238

7]14

74

423[929

220

3]15

21

354[114

422

82]

1347

411[738

216

0]Urine

volume(m

L)69

60[01

59]

46

50[01

55]

43

58[01

62]

46

54[01

76]

Urine

specificgravity

1.01

2

0.00

6[1.004

1.025

]1.01

0

0.00

6[1.003

1.022

]1.01

2

0.00

8[1.003

1.030

]1.00

6

0.00

3[1.003

1.014

]Num

berwith

urine-specificgravity

greater4

1.02

02

12

0Sweatvolume(L)

3132

603[215

938

43]

3077

545[240

338

67]

3081

833[147

744

02]

3013

551[220

039

82]

Sweatsodium

concentration(m

mol/L)

43

11[27

59]

46

8[25

53]

Sweatpo

tassium

concentration(m

mol/L)

3.5

0.5[2.94

.0]

3.5

0.3[3.23

.9]

Sweatsodium

loss

(mmol)

137

50[87

219]

140

26[97

189]

Calculatedsw

eatsaltloss

(g)

8.0

2.9[5.11

2.8]

8.2

1.5[5.61

1.0]

Valuesaremean

SDwith

theminim

umandmaxim

umvalues

insquare

parentheses.

Hydration in hot-weather football matches

135

In the second match, when the players in one teamwere given a sports drink and were encouraged todrink freely and as much as they desired, theseplayers did produce a pre-match urine sample witha lower specic gravity and no players had a urinespecic gravity41.014, perhaps suggesting that theydrank more in the lead up to this game than beforethe previous match. However, during the match,there was no change in the overall hydration out-come of these players. They consumed the same

overall drink volume, sweated the same amountand thus completed the match with the same extentof body mass loss. These players were not accus-tomed to having sports drinks freely available in thelead up to the matches nor during their matches. Thenovelty factor may have been expected to cause themto consume more overall, but this did not materialize.This may have been because they were familiar withadvice not to introduce new dietary practices beforegames, but this is only speculation.

0.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

1.0000 1.0050 1.0100 1.0150 1.0200 1.0250Pre-match urine specific gravity

Body

mas

s lo

ss (%

)

Fig. 2. Match 1 pre-match urine specic gravity and the body mass loss (%) over the course of the match. There is nosignicant relationship (r25 0.005, P5 0.749). Data from match 2 are shown in the smaller gure.

37.0

37.5

38.0

38.5

39.0

39.5

40.0

40.5

Start 5 20 35 Half time 5 20 35Time (minutes)

Tem

pera

ture

(C)

Match 1, Team SDMatch 1, Team WMatch 2, Team SDMatch 2, Team W

Fig. 1. Intestinal temperature (1C) before, during and at half time of the match. Values are mean SD.

Kurdak et al.

136

The data show a large elevation in core tempera-ture during the game, with the highest values tendingto be achieved toward the end of the rst half of thegame. This is similar to the response observed insimilar conditions as reported in the companion

paper (Ozgunen et al., 2010). In that study, peak Tcwas also recorded at about the 30th minute of thematch, at values of 39.1 0.4 1C for a match playedat 34 1 1C and 38 2% relative humidity, and at39.6 0.3 1C for a match played at 36 0 1C and

0

500

1000

1500

2000

2500

3000

1.0000 1.0050 1.0100 1.0150 1.0200 1.0250Pre-match urine specific gravity

Wat

er v

olum

e co

nsum

ed (m

l)

Fig. 3. Match 1 pre-match urine specic gravity and the drink volume consumed (mL) during the match. There is a signicantrelationship (r25 0.218, P5 0.028). Data from match 2 are shown in the smaller gure.

0

500

1000

1500

2000

2500

3000

1.400 1.600 1.800 2.000 2.200 2.400 2.600Sweat rate (l/h)

Drin

k vo

lum

e (m

l)

Fig. 4. Match 1 sweat rate (l/h) and the drink volume consumed (mL) during the match. There is no signicant relationship(r25 0.051, P5 0.311). Data from match 2 are shown in the smaller gure.

Hydration in hot-weather football matches

137

61 1%rh. This contrasts with the data of Edwardsand Clark (2006), who, also using an ingestibletemperature sensor system, found that the highesttemperatures were recorded at the end of gamesplayed in cooler conditions (1619 1C). There maybe limitations to the use of the ingestible temperaturesensor system when cool water is ingested duringexercise, as was the case in this study. Wilkinsonet al. (2008) suggested that ingestion of a relativelylarge bolus (250mL) of chilled water (58 1C) causedtransient excursions of 2 1C or more of the measuredtemperature. Goodman et al. (2009) suggested that atleast 5 h should elapse between ingestion of thetemperature sensors and the start of the monitoringperiod. In the present study, this amount of time wasallowed, but some individual values may have beenaected by the temperature of the ingested drinks.The temperature values should perhaps therefore beconsidered to be an underestimate of the true value.The intestinal temperature of these players duringeach of these two matches was the same as was thedistance that they covered. Hence, taking this infor-mation and the knowledge that the environmentalconditions were the same for the two matches, it isperhaps not surprising that the sweating responsewas the same. Had the players drinks been chilled,the body temperature rise may have been attenuated(Lee & Shirres, 2007; Lee et al., 2008a, b) and thusthe sweating rate may have been reduced.There is not a substantial body of data available on

which to ascertain conclusively any inuence ofhypohydration on football performance. Indeed, itis probably not possible to assess the inuence ofhydration status on football performance; successfulperformance is ultimately a winning performance,which is inuenced by physical, cognitive and otheraspects, including tactics and other external inu-ences. It is possible to investigate the inuence ofhydration status on some of the types of activitiesand processes that contribute to football perfor-mance, but even for this, there is limited informationavailable on which to draw strong conclusions (Shir-res, 2009). Endurance exercise is the type of perfor-mance for which there are the most reliable dataavailable and the current evidence suggests thatreductions in body mass in the order of 27%signicantly reduce endurance exercise performance,particularly in environments that are warmer than30 1C (Cheuvront et al., 2003). Football certainly hasan endurance aspect with in the order of 10 kmtraveled by outeld players over the course of a 90-min match (Bangsbo et al., 2006). As the matchreported here was played in warm conditions, itwould be reasonable to surmise that the enduranceaspect of these soccer players performance would benegatively inuenced. However, it is feasible thatplaying style was altered to account for this, thus

reducing the endurance aspect or in other words, thedistance covered by the players. Without studyingthese players in other situations, we do not know ifthis was the case. From studies that have investigatedaspects of football performance (McGregor et al.,1999; Edwards et al., 2007), reductions in the abilityto perform soccer-specic tests of dribbling andintermittent-type running/walking have been demon-strated in laboratory tests. McGregor et al. (1999)reported that uid replacement with avored water,sucient to limit body mass loss to 1.4% prevented areduction in soccer skill performance in comparisonwith a 5% deterioration in performance when bodymass was reduced by 2.5%. Edwards et al. (2007)indicated that body mass reductions of approxi-mately 2% resulted in a reduction in intermittent-type running/walking test performance in compar-ison with a trial when drinking resulted in a bodymass reduction of only 0.7%.It seems likely that all but three players were

euhydrated when they started the rst match andall but two started the second match euhydrated.Unlike data from a match played in cool conditions(Maughan et al., 2007), there was a signicantrelationship between the pre-match urine specicgravity and water volume consumed during thematch. Similar measurements made on elite playerstraining in a cool (5 1C) environment also showed arelationship between the pre-training hydration sta-tus, as assessed by urine osmolality, and the amountof uid consumed during the session (Maughanet al., 2005). There was still a considerable variationin the volume consumed, but it is interesting to notethe presence of this relationship in the absence of asignicant relationship between sweat rate and drinkvolume. The rules and nature of football matches dohave a signicant impact on the opportunities playershave to access drinks, but further research mayusefully verify this nding and address the mechan-isms that drive drinking behavior according to thephysiological situation before exercise rather thanthat during exercise.

Perspectives

The results of this study indicate that football playerscan nd themselves under considerable physiologicalstress if they play a match in warm or hot environ-mental conditions. Substantial sweat water and elec-trolyte losses can occur in this situation even whendrinks are freely available to players in accordancewith current FIFA rules.

Key words: hydration status, sweat loss, sweat com-position.

Kurdak et al.

138

Acknowledgements

The authors would like to thank the players of University ofAnkara Soccer Team for playing in these matches. AlsoAdana Football Club and its sta for allowing use of its pitchand facilities, and Coca-Cola, Turkey, for providing the

Powerade drinks for the second match. The assistance ofNuri Yildiz and Ercan Yeldan of Cukurova University isalso acknowledged.

Conicts of interest: The authors have no potential conictsof interest.

References

Bangsbo J, Mohr M, Krustrup P.Physical and metabolic demands oftraining and match-play in the elitefootball player. J Sports Sci 2006: 24:665674.

Cheuvront SN, Carter R III, Sawka MN.Fluid balance and endurance exerciseperformance. Curr Sports Med Rep2003: 2: 202208.

Edwards AM, Clark NA.Thermoregulatory observations insoccer match play: professional andrecreational level applications using anintestinal pill system to measure coretemperature. Br J Sports Med 2006: 40:133138.

Edwards AM, Mann ME, Marfell-JonesMJ, Rankin DM, Noakes TD,Shillington DP. Inuence of moderatedehydration on soccer performance:physiological responses to 45min ofoutdoor match-play and the immediatesubsequent performance of sport-specic and mental concentration tests.Br J Sports Med 2007: 41: 385391.

Goodman AD, Keneck RW, CadaretteBS, Cheuvront SN. Inuence of sensoringestion timing on consistency oftemperature measures. Med Sci SportsExerc 2009: 41: 597602.

Lee JKW, Shirres SM. The inuence ofdrink temperature onthermoregulatory responses duringprolonged exercise in a moderateenvironment. J Sports Sci 2007: 25:975985.

Lee JKW, Shirres SM, Maughan RJ.The inuence of serial feeding of drinksat dierent temperatures onthermoregulatory responses duringcycling. J Sports Sci 2008a: 26:583590.

Lee JKW, Shirres SM, Maughan RJ.Cold drink ingestion improvesexercise endurance capacity in the heat.Med Sci Sports Exerc 2008b: 40:16371644.

Maughan RJ, Shirres SM. Assessinghydration status and makingrecommendations. Int J Sport NutrExerc Metab 2008: 18: 457472.

Maughan RJ, Shirres SM, Merson SJ,Horswill CA. Fluid and electrolytebalance in elite male football (soccer)players training in a cool environment.J Sports Sci 2005: 23: 7379.

Maughan RJ, Merson SJ, Broad NP,Shirres SM. Fluid and electrolyteintake and loss in elite soccer playersduring training. Int J Sports NutrExerc Metab 2004: 14: 333346.

Maughan RJ, Watson P, Evans GH,Broad N, Shirres SM. Water balanceand salt losses in competitive football.Int J Sports Nutr Exerc Metab 2007:17: 583594.

McGregor SJ, Nicholas CW, LakomyHKA, Williams C. The inuence ofintermittent high-intensity shuttlerunning and uid ingestion on theperformance of a soccer skill. J SportsSci 1999: 17: 895903.

Mohr M, Krustrup P, Nybo L, NielsenJJ, Bangsbo J. Muscle temperature andsprint performance during soccermatches benecial eects of re-warm-up at half-time. Scand J Med Sci Sports2004: 14: 156162.

Ozgunen KT, Kurdak SS, Maughan RJ,Zeren C, Korkmaz S, Yazici Z, ErsozG, Shirres SM, Binnet MS, Dvorak J.Eect of extreme environmentalconditions on physical activity patternsand thermoregulation of football

(soccer) players. Scand J Med SciSports 2010: 20(Suppl. 3): 140147.

Rico-Sanz J, Frontera WR, Rivera MA,Rivera-Brown A, Mole PA, MeredithCN. Eects of hyperhydration on totalbody water, temperature regulationand performance of elite young soccerplayers in a warm environment. Int JSports Med 1996: 17: 8591.

Sawka MN, Burke LM, Eichner ER,Maughan RJ, Montain SJ, StachenfeldNS. Exercise and uid replacement.Med Sci Sports Exerc 2007: 39:377390.

Shirres SM. Markers of hydrationstatus. Eur J Clin Nutr 2003: 57(Suppl.2): S6S9.

Shirres SM. Hydration, uids andperformance. Proc Nutr Soc 2009: 68:1722.

Shirres SM, Aragon-Vargas LF,Chamorro M, Maughan RJ, SerratosaL, Zachwieja JJ. The sweating responseof elite professional soccer players totraining in the heat. Int J Sports Med2005: 26: 9095.

Shirres SM, Maughan RJ. Water andsalt balance in young male footballplayers in training during the holymonth of Ramadan. J Sports Sci 2008:26(Suppl. 3): S47S54.

Shirres SM, Sawka MN, Stone M.Water and electrolyte needs forfootball training and match-play.J Sports Sci 2006: 24: 699707.

Wilkinson DM, Carter JM, RichmondVL, Blacker AD, Rayson MP. Theeect of cool water ingestion ongastrointestinal pill temperature.Med Sci Sports Exerc 2008: 40:523528.

Hydration in hot-weather football matches

139