Educational intervention on water intake improves hydration status and enhances exercise performance in athletic youth.

0.15 MB·English

by  Kavouras, S A

ScandJMedSciSports 22001112: 22: 684–689 &2011JohnWiley&SonsA/S
doi:10.1111/j.1600-0838.2011.01296.x
Educational intervention on water intake improves hydration status
and enhances exercise performance in athletic youth
S. A. Kavouras, G. Arnaoutis, M. Makrillos, C. Garagouni, E. Nikolaou, O. Chira, E. Ellinikaki, L. S. Sidossis
LaboratoryofNutrition&ClinicalDietetics,DepartmentofNutritionandDietetics,HarokopioUniversity,Athens,Greece
Corresponding author: Stavros A. Kavouras, PhD, FACSM, Laboratory of Nutrition & Clinical Dietetics, Department of
Nutrition and Dietetics, Harokopio University, 70 El. Venizelou Ave, 17671 Athens, Greece. Tel:[phone],
Fax:[phone],E-mail:[email protected]
Acceptedforpublication10January2011
We aimed to evaluate whether an intervention program dining and resting areas. Hydration status was improved
emphasizinginincreasedfluidintakecanimproveexercise significantly in the INT [USG: pre51.031(cid:2)0.09,
performanceinchildrenexercisingintheheat.Ninety-two post51.023(cid:2)0.012, Po0.05; urine osmolality (mOsm/
young athletes participated in the study (age: 13.8(cid:2)0.4 kgwater):pre5941(cid:2)30,post5782(cid:2)34,Po0.05],while
years, weight: 54.9(cid:2)1.5kg). Thirty-one (boys: 13, girls: nostatisticallysignificantchangeswerefoundintheCON
18) children served as the control group (CON) and 61 [USG: pre51.033(cid:2)0.011, post51.032(cid:2)0.013, P4
(boys: 30, girls: 31) as the intervention (INT). Volunteers 0.05; urine osmolality (mOsm/kg water) 970(cid:2)38 vs
had free access to fluids. Hydration was assessed on the 961(cid:2)38,P40.05].Performanceinanendurancerunwas
basisoffirstmorningurine.Aseriesoffieldtestswereused improved significantly only in INT (time for 600m:
to evaluate exercise performance. All tests occurred out- pre5189(cid:2)5s, post5167(cid:2)4s, Po0.05). Improving hy-
doorsinthemorning(meanambienttemperature5281C). dration status by ad libitum consumption of water can
Afterbaselinetesting,INTattendedalectureonhydration, enhance performance in young children exercising in the
and urine color charts were mounted in all bathrooms. heat.
Additionally,wateraccessibilitywasfacilitatedintraining,
Water and electrolyte balance are critical for the temperature (Epstein et al., 1983; Falk et al.,
function of all organs and indeed, for maintaining 1992a,b; Marino et al., 2000). This fact limits their
health in general. It has been shown that losses as relianceinevaporativeheatloss(Meyeretal.,1992).
small as 2% of body weight (BW) increase signifi- Furthermore, children, similar to adults, do not
cantly physiologic strain (Gonzalez-Alonso et al., drink enough to adequately replace water losses
1995), decrease exercise performance (Montain & under warm conditions and exhibit hypohydration
Coyle, 1992; Gonzalez-Alonso et al., 1997) and evenwhenfluidsareprovidedadlibitum,aphenom-
hinder the thermoregulatory advantages conferred enon described as involuntary dehydration (Bar-Or
by high aerobic fitness (Cadarette et al., 1984) and et al., 1980; Greenleaf, 1992; Wilk & Bar-Or, 1996).
heat acclimatization (Sawka et al., 1983). However, contrary to the aforementioned observa-
Ithasbeenalsodocumentedthatevenwhenwater tions, current research information fails to indicate
or sports drink availability is present, inadequate thermoregulatory differences in the heat between
fluidintakeduringexerciseunderwarmconditionsis children and adults, demonstrating that data in this
disadvantageous for both children and adults (Bar- specific field are not entirely clear (Falk & Dotan,
Oretal.,1980;Meyeretal.,1995).Earlystudieshave 2008; Rowland, 2008).
indicatedthatchildrenusuallyexhibitlowermaximal Furthermore, little information is available con-
aerobiccapacity,higheradiposityandlesssweatthan cerningthecapacityofchildrenexercisingintheheat.
do adults when exercising in warm environments, The majority of the research to date has been per-
due to their greater body surface area-to-mass ratio, formed in sedentary non-acclimatized children under
whichinturnleadstofasterheatabsorptionfromthe controlled environments (Bar-Or et al., 1980; Meyer
environmentwhenambienttemperatureexceedsskin et al., 1995; Wilk & Bar-Or, 1996; Iuliano et al.,
1998). Additionally, there is a lack of studies investi-
gating the relationship between the hydration status
Re-use of this article is permitted in accordance with the Terms
of children and their physical performance in free-
and Conditions set out at http://wileyonlinelibrabray.com/online
open#OnlineOpen_Terms. living situations. To our knowledge, the relation of
684
Water intake and endurance performance
hydration status in children exercising in free-living Protocol
situations has not been investigated systematically
Thedailyprograminthecampconsistedofanearlymorning
(Wilk et al., 2007; Rivera-Brown et al., 2008). A workout, a mid-day rest and an evening training. Hydration
recent work by McDermott et al. (2009) showed status was assessed in the morning of the second (pre) and
thatchildrenarrivedatafootballcamphypohydrated fourth(post)dayofthecamp(08:00hours)basedonthefirst
morning urine sample and BW was also measured. After a
and maintained this condition throughout their stay
standardized breakfast-snack, a specific warm-up was per-
leading to impaired recovery and subsequent perfor-
formed, including mainly light running and basic stretching
mance. The educational intervention used did not exercises. Afterward, children were divided into groups and
reveal a clear change in hydration status. performedaseriesoffieldperformancetestsrandomly:600m
It was hypothesized that facilitation of water maximum running test, 30m maximum sprint running test,
vertical jump and a skill test for volley ball and basketball.
intake will lead to significant enhancement in the
Vertical jump was measured by getting the children to reach
field tests. Therefore, the purpose of the present
upagainstaflatwall,withaflatsurfaceundertheirfeetand
study was to investigate the effect of a nutrition mark off the highest point they could reach flat-footed
intervention program emphasizing water consump- (standing height). Then, they were instructed to complete
tion on the prevention of dehydration, and in addi- threejumpsfromasquattingposition,markingoffthehighest
point they could reach. The distance between the two marks
tion, study the effects of hydration improvement in
(standingheightvshighestpoint)wasmeasuredandservedas
the physical performance of young athletes.
theirverticaljump.Theskilltestinvolleyballwasthenumber
ofsuccessfulserviceoutoffivetrialsthatwillreachaspecific
metal rectangular target (130(cid:4)78(cid:4)68cm) on the opposite
partofthecourt.Forbasketball,theskilltestconsistedofthe
Materials and methods number of point scored in five consecutive free throws from
the keyhole. Heart rate was measured during the tests with
Data collection occurred in a summer training camp during
telemetryanditwasrecordedimmediatelyaftertheendofthe
two consecutive 5 days in Loutraki, Greece during August
600m and 30m run. The performance tests were performed
2007. A total of 92 young trained volleyball or basketball
onlyinthesecondandfourthdayofthechildren’sstayinthe
athletes participated in the study; their physiological charac-
camp, without any earlier familiarization, in order to avoid
teristicsarepresentedinTable1.Inthefirstweek,31children
any biased results due to learning effect. The environmental
(boys:13,girls:18)servedasthecontrolgroup(CON)andat
temperaturesfordays2and4forthecontrolgroupwere27.0
thesecondweek61children(boys:30,girls:31)servedasthe and 29.01C and wet bulb temperature (WBGT) 21.5 and
intervention group (INT). Although this study design, where 20.01C, respectively, while for the intervention group envir-
two completely separate sets of youths were used, may have onmental temperatures were 29.01C for day 2 and 281C for
hadsomelimitationsconcerningthebetween-weekdifferences day 4, while WBGT was 20.0 and 211C, respectively. Statis-
inenvironmentalfactorshowever,thiswasunavoidabledueto
ticalcomparisonsbetweenWBGTvaluesforbothgroupsdid
all the extra hydration info provided in the INT group. The
notrevealanysignificantdifferences.
study was approved by the University human subjects com- Bottled water (Volvics, Puy De Dome, France) was dis-
mittee and all volunteers and their parents were informed
tributedtoallcampfacilities,whilekidshadfreeaccesstothe
about the nature of the study and gave informed written
camp’s cafeteria, which also provided sport and soft drinks.
consent. All subjected were healthy, active individuals and
Nevertheless, according to a specific Food Frequency Ques-
trainedregularlyatleastfor2years(atmean:threetimesper
tionnairethatwasprovided,mostofthechildrenweredrink-
week) and had a normal BMI for age, according to Cole
ingmainlywater.
criteria (Cole et al., 2007). A medical history questionnaire
was used to exclude participant with conditions that could
affecttheinterpretationofourdata,including:
Hydrationassessment
(cid:3)Evidenceofclinicallyrelevantcardiovascular,hematologic, Hydrationstatuswasassessedfromfirstmorningurinesamples
hepatic,gastrointestinal,renal,pulmonary,endocrineorpsy- based on urine specific gravity (USG) and urine osmolality
chiatrichistoryofdisease. (Uosm). Cut off point for euhydration was based on
(cid:3)Surgicaloperationondigestivetract,exceptpossibleappen- USGo1.020 and Uosmo700mOsm/kg water, according to
dectomy. the ACSM position statement (Sawkaetal., 2007). USG was
(cid:3)Regulardrugtreatmentwithin15daysbeforestartofthestudy. measuredwithatable-basedrefractometer(GastManufactur-
ing Inc., Benton Harbor, Michigan, USA). Urine osmolality
(cid:3)Inabilitytoparticipateintheentirestudy. was measured induplicate, byfreezingpoint depression (3D3
AdvancedOsmometer,AdvancedInstrumentsInc.,Norwood,
Massachusetts,USA).Amodifiedversionoftheenvironmental
symptomquestionnaire(Sampson&Kobrick,1980)wasused
Table1. Physiologicalcharacteristicsofthestudyparticipants at the end of the performance tests both pre- and post-
intervention. An exit camp questionnaire was also provided
Characteristics n592 CON531 INT561
onday5inordertoassessvolunteersperceptionregardingtheir
fluidintakeandpracticalissuesrelatedtofluidaccess.
Age(years) 13.8(cid:2)4.2 13.2(cid:2)2.3 14.0(cid:2)4.8
Gender(men/women) 43/49 13/18 30/31
Weight(kg) 54.9(cid:2)13.7 55.75(cid:2)2.5 54.5(cid:2)13.7
Interventionplan
Height(cm) 164(cid:2)13.9 165(cid:2)14.8 163.1(cid:2)13.4
Bodyfat(%) 19.2(cid:2)7.3 18.8(cid:2)7.4 19.4(cid:2)7.2 Followingtheseconddayevaluationinthecontrolgroup,no
instructions or feedback was given to the kids, but they had
Valuesaremeans(cid:2)SE. free access to fluids as they do during typical workouts or
685
Kavouras et al.
games. In the intervention group following the hydration
assessment and the performance testing, the athletes
participatedinaninterventionprogramthatconsistedofthe
following:
(cid:3)One-hourlectureonhydrationanditsbenefits,duringwhich
subjects were given instructions for maintaining optimal
hydration. Verbal andwritten key pointsfor maintenanceof
goodhydrationstatuswerealsoprovided.
(cid:3) The urine color chart (Armstrong et al., 1994, 1998) was
explainedandcolorcopiesweremountedinallbathroomsof
thecampfacilities.
(cid:3)Improvedwateraccessibilitythroughoutthefacilitiesofthe
sportscamp,intraining,diningandrestareaswithbottlesof
waterplacedeverywhere. Fig.1. Urine specific gravity (USG) before and after the
(cid:3)Duringsomeoftheworkouts,athleteswereweightedbefore intervention in the control and intervention group.
andafterwithminimalclothingtoidentifyfluidlossesduring *Statistically significant difference between pre and post in
theworkouts,whilenoinstructionsweregiven. eachgroup.
The control group hadexactly thesame conditions except
thatnoeducationalinterventionwasprovided.
Authorizedpersonsperformeddataentryinablindfashion
using a personal computer equipped with statistical software
SPSS16.Forpurposesof datacontrol, asecond, authorized
person re-entered the data; and then, a computerized cross-
control was performed to assess data conformity. Once data
conformitywasachieved,thedatawereconsideredcleanand
ready for analysis. Data are presented as mean(cid:2)SE or
frequencies. A two-way analysis of variance model was used
to check differences between the two groups and over time
(pre- and post-intervention) in normally distributed data.
Normality was tested by the Shapiro–Wilk test. For non-
normally distributed variables, their log-transformation was
usedtotestdifferences.Differencesindemographiccharacter-
Fig.2. Urineosmolalitybeforeandaftertheinterventionin
istics as well as changes between groups were tested by one-
thecontrolandinterventiongroup.*Statisticallysignificant
wayanalysisofvariance.AtypeIerrorof0.05orlesswasthe
differencebetweenpreandpostineachgroup.
thresholdforstatisticalsignificance.
out of 61) of the CON and INT group, respectively,
Results
were dehydrated before the intervention (second
The 92 young trained volleyball and basketball day). As a response to the intervention, the percen-
athletes participated in the study, were separated in tageofthesubjectsthatwereclassifiedasdehydrated
twogroups,thecontrol(CON)(age13.3(cid:2)0.4years, in the INT group decreased to 62.1% (P50.005),
weight 55.7(cid:2)2.5kg, height 1.66(cid:2)0.25m and body while there was no difference in the CON group
fat 18.9(cid:2)1.5%) and the intervention (INT) group (90.0%).
(age 14.1(cid:2)0.6 years, weight 54.5(cid:2)1.8kg, height Table 2 presents the results in the performance
1.63(cid:2)0.73m and body fat 19.4(cid:2)1.3%). Non sta- tests performed by the children. Endurance perfor-
tisticalsignificancewasfoundbetweenthecharacter- mance in the 600m running test was improved only
isticsofthestudyparticipants.Hydrationassessment in INT [pre: 189(cid:2)5s, post: 167(cid:2)4s (P50.009)]
showed that based on the USG criteria (o1.020), while no differences were found in the heart rate
96.7%(30outof31)and91.7%(56outof61)ofthe immediately after the test [pre: 191(cid:2)1bpm, post:
CON and INT group, respectively, were dehydrated 190(cid:2)1bpm (P40.05)]. No differences were found
on the second day of the camp. At the fourth day, between the pre and post intervention in both of the
96.7%(30outof31)and66.1%(40outof61)ofthe groupsinsprintperformanceandverticaljump.Skill
CONandINTgroup,respectively, wereclassifiedas test score for the CON group was 1.48(cid:2)1.0 and
dehydrated. The data showed that a significantly 1.48(cid:2)1.17,preandpost,respectively(P40.05).For
smaller percent of subjects was classified as dehy- the INT group, the same score was 1.50(cid:2)1.0 and
drated as a response of the intervention (P50.003) 1.55(cid:2)1.0, pre and post, respectively (P40.05).
(Fig. 1). At the end of the camp, athletes were asked
AsshowninFig.2,whendehydrationwasassessed different questions related to self-perception of the
based on the urine osmolality (4700mOsm/kg hydration. The results presented in Table 3, were
water), then 90.3% (28 out of 31) and 83.3% (51 reported to a score ranging from 1 to 10 (15very
686
Water intake and endurance performance
Table2. Performancetests
Test CON CON %change INT INT %change
pre post pre post
600m(s) 186(cid:2)10 177(cid:2)5 (cid:5)7.7(cid:2)2.2 189(cid:2)5 167(cid:2)4* (cid:5)12.7(cid:2)1.5
30m(s) 5.6(cid:2)0.1 5.6(cid:2)0.1 0.74(cid:2)1.06 5.7(cid:2)0.5 5.6(cid:2)0.6 (cid:5)1.07(cid:2)0.72
Verticaljump(cm) 26.3(cid:2)1.5 25.3(cid:2)1.8 (cid:5)0.9(cid:2)1.05 25.0(cid:2)1.0 24.6(cid:2)1.1 (cid:5)0.4(cid:2)1.10
Skilltest 1.5(cid:2)1.0 1.5(cid:2)1.2 0.4(cid:2)0.9 1.5(cid:2)1.0 1.6(cid:2)1.0 0.9(cid:2)0.3
Valuesaremeans(cid:2)SE.*Statisticallysignificantdifferencebetweenpreandpost.
bad, 55ok, 105great job) for the CON and Table3. Hydrationawarenessquestionnairescores
INT group. From the environmental symptoms
Questions CON INT
questionnaire, no differences were found among the
groups in symptoms related to heat or dehydration. Doyouthinkyoudidagoodjobkeeping 8.2(cid:2)2.4 9.0(cid:2)1.9
yourselfhydratedduringthecamp?
Didthecampencouragehydration? 7.2(cid:2)3.0 9.3(cid:2)1.6
Didthecampallowyoutimetodrink? 8.4(cid:2)2.4 9.9(cid:2)1.9
Discussion Werefluidsreadilyaccessibleatthecamp? 9.4(cid:2)1.7 9.5(cid:2)1.9
Wasthereanythingthatpreventedyou 0.2(cid:2)0.4 0.04(cid:2)0.2
The main finding of the study was that a relative fromhydratingduringthecamp?
simple but comprehensive intervention program
Valuesaremeans(cid:2)SE.
proved successful for enhancing hydration status
over just a 2-day period. Additionally, the improve-
ment of hydration status through ad libitum water USG values ofyoung soccer players, resulting in the
intake, in free-living young athletes training in the factthatathletesshoweduptopracticeinahypohy-
heat,ledtosignificantincreasesinenduranceexercise drated state (Stover et al., 2006; Kotsis et al., 2007).
performance. These high values indicate that for the exercising
To our knowledge, this research is the first field children,educationconcerningthedeleteriouseffects
study which finds enhanced performance related to of dehydration and the possibility of heat injuries
hydration status in the rarely studied youth popula- during exercise and on theother hand, thebeneficial
tion.Apossibleexplanationfor thisimprovementin effects of optimal hydration status should be a
endurance performance time, taking into considera- priority at camps, games and practices.
tion the fact that no differences were found in the However, the intervention program that was used
heart rate immediately after the 600m performance through the lectures concerning the importance of
test, is that stroke volume was better preserved, goodhydrationonhealthandthefreeaccesstofluids
consequently cardiac output was maintained and as resulted in a significant decline in the percentage of
a final result, aerobic capacity was significantly im- thedehydratedchildrenintheinterventiongroup.In
proved.Theseconclusionsareinaccordancewiththe arecentstudy,itwasconcludedthattheprovisionof
results by Gonzalez-Alonso et al. (2000). Interest- two 591mL bottles of water or sport drink, one
inglyinarecentstudy,significantlygreaterheartrate consumed between dinner and sleep and the other
was observed in dehydrated athletes at the end of before morning training, is a simple method which
submaximalor10and20minafterthemaximaltrail leads to significant improvement to the hydration
running (Casa et al., 2010). However, in the present statusofhigh-schoolfootballplayers,asindicatedby
study the duration of the performance test was USG values (Stover et al., 2006). Therefore, inter-
shorter and more intense inducing in both trials the vention to teach and facilitation of hydration acces-
same, near maximal, heart rate. Similarly with Casa sibility, along with simple and realistic hydration
et al. (2010), no differences in heart rate during strategies will benefit youths exercising at summer
exercise were found during maximal exercise. camps.
Furthermore,althoughtheimprovementobserved There is a plethora of investigations examining
in performance time could be influenced by a learn- fluid intake before, during and after training and
ing effect from the first trial, no performance en- competition that have suggested that a lack of
hancement was revealed in the control group, adequate fluid intake impairs or decreases physical
supporting the finding of this investigation. performance (Sawka et al., 1983; Cadarette
Thehighincidenceofdehydrationobservedduring et al.,1984; Montain & Coyle, 1992; Gonzalez-
the summer camp, pointed out by the USG and Alonso et al., 1995, 1997; Armstrong et al., 1997;
Uosm values on the baseline measurements, is in Maughan, 2003). To our knowledge, no study until
accordance with the values measured by two indica- now has examined the effect of hydration status on
tive studies, which found consistently high baseline endurance performance in children. From the data
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Kavouras et al.
presented, it is documented that free accessibility in through the environmental symptoms questionnaire,
water and education concerning the benefits of which was provided, probably due to the fact that it
optimal hydration status, which in turn increased depictsincidenceandseverityofsymptomsproduced
the consumption of fluids, led to a significant im- byexposuretoextremeclimaticconditions(Sampson
provement to the endurance test (600m) performed & Kobrick, 1980).
by children.
Nevertheless, no significant differences were ob- Perspectives
served between the two groups in sprint perfor-
Few studies have investigated the capacity of chil-
mance, vertical jump and skill tests. In a review by
dren exercising in the heat and the relationship of
Maughan (2003), it is shown that muscle strength
their hydration status and performance. In the pre-
and sprint performance appear to remain relatively
sentstudy,wedemonstratedthattheimprovementin
unaffected under hypohydration state, explaining in
part the observed non-significant results in sprint hydration status, through an educational interven-
performance and vertical jump. However, Shirreffs tion led to significant enhancement in endurance
performance in exercising children. It is obvious
et al. (2004) suggests that mild dehydration reduces
that continued efforts must be made by coaches,
the subjective perception of alertness and ability to
camp staff and athletes, in order to educate the
concentrate.
youths toward the benefits of optimal hydration
Finally, in the present study it was observed that
state, the development of more efficient hydration
the subjects in both the control and the intervention
strategiesandthemethodsofassessingandmonitor-
groupwereinahypohydratedstatethroughouttheir
stay in the summer camp. Even though, most of the ing their hydration status.
athletes in the control group and in the intervention
groupremaineddehydratedtheyperceivedthatwere Keywords: urinespecificgravity,fluidingestion,sport
doing good job staying hydrated (8.2 out of 10). In camp,hydrationstate,dehydration,children,environ-
accordance with the results by a recent study, the mental symptoms questionnaire.
children in the camp generally recognized whether
they were doing a good or a bad job hydrating
(Decher et al., 2008). However, they established a Acknowledgements
lack of transforming the hydration knowledge into
The study was supported by Danone Research, Daniel Car-
effective hydration strategies. At last, it is important
asso Research Centre, France. No conflict of interest or any
to mention the lack of any significant differences financialdisclosureexists.
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