FATIGA Y GESTO TÉCNICO

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O R I G I N A L I N V E S T I G A T I O N SInternational Journal ot Sports Physiology and Performance. 2009, 4, 163-1752009 Human Kinetics, Inc.

The Effect of 45 Minutes of Soccer-Specific Exercise on the Performance ofSoccer SkillsKeeron J . Stone and Jonathan L. Oliver

Purpose: The aim of ihe Miidy was to examine ihc effect of fatigtie, developed duringprolonged high-inlcnsity intemiittetil exercise, on the performa nce of soccer shootingand dribbling skill. Methods: Nine semiprofessional soccer players with a mean ageof 20,7 1.4 years volunteered to participate in the study. Pariicipants completed aslalom dribble tesi and the Loiighborough Soccer Shooting Tesi (LSST). before anddirectly following the performance of three t5-min bouts of a modified version of theLoughborough intermittent Shuttle Tesi (LIST), Results: Mean heart rates and mean15-m sprint times remained unchanged across the three bouts of the LIST Followingthe LIST slalom dribbling time increased significantly by 4.5 4.()'7< iP = .(KW).while the mean total poitits scored during the LSST was signihcantly redttced by 7,6+ 7.0 points {P= .012). When fatigued the frequency of shots in the LSST achievingthe highest score of 5 points was reduced by 47% while the frequency of shots achiev-ing the lowest 0 point score increased by 5 %. Conclusion: Results show that while45 min of exercise caused no decrements in sprint pcrfonriance there were significantred uctio ns in the ability to perform soc cer-s pec i He skills. Both the spe ed (dribb lingtime) and accuracy (shot perfonnance) with which soccer-specific skills were exe-cuted was impaired following exercise replicating one-half of a soccer match.Keywords: Fat igue, shoot ing , d r ibb l ing , spr in t ingPetfortnatice in soccer is dependent upon many factors, including, technical.tactical, mental and physiological.' Throughout the course of a match players willexperience fatigue, manifested through a reduced work rale, a reduced ability toperfbrtn high intensity exercise' and a progressive reduction in muscle strengthtoward the end of match-play,' Resistance to fatigue is a key factor which deter-mines the effectiveness of a player's ability to continually peribrm cflicienl andprecise movements within soccer.-* Lyons et al^ highlighted that the developmentof fatigue may be the determinitig factor of success and failure, the differencebetween winning and losing. In addition, soccer is characterized not only by a


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164 Stone and OliverW hile soccer involves a mu lt ipl icity of s ki l ls, Re il ly and Holmes'' describedthat the most freque ntly used actions of passing, drib blin g and con tro lling are thefundamental skills that are essential for retaining possession and are precursorsfor the com pletion o f a skilled performance, regardless of playing position or skilllevel. The ac tion of shooting may be considered to be an even m ore crucial sk i l l ,with Ali et al^ highlighting that the fundamental principle of soccer is to scoremore goals than the oppos ing team . Ultimate ly, sk ill to execute a successful pass,dribble with pace and control, or shoot at goal with accuracy, will determine theoutcome of a game.'^The influence of fatigue on physical performance has been we ll researched insoccer, with previous research showing impaired physical abilit ies during andafter brief periods of high-intensity activity.- following 45 min of soccer-specificexercise.'' '"' and at the end of competitive and simulated games.--'"' Conversely,Lyons et a l ' ' highlighted that eco logica lly sound studies investigating fatigue andits effects on soccer-specific skills are surprisingly rare. Impaired skill has beenreported during competitive match play.'-^'"^ however, the variability inherent to agame makes it difficult to translate findings front one match to the next. To over-come match va riab ility standardized, soccer-specific, protoco ls have been devel-oped to replicate match-play.**'^"'' Fo llow ing a 90 m in Lo ughb oroug h Interm ittentShuttle Test (LIST) a 59'r reduction in dribbling skill has been observed," as has asignificant reduction in shooting skil l . '^ This previous research highlights an

impaired ability to perform soccer-skills at the end of a match. Similarly, it hasalso been shown that soccer skill is impaired following a bout of brief high-inten-sity exercise.'^ However, it is not clear wh ether sk ill deteriorates at any other stageduring a game. Sprint and jumping abil i ty are known to be impaired fol lowingonly 45 min of soccer-specific exercise.'"" but the ability to perform soccer-spe-cific skills after a similar time period is unknown. Therefore, the aims of the cur-rent study were to investigate whether co m pleting a 45 -m n LIS T impa irs theability to both dribble with the ball and shoot at goal. A further aim was to deter-mine individual variability in the magnitude of any change in the execution ofskills when fatigued, and relate this to estimated smallest worthwhile changes inperformance.

MethodSubjectsNine male semiprofessional soccer players (age 20.7 1.4 years, stature 177.7 6.1 cm , body mass 73.5 7,6 kg), playin g in the Welsh Div isio n 2 League, pa rtici-pated in the study. The p articipants were from a range of ou tfield p laying positionsand were involved in regular training and match-play. The institutional ethicalcommittee approved the project and written informed consent was obtained from


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Fatigue and soccer skill 165

day following a 45-min tnodified version of the Loughborough Intermittent Shut-tle Test (LIST),'^ In the first session participants were given the opportunity topractice the skills tests, each test was first demonstrated by the researcher withparticipants then given two full practice attempts of each test. Participants thencompleted a standardized warm-up before cotnp leting test trials of the dribble andshooting tests, which were used as the pre-LlST condition. In the warm-up par-ticipants completed 10 min of dynam ic movement drills increasing in movementintensity and including brief sprints {~\5 m). After completing the skills testsparticipants were familiarized to the LIST by completing a l.'^-niin block of thetest. In the second session participants completed the 45-min LIST immediatelyfollowed by the slalotn dribbling test and LSST. Participants completed both testsessions within 2 d and at the same time of day to avoid any circadian influences.Heart rates were monitored throughout the LIST using Polar heart rate monitors(Polar Electro. Finland). Both the LIST and slalom dribble test were performed inan indoor sports hall with the LSST completed on an adjacent sand basedAstroturf.

Slalom DribbleSoccer dribbling skill was assessed using the slalom dribble test.^ The test waschosen due its good ecological and construct validity as well as high intraclasscorrelation coefficient indicating a high test-retest reliability {r = ,95 ).' The testassesses total body movement, requiring participants to dribble around a setobstacle course us quickly as possible. The dimensions tor the slalom course areshown in Figure I. On the starter's comm and the participant dribbled the ball frombehind the start line to the right of the first cone and then alternately around iheoutside of the retiiaining five cones in a /ig-zag path. The participant stopped andleft the ball at the sixth cone before traveling in a straight line across the finish line(Figure I). The time taken to negotiate the obstacle course was measured andrecorded using Smart Speed timing gates (Fusion Sport. Brisbane. Australia). Theparticipants were required to perform the slalom dribble twice, with a rest of 1niin between trials with the mean of both times used as the test score.'Loughborough Soccer Shooting TestShooting accuracy was as.sessed using the Loughborough Soccer Shooting Test,which has been suggested to be a valid and reliable method of assessing soccerskill in research.** All boundary lines of the test were marked on the floor using5-cm gray tape. Shots were taken from within a square "shooting zone" measur-ing H.5 X 8.5 m. which was marked with the nearest line being 16.5 m from thegoal line. Four cones were used to mark each corner of the shooting /.one with astandard gymnasium bench being placed on the middle of the far side of the zone


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166 Stone and Oliver

7.32ni

4.88ni

4,8Kin

.3m

I.S.lm

1,83m

FINISH S T A R T 4,57tn

Figure 1 Diagram of the slalom dribble test course. Key: A = cone. I> = dribbling with the ball, > = running without the ball. = timing gate.

could have reduced the reliability ofthe test. Ftirtheniiore, the authors reported alow correlation (r = .36) between shot speed and points scored suggesting thatthere is no relationship between shot speed and shooting accuracy during the test.Procedure for the LSSTThe test began with the ball being placed on the marked circle located in thecenter of the shooting zone. The parlicipant'.s initial position was to stand facingaway from goal toward the bench, within playing distance of the ball. After thecall ofthe investigator, the player was required to sprint to the cone he had beendirected to move to. touch the top of it. and then return to the ball in the center of


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7..'i2m1.2m 2.52m

4 - * *

0.6m

!6.5m

RIGHT

8.5m

O.Kni

0 84n i

II . Km-\\

2.44m

5.5m

FINISH

LEFT

START Shooting

Cone BenchFig ure 2 Schematic of the Loughborough Soccer Shooting Test (/ = investigator).


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Modified Loughbo rough intermittent Shuttle TestThe test used in the study was a modification of the original LIST pro toco l."^''' Inthe original piotocol submaximal workloads were completed at speeds relative tomaximum velocity during a tiuiltistage litness test,''' consequently, there is vari-ability in the amount of external work completed across participants. In the cur-rent study fixed work intensities were used, standardizing the external workloadcompleted and alk)wing the possibility of testing multiple patiicipants simultane-ously. The exercise intensitie.s/shuttle duratiotis used in the study were based onresults previously published using a LIST"' and replicated the speeds observedduring soccer tnatch-play.'''

The test required participants to run between two lines. 20 in apart, at vatiousspeeds, The running and walking speeds during each 20 m of Ihe test were dic-tated by audible beeps and verbal instructions prerecorded onto a compact disc.To assist with pacing different pitch audible beeps signaled when a participantshould be turning and when they should be in the middle of the 20-ni shuttle. Theexercise protocol used consisted of 15-min activity blocks. The activity blocksfollowed the same activity pattern as in the original LIST protocol"' andincluded:3 X 20 m at a walking pace of 5 km h"'1 X 15 m at maximal running speed (plus 5 m deceleration)4-s recovery3 X 20 m at a runtiing speed of 9 km h"'3 X 20 tn at a running speed of 14 km h""'This pattern of exercise, lasting for 90 s. was repeated 10 titnes forming alii-min block which was then followed by a rest period of 3 min. Participants wereallowed to consume water ad libitutn during the 3-min rest period. Fifteen-metersprint times perfortned during the LIST were measured and recorded using SmartSpeed timing gates (Fusion Sport. Brisbane. Australia). Participants completedtest trials in pairs and each participant had their own LIST and slalom dribblecourse. Each pair of participants shared a single LSST area but worked simultane-ously, with one participant resting while the other participant completed a shot.

Statistical AnalysisA one-way repeated-trteasures ANOVA was used to determine whether there wereany differences in mean sprint times and heart rates recorded during each 15-minblock of the LIST. A Bonferroni post hoc test was employed tod eter tnin e the levelot significance where appropriate. Homogeneity of variance was evaluated usingMauchiy's test of sphericity and when violated the Greenhou.se-Geisser adju.st-


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to estimate the smallest worthwhile change in performance based on 0.2 of thebetween-subject standard deviation (SDj.-" All data are presented as the mean SD. The significance level was set atP< 0.05 for all analyses. All statistical analy-ses were calculated using SPSS for Windows, version 12 (SPSS Inc.. Ch icago . IL.USA).

ResultsLoughborough Intermittent ShuttieTestThe mean heart rates achieved during the first, second and third bouts of the LISTwere 155 II b m in" ', 155 13 b min ' and 156 12 b-min ', respectively , withno significant differences between bouts iP> .05). The overall mean HR through-out the LIST was 155 12 b m i n ' , corresponding to 78 5.7% of predicted HRmaximum. Sprint performance retrained unchanged over the three bouts of theLIST with mean sprint times of 2.54 + 0.15 s during bout L 2,56 0.14 s duringbout 2, and 2.58 0.14 s during bout 3 (F = 2.44, P = 0.12).Skili PerformanceA statistically significant difference was observed between the dribbling skilltrials performed before and after the prolonged exercise, with the post-LIST trialshowing a 4.5 4.0^?^ increase in mean s!ak)m dribbling time when comparedwith the pre-LIST trial {P = 0.009, Figure 3A). The smallest worthwhile changein dribbling time was estimated to be 1.1%. All nine participants displayed anincrease in m ean dribbling time following the LIST, with two participants record-ing an increase of < 1.1'/ and the remaining seven participants showing an increaseranging between 1.5 to 11.4%.

Figure 3B shows the mean total points scored for the pre and post-LIST LSS Ttrials. There w as a significant reduction in the points scored (-7.6 7.0, P = .012)when the shooting test was performed after the LIST. The smallest worthwhilechange in performance was estimated to be 6.5'!. From eight participants whorecorded a reduced LSST score after the LIST, six participants showed a changein score >25%. The frequency with which all participants scored points from eachscoring zone during the LSST is shown in Figure 4. In the pre-LIST LSST therewere a similar amount of shots achieving the maximum and minintum pointsscore of 5 and zero, respectively. Following the LIST results showed a 47%decrease in the number of shots that scored 5 points and an 85% increase in thenumber of shots that scored zero points. Removing the time requiremcnl to makeeach shot within 8,5 s and including shots taken outside of this limit made nosignificant difference to the pre-LIST LSST score (P = 0.19); however, it did


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pre-LlST post-L IST pre-LIST post-L ISTFigure 3 f.efl: Mean slalom dribble time before and after the LIST. Right: Mean toial pointsscored during the Loughbo rough SoexxT Sho oting Test before and after the LIST, with (filled squares)and without (open squares) an 8.5-s shot time limit. *Signifcant difference between pre- and post-LIST trials. P < .05. ^^Significant difference between pust-LIST LSST triuls with and without anS.3-S titne limit. P< .01.

2 3Points scored per shotFigure 4 frequency of points scored from all shots taken during pre- and post-LIST trials of theLoughborough Soccer Shooting Test.


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DiscussionThere were no significant decrements in sp rint performance du ring exercise sim u-lating o ne-half of a soccer match . Over the same time period soccer-specific sk illswere found Xo be significantly Impaired. This included a reduced ability to bothdribble and shoot at goal following 45 min of intermittent exercise. The magni-tude of the change in the skills tests suggest there was a " rea l " negative change inperformance for the majority of participants for both dribbling and shooting.However, for some individuals it was the inability to shoot within the prescribedtime requiretnents that resulted in poorer post-LIST shooting scores, rather thanthe ability to shoot on target.

The tola! distance covered during the 45-min LIST (6.000 m) is cotiiparablew ith distances covered d uring the fits i half o f a soecer match.- ' The ove rall HRresponse was slightly below that reported du ring match-^play-' and du ring a 90-minLIST."'-- however, the HR values were stil l within ihe expected range. Sprintperformance was not impaired throughout Ihe 4?-min LIST protocol, which is inagreement w ith previous research.*" -- The absence of any decrements in sprintperformance will in part be due to the relatively short distance (15 m) over whichsprints were ct)tnpleted. Force-generating capacity and acceleration have beenshown to be restored relatively quickly during a set of repeated sprints, whereasthe a bility to m aintain speed over longer distances can be redu ced .-'Previous research has identified a reduced ability to complete soccer skillsduring the second ha lf of a soccer m a tc h " and fol low ing a 90 -m in LIST:*" '^ how-ever, reduced skill was also accompanied by reduced physical performance inthese instances. The implications ofthe current study are that skill can deteriorateby the end of the first half of a soccer match , and decrements in s kil l may precedeany decrements in sprint performance. The effect of exercise on the perfonnanceof sports skills has been suggested to follow an inverted-U trend."* The inverted-Uresponse is thought to be linked to both physiological (watming-up and fatigue)and psychological (arousal) factors."^ Whether this relationship actually exists in

a complex sport such as soccer is not clear. While soccer-skill was previouslyknow n to be impaired fo l low ing 90 min of exe rcise/ ' '^ results of th e current studyshow that skill is already reduced following only 45 min of exercise.The skills tests used in the current study required participants to completewhole-body movements while performing skil ls with the ball , reflecting thedemands of competitive match-play. Both the slalom dribble and shooting testsfocused on the physical execution of skill and minimized any requirements forperceptual abilities (such as decision making, visual scanning, spatial awarenessand anticipation), wh ich wo uld also be important d uring com petitive play. None-

theless, a test invo lvin g an accuracy tequirem ent w il l always p artially rely onsome perceptual abilities, which could be susceptible to fatigue.'** However, it has


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ing with the hall, which included d ribbling in the slalom test and passing, possiblycontrolling and shooting with the ball in the LSST.A number of authors have shown that skill over a 90-min simulated soccermatch is better maintained with carbohydrate feeding.'' '' Total muscle glycogendepletion is unlikely to have occurred following only 45 min of exercise in thecurrent study, although depletion in specific repeatedly recruited fibers may haveixcurred-^ and may have contributed to the decline in soccer skills. Muscledamage has also been shown to occur following a 90-min LIS T' ' and suggested tooccur following 4 5 min of soccer-specific exe rcise .'" M uscle damage is associatedwith changes in the sense of joint position and force production.-'' which couldinterfere with motor control in .skilled movements. Reducing susceptibility to

muscle damage, for instance by utilizing the repeated bout effect, may be onemethod to attenuate any decline in soccer skills during the lirst half of a soccertnatch. Impaired soccer-skill hus also been suggested to be related to lactate accu -mulation following a brief bout of high-intensity activity.'** Reduced skill in a35-min intermittent tenn is test was suggested to be linked to lactate accum ulation,-^with laetate levels .similar to those expected during a LIST.^ '^ Davey et aP' sug-gested that players should avoid physiologically stressful conditions in training asthis would impair their ability to practice and stabilize their skills. An alternativeapproach may he to focus on technical training under conditions of fatigue toensure players can maintain skill execution when fatigued. It has also been sug-gested that increasing the exercise capacity of players will help to delay the on.setof fatigue and impairment of skills during a soccer match,'' However, playerswith improved fitness may simply work at a greater intensity and still sufferfatigue during a match, a suggestion that is supported by the observation that play-ers of lower and higher standards perform less physical work- and fewer skilledactiotis" in the second half of a match compared with the first.While all participants showed some increase in dribbling time when fatiguedit is important to interpret the magnitude ofthe individual changes. Hopkins-" hassuggested that when testing team players the smallest worthwhile change in per-formance can be estimated as 0.2 ofthe between participant standard deviation, aprocedure that has previously been employed with soccer-skills testing.'* Seven ofthe nine participants experienced a reduction in excess of the estimated smallestworthwhile effect of 1.1%, suggesting the likelihood that the majority of partici-pants experienced a "real" negative change in dribbling skill followins the 45-minLIST.Performance in the LSST was significantly impaired following the 45-minLIST, supporting previous observations following a 90-min LIST.'' From dataobtained in a reliability study. Ali et al'^ reported a critical value equating to a

minimum worthwhile change in LSST score of 6.9% in first team universitysoccer players. Based on the same criteria results of the current study indicate a


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participant variation, a criteria previously used with performance testing of ath-letes itivolved in individual sports.-** Based on the tnore stringent criteria, sixpatticipants showed a decrease in shooting performance gteater than the criticalvalue of 25%.

The LSST requires participants to make each shot within a set time limit,recreating the demands of the game where skills tnust be performed with limitedavailable time. Removing the time limit requirement meant that post-LIST LSSTperformance was significantly improved when shots made outside of the timelimit were included. With the time limit removed the overall group reduction inLSST performance bordered on significance (P = .06) and the number of indi-vidual players recording a drop-off in performance of >259i' was reduced from sixto four p layers. In tenns of shooting ability players may be split into three catego-ries; i) those showing no signs of fatigue, ii) those who can maintain shot accuracybut only by sacrificing speed of movement and iii) those who cannot maintain shotperfortnance irrespective of time limits. The varied individual responses tnayreHect physiological difteretices in the ability to tolerate fatigue (peripheral orcen tral), technical differences in the ability to execute skills when tatigued,-^ orcognitive differences such as regulatory focus influencing the individuals strategicresponse to a skilled task^'' or differing self-regulation strategies.-"^In a fatigued state players may be sacrificing speed of movetnent to maintainaccuracy, a phenomenon that has been termed the speed-accuracy trade-off."However, speed and accuracy may change independently of one another. whiledifferent individuals may place different importance levels on each these of vari-ables dependent on the task presented-'' and possibly the level of fatigue experi-enced. Reduced speed of skill execution when fatigued is supported by the increasein slalom dribble times, which is attributed to reduced tiiotor control when incontrol of the ball. During the LSST participants were unable to sacrifice speeddue to the time limits imposed and as a consequence accuracy suffered. Duringthe post-LIST trial the number of total shots with a zero score almost doubled,whereas the number of shots scoring five points almost halved. The changes in the

distribution of points scored clearly reflect reduced shooting accuracy whenfatigued, which would have obvious consequences during a gam e.

Practical ApplicationsDecrements in the execution of soccer skills during a (simulated) match may pre-cede any similar reductions in physical performance, such as sprint ability. Mea-suretnent tools should be used to assess the ability of players to complete itnpor-tant soccer skills when fatigued and appropriate training regimes employed toreduce any fatigue related impairment of soccer skills. However, more research isneeded on the effectiveness of different types of interventions and training/coach-


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ConclusionParticipation in 45 min of simulated soccer tnatch-play did not cause any decre-ments in sprint performance. Conversely, performance of prolonged intermittentexercise did significantly impair the ability to both dribble with the ball and shootat goal. Therefore, a reduced ability to perform soccer-skills may precede anyobserved decline in sprint performance. On an individual basis the majority ofplayers demonstrated a negative change in skill execution greater than the criticalsmallest worthwhile effect. It is clear that completing exercise equivalent to one-half of a siKcer match may be sufficient to impair the ability to perform soccer-specific skills.

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18. McMorris T Rayment T Short-duration, liigh-intcnsity exercise and perfomiance ofd sports-^pcciiic sk ill: a preliminary study. Percept Mot Skills. 2()O7;1O5:523-53O.19. Nicholas CW. Williams C. Lakoniy HK. Phillips G. Nowiiz A. Inliuence of ingestinga carbohydrate-electrolyte solution on endurance capacity during intermittent, high-intensity shuttle nmm ng.J Sports Sei. 1995; 13:283-290.20- Hopkins WG. How to Interpret Changes in an Athletic Performance Test. .Sport-Science. IDOAS:]-!.

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FATIGA Y GESTO TÉCNICO

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