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VARIABILITY OF OBJECTIVE ANDSUBJECTIVEINTENSITIES DURING BALL DRILLS IN YOUTH

SOCCERPLAYERSASIERLOS ARCOS,1 RAUL MARTINEZ-SANTOS,2 JAVIERYANCI,2 JUAN MARTIN,1 AND

CARLO CASTAGNA3

1Club Atletico Osasuna, Pamplona, Spain; 2Faculty of Physical Activity and Sport Science, University of the Basque Country,UPV/EHU, Vitoria-Gasteiz, Spain; and 3Technical Department, Football Training and Biomechanics Laboratory, Italian

Football Federation (FIGC), Florence, Italy

ABSTRACT

Arcos, AL, Martnez-Santos, R, Yanci, J, Martn, J, and Castagna, C.

Variability of objective and subjective intensities during ball drills in

youth soccer players. J Strength Cond Res 28(3): 752757,2014The aim of this study was to examine the intrasubject (intra-

class coefficient correlation [ICC]) and intersubject variability (coef-

ficient of variation [CV]) of soccer ball drills (BD) involving or not

opposition in male youth soccer. For this purpose, a collective

ball dribbling (DB) exercise and a 7-a-side ball game without

coach encouragements were considered. Exercise intensity

was assessed as heart rate (HR), training load (TL), and per-

ceived exertion scales. Fourteen U-14 male soccer players

(age, 14.79 6 0.43 years and experience, 6.5 years) of a Span-

ish First Division club academy participated in the study. Ball

drills were examined for variability over 5 successive training

sessions in similar field conditions. Results showed that 7-a-

side was significantly (p = 0.000) more demanding than DB.

Indeed the TL, HRmax, HRmean, overall perceived exertion, and

leg muscular perceived exertion (MPE) resulted 141, 8.7, 11,

56, and 72%, higher in 7-a-side than in DB, respectively. In the

7-a-side condition, good intersubject (CV , 10%) and low

intrasubject (ICC , 0.7) variability were observed. In the DB

condition, CVs were below 10% CV only for HR variables and

the ICC values were higher than 0.7 only for MPE. Despite the

moderate reproducibility of BD not considering opponents, this

condition did not reveal to induce homogeneous physiological

responses in young soccer players. Therefore, the use of this

kind of drills may be questionable when considered as alterna-

tive of moderate intensity generic aerobic training. Despite the

higher interaction between players variability in the opposition

drills resulted lower, this suggests their use as a specific con-

ditioning exercise.

KEYWORDS football, small-sided games, perceived exertion,

collaboration, collective duel

INTRODUCTION

Ball drills (BD) are considered a viable way of prac-ticing aerobic and anaerobic fitness and skills in soc-cer concurrently and successfully (15). However, theintermittent nature of small-sided games (SSG) and

their supposed interplayers exercise variability requires an accu-rate training load (TL) control to warrant targeted results (7). Inthis sense, some sustainable objective-subjective and subjectivemethods have been proposed recently to assess intensity in theSSG (35). The intensity of SSG has been monitored in field

conditions using on-line and post hoc exercise heart rate (HR)(i.e., objective-subjective method). Additionally, the use of per-ception scales to rate subjective exercise strain during the SSGpractice revealed to be a valid method to track individual re-sponses to fitness developmentoriented BD (23). Interestingly,the combined use of HR and perceived exertion scales showedto be a valid approach to assess exercise intensity of SSG insoccer (9).

Despite the interest of BD in daily soccer practice and theirexpected uneven individual drill responses, only a few articlesaddressed interplayers intensity variability and repeatability dur-ing BD in soccer (15). Furthermore, they were performed withadult elite-level players and provided results might not be appli-cable to less experienced and skilled young soccer players. Theinformation about interindividual and day-to-day intensity var-iability of BD is of great impact on coach daily practice whentraining drills are chosen to match methodological (i.e., fitnessdevelopment) aims in youth soccer (15).

The exercise intensity of SSG may be affected by structuralconstraints, such as the number of players, the set-up dimen-sions, the rules, and the coach encouragements (23). The BDintensity may also be affected by the presence of opposition,supposed to be more variable when opponents are involved.

Address correspondence to Carlo Castagna, [email protected].

28(3)/752757

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Although the optional use of opposition is a common routine inyoung soccer to satisfy methodological aims, no research iscurrently available about the possible effect of opposition onBDs variability.

Therefore, the aim of the present study was to examine thevariability and reproducibility (i.e., day-to-day variability) of 2

popular youth soccer BD proposing or not opposition in soccerand its effect on the exercise intensity. This is in the attempt toprovide full control of coaches over training BD during dailypractice.

The occurence of higher inter-players variability in BDwith opponents was assumed as work hypothesis.

METHODS

Experimental Approach to the Problem

To examine the effect of opposition consideration on BDintravariability and intervariability, 2 popular drills represent-ing the 2 exercise categories (i.e., with or without opponents)were considered taking into account their structural traits

(22). The opposition-free BD was represented by a passingconditioning game involving ball dribbling (DB) and passing(11). To produce opposition effect on exercise intensity,a modified rules 7-a-side SSG (i.e., collective duel drill,CD) was considered according to Ford et al. (11).

The study was conducted at the end of the 201011 com-petitive season (May-June). During this period of the season,players practiced 3 times per week reducing the TL to avoidundue effect of fatigue on BD. No matches were played duringthe period of the experimentation. Before the study, all playersperformed familiarization sessions to master SSG and BD.However, the drills used in this study were part of the usualtraining sessions during the considered competitive season. Datawere collected during 5 consecutive training sessions that alwaystook place at the same time of the day (19:00 hours) witha minimum of 48-hour rest in between. Each training sessioncomprised the same training tasks performed in the same orderafter a standard 5-minute warm-up. The DB and 7-a-side drillwere played in reason of 3 sets of 5 minutes with a between-setrest of 2 minutes. The recovery between both drills was 6 mi-nutes. All the BDs were performed outdoors on a third-gener-ation artificial grass soccer pitch that was watered 10 minutesbefore the training session according to the manufacturersguidelines.

To promote proper hydra-

tion ad libitum, water assump-tion was promoted to all playersduring the training sessions.Players were advised to maintaintheir usual diet to promote max-imal performance.

In this study with the aim toevaluate the DB and SSG exer-cise intensity, HRs were used.HRs monitoring was reportedto be a valid and sensitive

method to assess exercise intensity during SSG and training insoccer (6,7,10,16). Categorization of the HR was performedaccording to the procedures suggested by Stagno et al. (25).The subjective rating of perceived exercise (RPE)-effort wasmeasured using the Fosters 010 scale. The use of RPE wasreported to be a valid measure of the internal load during the

SSG in soccer (9,23).

Subjects

Fourteen U-14 male soccer players (age, 14.79 6 0.43 years;height, 1.746 0.04 m; body mass, 60.77 6 5.14 kg; and bodyfat, 9.96 60.77%) from a Spanish First Division (Liga BBVA)club academy participated in the study. All players hada minimum of 6.5 years experience in competitive soccer andcompeted for the same youth category at regional and nationallevel. The players and their parents were informed (word andwritten) about the research and its benefits and risks, and all ofthem gave their informed consent before the commencementsof all the procedures considered in this study. The study was

conducted according to the Declaration of Helsinki (2008) andthe fundamental law of Personal Data Protection. The localEthics Committee approved the study protocol.

In the attempt to avoid team imbalances, players position,players technical-tactical level, physical fitness, and participationin competitive matches were considered for team allocationaccording to Casamichana and Castellano (3). More specifically,allocation was performed using coach technical-tactical rate,time participation in matches, and endurance level (i.e., timeto exhaustion on Leger-Boucher test) (20).

Because of injury, lack of compliance with the research designrequirements, and technical failure, 9 of the original players wereconsidered for calculations eventually.

Procedures

In this study, 2 popular BDs were considered to improveindividual and team skills. The individual skill development taskconsisted in DB as fast as possible in a relay wise mode between2 lines 9 m apart before passing the ball to a teammate. Eachteam composed of 8 players who had to complete 6 relays. Twoballs per team were provided, and no coach encouragement wasconsidered during the drill.

A 7-a-side game without goalkeepers was considered asconditioning and team skill development drill. The considered

TABLE1. Exercise variables during the considered ball drills.*

Stagnos method % HRmax % HRmean OPE MPE

DB 40.6 6 9.1 90.1 6 3.6 82.3 6 4.3 4.8 6 1.1 3.6 6 1.4CD 62.9 6 6.3 97.9 6 1.7 91.3 6 2.2 7.5 6 0.9 6.2 6 1.6

*% HRmax= percentage of maximal heart rate; % HRmean= mean of heart rate respect tothe maximal heart rate; OPE = overall perceived exertion; MPE = muscular perceived exertion(the legs); DB = dribbling the ball; CD = collective duel.

p , 0.0001.

Journal of Strength and Conditioning Researchthe TM

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SSG was performed in a 45 3 45-m pitch with 5 nonstandardgoals and no ball touch restriction. The pitch was divided in to 4zones containing a goal, each having the fifth one placed in the

center of the field. Scores were considered valid only if made atthe first touch, and no goal could be scored in the very samequadrant where the team regained the possession of the balluntil it was played on any of the other 3. The 7-a-side game wasplayed without providing encouragements, with the coachesonly counting scored goals for the players to hear.

Exercise intensity was assessed recording (i.e., 5-secondinterval) HR with short-range telemetry (Polar Team SportSystem; Polar Electro Oy, Finland). Maximal heart rate(HRmax) was assessed using the Leger-Boucher test (19).The endurance test was performed outdoors on an artificialgrass soccer pitch 3 days before the study. The participantscompleted the test at the same hours of day as everydaypractice.

The obtained HRmax

was used as the reference for devel-oping individual training intensity zones (3,15). Intensity cat-egories were considered as the time spent in the arbitrarychosen HR zone multiplied by a selected weighting factor(i.e., TL) according to Stagno et al. (25). Specifically, time(in minutes) spent at 10093%, 9286%, 8579%, 7872%

and 7165% of HRmax weremultiplied by 5.16, 3.61, 2.54,1.71, and 1.25, respectively.

One minute after the end ofsoccer, BD players individuallyrated their effort exertion using

the Fosters 010 scale (12).They responded separatelyabout the overall perceivedexertion (OPE) and the legmuscular perceived exertion(MPE) (1,13,14,26). All partic-ipants were familiar with thisprocedure; they have used itto rate exercise effort percep-tion during SSG, friendly

matches, and maximal aerobic test training drills. All theprocedures involved in this study were performed at thesame hours of the day to avoid circadian variation that

may have an effect on effort outcomes.

Statistical Analyses

The results are reported as mean 6 SDs. Assumption of nor-mality was verified using the Shapiro-Wilk W-test. Day-to-daymean variations were detected with repeated-measures anal-ysis of variance with post-hoc Bonferroni test. Interplayervariability and intraplayer variability were calculated usingthe CV (17) and the intraclass correlation coefficient (ICC)(2), respectively. Statistical significance was set at p # 0.05.Data analysis was performed using the Statistical Package forSocial Sciences (version 18.0 for Windows; SPSS, Inc, Chica-go, IL, USA). Power calculation revealed that to achieve

a power of 80%, at least 12 subjects were required at theassumed level of significance.

RESULTS

Players mean endurance test performance was 21.51 61.34 minutes. The CD was more intense than DB drill(p, 0.001) in all variables (Table 1). Indeed, the TL, HRmax,

HRmean, OPE, and MPE re-sulted 141, 8.7, 11, 56, and72%, higher in 7-a-side thanin DB, respectively.

The CVs for the variables of

interest are reported in Tables2 and 3. Coefficient of varia-tion was greater in DB than in7-a-side for all measures. Inthe DB, only HRmean andHRmax values were below10%, with the remaining var-iables lying above 20%. Inthe 7-a-side condition, onlythe CV for the MPE exceeded12%.

TABLE3. Coefficients of variation in 7-a-side drill (collective duel) per day.*


Day 1 4.3 1.1 2.0 9.7 26.8Day 2 11.7 1.6 2.6 12.8 28.9Day 3 4.8 1.1 1.0 13.8 29.6Day 4 10.3 1.5 2.2 9.9 28.8Day 5 12.4 1.9 2.8 14.1 10.4Mean 8.7 6 3.9 1.5 6 0.3 2.1 6 0.7 12.0 6 2.1 24.9 6 8.2

*% HRmax= percentage of maximal heart rate; % HRmean= mean of heart rate respect tothe maximal heart rate; OPE = overall perceived exertion; MPE = muscular perceived exertion(the legs).

TABLE2. Coefficients of variation in the dribbling ball drill per day.*


Day 1 23.4 3.2 4.9 20.8 40.5Day 2 24.4 4.5 5.5 19.2 32.8

Day 3 11.9 2.7 3.2 27.3 34.4Day 4 23.2 4.1 4.9 20.9 39.0Day 5 25.9 3.8 4.9 24.7 40.0Mean 21.8 6 5.6 3.7 6 0.7 4.7 6 0.9 22.6 6 3.3 37.3 6 3.5

*% HRmax= percentage of maximal heart rate; % HRmean= mean of heart rate respect tothe maximal heart rate; OPE = overall perceived exertion; MPE = muscular perceived exertion(the legs).

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The ICC values for both exercises are presented in Table

4. Significant differences between days were found only forthe 7-a-side drill. In this BD, the ICC value was over 0.5 onlyfor MPE. The ICC values for DB variables were higher than0.5 for Stagnos method, HR

max, HR

mean, and MPE.

DISCUSSION

The aim of this study was to examine the variability of theintensity of 2 structurally different soccer drills considering thepresence or absence of opposition. The main finding of thisstudy was the evidence of a significant effect of opposition onthe exercises intensity and variability. This suggests that the7-a-side drill may be useful to promote conditioning training(i.e., HR above 90% of HRmax) in academy soccer.

The study results showed that spontaneous playing in thecollaboration-opposition drill (i.e., 7-a-side) promoted HRintensities in the range of those reported to be functional inenhancing aerobic fitness in soccer players (i.e., 9095% ofHRmax) (15). This enforcing HR peaks (i.e., 98% of HRmax)were close to the individual maximal values detected underfield condition using usual shuttle running tests for endurance.These results are in line with those reported in other studiesthat examined SSG with rules, number of opponents, and fielddimension variation (15). Interestingly, the reported effect ofthe 7-a-side drill was achieved without any external encour-agement (23). As a result, coaches are advised to consider

opposition when in need to develop aerobic fitness in acad-emy players attending to variety as one of the basic principlesof training planning (23).

Given that the CD here represented by DB may beconsidered as a useful training drill to develop endurance(i.e., 8085% HRmax) or to provide lower TL, this may resultof greater practical interest during the week for the practicesessions closest to the match. Furthermore, the resultingresponse promotes DB, aiming to individual skill develop-ment, as a potential activity functional to conditioning ifproper strategies are considered. This may result in a more

enjoyable alternative tomedium-to-low-intensity con-tinuous running in young soc-cer players. This finding is inline with that previously re-ported by Hoff et al. (16), which

showed relevant cardiovasculareffect as consequence of DB. Inlight of this, skill developmentshould be regarded as a compo-nent of soccer training thatmust be considered to affectTL in young soccer playersand proportionally sized in thedaily training routine.

Consistency of trainingresponse is vital for trainingprescription in team sports.

We know that BD produce per se intraplayers and inter-

players variability in physiological responses (7,21). Thesupposed activity-related variability might logically be exac-erbated considering or not opponent in drill development. Inthe collaboration drill (i.e., DB), maximal and mean exerciseHR showed low interplayers variability as per reported CVvalues (i.e., 3.7 and 4.7%, respectively). These CV values arelower than the 10% threshold suggested by Atkinson et al.(2) to determine practical acceptance of clinical variations.Despite this, a remarkable intersubject variation in the valuesobtained in the perceived exertions (i.e., general and muscu-lar) and in the TL was detected (i.e., CV .10%). Therefore,taking into account all intensity variables, we can assumethat there is a considerable intersubject variation in the col-laboration drill. The training physiological stimulus variesbetween players. The constancy of a RPE in guiding trainingintensity in young soccer players may be questionable butthe TL values (CV = 21.8 6 5.6%) also indicated a highvariation interplayer in this kind of drills. Because of thehuge practical interest of this kind of information, furtherstudies on the applicability of RPE to drill prescription arewarranted in soccer.

Differently from initially supposed, the 7-a-side BDshowed a low interplayer variability. The correspondingCVs for %HRmax and HRmean in the opposition exercisewere only 1.5 and 2.1%, respectively. This applies also for

the 7-a-side TL that resulted in a CV lower than 10%. Thesefindings are in line with those previously reported in otherstudies that used HR variations to profile intersubject andintrasubject variability during SSG (15,23). The resultingsmall interplayer variability in the 7-a-side may be the resultof the highly competitive nature of opposition games thatseem to elicit close to maximal response in the players,resulting in a reduced variability as far as the individual max-imal range of HR was achieved (7). In this regard, otherexercise variables, such as blood lactate concentrations,may be suggested (9) to avoid the limitation of HR values

TABLE4. Intraclass correlation coefficient values in the different indicators forboth exercises in 5 days.*


DB 0.65 0.61 0.70 0.37 0.72

CD 0.3 0.07 0.19 0.41 0.63Days 12z Days 12z

Days 23z Days 23zDays 25z

*% HRmax= percentage of maximal heart rate; % HRmean= mean of heart rate respect tothe maximal heart rate; OPE = overall perceived exertion; MPE = muscular perceived exertion(the legs); DB = dribbling the ball; CD = collective duel.

No significant difference was found between days in any indicator.zSignificant differences between days at p , 0.05.


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in monitoring very high-intensity activities. Given this, furtherstudies considering more sensible variables to very high-intensityexercise (i.e., higher than speed at HRmax) responses are war-ranted. Even though, if we consider the CV results in all varia-bles, we can affirm that the interplayer variation in oppositiondrill is lower than in the collaboration drill.

In this study, we also assessed session-to-session drillconsistency (i.e., reproducibility) using ICC. The resultsshowed that for the collaboration drill (i.e., DB), thereproducibility of the considered variables was good only infew cases (ICC . 0.70) (8), specifically HRmean and MPE.The HR variables (i.e., ICC = 0.610.70) do not match withthose obtained in other technical exercises (24) performed byelite junior soccer players that showed poor peak HR repro-ducibility (ICC = 0.38). In the 7-a-side condition, the resultingICC was very poor except for MPE (ICC = 0.63), althoughmean differences were found between training days in theselected variables (TL, %HR

max, and %HR

mean). Similarly,

these results are consistent with the findings obtained by

Rampinini et al. (24) for the considered 4 vs. 4, 4 vs. 2, and10 vs. 10 SSG. However, differences in BD rules, players skill,and exercise set-up or modality (i.e., set or free displacement)make comparison between the studies difficult. Therefore, theopposition BD should be thought of as low session-to-sessionconsistent while the collaboration drill presented a betterreproducibility.

It could be concluded that despite the moderate reproduc-ibility of BD without opponents (i.e., collaborative drill), thiscondition did not reveal to induce homogeneous physiolog-ical responses in young soccer players. Therefore, the use ofthis kind of drills may be questionable when considered as analternative to moderate-intensity generic aerobic training.Interplayers variability may be lower during team oppositiondrills despite the occurrence of frequent duel this suggestingtheir use as conditioning exercise when specific training (i.e.,ball use during drills) is to be prescribed. However, session-to-session low reproducibility suggests caution when implement-ing BD. In this case, strategies enabling higher players drillcommitment as per provided encouragements may result ofinterest. Therefore, further studies looking for training consis-tency enhancing strategies for specific training are warrantedin youth soccer.

PRACTICAL APPLICATIONS

Specific training conducted at high intensity has beenreported to significantly improve aerobic fitness and tomoderately affect match performance in youth soccer (18).Therefore, SSGs were proposed as aerobic fitness enhancingdrills (15). This study findings showed that BD involvingopposition may result of interest for high-intensity training(i.e., .90% HRmax) although played spontaneously. This pro-motes intrasession homogenous demand across players.However, caution should be paid when proposing this kindof drills again during the week as the response of the individ-ual player may be different. In this case, on-line monitoring of

HR may result of great interest to attain the targeted trainingintensity. Skill development drills performed as collective exer-cise may result useful for endurance (i.e., 8085% HRmax)development but strategies to warrant homogenous exerciseintensity must be considered as per drill games session-to-session reproducibility has to be addressed in this kind of

activities. In light of the practical interest of BD, studiesaddressing exercise reproducibility enhancing strategies inyouth soccer are necessary.

ACKNOWLEDGMENTS

The authors would like to thank C.A. Osasuna and coaches ofC.A. Osasuna U-14 team for the opportunity to investigate,and the help of Ibai Guridi and Txaber Hurtado students ofUniversity of Basque Country, UPV/EHU.

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