cambios en la temporada en los indicadores del stress en futbol profesional_2011

8/7/2019 Cambios en La Temporada en Los Indicadores Del Stress en Futbol Profesional_2011

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Training & Testing 259

Faude O et al. Stress in high level football Int J Sports Med 2011; 32: 259265

accepted after revision

November 13, 2010

Bibliography

DOI http://dx.doi.org/

10.1055/s-0030-1269894

Published online:

January 26, 2011

Int J Sports Med 2011; 32:259265 Georg Thieme

Verlag KG Stuttgart New York

ISSN 0172-4622

Correspondence

Dr. Oliver Faude, PhD

Saarland University

Institute of Sports and

Preventive Medicine

Campus Bldg. B8.2

66123 Saarbrcken

Germany

Tel.: +49/681/302 70405

Fax: +49/681/302 4296

[email protected]

Key words

soccer

overreaching

fatigue

performance

match exposure

recovery

Seasonal Changes in Stress Indicators in High LevelFootball

Up to now, there are only a few studies which

evaluated the psychological and physiological

responses throughout a competitive football sea-

son. Naessens et al. [28] analysed psychological

measures together with nocturnal urinary

noradrenalin excretion 6 times throughout one

season. Based on the finding that changes in

fatigue rate (subscore of the Profile of Mood

States (POMS) questionnaire) was related to

changes in urinary noradrenalin excretion it wassuggested that these means may be useful to

monitor overtraining and overreaching in high-

level football players. Those authors also claimed

that overreaching is not uncommon in football. A

detailed analysis of training and competition

exposure, however, was not conducted in that

study. Filaire and colleagues [9, 10] reported

changes in some haematological, immunological,

hormonal and psychological variables over the

course of one complete season (including a high-

intensity training period) in male professional

football players. They concluded that a combined

psychological (POMS) and physiological moni-

IntroductionDue to the high frequency of regular matches in

modern high level football it is often assumed

that there is danger of too little time remaining

for adequate recovery during intensive competi-

tion periods. Such high demands may have a

negative impact on match performance and

injury risk [5, 7]. In particular, this might be true

for highly demanding competition phasestowards the end of a football season [7]. Monitor-

ing of the recovery-stress state and performance

may be warranted to avoid an imbalance between

stress and recovery and, thus, to prevent exces-

sive fatigue or overtraining [9]. While many stud-

ies have been conducted which evaluated a large

number of physiological correlates for the timely

diagnosis of overreaching and overtraining, no

single valid marker has been established yet [30].

Therefore, it seems worthwhile to approach the

problem of diagnosing fatigue by a multi-dimen-

sional test panel which is easily applicable in

practical settings.

Authors O. Faude1,2, M. Kellmann3,4, T. Ammann2, R. Schnittker2, T. Meyer1,2

Affiliations 1 Institute of Sports and Preventive Medicine, Saarland University, Saarbrcken, Germany; FIFA Medical Centre of Excellence2 Institute of Sports Medicine, Department of Sports and Health, University of Paderborn, Germany3 Ruhr-University of Bochum, Faculty of Sport Science, Germany4 The University of Queensland, School of Human Movement Studies, Australia

Abstract

This study aimed at describing changes in stressand performance indicators throughout a com-

petitive season in high level football. 15 players

(19.5 3.0 years, 181 5 cm, 75.7 9.0 kg) com-

peting under professional circumstances were

tested at baseline and 3 times during the season

2008/09 (in-season 1, 2, 3). Testing consisted of

the Recovery-Stress Questionnaire for Athletes

(Total Stress and Recovery score), vertical jump

tests (counter movement and drop jump (DJ)),

and a maximal ramp-like running test. Average

match exposure was higher during a 3-weeks

period prior to in-season 3 compared to in-sea-

son 1 and 2 (1.5 vs. 1 h/week, p = 0.05). TotalStress score was elevated at in-season 1 and 2

compared to baseline (p < 0.01) with a further

increase at in-season 3 (p < 0.03; generalized

eta squared (2g) = 0.37). Total Recovery scorewas decreased at in-season 1 and 3 compared

to baseline (p < 0.05; 2g = 0.21). Maximal run-

ning velocity (Vmax) and jumping heights were

not significantly affected (2g0.04). Changes

in DJ height and Vmax between baseline and in-

season 3 were correlated with the correspond-

ing changes in Total Stress score (r = 0.55 and

r = 0.61, p < 0.03). Usual match exposure dur-

ing a professional football season does not

induce relevant changes in performance indica-

tors. Accumulated stress and a lack of recovery

towards the end of a season might be indicated

by psychometric deteriorations.


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Training & Testing260


toring (catabolic and anabolic hormones, uric acid) is appropri-

ate to monitor training stress in relation to performance (winning

percentage) in team sports. With regard to psychometric testing

the Recovery-Stress Questionnaire for Athletes enables a detailed

analysis of individual recovery-stress state and has previously

been used to monitor the influence of intense training periods

on psychological variables in different sports [4, 20, 21]. Coutts

et al. [2, 3] observed decrements in strength, speed, power and

maximal running capacity in semi-professional rugby playersafter an intensive 6-weeks training period. Similar changes in

sprint times and jumping height were reported by Kraemer and

colleagues [24] in 11 collegiate football (soccer) players compet-

ing in 19 matches during an 11-week period. As Coutts et al.

[2, 3] intended to induce a state of overreaching and Kraemer

et al. [24] analysed changes over a short season with extraordi-

nary high match exposure, data on performance changes

throughout a usual football season are still lacking.

In light of the described gaps in the existing scientific literature,

the present study aimed at describing changes in stress and per-

formance variables throughout one competitive season in high

level football players by means of a multi-dimensional panel of

diagnostic tools (Recovery-Stress Questionnaire for Athletes(RESTQ-Sport), lower leg explosive power, maximal running

capacity). To adequately simulate elite football, the study was

conducted within a professional setting.

Materials and MethodsStudy design and employed procedures are in accordance with

the Declaration of Helsinki as well as the ethical standards of the

IJSM [16]. The study was approved by the Ethics Committee of

the Medical Faculty of the University of Mnster (Northrhine-

Westphalia, Germany). Each athlete gave his written informed

consent before the start of the study.

Participants and General DesignTwo football teams (32 field players) competing under profes-

sional circumstances on a national level (3rd German league as

well as highest national U-19 league including 4 U-20 and U-19

national team members) conducted a total of 5 tests throughout

one complete season (July 2008 to May 2009 including a short

winter break (23 weeks in December) and a second short prep-

aration period (4 weeks in January), 44 weeks in total). Tests

were performed before the onset of pre-season conditioning as

well as evenly distributed throughout the season (September,November, February, April). There was at least one day between

the tests and the last match and no intensive training session on

the days prior to testing. Testing was conducted in the following

sequence: RESTQ-Sport, vertical jump testing, and a ramp-like

maximal exercise field test.

Players who were injured for more than 2 consecutive weeks

(N = 6) as well as players who changed the team during the sea-

son (N = 5) or missed at least 2 tests for other reasons (private

obligations, minor acute injuries or infections, N = 6) were

excluded. A total of 15 players (19.5 3.0 years, 181 5 cm,

75.7 9.0 kg, including 2 national team players) performed a test

at baseline (before pre-season preparation) as well as 3 times

(in-season 1, 10 weeks after baseline, in-season 2 after 21 weeks,in-season 3 after 36 weeks) during the season. There were no

significant differences at baseline between drop outs and players

who were analysed (p > 0.16). Due to testing schedule some play-

ers conducted the in-season test 2 before and the remaining

players after the winter break. There were no significant differ-

ences between those tests (p > 0.20).

Individual exposure times in training and matches (regular and

friendly matches) were recorded by the coaches. Exposure was

expressed as cumulative individual exposure (training and

match exposure [in hours] from baseline test to specifi

c test day)and acute individual exposure (training and match exposure [in

hours] in the 3 weeks prior to testing).

Material and ProceduresRecovery-Stress Questionnaire for AthletesThe RESTQ-Sport was developed with particular regard to the

requirements of high performance sports [20, 22, 23]. The

RESTQ-Sport has been used in various sports (e. g., triathlon,

swimming, football, rugby) to monitor the impact of training or

competitive seasons in athletes [20]. The version used in this

study consists of 52 items which can be aggregated to 19 scales.The items have to be self-rated on a 7-point Likert scale ranging

from 0 (never) to 6 (always) indicating how often the subject has

participated in various activities during the past 3 days/nights.

The scale values are calculated by taking the mean of the item

values (2 or 4 per scale). This enables a detailed, multi-dimen-

sional analysis of the individual recovery-stress state. The

RESTQ-Sport consists of 10 stress-associated scales (Total Stress

score, sum of scales 17 and 1315, see Table 1) and 9 recov-

ery-associated scales (Total Recovery score, sum of scales 812

and 1619, see Table 1). The questionnaire shows good relia-

bility as well as construct validity [20, 22, 23]. Players received

detailed instructions prior to the first test and were asked to

complete the RESTQ-Sport at the beginning of all testing ses-sions prior to all other tests and warm-up.

Vertical jump testingLower limb explosive power was assessed using a vertical coun-

ter movement jump (CMJ) and a drop jump (DJ) from a drop

height of 0.35 m. Flight times (t [s]) and contact time were meas-

ured using a contact mat (0.72 0.56 m). The electrical signal

was transmitted to a PC and flight time was recorded (NTG 2.0,

Haynl electronics, Schnebeck, Germany). Jumping height (h)

was calculated according to the formula: h =*9.81 m/s2*t2.

Jumps were performed with the hands placed on the hips. Dur-

ing CMJ players were advised to dip from a standing position and

immediately jump as high as possible. The take off had to bedone as a continuous movement with no observable pause

between downward and upward phases [31]. The drop jumps

had to be performed aiming at maximum height with minimum

contact time [31]. Since the flight time method can be biased by

methodological flaws (e. g. landing with leg or hip flexion, jump-

ing in horizontal direction), an experienced investigator vali-

dated each trial visually. Subjects were instructed to land in a

fully extended position. When a jump deviated from that

instruction, it was not included in the analysis. Both jumps were

performed several times (57) and the best 4 trials were recorded

and averaged for statistical analyses. Reliability of drop jump

height and contact time has previously been shown to be high

(ICC0.98) [11]. Within-subject variation has been shown to beabout 2 % for the CMJ [27].


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Maximal exercise field testMaximal running speed (Vmax) was assessed using an incremen-

tal ramp-like exercise test until volitional exhaustion (mod.

Montreal Track Test [29]). The test was completed on a 200-m

track marked by cones placed every 50 m on a regular soccer

pitch. An artificial turf surface was chosen to minimise the influ-

ence of changing climatic conditions during the season com-

pared to natural grass. Players ran with cleated shoes. Following

an acoustic signal, the subjects performed the incremental field

test, starting from 8.0 km*h1 with speed then increasing by

1.0 km*h1

every minute. The test was terminated when theparticipant failed to reach a marked 5 m zone before the next

cone within the required time for 2 successive 50 m intervals or

if he felt unable to cover another interval at the given speed.

During the test, athletes were verbally encouraged by the techni-

cians and by their coach. If the last step was not completed, Vmax

was calculated according to:

Vmax = Vcompl+ (t/60 s) [km/h]

with Vcompl [km/h] being the last completed step and t [s] the

elapsed time of the uncompleted step.

Vmax during the ramp test has been shown to correlate well with

distances covered at various speeds (total distance, high inten-sity running, very high intensity running; correlation r~0.6) dur-

ing a football match in professional players and, thus, can be

regarded as a valid estimate of football-specific endurance

capacity [29]. Test-retest reliability for the original version of the

Montreal Track test has been reported to be r = 0.97 [25]. Within-

subject variation for peak performance in incremental exercise

tests has been reported to be about 2 % [17].

Heart rate was continuously recorded by means of a heart rate

monitor (Polar S610 and S810, Polar Electro, Kempele, Finland).

The highest heart rate before termination was taken as maxi-

mum heart rate (HRmax). Capillary blood samples (20L) were

taken before, directly after termination as well as 2, 4 and 6 min

after cessation from the hyperemized earlobe for determinationof maximal blood lactate concentrations ([bLa]max, enzymatic-

amperometric method, EBIO Plus, Eppendorf, Hamburg, Ger-

many; CV = 2.9 % for lactate values of 7 mmol*L1).

Statistical proceduresExposure times were not normally distributed and, thus, are

presented as medians. To compare exposure data, non-paramet-

ric statistical procedures were used (Friedman test for seasonal

time course, post hoc: Wilcoxon test).

All other variables were normally distributed. To analyse the

time course of changes in all dependent variables during the

whole season a repeated measures analysis of variance was cal-culated. In case of a significant global time effect, the Scheff test

was applied post hoc. Pearsons product moment correlation

was calculated to analyse absolute changes in performance and

psychological parameters between baseline and in-season test 3.

Spearmans rank correlation was used to compare absolute

changes in stress indicators with exposure times.

To assess effect sizes generalized eta squared (2g) was calcu-

lated as this measure has recently been considered most appro-

priate for repeated measures designs [1]. However, up to now 2g

is not very common in exercise science research. These values

will gain meaning when compared with other findings from

similar, future studies [1] and, thus, are mainly reported to

develop a sense for typical strength and responsiveness of thevarious variables used in this study.

An level of p < 0.05 was accepted as statistically significant.

ResultsThere was a continuous increase in exposure times throughout

the season ( Fig. 1). When analysing the 3 weeks period prior

to the tests, there was a tendency for higher exposure times in

regular matches (p = 0.052) and significantly lower training

exposure (p = 0.007) at in-season 3 compared to in-season 1 and

2. Total exposure (matches and training) was not significantly

different during the 3 weeks prior to all tests (p = 0.15).

Table 1 Results of the Recovery-Stress Questionnaire for Athletes throughout the season. Data as mean SD.

N = 15 baseline in-season 1 in-season 2 in-season 3 ANOVA 2g

1 general stress 0.7 0.4* 2.1 1.2 2.2 0.8 2.3 1.1 < 0.001 0.33

2 emotional stress 1.4 0.5* 2.7 1.0 2.6 0.9 3.3 1.3 < 0.001 0.35

3 social stress 1.8 0.5* 2.9 1.0 3.0 0.9 3.0 1.0 < 0.001 0.27

4 conflicts/pressure 1.7 1.0 2.3 0.9 2.4 1.3( + ) 2.8 0.9 + < 0.001 0.14

5 fatigue 1.8 1.1 2.6 1.6 2.4 1.1 2.8 1.0 0.10 0.08

6 lack of energy 1.6 1.0 2.0 0.8 2.2 1.0 2.6 1.2+ 0.02 0.13

7 physical complaints 1.0 0.7 1.3 0.8 1.7 1.0( + ) 2.4 1.2 + ,# < 0.001 0.27

8 success 2.6 0.9 2.3 1.0 2.6 1.0 2.5 0.8 0.73 0.02

9 social recovery 4.0 0.9 3.9 0.9 3.9 1.1 3.2 1.0( + ),(#) 0.02 0.11

10 physical recovery 3.5 1.1 3.1 1.3 3.5 1.2 3.0 0.9 0.34 0.04

11 general well-being 4.4 0.8 3.6 1.0 3.8 1.2 3.3 1.0+ 0.01 0.14

12 sleep quality 4.3 1.3 3.6 1.5 3.6 1.1 3.3 1.1+ 0.03 0.09

13 disturbed breaks 1.3 0.7 1.4 0.9 1.5 0.7 2.3 1.1+ ,#,() 0.006 0.19

14 emotional exhaustion 0.8 0.7* 1.8 1.2 1.6 0.9 2.3 0.9 < 0.001 0.26

15 injury 2.2 1.3 2.0 1.2 1.6 0.8 3.0 1.0(#), 0.003 0.18

16 being in shape 3.7 1.2 3.3 1.1 3.5 1.0 2.9 0.6 0.09 0.09

17 personal accomplishment 3.5 0.7 2.3 0.8+ 3.0 1.2 2.4 0.8+ 0.001 0.23

18 self-efficacy 4.4 0.9 3.8 1.2 4.1 1.0 3.4 0.5+ ,() 0.006 0.15

19 self-regulation 4.9 0.6 4.3 1.0 4.4 1.0 3.7 0.7+ ,() < 0.001 0.23

2g = generalized eta squared; * = baseline vs. all other tests, + = sign. different from baseline, # = sign. different from in-season 1, = sign. different from in-season 2, (in paren-theses: 0.05 < p < 0.10); scales 17 and 1315 are stress-associated scales and summed up to the Total Stress score; scales 8 12 and 1619 are recovery-associated scales and

summed up to the Total Recovery score


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Recovery-Stress Questionnaire for AthletesSeveral stress scales of the RESTQ-Sport (General Stress, Emo-

tional Stress, Social Stress, Emotional Exhaustion) were signifi-

cantly elevated throughout the whole season compared to

baseline ( Table 1). Furthermore, results from in-season 3 were

significantly deteriorated in 5 scales (Conflicts/Pressure, Lack of

Energy, Sleep Quality, General Well-Being, Personal Accomplish-

ment) compared to baseline and in 6 scales (Physical Complaints,Injury, Disturbed Breaks, Social Recovery, Self-Regulation, Self-

Efficacy) compared to both other in-season tests. The remaining

4 scales (Fatigue, Success, Physical Recovery, Being in Shape)

showed no significant changes throughout the season.

There was a significant main time effect for Total Stress (p < 0.001,

2g= 0.37) and Recovery score (p = 0.001, 2

g= 0.21). Post hoc

testing revealed that Total Stress score was significantly enhanced

at all in-season tests when compared to baseline (p < 0.01) with

a further increase at in-season 3 (p < 0.03, Fig. 2). In addition,

Total Recovery score was decreased at in-season 1 (p = 0.05) and3 (p < 0.001) compared to baseline values and at in-season 3

compared to test 2 (p = 0.06).

Performance Tests

Jumping heights were not significantly affected throughout the

whole season ( Table 2). However, DJ contact time continu-

ously decreased with significantly lower values at in-season 2

(p = 0.02) and 3 (p < 0.001) compared to baseline. There was a sig-

nificant main time effect for the maximal velocity in the ramp

test (p = 0.04). However, post hoc analysis revealed a tendency

for a decrease in Vmax from in-season 1 towards in-season3 (p = 0.08, Table 2). No significant changes in HRmax and

[bLa]max were observed.

Individual reductions in DJ height and Vmax between baseline

and in-season test 3 were significantly correlated with corre-

sponding absolute increases in Total Stress score ( Fig. 3). In

addition, cumulative individual exposure until in-season 3 was

significantly related to absolute changes in Total Stress score

between baseline and in-season 3 ( Fig. 3). Changes in all other

parameters were not significantly related to exposure times

(p > 0.40).

DiscussionThe present study aimed at describing changes in stress indica-

tors during the competitive season in high level football players.

Our data suggest an increase in stress parameters after the prep-

aration period which is mainly displayed by changes in the

recovery-stress state. No relevant effects on physiological per-

formance could be observed throughout the competition period.

Further deteriorations in mood states parameters were apparent

towards the end of the season indicating accumulated stress and

a lack of recovery.

Meeusen et al. [26] recently defined different stages on the

(over)training continuum. Accordingly, overload training is usu-

ally designed to induce relevant adaptations leading to improvedperformance but results also in reversible acute fatigue. If train-

ing (or competition) stress is continued (possibly together with

further non-sport-specific stressors), temporary performance

decrements can occur. This state has been called functional

overreaching. Further disruptions of the balance between train-

ing or competitive stress and recovery will result in prolonged

performance decrements accompanied by severe changes in

psychological or hormonal parameters (non-functional over-

reaching or overtraining syndrome) [26].

A decreased maximal performance capacity during incremental

exercise tests has been observed in several overtraining studies

in endurance athletes [30]. Coutts et al. [2, 3] reported reduc-

tions in maximal oxygen uptake, maximal aerobic velocity andperformance in a multi-stage fitness test after 6 weeks of over-

350

300 regular matches

friendly matches

training250

200

150

100

50

0

30

25

20

15

10

3wee

ksexposuretime[h]

totale

xposuretime[h]

5

0in-season 1 in-season 2 in-season 3

*

Fig. 1 Total exposure until tests (top) as well as during the 3 weeks

period prior to tests (bottom). * = training exposure significantly different

from in-season 1 and 2; Data as medians with lower and upper quartiles.

50*

*

#

#

(*)

Total Stress scoreTotal Recovery score

40

30

score

20

10

0baseline in-season 1 in-season 2 in-season 3

Fig. 2 Total Stress score and Total Recovery score of the Recovery-Stress

Questionnaire for Athletes throughout the season. #= Total Stress score

significantly different from all other tests; * = Total Recovery score signifi-cantly different between marked tests; (in parentheses: 0.05 < p < 0.10).

Data as mean SD.


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load training in semi-professional rugby players. Thus, a

decreased maximal exercise capacity may also be useful as amarker of overreaching in team sport athletes. It seems, how-

ever, questionable, if the slight reduction in Vmax towards the

end of the season, which was observed in the present study, is

really indicative of overreaching. A slight decrease in endurance

capacity seems also possible.

A negative impact of excessive stress on power abilities has pre-

viously been reported in team sport athletes. For instance, Krae-

mer et al. [24] reported deteriorations in speed, jumping heights

and strength parameters during a 11-weeks competitive period

(including 19 matches) in 11 collegiate football (soccer) players.

Those impairments were considered critical for football players,

particularly during the latter stages of the season [24] . Similarchanges in power parameters after an intensive training period

in rugby players were reported by Coutts et al. [2, 3]. These stud-

ies either intended to induce a state of overreaching [2, 3] or ana-

lysed an 11-weeks period of extraordinary high match exposure

on performance markers [24]. The exact reasons for the reported

deteriorations in speed and power are unknown. In the present

study jumping heights remained unaffected. A significant

decrease in drop jump contact time from baseline to the first in-

season test was observed. This improvement is likely due to the

pre-season training which comprised plyometric training and

football-specific movement pattern including stretch-shorten-

ing-cycle activities. During the season drop jump contact time

remained nearly constant.To summarize, the slight changes in Vmax as well as in drop jump

contact time during the season seem to be of minor practical

relevance. Therefore, when comparing the results of Coutts et al.

[2, 3] and Kraemer et al. [24] with our data, it seems justified to

conclude that on a group average no relevant physiological signs

of fatigue or overreaching were present over the course of the

football season.

More pronounced changes could be observed in the recovery-

stress state. The RESTQ-Sport has been used in different sports

for monitoring the impact of training on mood states [4, 19 21].

Considerable differences in most RESTQ-Sport scales as well as

in Total Stress and Total Recovery scores between baseline and

in-season measurements may refl

ect increased stress during theseason compared to a more recovered state after the transition

period prior to the beginning of the season. However, no extraor-

dinary in-season values were observed. Mean group values for

all subscores were between 2 and 3 (according to sometimes)

for the stress scales and around 4 (according to often) for the

recovery scales on the 7-point Likert scale. Towards the end of

the season further deteriorations in several areas were present.

At in-season 3 players had the highest cumulated as well as the

highest acute match exposition. A moderate correlation was

observed between cumulated total football exposure and abso-

lute changes in Total Stress score. Furthermore, both participat-

ing teams were involved in the struggle against relegation. It

may be speculated that this could at least partly be responsiblefor the observed changes in the recovery-stress state. In particu-

4

2

0

r = 0.55,

r = 0.61,

r = 0.52,

p = 0.03

p = 0.02

p = 0.05

2

DJheight[cm]

Vmax

[km+h1]

Totalexposure[h]

4

6

8

10

1.0

0.5

0.0

0.5

1.0

1.5

450

400

350

300

250

200

150

5 0 5 10 15 20 25

5 0 5 10 15 20 25

5 0 5

RESTQ-Sport Total Stress score



10 15 20 25

Fig. 3 Correlations between absolute changes (baseline to in-season

test 3) in RESTQ-Sport Total Stress score and absolute changes in drop

jump height (DJ, top), maximal ramp test velocity (Vmax, middle) and

cumulative total exposure (bottom). RESTQ-Sport = Recovery-Stress

Questionnaire for Athletes.

Table 2 Results of the

performance tests throughout

the season. Data as mean SD.

N = 15 baseline in-season 1 in-season 2 in-season 3 ANOVA 2g

CMJ height [cm] 36.4 2.5 36.4 2.7 36.6 3.4 36.7 4.0 0.96 0.002

DJ height [cm] 34.6 3.4 34.9 4.2 34.2 4.7 33.4 4.6 0.21 0.02

DJ contact time [ms] 217 38* 203 26 198 34 192 28 < 0.001 0.08

Vmax [km*h1] 18.0 0.8 18.3 0.7 18.0 0.8 17.9 0.9(#) 0.08 0.04

HRmax [min1] 194 8 192 7 192 6 191 6 0.31 0.03

[bLa]max [mmol*L1] 11.2 2.0 10.7 2.2 10.3 2.1 10.3 2.0 0.23 0.03

2g = generalized eta squared; CMJ = counter movement jump, DJ = drop jump, V max = maximal velocity, HRmax= maximal heart rate,[bLa]max = maximal blood lactate concentration. * = baseline vs. in-season 2 and 3,

#

= sign. different from in-season 1, (in parentheses:0.05 < p < 0.10)


6/7



lar, the observed deteriorations in scales like Self-Efficacy, Self-

Regulation, Conflicts/Pressure, Emotional Exhaustion, Social

Recovery and Personal Accomplishment might have been influ-

enced by this fact.

Psychological deteriorations are among the first signs of over-

reaching in endurance sports [30]. Thus, the observed changes

might be interpreted as beginning overreaching, although no

physiological impairments were present. Whereas the mean

group scores are not extraordinary, individual players could beidentified who showed a diminished recovery-stress state.

Therefore, individual changes of the recovery-stress state might

indicate which players are at risk for developing (non-functional)

overreaching. In this regard the correlations between changes in

Total Stress score and DJ height and Vmax are of interest. Indi-

viduals with the greatest increase in stress state showed also the

most pronounced impairments in reactive power and maximal

running capacity.

In football deteriorations on a group level might have an impor-

tant impact on team performance. However, the early recogni-

tion of individual impairments seems to be more relevant to

identify players who are at risk of developing a state of (non-

functional) overreaching. Both psychometric questionnaires(intentional manipulation, for instance because players fear that

the coach will make substitutions [30]) as well as maximal per-

formance testing (repeated maximal effort necessary) are sus-

ceptible for methodological biases when frequent testing is

intended. Thus, a combined assessment of psychological and

performance measures might be recommended for practical

purposes.

Interestingly, deteriorations in the recovery-stress state towards

the end of the season were particularly present in scales like

Physical Complaints and Injury (indicating muscle stiffness and

vulnerability to injury). Junge et al. [18] observed that nearly

80 % of football players from the 3 highest Czech divisions suf-

fered from physical complaints with about half of those playersreporting muscle/tendon pain. The authors concluded that the

prevalence of such complaints should be considered in medical

care of football players. In addition, Ekstrand et al. [7] observed

that about 30 % of the players who played regularly in interna-

tional matches during the end of the season were injured during

the FIFA World Cup 2002. An influence of accumulated stress

and fatigue at the end of the season on injury proneness (in par-

ticular to muscle or overuse injuries) should, thus, be consid-

ered. This might be important because muscle injuries are the

most common injury type in high level male football [6, 8, 14] . In

accordance with Ekstrand et al. [7] it can be concluded that play-

ers may cope with high demands in the short-term (here: 3

weeks). However, negative impact of accumulated fatigue onperformance and injury proneness in the long-term cannot be

ruled out.

Limitations of the StudyAlthough our participants were playing at a national level, the

question remains whether the present results can be easily

transferred to professional football at the international level.

Average match and training exposure of the players in the

present study (1 to 1.5 match hours and 6 training hours per

week) is comparable to that of professional football players com-

peting at the highest level in the UEFA Champions League (41match hours and 213 training hours during a 44 weeks season

[6]). Nevertheless, these are average values and in single players

exposure times can be considerably higher [6, 7] . Moreover, no

statement with regard to the influence of training and match

intensity on the analysed parameters can be made from the

present data. Additionally, further stressors (e. g. mass media,

financial burdens, frequent travelling) have to be considered in

elite players which necessitates careful transfer of our results.

Further research is necessary for evaluating stress in more out-

standing players. Otherwise, professional players are probablyvery carefully monitored while, for instance, high level youth

players are also exposed to a high number of matches but medi-

cal and scientific support is less common. Thus, the present

results are certainly of interest for this population, too.

A further limitation might be seen in the choice of parameters

which were assessed in the present study. Exercise-induced

fatigue is a complex phenomenon resulting in symptoms of sev-

eral organ systems. A huge amount of possible markers has been

investigated during the past decades, including biochemical,

immunological, vegetative, hormonal, physiological, and psy-

chological parameters [12, 15, 26, 30]. The present study was not

designed as a broad based analysis of a wide variety of parame-

ters. In contrast, it was intended to assess stress and fatigue witha well-founded economical test panel which can be easily applied

in daily practice.

In addition to the chosen performance parameters, match analy-

sis may be seen as the best indicator of real competition per-

formance in football players and, thus, might be considered for

future research in this area. Such an approach, however, is very

complex and expensive. Moreover, as match performance char-

acteristics of football players are dependent on the opponent

and on tactical aspects and high-intensity activities during

match play show high match-to-match variability [13], it seems

questionable, whether such an approach would have benefit in

detecting acute fatigue-induced performance decrements.

Conclusions and Future PerspectivesFrom the results of the present study it is concluded that usual

match exposure under professional circumstances does not

induce relevant physiological signs of overreaching in high level

football players on a group level. Nonetheless, accumulated

stress and a lack of recovery towards the end of a season might

be indicated by deteriorations in the recovery-stress state. Com-

bined psychological and performance testing is recommended

to identify single players who are at risk for developing over-

reaching.

Future research should be designed to focus on individualresponses to excessive overload, on the transferability of the

results to the elite level, on a possible link between overreaching

and injury proneness as well as on appropriate interventions to

avoid severe deteriorations.

AcknowledgementsWe thank all players as well as the coaches of the participating

clubs. Oliver Faude received a Joo Havelange scholarship from

FIFA (Federation International de Football Associations, Zurich,

Switzerland) and the International Centre for Sports Studies

(CIES, Neuchatel, Switzerland) for this project.


7/7



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