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Mental Fatigue Impairs Soccer-Specific
Physical and Technical Performance
MITCHELL R. SMITH
1,2
, AARON J. COUTTS
1
, MICHELE MERLINI
3
, DIETER DEPREZ
2
, MATTHIEU LENOIR
2
,
and SAMUELE M. MARCORA
3
1
Sport and Exercise Discipline Group, Faculty of Health, University of Technology Sydney, AUSTRALIA;
2
Department of
Movement and Sports Sciences, Faculty of Medicine and Health Sciences, Ghent University, BELGIUM; and
3
Endurance
Research Group, School of Sport and Exercise Sciences, University of Kent at Medway, UNITED KINGDOM
ABSTRACT
SMITH, M. R., A. J. COUTTS, M. MERLINI, D. DEPREZ, M. LENOIR, and S. M. MARCORA. Mental Fatigue Impairs Soccer-
Specific Physical and Technical Performance. Med. Sci. Sports Exerc., Vol. 48, No. 2, pp. 267–276, 2016. Purpose: To investigate
the effects of mental fatigue on soccer-sp ecific physical and technical performance . Methods: This investigation consisted of
two separate studies. Study 1 assessed the soccer-specific physical performance of 12 moderately trained soccer players using the Yo-Yo
Intermittent Recovery Test, Level 1 (Yo-Yo IR1). Study 2 assessed the soccer-specific technical performance of 14 experienced soccer
players using the Loughborough Soccer Passing and Shooting Tests (LSPT, LSST). Each test was performed on two occasions and
preceded, in a randomized, counterbalanced order, by 30 min of the Stroop task (mentally fatiguing treatment) or 30 min of reading
magazines (control treatment). Subjective ratings of mental fatigue were measured before and after treatment, and mental effort and
motivation were measured after treatment. Distance run, heart rate, and ratings of perceived exertion were recorded during the Yo-Yo IR1.
LSPT performance time was calculated as original time plus penalty time. LSST performance was assessed using shot speed, shot ac-
curacy, and shot sequence time. Results: Subjective ratings of mental fatigue and effort were higher after the Stroop task in both studies
(P G 0.001), whereas motivation was similar between conditions. This mental fatigue significantly reduced running distance in the Yo-Yo
IR1 (P G 0.001). No difference in heart rate existed between conditions, whereas ratings of perceived exertion were significantly higher at
iso-time in the mental fatigue condition (P G 0.01). LSPT original time and performance time were not different between conditions;
however, penalty time significantly increased in the mental fatigue condition (P = 0.015). Mental fatigue also impaired shot speed (P =0.024)
and accuracy (P G 0.01), whereas shot sequence time was similar between conditions. Conclusions: Mental fatigue impairs soccer-specific
running, passing, and shooting performance. Key Words: COGNITIVE FATIGUE, FOOTBALL, SOCCER SKILLS, INTERMITTENT
RUNNING, PERCEPTION OF EFFORT
P
rolonged periods of demanding cognitive activity in-
duce mental fatigue; a psychobiological state charac-
terized by feelings of tiredness and lack of energy (3,23).
Many studies have demonstrated the negative impact of
mental fatigue on cognitive function and skilled performance
in settings such as driving (3,4,16). Several investigations
have also examined the effects of mental fatigue on physi-
cal performance, revealing that mental fatigue has limited
influence on maximal voluntary activation and strength, ex-
plosive power, and anaerobic work capacity (24,32,37,38).
In contrast, mental fatigue has been consistently shown to
impair performance during self-paced (8,31) and constant
load (23,32) tests of endurance. Although these investiga-
tions have identified the negative effect of mental fati gue
on performance during continuous exercise, little is known
about the impact of mental fatigue on physical performance
in team sports that require intermittent running. Furthermore,
despite many anecdotal reports in the media that mental fa-
tigue has a negative effect on team sport performance, to the
best of our knowledge, the effects of mental fatigue on tech-
nical and tactical performance in team sports have never been
investigated.
One previous study investigating the demands of rugby,
reported increased feelings of fatigue in players after a match
(25). However, these results should be interpreted with caution
as the Profile of Mood States questionnaire used to measure
fatigue is not able to distinguish between symptoms of physical
and mental fatigue after a match (26). Nevertheless, it is likely
that a combination of physical and mental fatigue contribute
to the reports of increased fatigue postmatch. Indeed, it has
been suggested that team sports place significant cognitive de-
mands on athletes as they are required to maintain concentration
over prolonged periods and make fast and accurate decisions
based on the retrieval and processing of information from a
dynamic environment (29,41).
Address for correspondence: Mitchell Smith, Bach (Hons), Sport and Exercise
Discipline Group, Faculty of Health, University of Technology Sydney, Eton
Rd, Lindfield, New South Wales, Australia; E-mail: Mitchell.Smith@uts.edu.au.
Submitted for publication April 2015.
Accepted for publication August 2015.
0195-9131/16/4802-0267/0
MEDICINE & SCIENCE IN SPORTS & EXERCISE
Ò
Copyright Ó 2015 by the American College of Sports Medicine
DOI: 10.1249/MSS.0000000000000762
267
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Examining changes in performance throughout a match
also provides some insight into the impact of fatigue on
performance in team sports. Several time-motion analysis
investigations have reported general reductions in distance
covered throughout a match and transient reductions in dis-
tance covered after high-intensity periods (9,27,34). Others
have shown reductions in quality and quantity (9,35,36) of
technical performance as matches progress. These reductions in
physical and technical performance (known as match-related
fatigue) are also likely to result from the combination of mental
and physical fatigue induced by a match. However, it is difficult
to isolate the impact of mental fatigue on team sport perfor-
mance in an ecological setting as it is impractical to induce
mental fatigue before competitive matches. Therefore, research
must use valid and reliable tests to assess the effects of mental
fatigue on factors that contribute to team sport performance.
To date however, only one study has examined the effects
of mental fatigue on a factor directly associated with team sport
performance: intermittent running (38). In this investigation,
10 team sport players performed a 45-min intermittent run-
ning protocol after a mentally fatiguing and control treatment.
Mental fatigue reduced running velocities at low intensities,
whereas high-intensity and peak sprint velocities remained
similar between cond ition s. This study provi des ini tia l evi-
dence that mental fatigue impairs intermittent running per-
formance and is likely to influence player activity profiles
during a match.
Although running profiles during a match partially con-
tribute to performanc e in most team sports, technical aspects
are also important in determining match outcome. Recently,
Duncan et al. (10) reported a negative influence of mental
fatigue on perceptual and motor skills of athletes. Although
the tasks performed in this previous investigation were
validated laboratory tests, they were not sport specific in
nature, and it is unknown whether the results would directly
translate into impaired team sport performance (10). There-
fore, investigation into the effects of mental fatigue on
sport-specific technical performance is warranted. Additional
research is also required to confirm the initial finding that
mental fati gue impairs intermittent running performance in
team sport players (38). Therefore, in this paper, we present
the findings of two related studies in soccer players. The
purpose of study 1 was to investigate the effects of mental
fatigue on physical performance assessed using the Yo-Yo
intermittent recovery test, level 1 (Yo-Yo IR1) (14).
The purpose of study 2 was to investigate the effects of
mental fatigue on technical performance assessed using the
Loughborough soccer passing (LSPT) and shooting (LSST)
tests (1). We hypothesised that mental fatigue would impair
both p hysical and technical performance in soccer players.
METHODS
Participants
Table 1 provides descriptive characteristics of participants
from both studies. All participants were male soccer players,
recruited from local soccer teams or universities and regu-
larly participating in training and competition. Participants
for study 1 were recreational players, whereas participants
from study 2 were well-trained competitive players (Belgian
league, divisions 2–7). All were free from medication and
provided written informed consent before participation. Pa-
rental consent was provided for participants younger than
18 yr (n = 3; study 2), and procedures set by the university
ethics committee for dealing with minors were follow ed.
The studies_ procedures were approved by the local research
ethics committees of the University of Kent (study 1) and
Ghent University (study 2) and follow the ethical principles
for medical research involving human subjects set by the
World Medical Association Declaration of Helsinki. Partici-
pation in this investigation resulted in no adverse effects.
Participants were provided with written instructions outlining
the studies_ procedures but were not informed of their aims.
Instead, participants were informed that the study was inves-
tigating the effects of reading, a common prematch activity, on
heart rate during intermittent running (study 1) or technical
performance (study 2).
Experimental Overview
Both studies were crossover trials. Participants visited the
respective testing facilities on three separa te occasions, with
the first visit functioning as a familiarization session. The
remaining two visits (control and mental fatigue sessions)
were performed in a randomized and counterbalanced order
generated by online software (rando mization.com). The re-
searchers asses sing the outcome measures were blin ded to
treatment. Participants completed all testing sessions at the
same time of day (within 1 h), separated by a minimum of
48 h. Session starting times ranged from 08:00 to 16:30, with
85% of sessions star ting between 09:30 and 11:30 or 13:00
and 15:30.
Study 1. On the first visit, participants in study 1 were
provided with standardized instructions for memory an-
choring of Borg_s 6 to 20 rating of perceived exertion (RPE)
scale (5) as well as visual analogue scales (VAS) for the
assessment of mental fatigue, mental effort, and motiva-
tion. Participants were also familiarized with the mentally
fatiguing task (Stroop task) and the Yo-Yo IR1. Pretest in-
structions were provided for the upcoming testing sessions.
Specifically, participants were instructed to sleep for at
least 7 h, drink at leas t 35 mL of water p er kilogram of body
mass, refrain from consumption of alcohol, and avoid vigor-
ous exercise the day before each of the following visits. Par-
ticipants were also requested to avoid caffeine and nicotine
TABLE 1. Participant characteristics.
Study 1 Study 2
No. of participants 12 14
Age (yr) 24.0 T 0.4 19.6 T 3.5
Height (cm) 175.3 T 1.3 176.7 T 5.7
Weight (kg) 76.1 T 2.0 67.8 T 8.3
Playing experience (yr) Unknown 13.6 T 3.2
Values presented as mean T SD.
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for 3 h prior and consume a light meal 2 h before testing.
Compliance with these instructions was assessed with
pretest checklists upon arrival for the testing sessions. All
participants reported adherence to the pretest instructions;
however compliance with these instructions was not assessed
using objective measures.
After completion of the pretest checklist, participants
provided a subjective rating of mental fatigue using a VAS,
before completing one of two 30-min reading tasks. In the
control session, participants leisurely read from a selection
of emotionally neutral magazines. In the mental fatigue
session, participants completed a paper version of the Stroop
task. Mental fatigue was again assessed after the reading task,
along with mental effort and motivation. After the VAS, par-
ticipants performed a 2-min running warm-up and the Yo-Yo
IR1. Heart rate (HR; Polar, OY, Finland) was measured beat
by beat and averaged every 5 s during the Yo-Yo IR1. HR
values and RPE were recorded at the end of each level of the
Yo-Yo IR1 and also at the point of exhaustion. In both con-
ditions, participants were instructed to run until exhaustion;
however, no additional motivational intervention was pro-
vided before or during the Yo-Yo IR1.
Study 2. On the first visit, participants in study 2 were
provided with the same standardized instructions for the use
of the VAS assessing mental fatigue, mental effort, and
motivation. Participants were also familiarized with the
mentally fatiguing task (Stroop task) and the LSPT and
LSST. Participants performed at least two trials of the LSPT
and eight shot sequences of the LSST. If after these initial
trials, participants were still uncomfortable with either test,
extra trials were completed until the participant and investi-
gators were satisfied with familiarization . Participants were
provided with the same pretest instructions as study 1, and
compliance was ensured using a pretest checklist upon arrival
for the testing sessions.
The control and mental fatigue sessions in study 2 followed
the same procedures as study 1 until the point of warm-up.
Study 2 involved a 3-min warm-up with a ball, incorporating
passing, dribbling, and ball control elements. After warm-up,
participants completed 2 trials of the LSPT; separated by a
1-min rest. After another 2-min rest, parti cipants completed
two trials of the LSST, separa ted by a 3-min rest. This 3-min
rest comprised 2 min of passive rest, followed by 1 min of
active rest with the ball. Therefore, all procedures were com-
pleted within 40 min of finishing the reading task. This study
used two trials of the LSPT and LSST to provide more reli-
able data and extend the session to a length similar to a half
soccer match. No motivational intervention was provided
before or during the soccer-specific skills tests.
Treatment
Mentally fatiguing treatment. Mental fatigue was
induced using a 30-min modified Stroop color-word task.
The Stroop task demands response inhibition and sustained
attention (20,31) and has previously been shown to induce
mental fatigue (37). The Stroop task used in this investi-
gation was a paper version of that previously used by
Pageaux et al. (31). Four words (red, blue, green, and yellow)
were displayed in a random order on five sheets of A4 paper
with 45 words printed on each sheet. Participants were
required to verbally respond to each word, with the correct
response corresponding to the ink color of the word (red,
blue, green, and yellow), rather than the words_ meaning.
Therefore, if the word ‘‘green’’ was printed in blue ink, the
correct response was ‘‘blue.’’ However, if the ink color of
the word was red, the correct response corresponded to the
meaning of the word, rather than its printed color. There-
fore, if the word ‘‘green’’ was displayed in red ink, the cor-
rect answer was ‘‘green.’’
Participants_ verbal responses were monitored by a member
of the research team who sat with the participants throughout
treatment. When an error was made, participants were re-
quired to return to the start of the current row of words and
continue as normal. To increase motivation for the task, a
competitive environment was created, whereby participants
were challenged to successfully complete more words than
the other participants within the 30-min period.
Control treatment. The control treatment invol ved
30 min of reading at a leisurely pace from a selection of
magazines, which varied in theme, including sport, cars, and
travel. Pilot testing on six individuals revealed that 30 min
of reading from these magazines was emotionally neutral,
according to the Brunel Mood Scale (BRUMS) (39). Partici-
pants completed both treatments in the same room, under the
supervision of the same researcher.
Subjective Ratings
Subjective ratings of mental fatigue, mental effort, and
motivation were scored using 100-mm VAS. The scales
were anchored at one end with ‘‘none at all’’ and at the other
end with ‘‘maximal.’’ No other markings were displayed on
the scales. Participants were asked to mark on the line the
point that they felt represented thei r perception of their
current state. The VAS score was determined by a member
of the research team by measuring in millimeters from the
left hand end of the line to the point that the participant
marked. Mental fatigue was measured before and after treat-
ment as a manipulation check, whereas mental effort and
motivation were only measured after treatment. Mental effort
referred to the reading task that had just been completed,
whereas motivation referred to the upcoming soccer-specific
performance tests.
Soccer-Specific Perform ance Tests
Yo-Yo intermittent recovery test, level 1. The Yo-
Yo IR1 is a valid and reliable test of physical performance
for soccer players (2,14). In a review of the Yo-Yo inter-
mittent recovery tests, Bangsbo et al. (2) reported coefficients
of variation between 4.9% and 8.7% for the Yo-Yo IR1. The
test involves repeating 2 20-m runs (up and back = 1 bout)
MENTAL FATIGUE AND SOCCER PERFORMANCE Medicine & Science in Sports & Exercise
d
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between cones at progressively increasing velocities. Run-
ning bouts are separated by 10 s of active recovery in which
the participant walks or jogs around a cone 5 m aw ay and
returns to the starting line. Participants continue the test until
they have failed to reach the finish line in time (dictated by
recorded beeping sounds) on two occasions, at which point the
distance covered is recorded as the test result. The Yo-Yo IR1
was completed on an indoor futsal pitch.
Loughborough soccer passing test. The LSPT and
LSST were developed and validated for research purposes
by Ali et al. (1) to assess soccer-specific technical perfor-
mance. The layout and detailed procedures of the LSPT and
LSST can be found in the validating study (1). Briefly, for
the LSPT, participants were required to make 16 passes (of
approximately 4 m) agains t standard gymnasium benches,
positioned in a rectangle around the player. A colored piece
of cardboard (0.6 0.3 m) was attached to each bench,
serving as a target area, and passes were performed in one
of four rando m color orders selec ted by an investigator.
Participants were instructed to complete the 16 passes as fast
as possible, while minimizing errors. Outcome measures
for the LSPT included original time (time taken to complete
all 16 passes), penalty time (time added for errors, inaccu-
rate passes, and slow performance), and performance time
(original time + penalty time). Penalty time was calculated
according to the following criteria:
+5 s for completely missing the bench or passing to the
wrong bench
+3 s for missing the target area (0.6 0.3 m)
+3 s for handling the ball
+2 s for passing the ball from outside of the p ass-
ing area
+2 s if the ball touched any cone
+1 s for every second taken over the allocated 43 s to
complete the test
j1 s for each pass that hit the 10-cm strip in the middle
of the target
The previously calculated standard errors of measurement
for these outcome variables are 2, 4, and 5 s for original time,
penalty time, and performance time, respectively (1).
Loughborough socc er shooting test. The LSST
primarily tests soccer shooting ability but also includes
passing, ball control, agility, and sprinting components.
Participants began the test 20 m away from the goal line,
with their back to the goal. They were required to sprint and
touch one of two cones (left or right) positioned 6 m diago-
nally behind them. Participants then returned to the starting
position and passed a ball against a bench before controlling,
turning, and shooting the ball at goal. Participants then
sprinted past a stationary goalkeeper to replicate following
their shot in a game. Each trial was made up of 10 shots
(5 with each foot), separated by 1-min rest periods. One of
six random trial orders was selected for each participant.
Performance in the LSST was assessed using shot accu-
racy, shot speed, and shot sequenc e time. Shot accuracy
was calculated as the mean of the total points accumu-
lated from all shots on target. Score zones were arranged to
encourage shooting toward the corners of the goal, and
points were only scored if the ball struck the open space
of the goal (oppos ite side to the goalkeeper). Time to com-
plete each shot sequence was timed, and shot speed was
estimated using high-speed (300 frames per second) video
recording and video analysis software (Kinovea open source
project, www.kinovea.o rg). Shots that were attempted from
outside of the shooting area, took more than 8.5 s to complete,
and/or traveled at less than 64 kmIh
j1
were discounted. As
shot speed was assessed using 2D video analysis rather than
radar technology, values should be viewed as estimates.
Furthermore, shot speed data was analyzed in only 12 of
the 14 participants because of poor video quality from two
testing sessions. The previously calculated standard errors
of me asu rem ent for these outcome variables are 0.54 points,
5.1 kmIh
j1
, and 0.25 s for shot accuracy, shot speed, and shot
sequence time, respectively (1).
Statistical Analyses
All data are presented as mean T SD. After testing for
normality, performance, HR and RPE (at exhaustion), mental
effort, and motivation data were analyzed using paired sam-
ples t tests. HR and RPE (during Yo-Yo IR1) and mental
fatigue data were analyszed using two-way (condition time)
fully repeated-measures analysis of variance. Analysis of
variance for HR and RPE (during Yo-Yo IR1) data included
values meas ured at the end of each level of the Yo-Yo IR1,
up to 760 m (end of level 14). Values recorded beyond
this point were excluded from analysis as players began to
drop out of the test from level 14 onward. When the sphe-
ricity assumption was violated, the Greenhouse–Geisser cor-
rection was used. Significance was set at 0.05 (two-tailed)
for all analyses, which were completed using SPSS (version
20; IBM, NY). Effect sizes (ES) were calculated in Micro-
soft Excel (Microsoft, Redmond) according to the methods
suggested by Morris and DeShon (28) for investigations using
repeated measures designs (equation 8).
RESULTS
Study 1
Subjective ratings. Subjective ratings of mental fatigue
increased significantly after the Stroop task but not the con-
trol treatment (condition–time interaction: F
(1,11)
= 255.74,
P G 0.001). Follow-up tests revealed no significant differ-
ence in subjective ratings of mental fatigue before treat-
ment (mental fatigue: 8 T 9 AU; control: 6 T 8AU;t
11
=1.332,
P = 0.210); however, after treatment, ratings were signifi-
cantly higher in the mental fatigue condition (52 T 11 AU)
compared with the control condition (12 T 8AU;
t(11) = 16.80, P G 0.001). Subjective ratings of mental effort
were also higher for the Stroop task (70 T 20 AU) than the
control treatment (23 T 20 AU; t
11
= 10.81, P G 0.001).
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Motivation for the upcoming Yo-Yo IR1 did not differ
between conditions (mental fatigue: 56 T 21 AU; control:
58 T 27 AU; t
11
= 0.833, P = 0.423).
Intermittent running performance. Figure 1 displays
the individual distances covered during the Yo-Yo IR1. On
average, participants covered significantly shorter distances
in the mental fatigue condition (1203 T 402 m) than in
the control condition (1410 T 354 m; t
11
=7.194,P G 0.001,
ES = 2.37). Individual distance covered was shorter in the
mental fatigue condition in all 12 participants, with an
average individual impairment of 16.3% T 5.1% (95%
confidence interval). No significant effects of session order
existed for Yo-Yo IR1 performance (Session 1: 1310 T
419 m; Session 2: 1302 T 356 m; t
11
= 0.109, P = 0.915).
Psychophysiological responses to intermittent
running. No significant condition–time interactions were
observed for HR or RPE; however, both HR and RPE in-
creased over time during the Yo-Yo IR1 (HR: F
(2.02, 22.16)
=
888.23, P G 0.001; RPE: F
(1.76, 19.32)
= 233.06, P G 0.001;
Fig. 2). HR was not significantly different between con-
ditions; however, RPE at iso-time was significantly higher
in the mental fatigue condition than in the control condi-
tion (main effect of condition: F
(1, 11)
= 43.11, P G 0.01).
No significant differences in HR or RPE (range, 18–20 in
both conditions) were measured at the point of exhaustion.
Study 2
Subjective ratings. Subjective ratings of mental fatigue
increased significantly after the Stroop task but not the con-
trol treatment (condition–time interaction: F
(1, 13)
= 18.14,
P = 0.001). Follow-up tests revealed that pretreatment sub-
jective ratings of mental fatigue wer e higher in the control
condition (35 T 22 AU) than the m ental fatigue condition
(22 T 11 AU; t
13
= 2.81, P = 0.015), but posttreatment
ratings of mental fatigue were signifi cantly higher in the
mental fatigue condition (58 T 22 AU) than in the control
condition (39 T 25 AU; t
13
=2.77,P = 0.016). Subjective
ratings of mental effort were also higher for the Stroop task
(69 T 19 AU) than the control treatment (29 T 18 AU; t
13
=
7.19, P G 0.001). M otiva tio n for the upcomin g LSP T an d
LSST did not differ between conditions (mental fatigue:
80 T 12 AU; control: 76 T 12 AU; t
13
=1.50,P = 0.159).
Passing and shooting performance. A summary of
the LSPT and LSST scores for both condit ions is presented
in Table 2. LSPT original time was not significantly differ-
ent between conditions; however, penalty time was signi-
ficantly higher in the mental fatigue condition than in the
control condition (Fig. 3). Performance time was not signi-
ficantly different between conditions. No significant effects
of session order existed for original time (Session 1: 46.8 T
5.0 s; Session 2: 48.9 T 3.8 s; t
13
= 1.25, P = 0.232), penalty
time (Session 1: 6.5 T 8.5 s; Session 2: 8.6 T 6.1 s; t
13
=0.625,
FIGURE 1—Effects of mental fatigue on Yo-Yo Intermittent Re-
covery Test, Level 1 performance. *Significant main effect of con-
dition (P G 0.05).
FIGURE 2—Effects of mental fatigue on psychophysiological responses
to Yo-Yo Intermittent Recovery Test, Level 1. A: heart rate . B: rating
of percei ved exertion. #Signific ant main effect of time (P G 0.05).
*Significant m ain effect of condition (P G 0.05). Data presented as
mean T SD.
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P = 0.543), or performance time (Session 1: 53.4 T 11.1 s;
Session 2: 57.5 T 7.9 s; t
13
=0.955,P =0.357).
Participants performed less accurate and slower shots on
the LSST in the mental fatigue condition. Average shot se-
quence time tended to be slower in the mental fatigue con-
dition, but differences were not significant. No significant
effects of session order existed for shot accuracy (Session 1:
1.6 T 0.8 points; Session 2: 1.8 T 0.5 points; t
13
= 0.834,
P = 0.419), shot speed (Session 1: 83.7 T 4.5 kmIh
j1
;Session
2: 83.1 T 6.3 kmIh
j1
; t
11
=0.409,P = 0.691), or shot se-
quence time (Session 1: 8.2 T 0.3 s; Session 2: 8.0 T 0.3 s;
t
13
=1.91,P =0.079).
DISCUSSION
The curren t investigation used two separate studies to test
the hypothesis that mental fatigue impairs soccer-specific
physical and technical performance. In agreement with our
hypotheses, the participants covered shorter distances during
intermittent running, committed more passing and ball con-
trol errors, and performed slower and less accurate shots on
goal when mentall y fatigued.
Mental Fatigue, Mental Effort, and Motivation
The Stroop task requires sustained attention and response-
inhibition and, when performed for prolonged periods, has
been shown to induce a state of mental fatigue (37). The
current results align with these previous findings, with sub-
jective ratings of mental fatigue increasing from pre- to
post-Stroop, whil e rem ai ning steady in the contro l con di-
tion. As previously menti oned, the Stroop task used in the
current study was a paper variation of that used by Pageaux
et al. (31). Interestingly, Pageaux et al. (31) did not observe
increased ratings of mental fatigue after the computer-
based version of the Stroop task. These contrasting find-
ings may result from the different scales used to assess
fatigue or the different variation of the Stroop task used to
induce mental fatigue.
In the current investigation, mental fatigue was assessed
using a 100-mm VAS, whereas Pageaux et al. (31) used the
fatigue subscale (score of 0–16 AU) of BRUMS (39) de-
rived from the Profile of Mood States. It is possible that
the VAS is a more sensitive measure of mental fatigue than
the BRUMS. Indeed, the VAS used in this investigation
provided a score range from 0 to 100 AU, specifically re-
lated to mental fatigue. In contrast, the BRUMS provides
a score range from 0 to 16 AU, based on subjective feelings
of tiredness (four synonymous words scored from 0 to 4 AU
each). Although the BRUMS is a validated mood scale, the
fatigue subscale is not specific to mental fatigue but as-
sesses general tiredne ss . Further more , the paper version of
the Stroop task may be more demanding than the c omputer-
based version. Indeed, response inhibition is a critical com-
ponent of mentally fatiguing tasks. In the paper version of
the Stroop task, participants are required to audibly respond
to each word, whereas in the computer version, participants
are only required to press a button matching the color of
the displayed word. It is likely that inhibiting the natural
response to audibly read each word in the paper version is
more difficult than the task of pressing a color-matched
button. Nevertheless, it is clear that performing the Stroop
task used in the current investigation for 30 min successfully
induced mental fatigue. This finding is to be expected,
considering the higher mental effort required by this de-
manding cognitive task compared with reading magazi nes
at leisurely pace.
TABLE 2. Effects of mental fatigue on soccer-specific technical performance.
Control Fatigue t df P ES
LSPT
Original time (s) 47.9 T 4.1 47.8 T 4.9 0.14 13 0.893 0.04
Penalty time (s) 5.2 T 7.6 9.9 T 6.5* 2.93 13 0.012 0.76
Performance time (s) 53.1 T 10.5 57.7 T 8.5 2.05 13 0.061 0.55
LSST
Points per shot 2.0 T 0.5 1.3 T 0.6* 3.24 13 0.006 0.75
Shot speed (kmIh
j1
) 85.0 T 5.6 81.8 T 4.7* 2.62 11 0.024 0.75
Shot sequence time (s) 8.0 T 0.3 8.2 T 0.3 1.90 13 0.080 0.48
*Significantly poorer performance than control (P e 0.05).
Values presented as mean T SD.
ES, Effect size; LSPT, Loughborough Soccer Passing Test; LSST, Loughborough Soccer Shooting Test.
FIGURE 3—Effects of mental fatigue on Loughborough soccer passing
test performance. *Significant main effect of condition for penalty time
(P G 0.05). Data presented as mean T SD.
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According to Brehm_s theory (7), motivational factors
play a key role in determining the maximal level of effort
one is willing to exert to succeed in a particular task (i.e.,
potential motivation). Although no incentive was offered in
the current investigation, results revealed that participants
were moderately to highly motivated for the soccer-specific
tests of physical and technical performance. Crucially, there
was no difference in motivation between conditions. This
finding is of particular interest, considering changes in moti-
vation are strongly linked to mental fatigue (4). Furthermore,
ego depletion and reward-based theories of cognitive control
suggest that reduct ions in motivation may be responsible
for performance impairments on the second of two demand-
ing tasks (6,11). However, changes in motivation after a de-
manding task are likely dependent on the subsequent task to
be performed. Indeed, Inzlicht et al. (13) suggest that acts of
self-control lead to shifts in motivation away from ‘‘have-to’’
goals toward ‘‘want-to’’ goals. It is likely that in the current
investigation, motivation was similar between conditions be-
cause participants ‘‘wanted to’’ perform the upcoming soccer-
specific tasks. Indeed, in the current investigation, motivation
was similar between conditions, suggesting that the observed
physical and technical performance impairments in the mental
fatigue condition must be attributed to factors other than re-
duced motivation. This finding is consistent with previous
studies on the effects of mental fatigue on motivation related
to subsequent physical tasks (23,32,38).
Effects of Mental Fatigue on Soccer-Specific
Physical Performance
The purpose of study 1 was to assess the effects of menta l
fatigue on soccer-specific physical performance. Previously,
we reported that mental fatigue impairs intermittent running
performance in a test simulating the demands of team sport
competitions (38). The intermi ttent running protocol used in
the previous investigation was performed on a nonmotorized
treadmill aft er 90 m in of demanding cognitive activity. In
the current investigation, we aimed to verify the previous
findings using a shorter mentally fatiguing task (30 min) and
a well-validated intermittent running test performed in a more
natural setting (futsal field). The test used in the current in-
vestigation (Yo-Yo IR1) has previously been validated for
assessing physical performance in soccer players (14) and as
a measure of tolerance to incremental and intermittent run-
ning exercise. The current finding that Yo-Yo IR1 running
distance was reduced after the Stroop task supports our pre-
vious findings, confirming that mental fatigue impairs soccer-
specific physical performance.
In the present study, all 12 participants performed worse
on the Yo-Yo IR1 when mentally fatigued, with an average
individual impairment of 16.3% (207.5 m). Previous research
has revealed that similar differences in Yo-Yo IR1 perfor-
mance (~200 m) exist between players at different levels of
competition (top elite = 2420 m; elite = 2190 m; subelite =
2030 m; moderately trained = 1810 m) (2). Furthermore,
similar percentage differences in Yo-Yo IR1 performance
have been observed in response to training and seasonal
changes (2). Previous research has also revealed that Yo-Yo
IR1 performance is significantly correlated with match run-
ning performance (2). Considering these previous find-
ings and the very large effect size (ES = 2.37), the changes
observed in this investigation have meaningful implica-
tions for soccer match performance. Indeed, it is likely that
the detrimental effects of mental fatigue on Yo-Yo IR1 per-
formance would translate to important running impairments
during a soccer match.
As in previous investigations, HR increased linearly
throughout the Yo-Yo IR1 in both conditions and was com-
parable to values recorded during soccer matches (2,15). The
traditional physiological model of exercise tolerance attri-
butes exhaustion to cardiovascular, metabolic, and/or neu-
romuscular factors leading to muscle fatigue (30). However,
in the current investigation, HR was not significantly dif-
ferent between conditions at any time point. This finding
aligns with those of several recent inves tigations, and alto-
gether, they suggest that the negative effects of mental fatigue
on exercise tolerance are not primarily mediated by changes
to peripheral physiological factors associated with muscle
fatigue (23 ,3 1 –33, 3 7, 38) .
The most likely explanation for the observed negative
effect of mental fatigue on total distance run during the Yo-Yo
IR1 test is that, when mentally fatigued, soccer players
perceive running at a given speed more effortful. According
to the psychobiological model of exercise tolerance, based
on motivational intensity theory (21,22), highly motivated
people stop exercise when they perceive effort to be very
high or maximal. This was indeed the case in the current
investigation with all soccer player s reporting RPE of 18 or
greater at the point of exhaustion in each condition. Fur-
thermore, subjective ratings of motivation before exercise
were not significantly different between conditions (although
motivation was not assessed during the Yo-Yo IR1). This
suggests that mental fatigue did not affect potential moti-
vation, that is, the maximal effort our participants were
willing to exert to succeed in the Yo-Yo IR1 test. How-
ever, RPE at iso-time was significantly higher in the mental
fatigue condition.
Previous investigations have also found that mental fatigue
increases RPE during subsequent exercise (23,32). As in these
previous investigations, this negative effect of mental fatigue
on perception of effort meant that our participants reached
their maximal perceived effort and decided to stop the Yo-Yo
IR1 test earlier than in the control condition, thus cumulating
a shorter total distance. In the context of self-paced exercise,
higher perception of effort forces participants to reduce their
speed/power so that no premature exhaustion occurs, as this
would have greater nega tive consequences on performance
(8,31). A similar behavioral adjustment to compensate for
higher perception of effort has been observ ed in our previ-
ous investigation of the effects of mental fatigue on inter-
mittent running performance (38). Therefore, the reduct ions
MENTAL FATIGUE AND SOCCER PERFORMANCE Medicine & Science in Sports & Exercise
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273
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in speed/activity observed during soccer matches (9,27,34)
may be explained, in part, by mental fatigue induced in-
creases in perception of effort over the course of a match.
Effects of Mental Fatigue on Soccer-Specific
Technical Performance
Although study 1 confirms previous findings that mental
fatigue impairs soccer-specific physical performance, several
other factors contribute to soccer performance and match
outcome. Therefore, the purpose of study 2 was to expand the
findings of study 1, by assessing the effects of mental fatigue
on another important aspect of soccer match-play: technical
performance of skill-based movements. As previously men-
tioned, reductions in quality and quantity of technical per-
formance have been observed toward the end of a soccer
match (9,35,36 ). This is likely in part because of an increase
in physical and mental fatigue throughout a match. To the
authors_ knowledge, however, this is the first study to exper-
imentally investigate the effects of mental fatigue on skill-
based tests of team sport performance. Results reveal that
mental fatigue impairs soccer-specific technical performance
as assessed by the LSPT and LSST.
In the LSST, shot speed and accuracy were both signifi-
cantly lower in the mental fatigue condition than in the control
condition. Additionally, LSPT penalty time was significantly
higher in the mental fatigue condition. Although not signifi-
cantly different, performance time was higher in the mental
fatigue condition with a moderate effect size (ES = 0.55). The
increased penalty time results from a greater number of pass-
ing and ball control errors committed when mentally fatigued.
These findings are not surprising as previous research has
reported mental fatigue-induced increases in errors during
cognitive tasks and skilled tasks such as driving (3,16) and
impaired performance on perceptual and motor skills tests
(10). The current study is the first to extend these find-
ings to the context of soccer-specific technical skills. These
novel findings support the hypothesis that mental fatigue
contributes to the decline in technical performance observed
toward the end of soccer matches.
In addition to assessing the quality of soccer-specific
technical skills, the LSPT and LSST measure the length of
time required to complete these skills. Interestingly, in the
current investigation, mental fatigue did not affect the
length of time required for players to complete either task.
Indeed, both original time (LSPT) and mean shot sequence
time (LSST) were not significantly different between con-
ditions. This may be due to the time constraints of these
tasks. In the LSPT overall performance is recorded as a unit
of time, although in the LSST, points are not awarded when
shot sequences exceed 8.5 s. Therefore, it is possible that a
speed accuracy trade-off operates in the mental fatigue condi-
tion, whereby players sacrifice accuracy to complete the tasks
within their respective time constraints. Lorist et al. (19) pre-
viously suggested that a similar speed–accuracy trade-off exists
when mentally fatigued individuals perform cognitive tasks.
Previous research suggests that mental fatigue leads to
impaired performance monitoring and inadequate perfor-
mance adjustment during cognitive tasks (18). Specifically,
participants performing a 120-min cognitively demanding
computer task slowed reaction time in the trial immediately
after an error. However, ‘‘post-error slowing’’ disappeared as
mental fatigue increased with time-on-task (18). Therefore, in
the current investigation, it is likely that when mentally fa-
tigued, players_ ability to identify errors and subsequently
adjust performance was diminished. This may also further
explain the finding that LSPT original time and LSST shot
sequence time were not affected by mental fatigue. Indeed,
‘‘post-error slowing’’ may have also been absent in the
mental fatigue condition of the current investigat ion . If
after an error, players slowed down to avoid subsequent
errors, it is likely that LSPT original time would have
been higher in the mental fatigue condition because of this
performance adjustment.
Mental fatigue also affects attentional direction and the
ability to use information provided in advance to prepare
for upcoming activities (3,4,19). Indeed, during cognitive
tasks, mental fatigue causes a change in attention f rom goal-
directed stimuli, toward stimuli unr el ated to tas k perfor-
mance (3). Furthermore, when mentally fatigued, participants
performing cognitive computer tasks do not effectively use
available cues to prepare for subsequent stimuli (4,19).
Therefore, the negative effect of mental fatigue on soccer -
specific technical performance may also be related to the
focussing of attention on irrelevant stimuli and a reduced
ability to anticipate the movement of the ball and prepare
to control it. This negative impact of mental fatigue may
be exacerbated in a match setting, where the addition of the
crowd, advertising, and other distractions increases the num-
ber of irrelevant stimuli compared with a controlled experi-
mental environment.
Limitations and Directions for Futu re Research
The current results confirm the negative impact of mental
fatigue on soccer-specific physical performance and iden-
tify similar impairm ents to technical performance. However,
this investigation does contain limitations. First, HR was
the only physiological parameter meas ured in study 1.
Therefore, it is possible that physiological mechanisms other
than HR could have affected Yo-Yo IR1 performance. It
is worth noting, however, that similar previous investigations
have reported that various other physiological variables
(blood glucose and lactate concentrations, stroke volume,
cardiac output, mean arterial pressure, and minute ventila-
tion) are unaffected by mental fatigue (23,31–33,37,38).
These previous investigations support the conclusion that
increased perception of effort is primarily responsible for the
negative effects of mental fatigue on exerci se tolerance.
Future experimental research should attempt to elucidate the
neurobiological mechanisms underpinning the relations hip
between mental fatigue and perception of effort.
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The soccer-specific technical performance data of this
investigation are somewhat limited by the use of 2D video
analysis for shot speed. Although, this method revealed clear
impairments to shot speed in mentally fatigued players,
these findings should be considered an estimate. Neverthe-
less, this limitation to the shot speed results does not transfer
to the other technical performance outcomes that were sig-
nificantly impaired by ment al fatigue.
Although soccer players may engage in mentall y fatigu-
ing tasks before a match, it is unlikely that any players would
perform a task similar to the Stroop task before competition.
Therefore, future research should identify common prematch
activities, particularly those that may induce mental fatigue
(e.g., tactical sessions and excessive use of smart phones,
tablets, and video games), and assess whether these activities
induce similar impairments to physical and technical performance.
A recent study has also demonstrated that emotional regulation is
mentally fatiguing and impairs physical performance (40). Be-
cause emotions are high before important soccer matches and
controlling emotions has complex effects on sport performance
(12), this is a very important area for future research.
Finally, the potential influence of mental fatigue on injury
risk is of great importance. Recently, mental fatigue has been
found to increase the chances of slips and falls and impair
slip detection and recovery (17). This preliminary finding
supports the need for future research on the effects of mental
fatigue on the risk of injury in sport-specific settings.
Conclusions and Practical Recommendations
This investigation, using two separate studies, demon-
strates that mental fatigue impairs both physical and technical
performance of soccer players. Study 1 revealed that mentally
fatigued soccer players reach the point of exhaustion during
the Yo-Yo IR1 test earlier than in the control condition. This
impairment to physical performance seems to be mediated by
the negative effect of mental fatigue on perception of effort
rather than peripheral changes to the cardiovascular, metabolic,
and neuromuscular factors commonly associated with exercise
tolerance and muscle fatigue. Study 2 revealed that mentally
fatigued soccer players maintain the ability to perform soccer-
specific technical tasks within similar time constraints as in the
control condition. However, when mentally fatigued, soccer
players commit more passing and ball control errors and re-
duce both shot speed and accuracy. This multifaceted effect of
mental fatigue on physical and technical performance of soccer
players suggests that mental fatigue may have a very negative
impact on performance during a soccer match. Therefore, we
suggest that coaches and players assess their prematch activi-
ties to ensure players do not engage in tasks requiring sustained
attention for 30 min or more before competition, as this may
induce mental fatigue and impair performance. Furthermore,
sport scientists and coaches should identify and implement
strategies, such a s half-time caffeine supplementation that
reduce the mental fatigue induced by the high cognitive de-
mands of playing soccer for up to 90 min.
Funding: Samuele Marcora, Ph.D., was funded by a grant from the
Union of European Football Associations (UEFA).
Conflict of Interest: The results of the present study do not constitute
endorsement by ACSM. No conflict of interest is declared by the authors.
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