The Effect of Mental Fatigue on Cognitive and Aerobic Performance in Adolescent Active Endurance Athletes: Insights from a Randomized Counterbalanced, Cross-Over Trial

m of this randomized counterbalanced, 2 2 cross-over study was to investigate the effects of mental fatigue on cognitive and aerobic performance in adolescent active endurance athletes. Ten active male endurance athletes (age = 16 1.05 years, height = 1.62 0.04 m, body mass =55.5 4.2 kg ) were familiarized to all experimental procedures on day 1. On days 2 and 3, participants provided a rating of mental fatigue before and after completing a 30 min Stroop test that measures selective attention capacity and skills and their processing speed ability (mentally fatigued condition), or a 30 min control condition in a randomized counterbalanced order. They then performed d2 test and a 20 m multistage tness test (MSFT), which was used to measure selective and sustained attention and visual scanning speed (i.e., concentration performance (CP) and total number of errors (E)) and aerobic tness (i.e., maximum oxygen uptake (VO2max) and velocity at which VO2max occurs (vVO2max)), respectively. Rating of perceived exertion (RPE) was assessed after a MSFT. Subjective ratings of mental fatigue were higher after the Stroop task (p< 0.001). CP (p= 0.0.1), E (p< 0.001), vVO2max (p=

visual scanning speed (i.e., concentration performance (CP) and total number of errors (E)) and aerobic tness (i.e., maximum oxygen uptake (VO2max) and velocity at which VO2max occurs (vVO2max)), respectively. Rating of perceived exertion (RPE) was assessed after a MSFT. Subjective ratings of mental fatigue were higher after the Stroop task (p< 0.001). CP (p= 0.0.1), E (p< 0.001), vVO2max (p= 0.020), and estimated VO2max (p= 0.021) values were negatively affected by mental fatigue. RPE were signi cantly higher in the mentally fatigued than in the control conditions (p= 0.02) post-MSFT. Mental fatigue impairs aerobic and cognitive performance in active male endurance athletes. Keywords: mental exertion; RPE; aerobic performance; active endurance athletes; psychophysiology 1. Introduction Mental fatigue, which has subjective, behavioral and physiological manifestations, is a psychobiological state induced by prolonged periods of demanding cognitive activity [1]. From a subjective standpoint, mental fatigue induces increased feelings of tiredness, lack of energy [2], decreased motivation [3], and alertness [4]. From a behavioral point of view, mental fatigue has been J. Clin. Med.2018,7, 510; doi:10.3390/jcm7120510

J. Clin. Med.2018,7, 510 2 of 10 shown to negatively in uence performance and cognitive functioning [5–7]. Physiologically speaking, mental fatigue may alter brain activity [7–9]. Most previous studies that have examined the effects of mental fatigue on physical performance have revealed that mental fatigue does not affect maximal strength, power, and anaerobic work capacity [10–13]. Only one study reported a decreased leg extension maximal voluntary contraction (796 150 N to 741 137 N) after a 100 min mentally fatiguing task [14]. In contrast, mental fatigue has been consistently shown to decrease endurance performance, as assessed using different tests such as time-clamped self-paced running/cycling protocols and the Yo-Yo intermittent recovery test (decreased time to exhaustion, lowered self-selected power output/velocity, or increased completion time [15]). Nevertheless, these investigations have highlighted the negative effect of mental fatigue in adult team-sport athletes. It has been shown that younger adults were more affected by mental fatigue tasks than older adults [16]. This difference is nicely mirrored in behavioral, neurophysiological and psychological data. More speci cally, younger adult/adolescent participants showed markedly decreased accuracy and motivation, and increased error rates and alpha activity in performing mental fatigue tasks [16]. However, to date, no study has evaluated the effects of mental fatigue on endurance performance in adolescent individual sports participants, in order to better understand whether mental fatigue-related responses in older adults translate to younger adults. For instance, fatigue imposes a clinically relevant burden among athletes. From a clinical standpoint, the present article may allow sports practitioners and coaches to design and adoptad hocinterventions to properly prevent or manage mental fatigue in this particular population. Evidence reveals that endurance sport performance relies on a complex inter-play of physiological and biomechanical factors [17]. Cardiovascular endurance, which can be de ned as “the entire body's ability to sustain prolonged, dynamic exercise using large muscle groups” ([18], p. 223), is one of the major limiting factors in endurance performance. Indeed, classical measures, such as maximal oxygen uptake (VO2max), have been traditionally used in the laboratory or in the eld to predict the performance potential of runners [19]. Additionally to the

de ned as “the entire body's ability to sustain prolonged, dynamic exercise using large muscle groups” ([18], p. 223), is one of the major limiting factors in endurance performance. Indeed, classical measures, such as maximal oxygen uptake (VO2max), have been traditionally used in the laboratory or in the eld to predict the performance potential of runners [19]. Additionally to the physiological parameters, mental factors would seem to affect cardiovascular endurance performance during running. Previously, McCormick et al. [20] suggested six psychological determinants of endurance performance, namely motivators, mental fatigue, priming interventions, experimenter effects, emotion suppression, and ef cacy strength. Typically, mental fatigue has been shown to undermine endurance performance, particularly time to exhaustion [5], running times in a 3 km time trial [21], and performance times in a 5 km running time trial [12], when compared with control conditions in adult athletes. No research, however, has examined the in uence of mental fatigue on aerobic performance, assessed using the 20 m multistage tness test (MSFT), in adolescent active endurance athletes. Therefore, the aim of the present study was to investigate the effects of mental fatigue on cognitive and aerobic performance, assessed using the MSFT and d2 test, respectively, in adolescent active endurance athletes. Speci cally, we hypothesized that a 30 min Stroop task leading to mental fatigue would (a) reduce estimated selective attention and estimated VO2max performance and (b) increase subjective ratings of mental fatigue and perceived exertion. 2. Experimental Section 2.1. Participants Ten adolescent active male endurance athletes (age = 16 1.05 years, height = 1.62 0.04 m, body mass = 55.5 4.2 kg) engaged in middle and long distance track events (i.e., 800, 1500, and 3000 m) volunteered to participate in this study after being informed of the nature and of the possible risks associated with the experiment. The participants were high school team sport athletes. To be eligible to participate in the study, participants were required to meet the following criteria: (a) no consumption of any supplements or drugs; (b) no history of use of medications that could alter the

nature and of the possible risks associated with the experiment. The participants were high school team sport athletes. To be eligible to participate in the study, participants were required to meet the following criteria: (a) no consumption of any supplements or drugs; (b) no history of use of medications that could alter the

J. Clin. Med.2018,7, 510 3 of 10 hypothalamic-pituitary-gonadal (HPG) axis, such as anabolic steroids (by responding to the question “Have you used or taken any dietary supplements, drugs or medications in the past 30 days?”); (c) no history of chronic disease, bronchospasm or atopy; (d) no respiratory infection during the previous month (by responding to the question “Were you ill in the past 30 days?”); (e) abstinence from strenuous exercise in the 48 h before testing and (f) not being color blind or vision-impaired (by responding to the questions “Do you have any problems in your vision?”). Local institutional ethical approval was provided for this study, which was conducted in accordance with the 1964 Helsinki declaration. Written informed assent was obtained from the participants and informed consent from their parents/guardians following verbal description of all experimental details, prior to experimental data collection. 2.2. Study Design and Procedure In this randomized counterbalanced, 2 2 cross-over study, reported according to the CONSORT guidelines [22], participants visited the laboratory on three separate occasions at the same time of day (2 p.m.), each separated by 1 week. The participants were familiarized with the testing procedures during visit 1. The order in which participants experienced the two conditions (mentally fatiguing task—experimental condition—and non-mentally fatiguing task—control condition) was randomized in such a way that the effect of the conditions (experimental rst—then control versus control rst—then experimental) was not confounded with the effect of the order in which the conditions themselves were given (randomized cross-over design). Sample size wasa prioricomputed taking into account the repeated measures with one between subjects factor (one half of the subjects undergoing rst the mentally fatiguing task and after the non-mentally fatiguing task and the other half of subjects receiving rst the non-mentally fatiguing task and thereafter the mentally fatiguing task) and one within subjects factor (all participants undergoing both conditions) design: y ijk=m k+y ik+s ij+# ijk (1) wherey ijkis the response/outcome from the j th participant in the i th sequence under the k th condition, m kthe effect/outcome of the k th condition,y ikthe xed effect/outcome of the i

non-mentally fatiguing task and thereafter the mentally fatiguing task) and one within subjects factor (all participants undergoing both conditions) design: y ijk=m k+y ik+s ij+# ijk (1) wherey ijkis the response/outcome from the j th participant in the i th sequence under the k th condition, m kthe effect/outcome of the k th condition,y ikthe xed effect/outcome of the i th sequence under the k condition,s ijthe between subjects variability, and, nally,# ijkthe within subjects variability. With an 80% power, the minimum number of required participants was 8. The rst visit consisted of the collection of anthropometric data. Furthermore, participants were familiarized with rating of perceived exertion (RPE, Borg's category 6–20 scale) scale [23] as well as the Brunel Mood Scale (BRUMS, [24,25]) for the assessment of mental fatigue. Participants were also familiarized with the mentally fatiguing task (Stroop task), the MSFT and the d2 test. During the second and the third visits, participants were asked to provide a subjective rating of mental fatigue using BRUMS, before completing one of two conditions (mentally fatiguing session or non-mentally fatiguing session/control session). In the control session, participants leisurely read from a selection of emotionally neutral magazines for 30 min. In the mentally fatiguing session, participants completed a paper version of the Stroop task. Mental fatigue was again assessed after each condition. After the BRUMS, participants completed the d2 test. After that, they performed a 5–7 min running warm-up and the MSFT. Finally, rating of perceived exertion (RPE) was assessed after a MSFT. Participants were advised to avoid exercise, caffeine, and alcohol 48 h before each laboratory visit. Food and uid intake was registered 48 h prior to the rst study visit, and subjects were asked to avoid such intake 3 h before the second and the third visits. 2.2.1. Mental Fatigue Task The Stroop task was used for the mental fatigue task [12]. Four words (red, blue, green, and yellow) were displayed in a random order on ve sheets of A4 paper with 45 words printed on each sheet. Participants were required to verbally respond to each word, with the correct response

the second and the third visits. 2.2.1. Mental Fatigue Task The Stroop task was used for the mental fatigue task [12]. Four words (red, blue, green, and yellow) were displayed in a random order on ve sheets of A4 paper with 45 words printed on each sheet. Participants were required to verbally respond to each word, with the correct response

J. Clin. Med.2018,7, 510 4 of 10 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. Therefore, if the word “green” was displayed in red ink, the correct answer was “green”. Of note, participants repeatedly read the ve sheets over and over for 30 min. A member of the research team recorded the number of incorrect answers with a control sheet, and asked participants to restart the current row of words when the answer was incorrect. Thus, the points awarded for speed and accuracy of responses were noted to increase the motivation of athletes. 2.2.2. Control Task The control task involved 30 min of reading at a leisurely pace from a selection of magazines, which varied in theme, including sport, cars, and travel. According to the BRUMS [24,25], 30 min of reading from these magazines was emotionally neutral. 2.2.3. Measures To assess the selective attention of participants, we used the d2-test as developed by Brickenkamp and Oosterveld [26]. The d2-test consists of 14 lines, each containing 47 symbols. A symbol is either a letter p or a letter d with one or two lines (either “or”) above and/or below the letter. The assignment is to mark each letter d that has a total of two lines above and below the letter. In order to make the test perfectly, respondents should not mark any other symbol than a d2, and all d2 symbols have to be marked. The d2-test is timed, and respondents are given 20 s to complete each line. After these 20 s, respondents have to continue on the next line. The total test lasted 4 min and 40 s. As such, the test assesses concentration in terms of both accuracy and speed. Two parameters were calculated after completion of the d2 test in our study; concentration performance (CP) and

respondents are given 20 s to complete each line. After these 20 s, respondents have to continue on the next line. The total test lasted 4 min and 40 s. As such, the test assesses concentration in terms of both accuracy and speed. Two parameters were calculated after completion of the d2 test in our study; concentration performance (CP) and total number of errors made by the participants (E). Concentration performance is assessed as the number of correctly marked d2-symbols minus the number of incorrectly marked symbols (symbols that are not d2-symbols). In addition to concentration performance, we calculated the total number of errors made by the participants (E). The total number of errors is assessed as the number of errors made by failing to identify a correct d2-symbol plus the number of errors made by incorrectly marking symbols that are not d2-symbols. 2.2.4. Aerobic Performance The MSFT was conducted as previously described [27]. Brie y, participants ran back and forth between two lines, spaced 20 m apart, in time with the “beep” sounds from an electronic audio recording. Each successful run of the 20 m distance was a completion of a shuttle. The test started with an initial speed of 8 km/h that increased by 0.5 km/h every minute and was stopped if the subject failed to reach the line (within 2 m) for two consecutive ends after a warning. Maximal speed was calculated as the velocity of the last stage fully completed and considered as the speed associated with VO2max for the shuttle run test (vVO2max). VO2max was estimated using the L²ger et al. [27] formula. 2.2.5. Mood The BRUMS developed by Terry et al. [25] was used to quantify current mood (“How do you feel right now?”) before and after the cognitive tasks. This questionnaire contains 24 items (e.g., “angry, uncertain, miserable, tired, nervous, and energetic”) divided into six respective subscales: anger, confusion, depression, fatigue, tension, and vigor. The items are answered on a 5-point Likert scale (0 = not at all, 1 = a little, 2 = moderately, 3 = quite a bit, and 4 =

before and after the cognitive tasks. This questionnaire contains 24 items (e.g., “angry, uncertain, miserable, tired, nervous, and energetic”) divided into six respective subscales: anger, confusion, depression, fatigue, tension, and vigor. The items are answered on a 5-point Likert scale (0 = not at all, 1 = a little, 2 = moderately, 3 = quite a bit, and 4 = extremely), and each subscale, with four relevant items, can achieve a raw score in the range from 0 to 16. Only the score for the fatigue subscale was considered in this study as the subjective marker of mental fatigue.

J. Clin. Med.2018,7, 510 5 of 10 2.3. Statistical Analyses Data were presented as mean values standard deviation (SD). Shapiro-Wilk's test was used to determine the data's normal distribution. Differences between cases and controls were computed performing repeated measures analysis of variance (ANOVA) analysis, withpost-hoc t-tests. Pairwise differences between the dependent variables were identi ed by using paired t-tests, correcting for multiple testing (pre- and post-design, cases versus controls). To allow a better interpretation of the results, the effect sizes (ES) were calculated, using Cohen's d, correcting for the pre-post design using Morris and DeShon's equation. A signi cance level ofp 0.05 was used for all analyses. All statistical analyses were carried out using the “Statistical Package for the Social Sciences” for Windows (SPSS Inc., Chicago, IL, USA, version 16.0). Graphs were generated using the commercial software MedCalc Statistical Software (MedCalc Software bvba, Ostend, Belgium;; 2017; version 17.9.7). 3. Results 3.1. Selective Attention There were statistically signi cant differences in the CP (p= 0.001) and errors (p< 0.001) values between mentally fatigued and control conditions (Table). Table 1. Mean values and standard deviations (SD) of the attention test, aerobic performance variables and rating of perceived exertion (RPE). Condition CP E vVO 2max (km/h) VO2max (mL/min/kg) RPE (a.u.) MFC (n= 10) 71.6 3.1 29.9 3.9 10.2 0.78 33.8 4.7 18.1 1.1 CC 77.2 3.5 * 22.2 3.3 * 11.1 0.8 * 39.2 4.8 * 16.8 1.2 * ES 1.79 (95% CI 0.41–3.16) 2.25 (95% CI 3.75– 0.75) 1.19, (95% CI 0.86–1.52) 1.19 (95% CI 0.81–3.18) 1.03 (95% CI 2.43– 0.16) * Different from MFC,p< 0.05; a.u.: arbitrary units; CC: control condition; CP: concentration performance; E: Errors; ES: effect size; MFC: mentally fatigued condition; RPE. 3.2. Aerobic Performance There were statistically signi cant differences (p= 0.021; standardized mean difference = 1.13, ES = 1.19 (95% CI 0.81–3.18)) in the estimated VO2max values between mentally fatigued and control conditions, with higher estimated VO2max values in the control condition than in the mentally fatigued condition. Furthermore, there were higher vVO2max values in the control condition than in the mentally fatigued condition (p= 0.021; standardized

This study investigates how mental fatigue affects cognitive and aerobic performance in adolescent endurance athletes.