THE EFFECT OF MENTAL FATIGUE ON PERFORMANCE IN ENDURANCE TASKS: A SYSTEMATIC REVIEW

EFECTO DE LA FATIGA MENTAL SOBRE EL RENDIMIENTO EN TAREAS DE RESISTENCIA: UNA REVISIÓN SISTEMÁTICA

Introduction

Mental fatigue is defined as a psychobiological state that can arise during or after cognitive activities. Increased fatigue rates influence the cognitive ability to act during prolonged periods of demanding physical exertion. It is characterized by a feeling of tiredness, decreased commitment, and therefore a greater aversion to continuing with the current activity (Van Cutsem et al., 2017). In other words, mental fatigue goes beyond cognition, as it also involves a significant emotional and motivational component (Van Cutsem et al., 2017). Although the total time spent on a demanding cognitive task influences the level of fatigue, tasks lasting as little as 30 minutes are capable of producing significant levels of mental fatigue (Boksem & Tops, 2008; MacMahon et al., 2019; Pageaux et al., 2014; Salam et al., 2018). Mental fatigue is different and should not be confused with chronic fatigue and cognitive decline associated with aging or disease. Unlike mental fatigue, in such conditions, subjective feelings of fatigue and cognitive impairment are chronic, and not necessarily related to mental exertion (Smith et al., 2015).

These findings have been corroborated in other studies that also suggest that impairment in physical performance induced by mental fatigue is more pronounced in those tasks that involve large muscle groups during prolonged periods of demanding exercise (> 75 s), such as time-to-exhaustion tasks (MacMahon et al., 2019; Marcora et al., 2009; Salam et al., 2018) or time trials (Filipas et al., 2020; Penna et al., 2018; Pires et al., 2018; Silva-Cavalcante et al., 2018) compared to exercises involving a shorter duration (Martin et al., 2019). However, not all studies corroborate the negative influence of mental fatigue on physical performance in endurance tasks (MacMahon et al., 2019; Martin et al., 2019; Penna et al., 2021). Consequently, more evidence is still required to establish firm conclusions about the possible link between mental fatigue and physical exercise performance (Holgado et al., 2020).

Therefore, the present systematic review aims to determine the effect of mental fatigue on endurance performance in dynamic multi-joint movements involving large muscle masses (e.g. running, cycling or rowing), such as time-to-exhaustion tests or time trials. In addition to analysing their effects on performance in these tasks, their effects on different parameters indicating effort at the cardiovascular (heart rate) and metabolic (blood lactate concentration) level as well as at the perceptual level (subjective perception of effort) will be examined. The initial hypothesis is that mental fatigue derived from a previously performed task will negatively influence performance in subsequent long-term activities, and that this deterioration in performance will be accompanied by higher rates of perceived effort, cardiovascular and metabolic effort.

Method

This review follows the recommendations of the Reference Items for Systematic Reviews and Meta-Analyses: the PRISMA Preferred Reporting Items for Systematic reviews and Meta-Analyses statement (Page et al., 2021).

Data Sources and Search Strategies

The search contains all those studies that have been published between 2009 and March 31, 2022 in the online databases Web of Science, PubMed and Scopus. After several combinations of the terms, a definitive search algorithm was selected with the following Boolean connectors: mental fatigue or cognitive fatigue and exercise or endurance and time to exhaustion or time trial or running or cycling.

Study Selection and Eligibility Criteria

The search strategy described was carried out by two independent authors (IMG and GM), who removed duplicates and analysed the remaining studies to determine if they met the inclusion criteria. This preliminary review consisted of the scrutiny of the titles and abstracts of each of the articles, excluding those that did not meet the criteria to be included. If reading the title or abstract was not sufficient to determine the inclusion of the article in the review, a detailed review of them was carried out, examining its complete version. To determine the inclusion or exclusion of the studies, the PICOS approach (Harris et al., 2014) was followed with the following criteria: (1) Population: Healthy adults who perform both recreational physical activity or any professional sport. (2) Intervention: Cognitive task that induces mental fatigue prior to performing an endurance test lasting ≥ to 30 minutes. (3) Comparator: A control condition in which the task that induces mental fatigue is replaced by another with a low cognitive load (e.g.: watch a documentary). (4) Variables: Performance in whole-body endurance tests with a duration of more than 75s, including time or distance trials, tasks to exhaustion or incremental tests to exhaustion. (5) Study Design: Randomized, controlled, crossover studies. In addition, we excluded systematic reviews and/or meta-analyses, studies using strategies for the reduction of mental and/or physical fatigue that were carried out during the experimental conditions (i.e.: caffeine consumption), studies where tests were carried out under specific temperature conditions of cold and/or heat, and studies in which the participants were not human or were clinically diagnosed for any pathological condition.

Data Extraction and Synthesis

One of the authors (IMG) extracted the following data from the included studies: study information (authors and date of publication), sample characteristics (size, sex, age of the subjects and type of sports practice), specific performance test, type of treatment and duration (experimental test and control condition), and results of both the main variable linked to performance in the task, as well as complementary results linked to physiological and/or perceptual variables.

Regarding the main variable, it was different depending on the type of test used in each study. In a constant load test until exhaustion, the main variable is how long the participant is able to sustain a given effort until exhaustion. In distance time trials, the main variable will also be the time, in this case the time invested in covering a certain distance. However, in time trials, the main variable will be the distance covered in a given time, the pedaling power (in the case of a cycle ergometer or rowing ergometer) or the average speed during the whole test. In intermittent running or cycling tests (e.g. YO-YO IR1), the main variables will be the distance traveled, the time or the intensity determined through the average or maximum speed.

The complementary or secondary variables are physiological variables that complement and support the conclusions of the result of the main variable. In the present systematic review, heart rate, maximal oxygen consumption, blood lactate accumulation, and subjective perception of exertion were included.

Assessment of Study Quality and Risk of Bias

To know and determine the methodological quality of the included studies, the "PEDro" scale (https://pedro.org.au/spanish/resources/pedro-scale/) was used, which has proven to be reliable enough for use in systematic reviews. This scale consists of 11 criteria, of which the first has no value in the "PEDro" score. Each criteria was assessed with "S" (S = meet the criteria) and "N" (N = do not meet the criteria), giving an "S" score only when the criteria is clearly met. The maximum score that can be obtained will be 10 points if all the criteria are met. Included studies with a PEDro score ≥ 6/10 were judged to be of high quality, while those with lower scores were judged to be methodologically of low quality. The methodological quality of each study was rated by three review authors (IMG, GMS, DCP). The information on quality assessment is summarized in table 1.

To understand the reliability of the findings presented, a graph reflecting the assessment of risk of bias with the RoB.2 tool implemented through the online version of Review Manager is included. It reflects current knowledge about how causes of bias can influence outcomes and contains the most appropriate way to assess this risk. Judgments about each of the domains may be "low," have "some concerns," or "high" risk of bias. The information is shown in figure 1.

Results

Search Results

After the initial search, 373 studies were identified. After duplicates removal, 311 studies remained. After reviewing the title, abstract or full text, a total of 28 studies were included. Figure 2 shows the flow diagram of the systematic review.

Results of the Assessment of Quality and Risk of Publication Bias

Table 1 shows the quality scores of each of the included studies. The methodological quality of the studies in this review is high, according to the PEDro scale, since 100% of the included studies had a quality ≥ 6 points.

The results of the risk of bias reveal some concerns about the nature and strength of the effects of mental fatigue on the overall computation in most research. These come mainly from the item (D2) of risk with respect to the deviation from the planned intervention and the item (D4) of risk in the measure of the results. The possible presence of information biases in this literature raises the need for an improvement in the methodology, detailing and complying with the blinding of the evaluators to draw firm conclusions about the possible effect of mental fatigue on physical performance, among other parameters such as the perception of effort. The results are shown in Figure 1.

Characteristics of the Participants and the Type of Performance Evaluation Test

All relevant information from each study is summarized in table 2. The publication dates of the studies range from 2009 to 2021. The sample size varies between eight (Pires et al., 2018; Silva-Cavalcante et al., 2018) and 36 subjects (Filipas et al., 2021). The mean age of participants ranges from 40 (Holgado et al., 2019) to 14 years (Filipas et al., 2021; Greco et al., 2017).

In relation to the sex of the participants, there are no studies including only women, and only in some of them included women as a part of the sample (Brown & Bray, 2019; Brownsberger et al., 2013; Filipas et al., 2018; Lam et al., 2021; Lopes et al., 2020; MacMahon et al., 2014, 2019; Marcora et al., 2009; Martin et al., 2019; Penna et al., 2018). In these studies, only two of them have female participation exceeding male participation. (Filipas et al., 2020; Martin et al., 2019).

Regarding the previous physical activity experience of the participants in the analyzed studies, I general (n = 23) participants are physically active except in one, where the participants are untrained young adults (Filipas et al., 2020). In five studies, this information is not reported (Brown & Bray, 2019; MacMahon et al., 2019; Marcora et al., 2009; Martin et al., 2019; Weerakkody et al., 2021). In addition, studies with well-trained athletes included runners (Lopes et al., 2020), cricket players (Veness et al., 2017), cyclists (Martin, Staiano, Menaspa, et al., 2016; Pires et al., 2018) or kayakers (Staiano et al., 2019). In the remaining cases, the participants were recreational athletes, or their level of performance was not reported. One study compared the results of both population profiles, trained and non-trained participants (Martin, Staiano, Menaspà, et al., 2016).

To determine the influence of mental fatigue on performance, all studies employed tests performed at maximal intensities or at various intensities corresponding to maximum oxygen consumption or a specific pedaling power output. Specifically, the studies included time-trial tests over a specific distance in swimming (Filho, Penna, Wanner, et al., 2018; Penna et al., 2021), rowing, running (Lam et al., 2021; MacMahon et al., 2014; Pageaux et al., 2014), or cycling (Brownsberger et al., 2013; Filipas et al., 2019; Martin, Staiano, Menaspà, et al., 2016; Pires et al., 2018; Silva-Cavalcante et al., 2018); or tests analyzing time to exhaustion using constant-load tests (Barzegarpoor et al., 2020; Lopes et al., 2020; Marcora et al., 2009; Martin et al., 2019) or incremental-load tests (MacMahon et al., 2019; Salam et al., 2018). Intermittent performance tests have also been considered (e.g., Yo-Yo IR1) (Filipas et al., 2021; Greco et al., 2017; Lam et al., 2021; Penna et al., 2018; Smith et al., 2016; Veness et al., 2017; Weerakkody et al., 2021) since they also met the inclusion criteria.

Results on the key Variable Depending on the Type of Test

Time to Exhaustion

Regarding heart rate during the time-to-exhaustion task, none of the studies (Barzegarpoor et al., 2020; Lopes et al., 2020; MacMahon et al., 2019; Salam et al., 2018) found differences between the experimental condition and the control condition. Regarding blood lactate, the results are inconclusive, since one study does not report differences between conditions (Marcora et al., 2009), while the results of (Salam et al., 2018) suggest a greater accumulation of lactate in the control test than in the tests performed after performing a demanding cognitive activity.

Time Trials

Several studies (n = 8) used time trials in which participants had to complete a certain distance in the shortest possible time. Most of them, regardless of whether the test was on a cycle ergometer (Pires et al., 2018), kayak (Staiano et al., 2019) or a treadmill (Lam et al., 2021; MacMahon et al., 2014; Pageaux et al., 2014), observed an increase in the time needed to complete the target distance in the cognitive fatigued condition. However, four of the seven studies that included this type of test did not observe a negative effect of mental fatigue on performance in cycling (Silva-Cavalcante et al., 2018), swimming (Penna et al., 2021), and rowing (Filipas et al., 2018) performance.

Other studies included different time-trial tests, where the maximum distance covered in a predetermined time (Filipas et al., 2020), power output (Holgado et al., 2019), or work generated (Brown & Bray, 2019), as well as average speed (Filho, Penna, Wanner, et al., 2018), were measured. These studies consistently showed a reduction in performance under conditions of mental fatigue prior to the test, with the exception of Holgado et al. (2019). The results of one study suggest that the effects of mental fatigue on a time-trial task on a cycle ergometer, where participants aimed to cover the maximum distance possible in 20 minutes, may be influenced by the participants' level of experience. No differences were observed between the control and experimental conditions in professional cyclists, but significant differences were found in recreational cyclists (Martin, Staiano, Menaspà, et al., 2016).

However, with regard to perceptual variables, the subjective perception of effort was higher in conditions of mental fatigue in only four out of 15 studies (Brownsberger et al., 2013; Pageaux et al., 2014; Pires et al., 2018; & Staiano et al., 2019). (Filipas et al., 2018, 2019; Holgado et al., 2019; Lam et al., 2021; MacMahon et al., 2014; Martin, Staiano, Menaspa, et al., 2016; Pageaux et al., 2014; Penna et al., 2018; & Silva-Cavalcante et al., 2018). it is reported that the differences between conditions are not significant. Only one study (Staiano et al., 2019) reports lower heart rate values in the experimental condition during a 2,000-meter time trial conducted by kayakers, when compared to the control condition. For blood lactate (La), we have four studies establishing that lactate accumulation does not differ between conditions (Filipas et al., 2019b; MacMahon et al., 2014; Martin, Staiano, Menaspa, et al., 2016; Pageaux et al., 2014). Staiano et al. (2019) reports higher levels of La in the experimental condition than in the control condition.

Intermittent Test Results

A total of eight articles were included in this review that analyse the effects of mental fatigue on performance in intermittent endurance tests. The main variable that informs about the performance in these tests is the distance covered (Campos, Filho, Penna, et al., 2018; Filipas et al., 2021; Greco et al., 2017; Lam et al., 2021; Penna, Filho, Campos, et al., 2018; Philippas et al., 2021; Smith et al., 2016; Veness et al., 2017; & Weerakkody et al., 2021), except in one study where average speed was used (Smith et al., 2015). The result of the main variable confirms that, in this type of test, both the average speed and the distance traveled are lower when the participants have been subjected to a previous demanding cognitive task.

On the other hand, all the articles have examined the subjective perception of effort in this type of test, providing results that confirm the effect of mental fatigue in the experimental condition, with this variable increasing compared to the control condition. Regarding cardiovascular control, only one study reports a higher heart rate in the condition with mental fatigue compared to the control condition (Filipas et al., 2021). La accumulation during this type of test also does not seem to be influenced by mental fatigue (Campos, Filho, Penna et al., 2018; Smith et al., 2015).

Discussion

The main objective of the present systematic review was to determine the effect of mental fatigue on performance in endurance tasks performed in dynamic multi-joint exercises involving large muscle masses (e.g., cycling, running, swimming, etc.). After the analysis of the 29 interventions included in this systematic review, the main results show that, regardless of the type of test included to evaluate performance, 86% of the interventions analyzed (25 of 29 interventions) showed that mental fatigue reduces performance in the endurance test compared to a control condition without mental fatigue. In addition, exertion indicators such as subjective perception of effort have been increased by mental fatigue, while heart rate or blood lactate concentration do not show any alteration.

Our analysis reveals that cognitive exhaustion produces negative effects on sports performance. This was evidenced by a decrease in the time to exhaustion, in the increase in time required to complete a fixed-distance time trial (e.g.: 20 km), a lower average speed, a decrease in self-selected power, and also in the distance covered during an intermittent test to exhaustion (YO-YO IR1). We might think that the fact that mental fatigue protocols have not been the same in all studies could have influenced the results, but even in the same study (Filipas et al., 2018) two interventions have been carried out with different cognitive tasks; the first a (stroop colour task) and the second, an arithmetic test, and the performance results support our initial hypothesis in both cases. In fact, if we take into account the results of the qualitative synthesis used to evaluate physical performance extracted from the present systematic review, we can observe that in 86% of the interventions (25 out of 29 studies) there is a deterioration in performance when the subjects were mentally fatigued.

Only in five studies (Holgado et al., 2019; Martin et al., 2019; Martin, Staiano, Menaspa, et al., 2016; Penna et al., 2021; Silva-Cavalcante et al., 2018) no negative effect on performance induced by mental fatigue has been observed. In this sense, two studies that used a maximum protocol of 3 minutes (Martin, Staiano, Menaspa, et al., 2016), and a protocol of 4 km pedaling on a cycle ergometer respectively (Silva-Cavalcante et al., 2018) are included, observing that mental fatigue did not deteriorate performance. This contradiction could be due to the fact that the task used is highly dependent on anaerobic metabolism and low cognitive load as it is so short in terms of duration, so cognitive strategies to maintain long-term effort are not decisive (Van Cutsem et al., 2017). In a study that assessed the effects of mental fatigue through average speed in a 20-minute time trial in two different population profiles: professional and recreational athletes (Martin, Staiano, Menaspa, et al., 2016), the results showed that professional cyclists were more resistant to the negative effects of mental fatigue over prolonged effort. The same was true not only with average speed, but also with a lower proportion of perceived effort than in non-professional athletes. These findings suggest that successful endurance performance, whether due to genetics or training, can generate greater inhibitory control and resistance to mental fatigue (Martin, Staiano, Menaspa, et al., 2016). In this sense, the results obtained by Martin et al. (2019) do not show a negative influence of mental fatigue on performance. However, these authors consider that the results could be due to the fact that the sample is composed of a larger number of women (15 of 23 participants are women) who are more resistant to fatigue (Ansdell et al., 2020). Despite this, the results obtained so far do not seem to indicate that there are differences in the effects of mental fatigue on performance between men and women (Lopes et al., 2020). However, the conclusions drawn regarding the relationship between sex and mental fatigue in different long-lasting activities should be taken with caution, due to the little research (one study only) in this area, and it would be advisable to generate new lines of research that carry out a more in-depth analysis of this factor.

After the analysis of the results and according to Martin et al. (2018) it can be observed that, regardless of the type of performance test studied, the variables that are traditionally considered to limit performance in endurance sports (heart rate, blood lactate accumulation, etc.) are not affected by mental fatigue. However, this assumption is somewhat misleading, since, if we take into account that the performance achieved in the physical tests carried out under conditions of mental fatigue was, in general, lower, with similar heart rate and lactate values, this would lead us to think that the physiological stress achieved in conditions of cognitive exhaustion is higher (i.e. the same heart rate for a lower average power or a shorter distance travelled). On the other hand, in general, there is an increase in the subjective perception of effort under conditions of fatigue by the participants, leading them to finish the stress test earlier until exhaustion (both continuous and intermittent). However, in time trials, in general, there are no differences in the response of this variable between conditions. According to what was established by Filipas et al. (2020) this could be justified because in a time-to-exhaustion test the power output remains constant for the duration of the test, while in a time trial, the power output fluctuates. This strategy could influence the results obtained in the subjective perception of effort. On the other hand, differences in the subjective rating of effort could also have their origins in the type of scale used. The variability in the results raises the need for well-controlled paradigms that take into account the relative contribution that other parameters, such as motivation and/or boredom in the test, may have (Möckel et al., 2015).

The information derived from this review should be interpreted with caution due to the limitations arising from the included studies. Some of them have used systems to examine fatigue, such as surface electroencephalography (Brownsberger et al., 2013) or subscales that evaluated the different cognitive tools used, through questionnaires or visual analog scales (Filipas et al., 2018; MacMahon et al., 2014; Smith et al., 2016) but not all study protocols have included these measures (Weerakkody et al., 2021). This review highlights the need for future research, with standardized protocols regarding the cognitive tasks used in which the magnitude of mental fatigue caused in the individual before physical exercise can be quantified. Likewise, it is worth highlighting the importance of studying the impact of mental fatigue by differentiating groups based on the level of practice, since the chronic exposure to cognitive stressors that a professional athlete may experience can undoubtedly be a conditioning factor for them to be more resistant to the deleterious effects of mental fatigue prior to exercise.

Conclusions

After the qualitative synthesis made in this systematic review, it could be stated that mental fatigue induced by previous demanding cognitive work produces a deterioration of subsequent performance in endurance tests. In addition, to some extent, this impairment of the maximum capacity to withstand prolonged efforts under conditions of mental fatigue is linked to an increase in the subjective perception of effort. On the other hand, the vast majority of the studies analysed do not show differences in physiological variables such as heart rate or lactate values, despite a worsening of physical performance, which indicates an increase in the physiological stress of subjects who have been exposed to a demanding cognitive load prior to performing these physical tests. Therefore, the impact of mental fatigue should be evaluated and controlled in those endurance activities of longer duration, due to the deleterious effects described above. However, we must be cautious when assuming these conclusions, since a recent meta-analysis (Holgado et al., 2020), has cast doubt on the possible effect of mental fatigue on sports performance, since, when possible, publication bias is taken into account, the effect of mental fatigue on performance is reduced.

Statement of the Ethics Committee

Not applicable due to the nature of the publication, as it is a systematic review of the literature.

Conflict of Interest

The funding entities or institutions had no influence on the study design, data analysis, or interpretation of the results. The authors declare that they have no conflict of interest.

Funding

This research was partially funded by the Ministry of Science, Innovation and University of Spain, subsidised cities (PID2021-128204OA-I00-AEI/ERDF, EU); Xunta de Galicia, University of A Coruña/CISUG (ED431B 2021/28).

Contribution of the Authors

I.M.-G., DC-P., VL-A., and G.M. devised the study. I.M.-G., D.C.-P. & G.M developed the methodology. I.M.-G. performed a database search, executed the selection process, data extraction and risk of bias assessment. When in doubt, D.C.-P. and G.M. participated in the process. I.M.-G. and G.M. wrote the initial draft of the manuscript. DC-P and VL-A. critically revised and corrected the initial draft of the manuscript. All authors have read and agree with the published version of the manuscript.

Data Availability Statement

Not applicable due to the nature of the publication.

References

Author notes

^aCorrespondence: Gonzalo Márquez, gonzalo.marquez@udc.es

Additional information

Short title: Mental Fatigue and Physical Performance

How to cite the article: Mera-González, I., Colomer-Poveda, D., López-Alonso, V. & Márquez, G. (2025). Effect of mental fatigue on performance in endurance tasks: a systematic review. Cultura, Ciencia y Deporte, 20(63), 2269. https://doi.org/10.12800/ccd.v20i63.2269