Assessing the Evidential Value of Mental Fatigue and Exercise Research.

It has often been reported that mental exertion, presumably leading to mental fatigue, can negatively affect exercise performance; however, recent findings have questioned the strength of the effect. To further complicate this issue, an overlooked problem might be the presence of publication bias in studies using underpowered designs, which is known to inflate false positive report probability and effect size estimates. Altogether, the presence of bias is likely to reduce the evidential value of the published literature on this topic, although it is unknown to what extent. The purpose of the current work was to assess the evidential value of studies published to date on the effect of mental exertion on exercise performance by assessing the presence of publication bias and the observed statistical power achieved by these studies. A traditional meta-analysis revealed a Cohen's dz effect size of - 0.54, 95% CI [- 0.68, - 0.40], p < .001. However, when we applied methods for estimating and correcting for publication bias (based on funnel plot asymmetry and observed p-values), we found that the bias-corrected effect size became negligible with most of publication-bias methods and decreased to - 0.36 in the more optimistic of all the scenarios. A robust Bayesian meta-analysis found strong evidence in favor of publication bias, BFpb > 1000, and inconclusive evidence in favor of the effect, adjusted dz = 0.01, 95% CrI [- 0.46, 0.37], BF10 = 0.90. Furthermore, the median observed statistical power assuming the unadjusted meta-analytic effect size (i.e., - 0.54) as the true effect size was 39% (min = 19%, max = 96%), indicating that, on average, these studies only had a 39% chance of observing a significant result if the true effect was Cohen's dz = - 0.54. If the more optimistic adjusted effect size (- 0.36) was assumed as the true effect, the median statistical power was just 20%. We conclude that the current literature is a useful case study for illustrating the dangers of conducting underpowered studies to detect the effect size of interest.

Individualized Mental Fatigue Does Not Impact Neuromuscular Function and Exercise Performance.

INTRODUCTION: Recent studies have questioned previous empirical evidence that mental fatigue negatively impacts physical performance. The purpose of this study was to investigate the critical role of individual differences in mental fatigue susceptibility by analyzing the neurophysiological and physical responses to an individualized mental fatigue task. METHODS: In a preregistered ( https://osf.io/xc8nr/ ), randomized, within-participant design experiment, 22 recreational athletes completed a time to failure test at 80% of their peak power output under mental fatigue (individual mental effort) or control (low mental effort). Before and after the cognitive tasks, subjective feeling of mental fatigue, neuromuscular function of the knee extensors, and corticospinal excitability were measured. Sequential Bayesian analysis until it reached strong evidence in favor of the alternative hypothesis (BF 10 > 6) or the null hypothesis (BF 10 < 1/6) were conducted. RESULTS: The individualized mental effort task resulted in a higher subjective feeling of mental fatigue in the mental fatigue condition (0.50 (95% confidence interval (CI), 0.39-0.62)) arbitrary units compared with control (0.19 (95% CI, 0.06-0.339)) arbitrary unit. However, exercise performance was similar in both conditions (control: 410 (95% CI, 357-463) s vs mental fatigue: 422 (95% CI, 367-477) s, BF 10 = 0.15). Likewise, mental fatigue did not impair knee extensor maximal force-generating capacity (BF 10 = 0.928) and did not change the extent of fatigability or its origin after the cycling exercise. CONCLUSIONS: There is no evidence that mental fatigue adversely affects neuromuscular function or physical exercise; even if mental fatigue is individualized, computerized tasks seem not to affect physical performance.

An umbrella review of randomized control trials on the effects of physical exercise on cognition.

Extensive research links regular physical exercise to an overall enhancement of cognitive function across the lifespan. Here we assess the causal evidence supporting this relationship in the healthy population, using an umbrella review of meta-analyses limited to randomized controlled trials (RCTs). Despite most of the 24 reviewed meta-analyses reporting a positive overall effect, our assessment reveals evidence of low statistical power in the primary RCTs, selective inclusion of studies, publication bias and large variation in combinations of pre-processing and analytic decisions. In addition, our meta-analysis of all the primary RCTs included in the revised meta-analyses shows small exercise-related benefits (d = 0.22, 95% confidence interval 0.16 to 0.28) that became substantially smaller after accounting for key moderators (that is, active control and baseline differences; d = 0.13, 95% confidence interval 0.07 to 0.20), and negligible after correcting for publication bias (d = 0.05, 95% confidence interval -0.09 to 0.14). These findings suggest caution in claims and recommendations linking regular physical exercise to cognitive benefits in the healthy human population until more reliable causal evidence accumulates.

The effect of benzodiazepines on exercise in healthy adult participants: A systematic review.

The use of benzodiazepines among athletes is a new and growing phenomenon according to the recent case reports published. Therefore, there is an urgent need to identify if there is rationale for the use of benzodiazepines and its effects on exercise. This review aims to provide an overview of the effects of benzodiazepine in exercise among healthy adult participants and if they might have an additional ergogenic or ergolytic effect. Electronic searches were conducted in Pubmed, Scopus and Web of Science databases up to December 2020. Search terms covered all active substance names of benzodiazepine class and search terms about sport, exercise performance and athletes. We used the Physiotherapy Evidence Database (PEDro) to assess the methodological quality of the studies included in the qualitative synthesis. The methods and planned analyses of this systematic review were pre-registered at Open Science Framework (OSF: https://osf.io/uq6j8). A total of thirty-one full articles were assessed for eligibility and ten of them were included in the qualitative analysis. We found 7 studies which investigated benzodiazepine effects after an acute dose administered, whereas only 3 studies studied long-term effects after several doses used. According to our findings it does not seem that benzodiazepines might have an ergogenic or ergolytic effect on exercise performance. The small number of articles included (n = 10) with a relatively low sample of participants (N = 16, range = 6-58) does invite us to take our results with caution. This review evidences valuable insights into the use of benzodiazepines from a physical performance point of view. Our findings highlight the unclear effects benzodiazepines might have on exercise performance and its possible mechanisms of actions. Hence, the need to conduct new studies to understand its possible effects becomes essential to protect the health of athletes of all levels.

Correction: Mental Fatigue Might be Not So Bad for Exercise Performance After All: A Systematic Review and Bias-Sensitive Meta-Analysis.

[This corrects the article DOI: 10.5334/joc.126.].

Novel evidence on the effect of tramadol on self-paced high-intensity cycling.

The use of tramadol is a controversial topic in cycling. In order to provide novel evidence on this issue, we tested 29 participants in a pre-loaded cycling time trial (TT; a 20-min TT preceded by 40-min of constant work-rate at 60% of the VO2max) after ingesting 100 mg of tramadol (vs placebo and paracetamol (1.5 g)). Participants performed the Psychomotor Vigilance Task (PVT) at rest and a Sustained Attention to Response Task (SART) during the 60 min of exercise. Oscillatory electroencephalography (EEG) activity was measured throughout the exercise. The results showed higher mean power output during the 20-min TT in the tramadol vs. paracetamol condition, but no reliable difference was reported between tramadol and placebo (nor paracetamol vs. placebo). Tramadol resulted in faster responses in the PVT and higher heart rate during exercise. The main effect of substance was reliable in the SART during the 40-min constant workload (no during the 20-min TT), with slower reaction time, but better accuracy for tramadol and paracetamol than for placebo. This study supports the increased behavioural and neural efficiency at rest for tramadol but not the proposed ergogenic or cognitive (harmful) effect of tramadol (vs. placebo) during self-paced high-intensity cycling.

Does mental fatigue impair physical performance? A replication study.

The aim of this study is to replicate the hypothesis that mental fatigue impairs physical performance in a pre-registered (https://osf.io/wqkap/) within-subjects experiment. 30 recreationally active adults completed a time-to-exhaustion test (TTE) at 80% VO2max in two separate sessions, after completing a mental fatigue task or watching a documentary for 90 min. We measured power output, heart rate, (session) rating of perceived exertion (RPE) and subjective mental fatigue. Bayes factor analyses revealed extreme evidence supporting the alternative hypothesis that the mental fatigue task was more mentally fatiguing than the control task, BF01 = 0.009. However, we found moderate-to-strong evidence for the null hypothesis (i.e., no evidence of reduced performance) for average time in TTE (BF01 = 9.762) and anecdotal evidence for the null hypothesis in (session) RPE (BF01 = 2.902) and heart rate (BF01 = 2.587). Our data seem to challenge the idea that mental fatigue has a negative influence on exercise performance. Although we did succeed at manipulating subjective mental fatigue, this did not impair physical performance. However, we cannot discard the possibility that mental fatigue may have a negative influence under conditions not explored here, e.g., individualizing mentally fatiguing tasks. In sum, further research is warranted to determine the role of mental fatigue on exercise and sport performance.

Mental Fatigue Might Be Not So Bad for Exercise Performance After All: A Systematic Review and Bias-Sensitive Meta-Analysis.

There is an ongoing debate in the scientific community regarding whether a state of mental fatigue may have a negative effect upon a range of objective and subjective measures of human performance. This issue has attracted attention from several fields, including sport and exercise sciences. In fact, a considerable body of literature in the sport science field has suggested that performing a long and demanding cognitive task might lead to a state of mental fatigue, impairing subsequent exercise performance, although research in this field has shown contradictory results. Here, we performed a meta-analysis to investigate these inconsistent findings. The analysis yielded small-to-medium effects of mental fatigue on exercise performance, d z = 0.50, and RPE, d z = 0.21. However, a three-parameter selection model also revealed evidence of publication or reporting biases, suggesting that the bias-corrected estimates might be substantially lower (0.08 and 0.10, respectively) and non-significant. In sum, current evidence does not provide conclusive support for the claim that mental fatigue has a negative influence on exercise performance.

Correction: No evidence of the effect of cognitive load on self-paced cycling performance.

[This corrects the article DOI: 10.1371/journal.pone.0217825.].

No evidence of the effect of cognitive load on self-paced cycling performance.

OBJECTIVES: To test the hypothesis that cognitive load (low vs. high load) during a 20 min self-paced cycling exercise affects physical performance. DESIGN: A pre-registered (https://osf.io/qept5/), randomized, within-subject design experiment. METHODS: 28 trained and experienced male cyclists completed a 20 min self-paced cycling time-trial exercise in two separate sessions, corresponding to two working memory load conditions: 1-back or 2-back. We measured power output, heart rate, RPE and mental fatigue. RESULTS: Bayes analyses revealed extreme evidence for the 2-back task being more demanding than the 1-back task, both in terms of accuracy (BF10 = 4490) and reaction time (BF = 1316). The data only showed anecdotal evidence for the alternative hypothesis for the power output (BF10 = 1.52), moderate evidence for the null hypothesis for the heart rate (BF10 = 0.172), anecdotal evidence for RPE (BF10 = 0.72) and anecdotal evidence for mental fatigue (BF10 = 0.588). CONCLUSIONS: Our data seem to challenge the idea that self-paced exercise is regulated by top-down processing, given that we did not show clear evidence of exercise impairment (at the physical, physiological and subjective levels) in the high cognitive load condition task with respect to the low working memory load condition. The involvement of top-down processing in self-pacing the physical effort, however, cannot be totally discarded. Factors like the duration of the physical and cognitive tasks, the potential influence of dual-tasking, and the participants' level of expertise, should be taken into account in future attempts to investigate the role of top-down processing in self-paced exercise.

Transcranial direct current stimulation (tDCS) over the left prefrontal cortex does not affect time-trial self-paced cycling performance: Evidence from oscillatory brain activity and power output.

OBJECTIVES: To test the hypothesis that transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) influences performance in a 20-min time-trial self-paced exercise and electroencephalographic (EEG) oscillatory brain activity in a group of trained male cyclists. DESIGN: The study consisted of a pre-registered (https://osf.io/rf95j/), randomised, sham-controlled, single-blind, within-subject design experiment. METHODS: 36 trained male cyclists, age 27 (6.8) years, weight 70.1 (9.5) Kg; VO2max: 54 (6.13) ml.min-1.kg-1, Maximal Power output: 4.77 (0.6) W/kg completed a 20-min time-trial self-paced exercise in three separate sessions, corresponding to three stimulation conditions: anodal, cathodal and sham. tDCS was administered before each test during 20-min at a current intensity of 2.0 mA. The anode electrode was placed over the DLPFC and the cathode in the contralateral shoulder. In each session, power output, heart rate, sRPE and EEG (at baseline and during exercise) was measured. RESULTS: There were no differences (F = 0.31, p > 0.05) in power output between the stimulation conditions: anodal (235 W [95%CI 222-249 W]; cathodal (235 W [95%CI 222-248 W] and sham (234 W [95%CI 220-248 W]. Neither heart rate, sRPE nor EEG activity were affected by tDCS (all Ps > 0.05). CONCLUSION: tDCS over the left DLFC did not affect self-paced exercise performance in trained cyclists. Moreover, tDCS did not elicit any change on oscillatory brain activity either at baseline or during exercise. Our data suggest that the effects of tDCS on endurance performance should be taken with caution.

Oscillatory brain activity during acute exercise: Tonic and transient neural response to an oddball task.

Intense physical exercise exerts measurable changes at various physiological levels that are well documented in the literature. However, despite the key role of the brain in processing inputs from internal organ systems and the external environment to coordinate and optimize behavior, little is known about brain dynamics during exercise. The present study investigates tonic and transient oscillatory brain activity in a group of participants performing an oddball task during a single bout of aerobic exercise. Twenty young males (19-32 years) were recruited for two experimental sessions on separate days. EEG activity was recorded during a session of cycling at 80% (moderate-to-high intensity) of VO2max (maximum rate of oxygen consumption) while participants responded to infrequent targets (red square and big blue circle) presented among frequent nontargets (small blue circle). This was compared to a (baseline) light intensity session (30% VO2max ) to control any potential effect of dual tasking (i.e., pedaling and performing the oddball task). A cluster-based nonparametric permutations test revealed an increase in power across the entire frequency spectrum during the moderate-to-high intensity exercise compared to light intensity. Furthermore, the more salient target (red square) elicited a lower increase in (stimulus-evoked) theta power in the 80% VO2max than in the light intensity condition. Alpha and lower beta power decreased less in the standard trials (small blue circle) during the moderate-to-high exercise condition than in the light exercise condition. The present study unveils, for the first time, a complex brain activity pattern during vigorous exercise while attending to task-relevant stimuli.

Effect of induced alkalosis on performance during a field-simulated BMX cycling competition.

OBJECTIVES: The aim of the present study was to test the effect of sodium bicarbonate (NaHCO3-) ingestion on performance during a simulated competition on a Bicycle Motocross (BMX) track. DESIGN: Double-blind cross-over study. METHODS: Twelve elite male BMX cyclists (age: 19.2±3.4 years; height: 174.2±5.3cm; body mass: 72.4±8.4kg) ingested either NaHCO3- (0.3g.kg-1 body weight) or placebo 90min prior to exercise. The cyclists completed three races in a BMX Olympic track interspersed with 15min of recovery. Blood samples were collected to assess the blood acid-base status. Performance, cardiorespiratory, heart rate variability (HRV) as well as subjective variables were assessed. RESULTS: The main effect of condition (NaHCO3- vs. placebo) was observed in pH, bicarbonate concentration and base excess (p<0.05), with a significant blood alkalosis. No changes were found in time, peak velocity and time to peak velocity for condition (p>0.05). The HRV analysis showed a significant effect of NaHCO3- ingestion, expressed by the rMSSD30 (root mean square of the successive differences) (p<0.001). There was no effect of condition on oxygen uptake, carbon dioxide production, or pulmonary ventilation (p>0.05). Finally, there was no effect of condition for any subjective scale (p>0.05). CONCLUSIONS: We present here the first field condition study to investigate the effect of bicarbonate ingestion over performance in BMX discipline. The results showed that NaHCO3--induced alkalosis did not improve performance in a simulated BMX competition in elite BMX cyclists, although future studies should consider the effects of NaHCO3- on autonomic function as a component of recovery.

The effects of transcranial direct current stimulation on objective and subjective indexes of exercise performance: A systematic review and meta-analysis.

OBJECTIVE: To examine the effects of transcranial direct current stimulation (tDCS) on objective and subjective indexes of exercise performance. DESIGN: Systematic review and meta-analysis. DATA SOURCES: A systematic literature search of electronic databases (PubMed, Web of Science, Scopus, Google Scholar) and reference lists of included articles up to June 2018. ELIGIBILITY CRITERIA: Published articles in journals or in repositories with raw data available, randomized sham-controlled trial comparing anodal stimulation with a sham condition providing data on objective (e.g. time to exhaustion or time-trial performance) or subjective (e.g. rate of perceived exertion) indexes of exercise performance. RESULTS: The initial search provided 420 articles of which 31 were assessed for eligibility. Finally, the analysis of effect sizes comprised 24 studies with 386 participants. The analysis indicated that anodal tDCS had a small but positive effect on performance g = 0.34, 95% CI [0.12, 0.52], z = 3.24, p = .0012. Effects were not significantly moderated by type of outcome, electrode placement, muscles involved, number of sessions, or intensity and duration of the stimulation. Importantly, the funnel plot showed that, overall, effect sizes tended to be larger in studies with lower sample size and high standard error. SUMMARY: The results suggest that tDCS may have a positive impact on exercise performance. However, the effect is probably small and most likely biased by low quality studies and the selective publication of significant results. Therefore, the current evidence does not provide strong support to the conclusion that tDCS is an effective means to improve exercise performance.

Analgesics and Sport Performance: Beyond the Pain-Modulating Effects.

Analgesics are used widely in sport to treat pain and inflammation associated with injury. However, there is growing evidence that some athletes might be taking these substances in an attempt to enhance performance. Although the pharmacologic action of analgesics and their use in treating pain with and without anti-inflammatory effect is well established, their effect on sport performance is debated. The aim of this review was to evaluate the evidence of whether analgesics are capable of enhancing exercise performance and, if so, to what extent. Paracetamol has been suggested to improve endurance and repeated sprint exercise performance by reducing the activation of higher brain structures involved in pain and cognitive/affective processing. Nonsteroidal anti-inflammatory drugs affect both central and peripheral body systems, but investigation on their ergogenic effect on muscle strength development has provided equivocal results. The therapeutic use of glucocorticoids is indubitable, but clear evidence exists for a performance-enhancing effect after short-term oral administration. Based on the evidence presented in this review article, the ergogenic benefit of analgesics may warrant further consideration by regulatory bodies. In contrast to the aforementioned analgesics, there is a paucity of research on the use of opioids such as tramadol on sporting performance. LEVEL OF EVIDENCE: III.

Tramadol effects on physical performance and sustained attention during a 20-min indoor cycling time-trial: A randomised controlled trial.

OBJECTIVES: To investigate the effect of tramadol on performance during a 20-min cycling time-trial (Experiment 1), and to test whether sustained attention would be impaired during cycling after tramadol intake (Experiment 2). DESIGN: Randomized, double-blind, placebo controlled trial. METHODS: In Experiment 1, participants completed a cycling time-trial, 120-min after they ingested either tramadol or placebo. In Experiment 2, participants performed a visual oddball task during the time-trial. Electroencephalography measures (EEG) were recorded throughout the session. RESULTS: In Experiment 1, average time-trial power output was higher in the tramadol vs. placebo condition (tramadol: 220W vs. placebo: 209W; p<0.01). In Experiment 2, no differences between conditions were observed in the average power output (tramadol: 234W vs. placebo: 230W; p>0.05). No behavioural differences were found between conditions in the oddball task. Crucially, the time frequency analysis in Experiment 2 revealed an overall lower target-locked power in the beta-band (p<0.01), and higher alpha suppression (p<0.01) in the tramadol vs. placebo condition. At baseline, EEG power spectrum was higher under tramadol than under placebo in Experiment 1 while the reverse was true for Experiment 2. CONCLUSIONS: Tramadol improved cycling power output in Experiment 1, but not in Experiment 2, which may be due to the simultaneous performance of a cognitive task. Interestingly enough, the EEG data in Experiment 2 pointed to an impact of tramadol on stimulus processing related to sustained attention. TRIAL REGISTRATION: EudraCT number: 2015-005056-96.