Acute Exercise Fatigue Impairs Cognitive Control: Neurophysiological Mechanisms Revealed by ERP and ERSP Analyses

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study “Acute Exercise Fatigue Impairs Cognitive Control: Neurophysiological Mechanisms Revealed by ERP and ERSP Analyses” focused on the effects of acute exhaustion exercise on cognitive control, by using the event-related potential (ERP) and the event-related spectral perturbation (ERSP). And the study found that “Acute exercise exhaustion impairs cognitive control by weakening conflict monitoring (reduced N2 amplitude), impairing late cognitive resource allocation and evaluation (reduced P3 amplitude, prolonged latency), and disrupting neural oscillations related to inhibitory control (reduced alpha energy”.

In my view, there are several major and minor concerns.

 

Major:

• The topic of the study is not something new. Or in other words, at least from the introductions, I did not get the idea why this study is needed and what is different from other previous studies. As far as I know, there are already several studies investigated the exercise-induced fatigue and cognitive function. Apart from that, there are also lots of studies explored the effects of acute high-intensity exercise (which seems to be similar to what the authors claimed “acute exercise fatigue”) on cognitive functions.
• The terms “exercise-induced fatigue”, “exercise fatigue” seem not to be well defined or introduced, nor well explained and discussed with the current results and discussion. As the authors claimed, the “exercise-induced fatigue” contains both physiological and mental fatigue induced by physical exercise. While, where do the effects come from? From the physiological or from the mental parts? Or both? And how? Given that the definition is not clear, the explanations cannot be clear.
• Number of trials. In the method part, I found there are only 60 trials in total for this experiment (P4L138: “4 blocks”; P4L149: each block includes 15 randomly presented trials; 15*4 = 60). And nothing was mentioned about whether there were some trials that were rejected from analysis due to the incorrect response or the artifacts in the EEG. Given the number of trials per condition (Cong vs Incong) is just 30 (not too many), therefore, it would be important to report the number of trials that were included into analysis for both RT and ERP/ERSP.
• Statistical analysis (2-way RM ANOVA) for ERP/ERSP. The authors analyzed the ERP/ERSP results by using 2-way RM ANOVAs on each mid-line electrode separately (and directly) without having a sig. 3-way interaction effect (time*condition* electrode position). That is really “dangerous” for having a higher chance of “false positive” (type I error).

 

Minor:

• In the part 2.3 (P4L137-152), at the beginning, the stroop task seemed to be block-designed (4 block: 2 congruent, 2 incongruent), while, in the later part, it looks like that the congruent/incongruent trials were randomly assigned in the 15 trials per block (L149) and Figuer 1.
• L157 “Neuroscan company (Brain Vision Recorder, U.S.)”. Neuroscan? Brain Products? As far as I know Brain Products software (Brain Vision Recorder) cannot connect to Neuroscan amplifier…
• The subtitle for ERSP results is missing…

Author Response

We sincerely thank the reviewers for their insightful comments and constructive suggestions, which have greatly helped us improve the quality of our manuscript. We have carefully addressed each point raised, as detailed below.(*^▽^*)
Comment 1:

“The topic of the study is not something new. Or in other words, at least from the introductions, I did not get the idea why this study is needed and what is different from other previous studies. As far as I know, there are already several studies investigated the exercise-induced fatigue and cognitive function. Apart from that, there are also lots of studies explored the effects of acute high-intensity exercise (which seems to be similar to what the authors claimed ‘acute exercise fatigue’) on cognitive functions.”

Response 1:
We thank the reviewer for this important comment. We have now revised the Introduction to better clarify the novelty and rationale of our study. While previous studies have indeed examined the effects of acute high-intensity exercise on cognitive function, most have focused on behavioral outcomes or basic event-related potential components (P3, N2) without incorporating time-frequency analyses to investigate neural oscillatory mechanisms. Our study is among the first to combine ERP and event-related spectral perturbation  analyses to explore how acute exercise-induced fatigue specifically impairs cognitive control at both temporal and oscillatory levels. This approach provides a more comprehensive understanding of the neurophysiological mechanisms underlying exercise-induced cognitive deficits. We have added a paragraph in the Introduction (L 87–94) to emphasize this research gap and our contribution.

Comment 2:
“The terms ‘exercise-induced fatigue’, ‘exercise fatigue’ seem not to be well defined or introduced, nor well explained and discussed with the current results and discussion. As the authors claimed, the ‘exercise-induced fatigue’ contains both physiological and mental fatigue induced by physical exercise. While, where do the effects come from? From the physiological or from the mental parts? Or both? And how? Given that the definition is not clear, the explanations cannot be clear.”

Response 2:

We thank the reviewer for this valuable comment. We have revised the manuscript to address this concern as follows:

（a）In the Introduction, we have added a precise definition of "exercise-induced fatigue" (L 50–52).

（b）In the Discussion, we have significantly expanded and structured the explanation of the relevant mechanisms. As suggested by the reviewer, we enhanced the Discussion by adding a dedicated new subsection (4.4. Significance and Practical Implications). In this subsection, we explicitly discuss how our neurophysiological findings may reflect the interaction of physiological and psychological mechanisms:Physiological mechanisms: We linked the observed reduction in P3 amplitude and alpha power to potential physiological underpinnings, stating: "The prefrontal cortex, a key region for cognitive control, has high metabolic demands and is particularly vulnerable to systemic physiological changes, such as hypoglycemia or hypoxia, that can accompany exhaustive exercise. The observed reduction in P3 amplitude likely reflects a neurophysiological state of prefrontal hypoactivation, indicating a diminished capacity to engage top-down control circuits." (L 521–526) Psychological mechanisms: We also discussed the role of subjective perception and resource allocation, connecting it to the theoretical framework: "Both the physical fatigue induced in this study and the mental fatigue elicited by prolonged cognitive tasks in previous literature demonstrate impairing effects on executive function, suggesting they may share underlying psychophysiological mechanisms." (L 518–521)

（c）We explicitly acknowledged the limitations and future directions in the Study Limitations section (4.5), directly admitting the challenge of fully dissociating these components with our current measures (L 554–558).

Comment 3:
“Number of trials. In the method part, I found there are only 60 trials in total for this experiment (P4L138: ‘4 blocks’; P4L149: each block includes 15 randomly presented trials; 154 = 60). And nothing was mentioned about whether there were some trials that were rejected from analysis due to the incorrect response or the artifacts in the EEG. Given the number of trials per condition (Cong vs Incong) is just 30 (not too many), therefore, it would be important to report the number of trials that were included into analysis for both RT and ERP/ERSP.”

Response 3:

Dear Reviewer, we sincerely appreciate your careful attention to this methodological detail. Your comment is entirely valid, and it is indeed essential to clearly describe the effective trial selection process and the final number of trials included in the analysis. As requested, we have added a paragraph at the end of the "2.4 EEG Data Acquisition and Processing" section (L 179-188) in the manuscript.

Comment 4:
“Statistical analysis (2-way RM ANOVA) for ERP/ERSP. The authors analyzed the ERP/ERSP results by using 2-way RM ANOVAs on each mid-line electrode separately (and directly) without having a sig. 3-way interaction effect (time*condition* electrode position). That is really ‘dangerous’ for having a higher chance of ‘false positive’ (type I error).”

Response 4:

We thank the reviewer for this important statistical comment. To reduce the risk of Type I error, we have now performed a three-way repeated-measures ANOVA (Time × Condition × Electrode) for the ERP/ERSP measures. Subsequent two-way ANOVAs at individual electrodes were only conducted to interpret significant higher-order interactions that involved the Electrode factor. We have updated the 2.7 Statistical Analysis section (L 231-233) and have revised the Results section accordingly.

Minor Comments:

Comment 5:
“In the part 2.3 (P4L137-152), at the beginning, the stroop task seemed to be block-designed (4 block: 2 congruent, 2 incongruent), while, in the later part, it looks like that the congruent/incongruent trials were randomly assigned in the 15 trials per block (L149) and Figure 1.”

Response 5:
We apologize for the confusion. The Stroop task was indeed administered in a mixed-trial design within each block, with congruent and incongruent trials randomly presented. We have revised the text to clarify this:[L153-154].

Comment 6:
“L157 ‘Neuroscan company (Brain Vision Recorder, U.S.)’. Neuroscan? Brain Products? As far as I know Brain Products software (Brain Vision Recorder) cannot connect to Neuroscan amplifier…”

Response 6:
We thank the reviewer for catching this error. The EEG data were recorded using a Neuroscan SynAmps2 amplifier and Acquire software. The reference to “Brain Vision Recorder” was incorrect and has been removed[L162].

Comment 7:
“The subtitle for ERSP results is missing…”

Response 7:
We sincerely thank the reviewer for pointing out this issue. Following the suggestion, we have added subtitles to the "3.4 Event-Related Spectral Perturbation Results" section to present the analysis results of each frequency band more clearly. The revised structure is as follows:

3.4.1 Theta Band Analysis Results
3.4.2 Alpha Band Analysis Results
3.4.3 Beta Band Analysis Results

This structural reorganization improves the organization of the results for better readability. We have accordingly placed the results for each frequency band under their respective subtitles.

We believe that these revisions have significantly strengthened the manuscript and addressed all of the reviewer’s concerns. We are grateful for the opportunity to improve our work and hope that the revised version is now suitable for publication.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors present an interesting and timely study that investigates the effects of acute exhaustive exercise on cognitive control using ERP and ERSP measures.

The first observation—that individuals perform worse on cognitive tasks when exhausted—is not new. It has long been established that physical fatigue impairs executive performance. However, the second observation regarding the electrophysiological correlates has potential value and deserves further exploration.

The interpretation of the alpha-band findings is conceptually weak. In the Stroop task, alpha suppression over parietal and frontal regions typically indicates increased cortical engagement and active information processing, rather than a mere loss of inhibition. If exhaustion leads to a smaller reduction in alpha power (weaker desynchronization), this could suggest reduced cognitive engagement. Conversely, a greater reduction might indicate overactivation or compensatory effort, rather than impaired inhibitory control. The authors should revisit this section and refine their interpretation accordingly.

Another concern is the lack of analysis regarding the theta and gamma frequency bands. Theta oscillations are closely linked to executive function and conflict-monitoring processes and are often reduced in individuals with impaired cognitive function, such as in dementia. On the other hand, gamma activity is associated with high-level cognitive integration during demanding tasks. Including analyses of both frequency ranges, along with a thorough discussion, would provide a more comprehensive understanding of the neurophysiological dynamics of fatigue.

Additionally, the absence of significant findings in the beta band warrants deeper consideration. Beta oscillations are related not only to motor preparation but also play an important role in maintaining higher-order cortical functions. The authors should provide a more detailed explanation for the lack of beta modulation following exhaustion.

Overall, the manuscript requires major revisions. The authors should include the missing analyses, clarify their theoretical interpretations, and improve the manuscript’s language quality.

The current English expression is inadequate, containing numerous typographical and grammatical errors, as well as unedited template sections that require removal.

After implementing these substantial improvements and performing reanalysis, the paper should be revised.

Comments on the Quality of English Language

see above

Author Response

We sincerely thank the reviewers for their insightful comments and constructive suggestions, which have greatly helped us improve the quality of our manuscript. We have carefully addressed each point raised, as detailed below.
Comment 1:

The interpretation of the alpha-band findings is conceptually weak. In the Stroop task, alpha suppression over parietal and frontal regions typically indicates increased cortical engagement and active information processing, rather than a mere loss of inhibition. If exhaustion leads to a smaller reduction in alpha power (weaker desynchronization), this could suggest reduced cognitive engagement. Conversely, a greater reduction might indicate overactivation or compensatory effort, rather than impaired inhibitory control. The authors should revisit this section and refine their interpretation accordingly.

Response 1:

We sincerely thank the reviewer for this insightful comment, which has helped us refine our interpretation. We agree that alpha event-related desynchronization (ERD) is a complex phenomenon. In our revised discussion (Section 4.3), we have significantly expanded upon our initial interpretation. We now explicitly address the paradox of observing enhanced alpha ERD alongside behavioral impairment. We propose that this does not merely reflect a loss of inhibition, but rather signifies a state of neural inefficiency or compensatory overactivation. The fatigued brain may be expending more effort (leading to greater alpha suppression) but achieving diminished behavioral outcomes due to inefficient processing, consistent with load theory. This interpretation now more accurately reconciles the typical role of alpha ERD with our specific findings in the context of fatigue. The relevant text has been revised in lines [L458-471].

Comment 2:

Another concern is the lack of analysis regarding the theta and gamma frequency bands. Theta oscillations are closely linked to executive function and conflict-monitoring processes and are often reduced in individuals with impaired cognitive function, such as in dementia. On the other hand, gamma activity is associated with high-level cognitive integration during demanding tasks. Including analyses of both frequency ranges, along with a thorough discussion, would provide a more comprehensive understanding of the neurophysiological dynamics of fatigue.

Response 2:

• We thank the reviewer for this valuable suggestion. In response, we have now included the analysis and discussion of the theta frequency band. As presented in the new Section 3.4.1 (Theta Band Analysis Results), our analysis revealed that mid-frontal theta power did not show a significant change following exhaustive exercise. This null finding is highly informative. As we now discuss in depth in Section 4.3[L472-482], the preservation of conflict-related theta oscillations, despite behavioral impairment, is a key piece of evidence that allows us to dissociate the conflict monitoring stage (which remains intact) from the resource allocation and conflict resolution stages (which are impaired). This finding significantly strengthens our central argument for a multi-stage model of cognitive control failure under fatigue.
• Regarding the gamma band, we sincerely appreciate this suggestion. We sincerely appreciate this suggestion regarding the gamma frequency band. Gamma oscillations are highly susceptible to muscle artifacts, particularly in studies involving intense physical exercise. Therefore, to maintain the highest standards of data quality and interpretation, we have decided not to include gamma band analysis in the present manuscript.

Comment 3:

Additionally, the absence of significant findings in the beta band warrants deeper consideration. Beta oscillations are related not only to motor preparation but also play an important role in maintaining higher-order cortical functions. The authors should provide a more detailed explanation for the lack of beta modulation following exhaustion.

Overall, the manuscript requires major revisions. The authors should include the missing analyses, clarify their theoretical interpretations, and improve the manuscript’s language quality.

Response 3:
We agree with the reviewer that the null finding in the beta band is theoretically important and deserves a more detailed explanation. We have now expanded our discussion of this result in Section 4.[L505-514]. We propose that the stability of beta activity under fatigue suggests that the brain's macroscopic ability to maintain the current task set and stabilize higher-order cortical networks remains largely unaffected by acute exhaustive exercise. This reinforces our model of a selective impairment, where fatigue specifically targets dynamic processes like attentional allocation (alpha) and response implementation (P3), while sparing other functions like conflict monitoring (theta) and task-set maintenance (beta). This "function-specific impairment" pattern provides a more nuanced understanding of the neural mechanisms of fatigue.

Comment 4:

The current English expression is inadequate, containing numerous typographical and grammatical errors, as well as unedited template sections that require removal.

Response 4:

We sincerely apologize for the language issues in the previous version. The entire manuscript has now been professionally proofread and edited by a native English-speaking colleague with expertise in the field. We have carefully checked for and corrected all typographical and grammatical errors and have ensured that all template text and comments have been removed. We are confident that the language quality of the current version meets the high standards of the journal.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have reviewed the revised manuscript. The authors have satisfactorily addressed all my previous concerns. I have no further suggestions and recommend acceptance.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors addressed the raised concerns and improved their work. The article is suitable for acceptance.

Comments on the Quality of English Language

see above