Combined Action Observation and Motor Imagery Elicits Superior Frontoparietal Activation in Elite Ski Jumpers: An fNIRS Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The present study addresses an underexplored topic, namely the neural effects of combined action observation and motor imagery (AO+MI) in elite ski jumpers using fNIRS. The focus on highly trained athletes and ecologically relevant motor simulation tasks is a notable strength, particularly because most previous AO/MI studies have relied on simplified laboratory paradigms. Furthermore, the integration of the DASH framework with neuroimaging data provides a relevant theoretical basis for the investigation. Nevertheless, despite the scientific relevance of the topic, the manuscript still requires substantial revision to improve its clarity, methodological rigor, linguistic quality, and interpretative precision before it can be considered for publication.

One of the main issues throughout the manuscript is the presence of numerous grammatical inaccuracies, awkward sentence constructions, and inconsistencies in academic writing style. Several sentences contain capitalization problems, punctuation errors, duplicated words, missing connectors, or unclear phrasing. For example, expressions such as “but its effects on complex whole-body movements in elite athletes remain unclear” immediately after a period in the abstract should begin with a capital letter. Similar issues appear repeatedly throughout the text, including phrases such as “concurrent AO+MI Based on the DASH model,” “it combines involves movements,” and “The duration and movement content of the MI trials were matched to the AO videos, with each trial lasting 8 seconds to those of ensure consistency across conditions.” These language problems reduce readability and occasionally compromise scientific clarity. The manuscript would strongly benefit from professional English editing by a native speaker or specialized scientific editing service.  

The introduction provides an adequate overview of AO and MI, but the conceptual development could be more cohesive and critical. The authors rely heavily on general statements regarding the benefits of AO+MI without sufficiently discussing contradictory findings or methodological limitations in the existing literature. The rationale for selecting elite ski jumpers as the experimental model should be expanded. Although the authors mention the complexity and risk associated with ski jumping, they do not sufficiently explain why this specific sport would theoretically benefit more from AO+MI than other sports requiring visuomotor integration. A deeper discussion of motor automaticity, internal models, and sensorimotor prediction in elite ski jumping would strengthen the theoretical framework.

The hypotheses are generally understandable, but they could be formulated more precisely. The third hypothesis regarding athlete skill level appears relatively weak and insufficiently justified. Since all participants were already elite athletes, the theoretical rationale for expecting differences between Master-level and First-class athletes should be explained more clearly. Without a broader skill range, including intermediate or novice athletes, the absence of differences becomes somewhat predictable and limits the interpretability of this analysis.

The methods section is generally organized, but several methodological details remain insufficiently described. The participant characterization lacks important information regarding training routines, competition levels, injury history, and frequency of mental training practices. These factors may substantially influence imagery-related cortical activation. Moreover, although imagery ability was assessed with the MIQ-R, the authors do not report whether imagery scores differed between groups or whether imagery ability correlated with cortical activation outcomes. Such analyses could substantially enrich the interpretation of the findings.

The description of the fNIRS setup also requires clarification. Although the authors mention 45 channels and the use of the AAL atlas, the manuscript does not provide sufficient information regarding optode localization procedures, registration accuracy, or anatomical reliability of channel mapping. Given the limited spatial resolution of fNIRS, greater methodological transparency is necessary. In addition, short-separation channels are not mentioned. Since superficial physiological signals can contaminate fNIRS measurements, the absence of short-channel regression should be acknowledged explicitly as a limitation.

The experimental protocol is understandable, but the rationale for selecting an 8-second imagery/observation window and a 5-8 second hemodynamic extraction window should be better justified with references specific to AO/MI paradigms and fNIRS temporal dynamics. The manuscript does not clarify whether participants kept their eyes open during MI trials, how compliance with kinesthetic imagery was verified, or whether subjective vividness ratings differed across conditions. These aspects are important because variability in imagery engagement may directly influence cortical activation patterns.

Concerning the statistics, the authors state that paired-sample t-tests were conducted across 45 channels, but the manuscript does not specify whether assumptions of normality were verified. Moreover, the use of multiple pairwise channel comparisons substantially increases the risk of type I error, even with FDR correction. The authors should provide more detail regarding the exact correction procedure, adjusted q-values, and effect sizes for all major comparisons. Importantly, no statistical power analysis is reported. Given the relatively small sample size and the high dimensionality of channel-wise comparisons, the possibility of type II errors should be discussed more explicitly.

The results section is generally coherent, but some interpretations seem overstated. The conclusion that AO and MI alone failed to activate cortical regions should be phrased more cautiously. The absence of statistically significant activation after correction does not necessarily imply absence of neural engagement. Rather, it may reflect subtle activation patterns below the detection threshold given the sample size and analytical strategy. This distinction is particularly important because previous literature consistently demonstrates cortical recruitment during isolated AO and MI paradigms.

The discussion section is one of the strongest parts of the manuscript, especially in its integration of the DASH framework and neural efficiency hypothesis. However, several interpretations remain somewhat speculative. The argument that AO+MI increases “overall cognitive load” is plausible but was not directly measured in the study. The inference that elite athletes exhibit reduced activation due to neural efficiency should be presented more cautiously because the study lacks comparison groups with lower expertise levels. Without such comparisons, the data cannot definitively support the neural efficiency hypothesis. The authors should therefore moderate these claims and frame them as possible interpretations rather than direct evidence.

Another issue concerns the neuroanatomical interpretation of the activated regions. The manuscript often attributes highly specific cognitive functions to areas such as the MFG, IPL, and SMG without adequately acknowledging the multifunctional nature of these regions. Some statements seem overly deterministic, particularly when linking activation patterns to executive control or embodied motor representation. More balanced wording would improve scientific rigor.

The limitations section is appropriate but could be expanded considerably. The authors should discuss the intrinsic limitations of fNIRS, including restricted penetration depth, inability to measure subcortical structures, susceptibility to extracerebral contamination, and relatively low spatial specificity compared to fMRI. Additionally, the absence of behavioral outcome measures is a significant limitation because the study demonstrates neural differences without confirming whether these differences translate into improved motor performance. This point deserves stronger emphasis.

There are also several formatting and editorial inconsistencies that should be corrected before publication. Some references appear duplicated or inconsistently formatted. For instance, Hardwick et al. are cited both as a meta-analysis reference and again later with slightly different formatting. There are also typographical inconsistencies in spacing around citations and symbols such as “AO + MI” versus “AO+MI.” The manuscript also still contains template placeholders such as “Firstname Lastname” and “To be added by editorial staff during production,” indicating that the submission was not fully finalized.

Author Response

The present study addresses an underexplored topic, namely the neural effects of combined action observation and motor imagery (AO+MI) in elite ski jumpers using fNIRS. The focus on highly trained athletes and ecologically relevant motor simulation tasks is a notable strength, particularly because most previous AO/MI studies have relied on simplified laboratory paradigms. Furthermore, the integration of the DASH framework with neuroimaging data provides a relevant theoretical basis for the investigation. Nevertheless, despite the scientific relevance of the topic, the manuscript still requires substantial revision to improve its clarity, methodological rigor, linguistic quality, and interpretative precision before it can be considered for publication.

Our responses: We sincerely thank the reviewer for this overall assessment and for recognizing the scientific value of our study, particularly the investigation of combined AO+MI in elite ski jumpers using ecologically valid tasks and the integration of the DASH framework with neuroimaging data. We fully acknowledge the reviewer's concern regarding the clarity, methodological rigor, linguistic quality, and interpretative precision of the original manuscript.

In response, we have carefully revised the manuscript throughout:

1. Clarity and Cohesion:We reorganized the Introduction and Discussion to improve logical flow, reduce repetition, and clarify theoretical rationale.
2. Linguistic Quality:We conducted thorough proofreading to correct grammatical issues, improve sentence structure, and ensure consistent academic style. All changes have been marked in red in the revised manuscript, including capitalization, punctuation, phrasing, and clarity improvements.
3. Methodological Rigor:We added details on fNIRS optode placement, registration accuracy, channel anatomical mapping, statistical procedures, normality checks, Wilcoxon sensitivity analyses, and power estimation. Limitations, including the absence of short-separation channels and condition-specific vividness ratings, are now explicitly acknowledged.
4. Interpretative Precision:We moderated statements regarding AO+MI advantages, clarified exploratory analyses of athlete level, and emphasized that certain interpretations are consistent with existing hypotheses (e.g., neural efficiency) rather than direct evidence.

We believe that these revisions address the reviewer's concerns and substantially improve the readability, methodological transparency, and scientific rigor of the manuscript. All modifications are clearly marked in red in the revised version. We sincerely thank the reviewer for this constructive feedback, which helped us strengthen the quality of our work.

1.One of the main issues throughout the manuscript is the presence of numerous grammatical inaccuracies, awkward sentence constructions, and inconsistencies in academic writing style. Several sentences contain capitalization problems, punctuation errors, duplicated words, missing connectors, or unclear phrasing. For example, expressions such as “but its effects on complex whole-body movements in elite athletes remain unclear” immediately after a period in the abstract should begin with a capital letter. Similar issues appear repeatedly throughout the text, including phrases such as “concurrent AO+MI Based on the DASH model,” “it combines involves movements,” and “The duration and movement content of the MI trials were matched to the AO videos, with each trial lasting 8 seconds to those of ensure consistency across conditions.” These language problems reduce readability and occasionally compromise scientific clarity. The manuscript would strongly benefit from professional English editing by a native speaker or specialized scientific editing service. 

Our responses: We sincerely thank the reviewer for pointing out the grammatical inaccuracies, awkward sentence constructions, and inconsistencies in academic writing style. We fully acknowledge that the language quality of the original manuscript was limited and that these issues may have reduced readability and scientific clarity.

In the revised manuscript, we have carefully reviewed the entire text and corrected capitalization errors, punctuation problems, duplicated words, missing connectors, and unclear phrasing. The specific examples mentioned by the reviewer, including “but its effects on complex whole-body movements in elite athletes remain unclear,” “concurrent AO+MI Based on the DASH model,” “it combines involves movements,” and “The duration and movement content of the MI trials were matched to the AO videos, with each trial lasting 8 seconds to those of ensure consistency across conditions,” have all been revised. In addition, we conducted a line-by-line proofreading of the manuscript to improve sentence structure, terminology consistency, and overall academic readability.

All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this helpful suggestion, which improved the clarity and presentation quality of the manuscript.

2.The introduction provides an adequate overview of AO and MI, but the conceptual development could be more cohesive and critical. The authors rely heavily on general statements regarding the benefits of AO+MI without sufficiently discussing contradictory findings or methodological limitations in the existing literature. The rationale for selecting elite ski jumpers as the experimental model should be expanded. Although the authors mention the complexity and risk associated with ski jumping, they do not sufficiently explain why this specific sport would theoretically benefit more from AO+MI than other sports requiring visuomotor integration. A deeper discussion of motor automaticity, internal models, and sensorimotor prediction in elite ski jumping would strengthen the theoretical framework.

Our responses: We sincerely thank the reviewer for this insightful and constructive comment. We agree that the original Introduction provided a general overview of AO and MI, but the conceptual development was not sufficiently cohesive or critical. In particular, the previous version placed greater emphasis on the potential benefits of AO+MI, while insufficiently discussing the variability, boundary conditions, and methodological limitations of existing AO+MI research. We also acknowledge that the theoretical rationale for selecting elite ski jumpers as the experimental model required further clarification.

In the revised manuscript, we have substantially revised the Introduction to provide a more balanced and theoretically grounded framework. First, we expanded the discussion of AO+MI by clarifying that its effects should not be considered universal or purely additive. We now emphasize that AO+MI-related benefits may depend on task characteristics, participant expertise, imagery ability, and the correspondence between observed and imagined actions. We further explain that the effects of AO+MI may be stronger when the observed and imagined actions are temporally and spatially congruent, when participants can maintain vivid kinesthetic imagery during observation, and when the task requires the integration of external visual information with internally generated motor representations.

Second, we expanded the rationale for using elite ski jumpers as the experimental model. In the revised Introduction, we explain that ski jumping is not only complex and high-risk, but also represents a highly automated and prediction-dependent motor skill. During the take-off and early flight phases, athletes have limited time to correct their movements through ongoing feedback and must rely strongly on anticipatory control and refined internal models to predict the sensory consequences of action. We further discuss that, in elite ski jumpers, long-term training may automatize these sport-specific action representations. From this perspective, AO+MI may be particularly relevant because it requires athletes to couple externally observed movement cues with internally generated kinesthetic representations, potentially engaging cortical processes related to sensorimotor prediction, visuomotor transformation, and sport-specific action representation more strongly than either AO or MI alone.

In addition, we revised the final part of the Introduction to make the transition from the theoretical framework to the use of fNIRS and the study hypotheses clearer. We clarified that fNIRS is suitable for investigating task-related cortical hemodynamics in athletes because of its tolerance to body movement and applicability in ecologically valid settings. We then linked this methodological choice to the present comparison of AO, MI, and AO+MI in professional ski jumpers.

All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this valuable suggestion, which helped us strengthen the conceptual coherence, critical discussion, and theoretical rationale of the Introduction.

3.The hypotheses are generally understandable, but they could be formulated more precisely. The third hypothesis regarding athlete skill level appears relatively weak and insufficiently justified. Since all participants were already elite athletes, the theoretical rationale for expecting differences between Master-level and First-class athletes should be explained more clearly. Without a broader skill range, including intermediate or novice athletes, the absence of differences becomes somewhat predictable and limits the interpretability of this analysis.

Our response: We sincerely thank the reviewer for this helpful comment. We agree that the original formulation of the third hypothesis regarding athlete level was not sufficiently precise, especially because all participants in the present study were already highly trained elite ski jumpers.

In the revised manuscript, we have reformulated this part as an exploratory analysis rather than a directional hypothesis. Specifically, athlete level was included as an exploratory between-subject factor to examine whether AO, MI, and AO+MI-related cortical responses varied within an elite athlete sample. We did not assume a specific direction of difference between Master-level and First-class athletes.

Although direct neuroimaging comparisons between Master-level and First-class athletes are limited, previous sports science studies have sometimes examined athlete classification as an exploratory factor when investigating individual characteristics. For example, Piepiora and Naczyńska (2023) compared personality traits across sports classes in Polish junior sports acrobatics representatives and reported differences between master-class and first-class athletes in several Big Five personality dimensions. Inspired by this general exploratory approach, we treated athlete level as an exploratory factor rather than as a strong confirmatory hypothesis.

In the revised Discussion, we have also clarified that the broadly comparable activation patterns between ML and FC athletes may reflect their shared high training status and refined sport-specific motor representations. Nevertheless, future studies including athletes across a broader skill-level continuum could further examine how AO, MI, and AO+MI effects vary with expertise, providing additional insight into how skill level may modulate cortical responses during motor simulation.

All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this constructive suggestion, which helped us clarify the rationale and scope of the athlete-level analysis.

Piepiora, P.; Naczyńska, A. Personality Traits vs. Sports Classes of Polish Representatives in Junior Sports Acrobatics. Sports 2023, 11, 194. https://doi.org/10.3390/sports11100194.

4.The methods section is generally organized, but several methodological details remain insufficiently described. The participant characterization lacks important information regarding training routines, competition levels, injury history, and frequency of mental training practices. These factors may substantially influence imagery-related cortical activation. Moreover, although imagery ability was assessed with the MIQ-R, the authors do not report whether imagery scores differed between groups or whether imagery ability correlated with cortical activation outcomes. Such analyses could substantially enrich the interpretation of the findings.

Our response: We sincerely thank the reviewer for this thoughtful comment. We agree that additional participant characteristics, such as detailed training routines, competition history, injury history, and frequency of mental training practices, may provide useful contextual information for interpreting imagery-related cortical activation.

In the present study, all participants were highly trained ski jumpers and were classified as Master-level or First-class athletes according to the Chinese national athlete grading system. We reported their basic demographic and sport-related characteristics, including age, sex, athlete level, and training experience. However, we acknowledge that more detailed information regarding daily training routines, recent injury history, and habitual mental training practices was not systematically collected. We have now explicitly added this point to the Limitations section and noted that future studies should include these variables to better examine their potential influence on AO/MI-related cortical responses.

Regarding imagery ability, the MIQ-R was used primarily as an inclusion and screening measure to ensure that all participants had adequate visual and kinesthetic imagery ability before participating in the experimental tasks. All participants met the inclusion criterion, with mean visual and kinesthetic imagery scores above the required threshold, indicating sufficient imagery ability for the present AO/MI paradigm.

Because the main aim of this study was to compare cortical activation across the AO, MI, and AO+MI conditions and to explore the neural mechanisms underlying combined action observation and motor imagery in elite ski jumpers, MIQ-R scores were not treated as a primary explanatory variable. Therefore, we did not perform additional group comparisons or correlation analyses between MIQ-R scores and cortical activation outcomes. We have now acknowledged this as a limitation and clarified that future studies could further investigate whether individual differences in imagery ability are associated with task-related ΔHbO responses.

All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this constructive suggestion, which helped us improve the methodological transparency and clarify the scope of the present study.

5. The description of the fNIRS setup also requires clarification. Although the authors mention 45 channels and the use of the AAL atlas, the manuscript does not provide sufficient information regarding optode localization procedures, registration accuracy, or anatomical reliability of channel mapping. Given the limited spatial resolution of fNIRS, greater methodological transparency is necessary. In addition, short-separation channels are not mentioned. Since superficial physiological signals can contaminate fNIRS measurements, the absence of short-channel regression should be acknowledged explicitly as a limitation.

Our response: We sincerely thank the reviewer for this helpful comment. We agree that the original manuscript did not provide sufficient detail regarding the fNIRS montage, optode localization, and anatomical channel mapping. In the revised manuscript, we have clarified that the optodes were positioned according to the international 10–20 EEG system and that cap placement was carefully adjusted for each participant based on anatomical landmarks to improve consistency across participants.

We have also provided more detailed information regarding anatomical channel mapping. Specifically, channel locations were estimated with reference to the 10–20 system and converted to corresponding MNI coordinates, and anatomical labels were assigned according to the Automated Anatomical Labeling (AAL) atlas. The source–detector pairs, 10–20 positions, MNI coordinates, and anatomical labels for all 45 channels are provided in Supplementary Table S1. To avoid overinterpretation, we have also clarified that these anatomical labels should be interpreted as approximate cortical correspondence rather than precise anatomical localization, given the limited spatial resolution of fNIRS.

We also acknowledge the reviewer’s concern regarding short-separation channels. The current fNIRS montage did not include short-separation channels; therefore, short-channel regression could not be applied. We have now explicitly added this point to the Limitations section as a potential source of extracerebral physiological contamination.

All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this constructive suggestion, which helped us improve the methodological transparency of the fNIRS setup.

6. The experimental protocol is understandable, but the rationale for selecting an 8-second imagery/observation window and a 5-8 second hemodynamic extraction window should be better justified with references specific to AO/MI paradigms and fNIRS temporal dynamics. The manuscript does not clarify whether participants kept their eyes open during MI trials, how compliance with kinesthetic imagery was verified, or whether subjective vividness ratings differed across conditions. These aspects are important because variability in imagery engagement may directly influence cortical activation patterns.

Our response: We sincerely thank the reviewer for this helpful and detailed comment. We agree that the original manuscript did not provide sufficient methodological clarification regarding the task duration, fNIRS extraction window, and imagery engagement.

First, we have clarified the rationale for the 8-s task duration. The 8-s duration was selected to match the duration of the ski-jumping take-off and early flight video clips and was kept identical across the AO, MI, and AO+MI conditions to ensure temporal consistency across tasks. This design is consistent with previous fNIRS studies using AO, MI, and AO+MI paradigms, including Almulla et al., 2022; Emerson et al., 2022; and Yokota et al., 2023. We have also clarified that the 5–8 s window refers to the fNIRS analysis window rather than the task duration. This window was selected to capture the delayed task-related HbO response after task onset and is broadly consistent with previous AO/MI fNIRS studies using comparable post-stimulus HbO extraction periods.

Second, we have clarified that participants kept their eyes closed during the MI trials and performed first-person kinesthetic motor imagery of the ski-jumping approach, take-off, and early flight phases. During the AO+MI condition, participants watched the video while simultaneously performing first-person kinesthetic imagery of the same movement sequence.

Third, we have further clarified how compliance with kinesthetic imagery instructions was monitored. Imagery ability was first assessed using the Movement Imagery Questionnaire-Revised (MIQ-R), and all participants met the inclusion criterion for imagery ability. In addition, an Imagery Assessment Scale adapted from Zhang [17] was administered after the MI and AO+MI tasks to monitor imagery engagement and evaluate first-person kinesthetic imagery use, imagery controllability, and imagery vividness/clarity. The average imagery scores indicated that participants were generally able to perform the required kinesthetic imagery.

We also acknowledge the reviewer’s important point regarding condition-specific vividness ratings. In the present study, the imagery assessment was administered after completion of the MI and AO+MI tasks rather than separately after each condition. Therefore, we were unable to statistically compare subjective vividness ratings between MI and AO+MI. We have now explicitly acknowledged this issue as a limitation, because variability in imagery engagement may influence cortical activation patterns.

1.Almulla, L.; Al-Naib, I.; Ateeq, I.S.; Althobaiti, M. Observation and motor imagery balance tasks evaluation: An fNIRS feasibility study. PLOS ONE 2022, 17, e0265898.

2.Emerson, J.R.; Scott, M.W.; van Schaik, P.; Butcher, N.; Kenny, R.P.W.; Eaves, D.L. A neural signature for combined action observation and motor imagery? An fNIRS study into prefrontal activation, automatic imitation, and self-other perceptions. Brain and Behavior 2022, 12, e2407.

3.Yokota, M.; et al. Motor imagery and action observation of whole-body movements for experienced motor repertoire: an fNIRS study. Journal of Physiological Sciences 2023, 12(4), 107–120.

All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this constructive suggestion, which helped us improve the methodological clarity of the experimental protocol.

7. Concerning the statistics, the authors state that paired-sample t-tests were conducted across 45 channels, but the manuscript does not specify whether assumptions of normality were verified. Moreover, the use of multiple pairwise channel comparisons substantially increases the risk of type I error, even with FDR correction. The authors should provide more detail regarding the exact correction procedure, adjusted q-values, and effect sizes for all major comparisons. Importantly, no statistical power analysis is reported. Given the relatively small sample size and the high dimensionality of channel-wise comparisons, the possibility of type II errors should be discussed more explicitly.

Our response: We sincerely thank the reviewer for this important and constructive comment. We agree that the original manuscript did not provide sufficient details regarding the statistical procedures.

In the revised manuscript, we have clarified that the normality assumption was examined using the Shapiro–Wilk test before conducting parametric analyses. The results indicated that the normality assumption was generally acceptable for the primary significant channels, although minor deviations were observed in a small number of channels. To further verify the robustness of the findings, Wilcoxon signed-rank tests were additionally conducted as supplementary sensitivity analyses for the main significant channels. These analyses confirmed that AO+MI-related activation remained significant relative to baseline in ch5 (Z = -3.709, p < 0.001), ch11 (Z = -3.798, p < 0.001), and ch27 (Z = -3.366, p = 0.001).

We have also specified that multiple comparisons across the 45 fNIRS channels were corrected using the Benjamini–Hochberg false discovery rate (FDR) procedure, with q < 0.05 considered statistically significant. FDR-adjusted q-values are now reported for the major channel-wise comparisons. In addition, we have reported effect sizes for the main statistical analyses: Cohen’s d for one-sample t-tests, Cohen’s dz for paired-sample t-tests, and partial eta squared (ηp²) for mixed-design ANOVA results.

In addition, we conducted an a priori power analysis using G-Power 3.1.9.7. The analysis indicated that 28 participants would be required to detect a medium effect with 80% power at α = 0.05. Our final sample included 27 elite ski jumpers, which was close to the estimated requirement. This small difference reflects the limited availability of eligible elite athletes in this highly specialized sport.

Finally, we expanded the Limitations section to acknowledge the possibility of type II errors. We now clarify that the absence of significant activation in AO and MI after FDR correction should not be interpreted as definitive evidence of no neural engagement, but rather as a lack of statistically detectable activation under the present sample size and correction strategy.

All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this helpful suggestion, which improved the transparency and rigor of the statistical reporting.

8.The results section is generally coherent, but some interpretations seem overstated. The conclusion that AO and MI alone failed to activate cortical regions should be phrased more cautiously. The absence of statistically significant activation after correction does not necessarily imply absence of neural engagement. Rather, it may reflect subtle activation patterns below the detection threshold given the sample size and analytical strategy. This distinction is particularly important because previous literature consistently demonstrates cortical recruitment during isolated AO and MI paradigms.

Our response: We sincerely thank the reviewer for this important comment. We agree that the original wording may have overstated the interpretation of the AO and MI results. In the revised manuscript, we have avoided stating that AO and MI “failed to activate” cortical regions. Instead, we now describe the findings more cautiously by stating that activation in the AO and MI conditions did not survive FDR correction for multiple comparisons.

We also agree that the absence of statistically significant activation after correction does not necessarily indicate the absence of neural engagement. Therefore, we have revised the Results and Discussion sections to clarify that AO and MIrelated cortical responses may have been relatively subtle, spatially restricted, or below the detection threshold under the present sample size and analytical strategy. This revision is also consistent with previous literature showing cortical recruitment during isolated AO and MI paradigms.

In the revised Discussion, we further note that MI itself requires active first-person motor simulation and may recruit neural processes related to action planning, motor representation, and sensorimotor simulation. For elite ski jumpers with stable and highly practiced sport-specific motor representations, MI may therefore engage part of the motor simulation network relatively efficiently. This may help explain why AO+MI showed a clearer advantage over AO than over MI.

All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this constructive suggestion, which helped us present the results with greater interpretative caution.

9. The discussion section is one of the strongest parts of the manuscript, especially in its integration of the DASH framework and neural efficiency hypothesis. However, several interpretations remain somewhat speculative. The argument that AO+MI increases “overall cognitive load” is plausible but was not directly measured in the study. The inference that elite athletes exhibit reduced activation due to neural efficiency should be presented more cautiously because the study lacks comparison groups with lower expertise levels. Without such comparisons, the data cannot definitively support the neural efficiency hypothesis. The authors should therefore moderate these claims and frame them as possible interpretations rather than direct evidence.

Our response: We sincerely thank the reviewer for this insightful comment. We agree that several interpretations in the original Discussion, including the suggestion that AO+MI increases overall cognitive load and that elite athletes exhibit reduced cortical activation due to neural efficiency, were presented too strongly.

In the revised manuscript, we have moderated these statements throughout the Discussion. Specifically, we now describe the increased demands during AO+MI as “may reflect additional cognitive processing” rather than a direct measure of cognitive load. Similarly, we frame the neural efficiency interpretation as tentative and compatible with previous literature, noting that the study did not include comparison groups with lower skill levels and thus cannot provide direct evidence for neural efficiency. All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for helping us improve the precision and caution of our interpretations.

10. Another issue concerns the neuroanatomical interpretation of the activated regions. The manuscript often attributes highly specific cognitive functions to areas such as the MFG, IPL, and SMG without adequately acknowledging the multifunctional nature of these regions. Some statements seem overly deterministic, particularly when linking activation patterns to executive control or embodied motor representation. More balanced wording would improve scientific rigor.

Our response: We sincerely thank the reviewer for this helpful comment. We agree that the neuroanatomical interpretation of MFG, IPL, and SMG activation should be presented with appropriate caution, given the multifunctional nature of these regions and the spatial limitations of fNIRS.

In the revised manuscript, we have moderated the wording throughout the Discussion. Specifically, we replaced overly deterministic expressions with more cautious phrasing, such as “has been implicated in,” “has been associated with,” “may contribute to,” and “may reflect.” We have also avoided attributing the observed activation pattern to a single specific cognitive function. Instead, we now interpret the frontoparietal activation pattern more broadly as being potentially related to integrated action simulation, including the processing of external visual motion information and the maintenance of internal kinesthetic representations.

We have also clarified in the Methods section that the AAL-based anatomical labels were used to provide approximate cortical correspondence rather than precise anatomical localization, given the limited spatial resolution of fNIRS. All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this constructive suggestion, which helped us improve the interpretative balance and scientific rigor of the Discussion.

 

11.The limitations section is appropriate but could be expanded considerably. The authors should discuss the intrinsic limitations of fNIRS, including restricted penetration depth, inability to measure subcortical structures, susceptibility to extracerebral contamination, and relatively low spatial specificity compared to fMRI. Additionally, the absence of behavioral outcome measures is a significant limitation because the study demonstrates neural differences without confirming whether these differences translate into improved motor performance. This point deserves stronger emphasis.

Our response: We sincerely thank the reviewer for this important and constructive comment. We agree that the limitations section in the original manuscript was not sufficiently detailed, particularly regarding the intrinsic limitations of fNIRS and the absence of behavioral outcome measures.

In the revised manuscript, we have expanded the limitations section accordingly. Specifically, we now acknowledge that the sample size was modest due to the limited availability of elite ski jumpers, which may reduce statistical sensitivity and prevent the detection of subtle activation in the AO or MI conditions. We also clarified that the fNIRS montage covered only frontoparietal regions and therefore could not measure other cortical areas potentially involved in motor simulation. In addition, we explicitly noted that short-separation channels were not included, which prevented the explicit removal of superficial physiological signals and should be considered when interpreting the fNIRS results.

Importantly, we have also placed stronger emphasis on the absence of behavioral outcome measures. We now state that behavioral performance was not assessed; therefore, although the present study demonstrates differences in cortical activation among AO, MI, and AO+MI conditions, it cannot determine whether these neural differences translate into improved ski-jumping performance or motor learning. We further acknowledged that imagery vividness ratings were collected post-task rather than condition-specifically, and that training routines and recent injury history were not systematically recorded.

Finally, we added that future studies should include larger samples, broader skill-level comparisons, behavioral outcomes, and condition-specific imagery assessments to further validate and extend the present findings. All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this helpful suggestion, which allowed us to present a more balanced and cautious interpretation of the study findings.

12.There are also several formatting and editorial inconsistencies that should be corrected before publication. Some references appear duplicated or inconsistently formatted. For instance, Hardwick et al. are cited both as a meta-analysis reference and again later with slightly different formatting. There are also typographical inconsistencies in spacing around citations and symbols such as “AO + MI” versus “AO+MI.” The manuscript also still contains template placeholders such as “Firstname Lastname” and “To be added by editorial staff during production,” indicating that the submission was not fully finalized.

Our response: We sincerely thank the reviewer for carefully identifying these formatting and editorial inconsistencies. We fully acknowledge that the original manuscript contained several inconsistencies in reference formatting, citation spacing, terminology, and template-related placeholder text, which may have affected the overall presentation quality of the manuscript.

In the revised manuscript, we have carefully checked and corrected the reference list and in-text citations. Specifically, duplicated or inconsistently formatted references have been reviewed, and the citation of Hardwick et al. has been standardized to avoid duplication and inconsistent formatting. We also checked the formatting of all in-text citations to ensure consistent spacing around citation brackets and punctuation.

In addition, we standardized the terminology throughout the manuscript. In particular, inconsistent expressions such as “AO + MI” and “AO+MI” have been unified as “AO+MI” throughout the text, tables, and figure captions. We also reviewed the manuscript for other typographical inconsistencies, including spacing around symbols, abbreviations, and statistical notation.

Finally, we removed the template placeholders mentioned by the reviewer, including “Firstname Lastname” and “To be added by editorial staff during production,” and carefully checked the manuscript to ensure that no template text remained. All related revisions have been marked in red in the revised manuscript. We sincerely thank the reviewer for this helpful comment, which improved the formatting accuracy and editorial quality of the manuscript.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript describes the results of AO, MI, and AO+MI in elite ski jumpers. It reports that only the association of AO and MI induces significant activation of the brain areas of interest compared to baseline.

I think that the methods are appropriate and that the Introduction, Methods, and Results sections are clear. I have only one concern regarding the Methods and one regarding the Discussion

Methods

Although the sample size depended on the availability of  elite ski jumpers, it would be useful to report the theoretically required sample size

Discussion

The authors report the absence of activations during AO and MI with respect to baseline. Such absence could be due to automaticity created by motor training.

In channels 20, 36. 37, and 39, there is no significant difference between MI and MI+AO.  I suggest that elite jumpers may not activate brain areas during MI owing to their jumping training, and thus MI alone may be as efficient as MI+AO. In contrast, AO is less efficient that AO+MI

Please consider these points in the Discussion

Author Response

This manuscript describes the results of AO, MI, and AO+MI in elite ski jumpers. It reports that only the association of AO and MI induces significant activation of the brain areas of interest compared to baseline.

I think that the methods are appropriate and that the Introduction, Methods, and Results sections are clear. I have only one concern regarding the Methods and one regarding the Discussion

Our responses: We sincerely thank the reviewer for the positive evaluation of our manuscript and for recognizing that the Introduction, Methods, and Results sections are clear and that the methodological approach is appropriate. We are also grateful for the reviewer’s constructive comments regarding the sample-size justification and the interpretation of the Discussion. We have carefully considered both points and revised the manuscript accordingly. Detailed responses to each comment are provided below.

1. Methods

Although the sample size depended on the availability of elite ski jumpers, it would be useful to report the theoretically required sample size

Our response: We sincerely thank the reviewer for this valuable and constructive suggestion. We fully agree that reporting the theoretically required sample size is important for improving the transparency and methodological rigor of the study. In the original manuscript, although we explained that the sample size was constrained by the availability of elite ski jumpers, we did not explicitly report the theoretically required sample size. We acknowledge that this information should be provided to help readers better evaluate the adequacy and limitations of the sample.

In response to the reviewer’s suggestion, we have added an a priori power analysis to the Participants section of the revised manuscript. Specifically, the analysis was conducted using G-Power 3.1.9.7 for the repeated-measures design. The results indicated that 28 participants would be required to detect a medium effect with 80% power at α = 0.05. The final sample included 27 elite ski jumpers, which was very close to the estimated requirement.

We would also like to clarify that we made every effort to recruit eligible participants. However, elite ski jumpers represent a highly specialized and relatively small athlete population, and their availability is limited by national team schedules, training arrangements, competition preparation, and eligibility criteria. Therefore, although the final sample size was slightly smaller than the theoretically required sample size, it reflects the practical constraints of conducting neuroimaging research in this elite sporting population. We have also acknowledged this issue in the limitations section and interpreted the findings cautiously.

The relevant revision has been added to the Participants section and marked in red in the revised manuscript. We sincerely thank the reviewer again for raising this constructive point. If further clarification or additional revision is required, we would be very willing to make further improvements accordingly.

2. Discussion

The authors report the absence of activations during AO and MI with respect to baseline. Such absence could be due to automaticity created by motor training.

In channels 20, 36. 37, and 39, there is no significant difference between MI and MI+AO.  I suggest that elite jumpers may not activate brain areas during MI owing to their jumping training, and thus MI alone may be as efficient as MI+AO. In contrast, AO is less efficient that AO+MI

Please consider these points in the Discussion

Our responses: We sincerely thank the reviewer for this insightful and constructive comment. We agree that the absence of significant activation during AO and MI relative to baseline should not be interpreted too simplistically, and that motor automaticity resulting from long-term ski-jumping training provides an important explanation for this finding.

In the revised Discussion, we have expanded the interpretation of the non-significant AO and MI activation relative to baseline. Specifically, we now discuss that elite ski jumpers may have developed highly automatized and efficient sport-specific motor representations through long-term training. Therefore, MI alone may be sufficient to access internal action representations related to the take-off and early flight phases with relatively low additional cortical demand. From this perspective, the absence of significant MI activation after FDR correction may reflect neural efficiency or motor automaticity rather than a failure of MI to engage motor simulation processes.

We have also revised the interpretation of the between-condition comparisons. As the reviewer correctly noted, in channels 20, 36, 37, and 39, there was no significant difference between MI and AO+MI. We now explicitly state that the advantage of AO+MI was more evident when compared with AO than when compared with MI. This pattern suggests that MI alone may already be an efficient form of motor simulation in elite ski jumpers, whereas AO alone may be less effective because it relies mainly on externally presented visual information. The stronger activation observed during AO+MI relative to AO may therefore reflect the additional contribution of first-person kinesthetic imagery during action observation.

These points have been incorporated into the Discussion section and marked in red in the revised manuscript. We sincerely thank the reviewer for this valuable suggestion, which helped us provide a more balanced and theoretically appropriate interpretation of the findings.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript has been sufficiently improved