Review Reports - Jaw Clenching Alters Neuromuscular Coordination in Dynamic Postural Tasks: A Pilot Study on Single-Leg Sit-to-Stand Movements

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The enclosed manuscript titled “Jaw clenching alters neuromuscular coordination in dynamic postural tasks: a pilot study on single-leg sit-to-stand movements” is a research article dealing with the interesting topic on how the motor activity of the stomatognathic influences and modulates postural control. Introduction is well written, as well as discussion part. However, there are methodological concerns that must be addressed and might have potential impact on the results and interpretation. Mainly, although the authors claim to investigate the differences between task execution during jaw clenching and no clenching, no direct comparisons were made between the two conditions. The authors should extensively revise the manuscript before it can be considered suitable for publication.

Specific comments in the following:

In the data processing part. How was the COM computed/estimated? What was the measure explained at lines 155-157 used for, and what is it actual meaning? Moreover, how could you obtain the position of the lateral malleolus using IMUs sensors, and compute the distance between this and the COM, which I believe has been derived from the force plate? Please describe and detail this methodological aspect better.
The number of successful and unsuccessful trials should be reported. Additionally, in Table 2, the success rate of the clenching group is shown as 1.0 ± 0.5. It is unclear how this value was defined. If a value of 1.0 represents a 100% success rate, it should not exhibit a standard deviation of 0.5 (i.e., 50%). The authors should clarify the calculation method and interpretation of this metric
The authors stated that the objective of the study was to compare the effects of jaw clenching versus no clenching. However, the actual analyses focused on the effects of jaw clenching within successful and unsuccessful task executions, without exploring how these outcomes differed between the two conditions. Consequently, it would have been valuable (and fundamental to answer the authors research question) to include statistical analyses examining differences in muscle activity and joint kinematics between jaw clenching and no clenching, both in successful and unsuccessful trials.
The authors report using linear mixed-effects models for statistical analysis. However, the specific model formula employed is not provided and should be explicitly stated. Additionally, clarification is needed on how the EMG time series were statistically compared. Were linear mixed-effects models applied point by point to each normalized time sample? If so, statistically significant differences along the EMG curves should be indicated in the corresponding figure, showing the precise time instant at which these differences occur. Furthermore, when comparing successful and unsuccessful trials within the same condition, one would expect inherent differences in task execution, as successful trials reflect correct performance whereas unsuccessful trials represent incomplete or incorrect task completion. It is therefore unclear how the authors ensured meaningful time-series comparisons between these two biomechanically distinct events.

Minor comments:

The authors used 16 IMUs, placed on the lower and upper limbs. However, they did not report results for the upper limb muscles. Why did the authors make this choice?

Author Response

General comment

>> Response

We sincerely appreciate the reviewer’s thoughtful and constructive feedback on our manuscript. We are grateful for the positive evaluation of the Introduction and Discussion sections, and we thank the reviewer for highlighting the importance of the methodological aspects. Based on the reviewer’s valuable comments, we have extensively revised the manuscript to address the raised concerns, particularly regarding the comparison between the jaw clenching and no-clenching conditions. We believe that these revisions have substantially improved the methodological clarity and overall quality of the paper. Detailed responses and corresponding changes are described below.

Specific comments in the following:

Comment 1

In the data processing part. How was the COM computed/estimated? What was the measure explained at lines 155-157 used for, and what is it actual meaning? Moreover, how could you obtain the position of the lateral malleolus using IMUs sensors, and compute the distance between this and the COM, which I believe has been derived from the force plate? Please describe and detail this methodological aspect better.

>> Response

We appreciate the reviewer’s insightful comment regarding the estimation of the center of mass (COM) and anatomical landmark positions. In the original submission, the COM and lateral malleolus positions were estimated using the MR3 software (Noraxon, USA), which calculates these positions based on body segment lengths derived from participants’ height. However, as the reviewer correctly pointed out, the validity and reliability of estimating COM and landmark positions using IMU-based algorithms have not yet been fully established.

Considering this methodological limitation and the fact that COM-related variables were secondary outcomes in the present study, we decided to remove these parameters from the revised manuscript. Accordingly, all related descriptions and analyses referring to COM or landmark distances have been deleted from the Methods, Results, and Discussion sections. We believe this modification improves the methodological transparency and focus of the study.

Comment 2

The number of successful and unsuccessful trials should be reported. Additionally, in Table 2, the success rate of the clenching group is shown as 1.0 ± 0.5. It is unclear how this value was defined. If a value of 1.0 represents a 100% success rate, it should not exhibit a standard deviation of 0.5 (i.e., 50%). The authors should clarify the calculation method and interpretation of this metric.

>> Response

We thank the reviewer for pointing out the ambiguity regarding the definition and calculation of the success rate. In the revised manuscript, we have now reported both the total number of trials and the number of successful trials for each condition to ensure clarity.

We also rechecked the success rate values presented in Table 2, identified the calculation error, and corrected the data accordingly. The success rate is now clearly defined as the proportion of successful trials relative to the total number of trials for each participant. We have updated the table and corresponding text to accurately reflect this definition.

Comment 3

The authors stated that the objective of the study was to compare the effects of jaw clenching versus no clenching. However, the actual analyses focused on the effects of jaw clenching within successful and unsuccessful task executions, without exploring how these outcomes differed between the two conditions. Consequently, it would have been valuable (and fundamental to answer the authors research question) to include statistical analyses examining differences in muscle activity and joint kinematics between jaw clenching and no clenching, both in successful and unsuccessful trials.

The authors report using linear mixed-effects models for statistical analysis. However, the specific model formula employed is not provided and should be explicitly stated. Additionally, clarification is needed on how the EMG time series were statistically compared. Were linear mixed-effects models applied point by point to each normalized time sample? If so, statistically significant differences along the EMG curves should be indicated in the corresponding figure, showing the precise time instant at which these differences occur. Furthermore, when comparing successful and unsuccessful trials within the same condition, one would expect inherent differences in task execution, as successful trials reflect correct performance whereas unsuccessful trials represent incomplete or incorrect task completion. It is therefore unclear how the authors ensured meaningful time-series comparisons between these two biomechanically distinct events.

>> Response

We sincerely thank the reviewer for these important and constructive comments. As correctly pointed out, it was essential to include direct comparisons between the jaw clenching and control conditions to properly address the main research question. In the revised manuscript, we have therefore added these analyses and presented the results as Table 3 and Table 4. The comparisons between successful and unsuccessful trials within each condition are now summarized in Table 5 and Table 6. We believe that these additions provide a more comprehensive overview of the effects of jaw clenching on task performance.

Regarding the statistical analysis, we have added a detailed description of the linear mixed-effects model (LMM) in the Statistical Analysis section (Section 2.5; Lines 185-195). The explanation now explicitly specifies the dependent and independent variables, as well as the random effects structure used in the model.

In response to the reviewer’s comment about the EMG time-series analysis, we did not apply point-by-point comparisons across the entire time-normalized signal. Instead, we focused on a specific movement phase to ensure biomechanical relevance and comparability between trials. The sit-to-stand task can be divided into three main phases: (1) trunk flexion, (2) seat-off, and (3) extension. Because trunk and lower-limb kinematics differ substantially between successful and unsuccessful trials during the extension phase, direct time-series comparisons could be misleading. Therefore, we restricted our analysis to the seat-off phase, which represents a critical transition where movement patterns remain comparable between success and failure but determine task outcome. To clarify this methodological approach, we have added an explanation in the Data Processing section (Lines 165–172) of the revised manuscript, specifying that all kinematic and EMG analyses were conducted within the seat-off phase.

Minor comments:

The authors used 16 IMUs, placed on the lower and upper limbs. However, they did not report results for the upper limb muscles. Why did the authors make this choice?

>> Response

We appreciate the reviewer’s observation. In the present study, participants performed the sit-to-stand task with their arms crossed in front of the chest. Because the upper limbs remained stationary and did not actively contribute to postural control or balance regulation, we did not include upper limb muscle activity in the analysis.

Nevertheless, we used a 16-sensor full-body IMU model to ensure consistent measurement across all participants and to verify post hoc that the arm-crossed posture was maintained throughout each trial. This approach allowed us to confirm the reproducibility and standardization of the experimental setup without focusing on upper limb kinematics or EMG data.

Reviewer 2 Report

Comments and Suggestions for Authors

Jaw Clenching Alters Neuromuscular Coordination in Dynamic Postural Tasks: A Pilot Study on Single-Leg Sit-to-Stand Move-ments REVIEW

This study aimed to to investigate the effects of jaw clenching on muscle activity and kinematics during repetitive single-leg sit-to-stand task performance.

An interesting research question as well as a pure experimental design represent the greatest strength of this study, on the other hand, the size of the sample and its representativeness represent the greatest flaw. It should be noted that there is certainly a gap in the research so far and that we definitely need a pilot study of this topic.

The title is appropriate and informative. As for the abstract, I recommend that information on the quantitative characteristics of the sample be added to the methodological section. I suggest that the authors go through the key points again, some are too similar to the title.

The introduction is clear and effective. The gap in previous research is clearly visible, even the practical significance in addition to the undoubted theoretical one. The research question and hypotheses clearly follow from the introduction. I think the work in this segment is well done.

Lines 85-87: the data for the power analysis are not complete, I ask the authors to supplement it so that we can further discuss the sample size and the results obtained in light of the power analysis. Also, the statistical analysis section lacks determination of the effect size, which also makes it impossible to understand and interpret the results obtained. Since the sample is the weakest point of the research, it is necessary to provide more detailed information about its design and formation. It is not clear how and why these respondents were selected. The rest of the methodological section is good, it gives us all the relevant data so that we can repeat the research. The method chosen to conduct the study is appropriate in relation to the objectives and research question.

As I have already said, in order to be able to comment and discuss the obtained results properly, it is necessary to calculate the effect. In addition, the results seem to be presented correctly. The discussion should also be revised in relation to the effect sizes, the same applies to the conclusions. It seems that these parts of the text are done correctly and that the conclusions are supported by the results, but it will become clearer when the effects are calculated. I suggest that the authors focus more on the practical implications of the study conducted and the obtained results.

The literature is relevant.

Author Response

General comment

This study aimed to to investigate the effects of jaw clenching on muscle activity and kinematics during repetitive single-leg sit-to-stand task performance. An interesting research question as well as a pure experimental design represent the greatest strength of this study, on the other hand, the size of the sample and its representativeness represent the greatest flaw. It should be noted that there is certainly a gap in the research so far and that we definitely need a pilot study of this topic.

>> Response

We sincerely thank the reviewer for the encouraging and constructive feedback on our manuscript. We are grateful for the recognition of the study’s research question and experimental design as key strengths, and we also acknowledge the reviewer’s concern regarding the sample size and representativeness. A detailed point-by-point response to each of the reviewer’s comments is provided below.

Comment 1

>> Response

We appreciate the reviewer’s helpful comments. In the revised manuscript, we have added information about the participants’ quantitative characteristics (e.g., sample size and demographics) in the Methods section of the Abstract to enhance clarity.

Additionally, we revised the concluding sentences of the Abstract to avoid redundancy with the title and to better highlight the key findings and implications of the study.

Comment 2

>> Response

We sincerely thank the reviewer for the positive and encouraging evaluation of the Introduction section. To further enhance clarity and logical flow, we have made minor linguistic and structural revisions throughout this section while preserving the original content and intent.

Comment 3

>> Response

We sincerely thank the reviewer for these constructive and important comments regarding the sample size, power analysis, and effect size reporting. In the revised manuscript, we have addressed these issues as follows:

We added the details of the power analysis in the Statistical Analysis section (Lines 196–202), including the parameters used (sample size, alpha level, assumed effect size, and achieved power).
We calculated and reported effect sizes for all key results, which are now included in all relevant Tables.
These additions allow for better interpretation of the statistical results and demonstrate that, despite the small sample, the observed large effect sizes support the validity of the findings within this pilot framework.
Furthermore, we clarified the participant recruitment and selection criteria in the Participants subsection to enhance transparency regarding study design.
Finally, we explicitly acknowledged the small sample size as a limitation in the Limitations section (Lines 422–429).

We believe these revisions have strengthened the methodological rigor and interpretation of the study findings.

Comment 4

The literature is relevant.

>> Response

We sincerely thank the reviewer for this valuable suggestion. In the revised manuscript, we have added effect sizes for all outcome variables (Tables 2–6), which allow for more accurate interpretation of the magnitude and practical relevance of the observed effects.

We believe that these revisions provide a clearer understanding of the study’s contribution and strengthen the overall interpretability of the results.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is generally well written, with a clear presentation of both the methods and the results, and a coherent discussion. However, I have two main suggestions that could further enhance the clarity and overall impact of the study:

Clarify the IMU mounting system — Please provide a more detailed description of how the IMUs were attached and how potential sensor movement relative to the body surface was prevented during data collection. This clarification would strengthen confidence in the accuracy and reliability of the recorded measurements.
Expand the discussion of results — The relationship observed between jaw clenching and motor task performance merits a more in-depth discussion. Specifically, what is the nature of the cause–effect relationship? Which mechanisms may underlie muscle activation or coactivation of the muscles involved? Does jaw clenching directly facilitate activation in the lower limb muscles, or could it represent an additional motor task that competes with, or interferes with, other motor actions?

While the authors touch upon some of these points in their discussion and suggest future research directions, a more detailed examination of these aspects would make the paper more compelling and strengthen its applied relevance.

Author Response

General comment

First of all, I would like to thank the editor for the opportunity to review this interesting and well-conceived article. In their work, the authors aim to explore the relationship between the ability to perform a coordinated motor task (standing up from a chair using one leg) and the action of jaw clenching. The manuscript is generally well written, with a clear presentation of both the methods and the results, and a coherent discussion. However, I have two main suggestions that could further enhance the clarity and overall impact of the study:

>> Response

We sincerely thank the reviewer for taking the time to evaluate our manuscript and for the encouraging comments regarding the overall clarity, structure, and rationale of our study. We appreciate the insightful suggestions provided, and we have revised the manuscript accordingly. We believe that these improvements have strengthened the methodological clarity and enhanced the overall impact of the work, making the manuscript more compelling and scientifically robust.

A detailed, point-by-point response to each of the reviewer’s comments is provided below.

Comment 1

Clarify the IMU mounting system — Please provide a more detailed description of how the IMUs were attached and how potential sensor movement relative to the body surface was prevented during data collection. This clarification would strengthen confidence in the accuracy and reliability of the recorded measurements.

>> Response

We appreciate the reviewer’s important comment regarding IMU attachment and motion artifact prevention. In the revised manuscript, we have expanded the description of the mounting system in the Experimental Setup section.

Specifically, participants were instrumented with 16 wireless IMUs (myoMOTION, Noraxon, Scottsdale, AZ, USA), which were securely attached to anatomical landmarks using elastic straps and medical-grade double-sided adhesive tape to minimize sensor movement relative to the skin. Each sensor’s placement and orientation were verified both visually and through the MR3 (Noraxon, Scottsdale, AZ, USA) software interface prior to data collection. We have also clarified that the system uses fused measurements from the accelerometer, gyroscope, and magnetometer to compute segment orientation in MR3, which contributes to improving the stability and accuracy of kinematic recordings (Lines 109-115).

“Kinematic data were collected using 16 inertial measurement unit (IMU) sensors (Figure 2; myoMOTION, Noraxon, Scottsdale, AZ, USA) at a sampling frequency of 100 Hz. The sensors were securely attached to anatomical landmarks on the trunk and limbs using elastic straps and medical-grade double-sided adhesive tape to minimize movement relative to the skin. Segment orientations and joint kinematics were computed in MR3 software based on sensor fusion of tri-axial accelerometer, gyroscope, and magnetometer signals.”

Comment 2

Expand the discussion of results — The relationship observed between jaw clenching and motor task performance merits a more in-depth discussion. Specifically, what is the nature of the cause–effect relationship? Which mechanisms may underlie muscle activation or coactivation of the muscles involved? Does jaw clenching directly facilitate activation in the lower limb muscles, or could it represent an additional motor task that competes with, or interferes with, other motor actions?

>> Response

We revised the Discussion extensively to provide a deeper mechanistic explanation of clenching effects (Lines 344-403). The revised text highlights spinal inhibitory–excitatory modulation via masseter spindle pathways, task-specific facilitation versus coordination disruption, and trial-to-trial variability in neuromuscular state. These revisions strengthen the causal interpretation and applied relevance of the findings.

“The increased medial gastrocnemius activation and reduced success rate observed during jaw clenching can be explained by spinal-level modulation driven by masseter spindle input. Masseter muscle spindles exhibit unique mechanosensory properties that precisely regulate isometric contraction and jaw stability [31,32]. Activation of these spindles during clenching facilitates motor neuron excitability in remote muscle groups through trigeminal–spinal pathways, a phenomenon known as the remote effect. Strong evidence for this mechanism is provided by H-reflex studies showing increased excitability of the soleus muscle during jaw clenching [29,30] and attenuation of reciprocal Ia inhibition between antagonist ankle muscles [34]. These neural changes promote non-reciprocal facilitation of both the agonist and antagonist muscles. This mechanism aligns with our findings that failure trials exhibited significantly increased gastrocnemius–tibialis anterior coactivation during the seat-off phase (Table 5). During this phase, successful sit-to-stand execution requires coordinated tibialis anterior activity to counteract the external dorsiflexion moment and stabilize the shank relative to gravity [35]. Excessive gastrocnemius facilitation may therefore disrupt optimal reciprocal control, resulting in inefficient moment generation and failure to achieve forward–upward progression.

Jaw clenching effects are highly task-specific. In dynamic or externally perturbed tasks, clenching facilitates anticipatory and reactive postural adjustments (APAs and RPAs) by increasing muscle activation amplitudes and advancing the onset timing [12,18]. Clenching has also been shown to improve dynamic steady-state balance with lasting effects, even after the novelty of the task diminishes, potentially reflecting neuromuscular optimization [15–17]. Moreover, increased joint stiffness resulting from non-reciprocal coactivation may help stabilize the stance under challenging static or perturbed conditions [13,14]. However, these same facilitatory mechanisms may be-come maladaptive when a task demands smooth, precise reciprocal coordination, such as during voluntary sit-to-stand. Our results showed that jaw clenching did not con-sistently elevate muscle activity across all trials (Table 3) yet selectively increased the likelihood of coordination failure (Table 2). This suggests that performance impairment is not due to cognitive or attentional interference. Indeed, previous research indicates minimal dual-task competition arising merely from the act of clenching [16]. Instead, trial-to-trial differences in the degree of masseter-driven spinal modulation may determine whether a heightened neuromuscular state improves or disrupts balance control. Taken together, these findings highlight that jaw clenching modifies neuromuscular coordination primarily by altering spinal inhibitory–excitatory balance rather than through central attentional competition. Facilitation of muscle activity through the trigeminal–spinal pathway can be advantageous for stability-dominant tasks but detrimental for coordination-dominant movements requiring finely tuned reciprocal control. Thus, the functional consequences of jaw clenching depend not only on postural task dynamics (stability vs. mobility demands), but also on whether the required balance control is voluntary or reactive. Further investigation is needed to determine the conditions under which jaw clenching contributes to functional improvement compared to neuromechanical interference.”

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I would like to thank the authors for having implemented the required revisions. Manuscript quality is greatly improved.

However, there are still some methodological aspects that must be clarified before acceptance.

Specifically, it is still not clear to me wether the linear mixed model accounted for multiple repetitions or successful/unsuccessful trials were averaged at the subject level.

I would be grateful if authors could address these concerns before considering the manuscript for publication.

Author Response

General comment

I would like to thank the authors for having implemented the required revisions. Manuscript quality is greatly improved. However, there are still some methodological aspects that must be clarified before acceptance.

>> We sincerely thank the reviewer for the positive evaluation and constructive feedback. We appreciate the reviewer’s helpful methodological suggestions. In response, we have now provided a detailed clarification of the mixed-effects modeling approach, explicitly stating that all analyses were conducted at the trial level with Subject modeled as a random intercept and without averaging across repetitions. We hope that these revisions fully address the reviewer’s remaining concerns.

Comment 1

Specifically, it is still not clear to me whether the linear mixed model accounted for multiple repetitions or successful/unsuccessful trials were averaged at the subject level.

>> Response

We thank the reviewer for raising this important methodological point. To clarify, all linear mixed-effects models were conducted at the trial level, and no averaging was performed at the subject level. This approach accounts for multiple repetitions per subject by including Subject as a random intercept, allowing us to model the within-subject correlation across trials.

A clarifying description has now been added to the Statistical analysis section (Lines 190-194; 201-202). Furthermore, the essential R analysis script is provided in the Supplementary Material to enhance transparency and reproducibility.

Comment 2

Furthermore, it is not clear from the text if the comparison between clenching/no clenching were done only considering successful trials or if all successful+unsuccessful trials were included in the analysis. I would be grateful if authors could address these concerns before considering the manuscript for publication.

>> Response

We appreciate the reviewer’s request for clarification. The comparison between the control and clenching conditions was performed using all trials (successful + unsuccessful). The rationale for this decision is that jaw clenching itself influenced task success; therefore, restricting the analysis to only successful trials would systematically exclude the very performance failures caused by the clenching manipulation, and would bias the estimated condition effect.
By including all repetitions, the mixed-effects model captures both direct neuromuscular changes and their functional consequences on task performance, allowing for a comprehensive evaluation of clenching-induced effects. To avoid ambiguity, we have explicitly revised the Statistical analysis section to state that all trials were included in the condition-level comparison (Lines 190-192).

Reviewer 2 Report

Comments and Suggestions for Authors

I thank the authors for their cooperation and cooperation. I congratulate them on a job well done. If my comments helped them to make the final version of the text better than the initial one, it would be a great honor and pleasure for me. Good luck in continuing your research.

Author Response

Comment

>> Response

We sincerely thank the reviewer for the kind and encouraging comments. We are grateful for the constructive suggestions, which contributed greatly to improving the quality of our manuscript. We truly appreciate your support and encouragement.