Classifications Based on Dynamic Navicular Drop during Gait and Characteristics of Flat Foot Muscle Morphology

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript entitled “Classifications based on dynamic navicular drop during gait and characteristics of flat foot muscle morphology” was primarily aimed to summarize the technique variables relevant to the performance of fat bowling. Authors bring an interesting study, but there are still some problems that cannot up this article to a publishing level. Suggestions are listed in the specific comments below.

Specific comments:

1.     In the Abstract part, line 16, “This study investigates the collapse of…” Please replace “investigates” with “investigated”.

2.     In the Abstract part, line 18, “Twenty healthy adults (39 feet) …” Please provide detailed anthropometry information for participants, such as height, weight and body mass index.

3.     In the Introduction part, line 52-53, “Consequently, there has been growing interest in dynamic evaluation of foot kinematics [14,15].” Can you provide more information about the dynamic evaluation?

4.     In the Introduction part, line 59, “Therefore, this study aims to investigate the characteristics…” Please replace “aims” with “was aimed”.

5.     In the Materials and Methods part, participants, line 73-74, “Participants meeting the eligibility criteria based on these standards were included in the study.” Please be more specific about how many participants met the eligibility criteria.

6.     In the Materials and Methods part, Statistical analysis, what is the level of significance? Please add the relevant description.

7.     In the discussion part, it is recommended to provide a brief description of the aim and main findings in the first paragraph of the discussion part.

8.     In the Discussion part, line 168-169, “This finding partially aligns with previous studies reporting the crucial role of FDL in preventing MLA compression.” Can you be more specific about that the crucial role of FDL is? Some recently studies could be added in the discussion, such as: ‘Foot Morphology and Running Gait Pattern between the Left and Right Limbs in Recreational Runners’, Physical Activity and Health, 7(1), p. 43–52.

9.     In the Conclusion part, line 209, “…suggesting potential variations in the cross-sectional area (CSA) of the flexor digitorum longus (FDL) muscle.”. Please delete the explanations of the abbreviations here, which you have already explained before.

10.  In the Conclusion part, it is suggested that the authors should abbreviate the section and focus on the main findings of this study.

11.  There are way too many abbreviations in the manuscript, which detracts from the reading. Besides, some abbreviations are not yet uniform. For instance, cross-sectional areas (CSAs) (line 92), and cross-sectional area (CSA) (line 163). Please delete some unnecessary abbreviations.

Comments on the Quality of English Language

 Minor editing of English language required.

Author Response

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper, entitled 'Classifications based on dynamic navicular drop during gait and characteristics of flat foot muscle morphology', represents a valuable contribution to the field of research into flat feet. The topic is of clear clinical significance and has promising potential for future applications. On careful review of the full text and assessment of its scientific content and research methodology, I would like to offer the following comments:

1. Further exploration of the comparative advantages of this research method in comparison to existing flatfoot research methods would help to highlight the innovation of the study better. 

2. While hierarchical cluster analysis was employed to categorize the participants, it is advisable that the authors consider incorporating validation of the clustering results, such as testing the robustness of the clustering algorithm through cross-validation.

3. It would be beneficial to consider including additional measures or methods to more comprehensively assess the characteristics of flatfoot, such as plantar pressure distribution.

4. It is recommended that the authors include effect sizes and confidence intervals in the statistical analyses, which will help readers understand the clinical significance of the results more fully.

5. The discussion section provides a more in-depth analysis of the results but could be more systematically compared and discussed with previous studies. For example, the results of this study could be compared in more detail with the study by Angin et al. to analyze the reasons for the differences and to discuss their implications for clinical practice.

6. The small sample size may affect the generalisability and statistical efficacy of the results.

7. It is recommended that the authors update the reference list to ensure that more recent and relevant sources are included.

The article offers valuable insights into the field of foot biomechanics and is expected to positively impact clinical practice. This article will be improved after considering the above suggestions.

Best wishes for further research success.

Best Regards

Comments on the Quality of English Language

The English language quality of this article is generally good. 

Author Response

Comments and Suggestions for Authors

The paper, entitled 'Classifications based on dynamic navicular drop during gait and characteristics of flat foot muscle morphology', represents a valuable contribution to the field of research into flat feet. The topic is of clear clinical significance and has promising potential for future applications. On careful review of the full text and assessment of its scientific content and research methodology, I would like to offer the following comments:

1. Further exploration of the comparative advantages of this research method in comparison to existing flatfoot research methods would help to highlight the innovation of the study better. 

Response:

Thank you for thoroughly reviewing of our paper and providing valuable feedback. Our responses to your comments are presented below.

1. Further exploration of the comparative advantages of this research method in comparison to existing flatfoot research methods would help to highlight the innovation of the study better. 

Response:

Thank you for pointing this out. I compared previous studies and this study in the introduction and added the advantages. (L62-69)

Our study offers several key advantages over existing flatfoot research methods. First, unlike traditional static measures, our method captures the dynamic behavior of the MLA during gait, providing a more functional assessment of flatfoot. Second, we combine kinematic analysis with muscle morphology evaluation, offering a comprehensive understanding of the relationship between foot structure and function. This research could provide valuable insights into the compensatory mechanisms in flat feet and contribute to more effective prevention and treatment strategies for related overuse injuries. (L62-69)

2. While hierarchical cluster analysis was employed to categorize the participants, it is advisable that the authors consider incorporating validation of the clustering results, such as testing the robustness of the clustering algorithm through cross-validation.

Response:

Thank you for pointing this out. I presented the silhouette score results and added that the number of clusters, 3, is appropriate.(L131-133)

We conducted hierarchical cluster analysis using ICNAV and DND, resulting in three distinct clusters (Fig. 3), which was confirmed as the optimal solution by silhouette analysis (silhouette score = 0.5247).(L131-133)

3. It would be beneficial to consider including additional measures or methods to more comprehensively assess the characteristics of flatfoot, such as plantar pressure distribution.

Response:

Thank you for pointing this out. I added the point that I did not conduct a comprehensive evaluation such as foot pressure distribution in the limitation.(244-257)

However, this study has several limitations that should be addressed in future research. The small sample size and uneven distribution of participants across clusters may affect the generalizability and statistical efficacy of the results, potentially contributing to the lack of statistical significance in some findings, particularly regarding FDL CSA differences between clusters (p = 0.051). Additionally, the use of ultrasound for muscle evaluation and the focus on only ICNH and DND for MLA kinematics clustering may oversimplify the complex nature of foot function.

Future studies should aim to recruit larger, more balanced samples, employ direct muscle activity evaluation methods such as electromyography, and incorporate additional MLA kinematic indicators and plantar pressure distribution measures for a more comprehensive assessment. Despite these limitations, our study provides valuable preliminary insights into the relationship between MLA kinematics during gait and foot muscle morphology in individuals with flat feet, laying the groundwork for future investigations in this area. (L244-257)

4. It is recommended that the authors include effect sizes and confidence intervals in the statistical analyses, which will help readers understand the clinical significance of the results more fully.

Response:

Thank you for pointing this out. I have described the effect size of muscle using the capture material.(L144-145)

The p-values and effect sizes for CSA comparisons among clusters are provided in the supplementary material.(L144-145)

5. The discussion section provides a more in-depth analysis of the results but could be more systematically compared and discussed with previous studies. For example, the results of this study could be compared in more detail with the study by Angin et al. to analyze the reasons for the differences and to discuss their implications for clinical practice.

Response:

Thank you for pointing this out. I have added a discussion comparing this with previous studies by Angin.(L214-229)

Our findings present an interesting contrast to those reported by Angin et al. [10]. While they found a negative correlation between FPI scores and the CSA of intrinsic muscles like abductor hallucis and flexor hallucis brevis, our study did not reveal significant differences in intrinsic muscle CSA across the clusters. This discrepancy might be attributed to several factors. Firstly, our study focused on participants with similar flat-footed characteristics (FPI < 6), whereas Angin et al. examined a broader range of foot types. This narrower range in our study might have limited the variability in intrinsic muscle size. Secondly, our classification was based on dynamic measures (ICNH and DND) rather than static measures like the FPI. This suggests that static measures of foot posture may not fully capture the complexity of foot function during gait. The lack of clear differences in intrinsic muscles in our study, despite variations in MLA kinematics, implies that the relationship between foot posture, muscle morphology, and dynamic function may be more complex than previously thought. These findings underscore the importance of considering both static and dynamic measures in clinical assessment and highlight the need for further research to elucidate the intricate relationships between foot structure, muscle morphology, and function in individuals with flat feet. (L214-229)

6. The small sample size may affect the generalisability and statistical efficacy of the results.

Response:

Thank you for pointing this out. I have added a small sample size point in limitation. (L251-257)

Future studies should aim to recruit larger samples, directly evaluate muscle activity using electromyography, and employ more comprehensive MLA kinematic indicators. The inclusion of additional measures such as plantar pressure distribution could provide a more nuanced assessment of flatfoot characteristics. Despite these limitations, our study provides valuable preliminary insights into the relationship between MLA kinematics during gait and foot muscle morphology in individuals with flat feet, laying the groundwork for future investigations in this area. (L251-257)

7. It is recommended that the authors update the reference list to ensure that more recent and relevant sources are included.

Response:

Thank you for pointing this out. I have added the following references that suggest FDL can help support MLA.

19.Pan Foot Morphology and Running Gait Pattern between the Left and Right Limbs in Recreational Runners(L334)

20.Fukano M Damage and recovery of the intrinsic and extrinsic foot muscles from running a full marathon(L336)

Reviewer 3 Report

Comments and Suggestions for Authors

Classifications based on dynamic navicular drop during gait and characteristics of flat foot muscle morphology

Line 82: Seems apparent from the fact you mention 6 force plates and your markering approach but be clear this is overground data and that the participants were walking unshod.

Line 89: Taking the average rather than using all the data points for a subject doesn’t make any sense here, this is removing the variability of human response. Five gait steps is really not enough either to make conclusions from.

Line 99: Normalized to weight is good. Might be good to know if there were any BMI considerations, as in were all the participants within normal BMI range (non-obese). I see this in Table 2 but possibly add a note also up here.

Figure 3.2 Possibly this plot can have y range of 0-30mm. Not clear why it goes to -10mm.

Figure 4. Same comment about the range. Also suggest strongly to make this one plot with three lines on it and differentiate with dash, solid, dot-dash. A reader can’t really compare these profiles as presented. If you want to leave separate please mark the plots so readers can connect the ideas of high/low ICNH and large/small DND to the cluster plots. Ideally reference lines at y=reference magnitude. The Axis labels should be large and centered ex: Navicular Height (mm) and Percent of Stance (%). Currently this is labeled very poorly. The Class 1/2/3 should ideally also be descriptive of what that group reflects (ex: High ICNH, small DND) and should be a proper title not inside the plot area.

Table 2. I’m not very familiar with appropriate statistical methods where the groups are very different sizes. You note about checking normality in the statistical analysis section. Please also make a note that the approach was appropriate for comparing different sized groups (in your case 20 vs 10/9).

Line 166: For key comparisons so close to significance cut off there is a valid reasoning to recruit further and particularly to even out the group sizes. The uneven group sizes may make it very difficult to determine a true difference or non-difference. If the research is important then arguably it’s important to know if this is a difference or not.

Line 189: You discuss load and possible shifting of load. You stated in the methods that you used force plates but no force plate data is presented. It would be very helpful to see how the force data (COP profiles) related to the NH profiles. That would improve the quality of the article. If you don’t want to present the force plate data you should remove references to it in the methods as currently it gives readers wrong expectations.

Author Response

Line 82: Seems apparent from the fact you mention 6 force plates and your markering approach but be clear this is overground data and that the participants were walking unshod.

Response:

Thank you for pointing this out. I have added that the participants went barefoot for the exam.(L84-86)

This study examined the kinematic characteristics of barefoot subjects' feet during gait, focusing on two key measures: initial contact navicular height (ICNH) and dynamic navicular drop (DND).(L84-86)

Line 89: Taking the average rather than using all the data points for a subject doesn’t make any sense here, this is removing the variability of human response. Five gait steps is really not enough either to make conclusions from.

Response:

Thank you for pointing this out. I changed the potentially misleading phrase “five gait steps” to “we used the average values of ICNH and DND from five stance phases.(L94-99)

Also, as you pointed out, it is preferable to use all data points during the gait, but I clearly explained the limitations of the experimental setup.(L96-100)

Due to the constraints of our experimental setup, including the positioning of cameras and the limited capture volume, we were only able to measure one complete gait cycle per trial. While we acknowledge that this may not capture the full variability of gait, it was the maximum achievable with our current facility setup. For statistical analysis, the mean ICNH and DND values of the stance phase for five separate trials were used.(L94-99)

Line 99: Normalized to weight is good. Might be good to know if there were any BMI considerations, as in were all the participants within normal BMI range (non-obese). I see this in Table 2 but possibly add a note also up here.

Response:

Thank you for pointing this out. We added that all participants were within the normal BMI range .(L111)

We also added in Table 2 that CSA was normalized by body weight. (L177-178)

Figure 3.2 Possibly this plot can have y range of 0-30mm. Not clear why it goes to -10mm.

Response:

Thank you for pointing this out. I have changed the range of y in Figure 2 and Figure 4 to 0-30mm.(L147)

(L147)

 (L160)

Figure 4. Same comment about the range. Also suggest strongly to make this one plot with three lines on it and differentiate with dash, solid, dot-dash. A reader can’t really compare these profiles as presented. If you want to leave separate please mark the plots so readers can connect the ideas of high/low ICNH and large/small DND to the cluster plots. Ideally reference lines at y=reference magnitude. The Axis labels should be large and centered ex: Navicular Height (mm) and Percent of Stance (%). Currently this is labeled very poorly. The Class 1/2/3 should ideally also be descriptive of what that group reflects (ex: High ICNH, small DND) and should be a proper title not inside the plot area.

Response:

Thank you for pointing this out. I have combined the three graphs into one. I also expressed the division of Figure 4 with the colors of Figure 3.                                                      

Table 2. I’m not very familiar with appropriate statistical methods where the groups are very different sizes. You note about checking normality in the statistical analysis section. Please also make a note that the approach was appropriate for comparing different sized groups (in your case 20 vs 10/9).

Response:

Thank you for pointing this out. I have reviewed the statistical methods as you suggested and changed to the Games-Howell test because the Tukey test was problematic.(L123-124)

For post hoc comparisons, we used the Games-Howell and Steel-Dwass methods, as they do not require the assumption of equal variances between groups.(L123-124)

Line 166: For key comparisons so close to significance cut off there is a valid reasoning to recruit further and particularly to even out the group sizes. The uneven group sizes may make it very difficult to determine a true difference or non-difference. If the research is important then arguably it’s important to know if this is a difference or not.

Response:

Thank you for pointing this out. As you indicated, we have added to the limitation the issue of differences in participants between groups.(L245-248)

The small sample size and uneven distribution of participants across clusters may affect the generalizability and statistical efficacy of the results, potentially contributing to the lack of statistical significance in some findings, particularly regarding FDL CSA differences between clusters (p = 0.051).(L245-248)

Line 189: You discuss load and possible shifting of load. You stated in the methods that you used force plates but no force plate data is presented. It would be very helpful to see how the force data (COP profiles) related to the NH profiles. That would improve the quality of the article. If you don’t want to present the force plate data you should remove references to it in the methods as currently it gives readers wrong expectations.

Response:

Thank you for pointing this out. I have removed the force plate description.(L90-91)

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All my questions have been well addressed, I recommend to accept it now. 

Comments on the Quality of English Language

Minor editing of English language required.

Reviewer 2 Report

Comments and Suggestions for Authors

Upon reexamining the revised manuscript and the authors' point-to-point responses, I can now confirm that they have addressed my concerns thoroughly. The revised version is in line with the journal's requirements and is worthy of acceptance.

Comments on the Quality of English Language

no

Reviewer 3 Report

Comments and Suggestions for Authors

The write up is improved. The data content is more clear (mocap only, no force data), statistical test appropriateness (post hoc appropriate for non-equal group sizes), and plot clarity are improved.

It doesn't change the core issues that this could actually be much more good/useful work if additional recruitment was performed to even the group sizes or if the associated force data was included. As a brief communication it's passable for being clear in what was done. But with the method constraints I don't take away very much as far as the meaning of the results.