Effects of Wheelchair Seat Sagging on Seat Interface Pressure and Shear, and Its Relationship with Changes in Sitting Posture

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

The authors addressed my comments and concerns adequately.

Author Response

Reviewer 1: The authors addressed my comments and concerns adequately.

Response : I would like to express my sincere gratitude for your thoughtful and detailed review. Thank you for your valuable feedback.

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

The manuscript investigates the effects of correcting wheelchair seat sagging on ischial pressure, shear and posture in a healthy population in seated position. The data were collected through pressure mapping systems, specialized sensors and accelerometers. It was found that the wheelchairs with correction are effective in reducing shear forces and sliding to decrease the risk of potential injury. 

1. The effects of shear and sliding on pressure injuries in the introduction section are not comprehensive and needed to add references(e.g. https://doi.org/10.1016/j.cmpb.2025.108648).
2. Why only the anterior and posterior (wheelchair center and patella) were considered but not the left and right sides of the posture and pelvic height change?
3. Line 201, you chose Shapiro-Wilk test to assess the normalityof PPI or the differences of PPI between the with correction and no correction? Please make it clearer.
4. Is the peak of pressure and the maximum shear force occurring at the same moment? The sampling frequencies for pressure and shear force are different, will this affect the accuracy of the maximum values?
5. You described the use of a specialized sensor to capture shear force, more details could be suppled in 2.3 equipment.
6. Please add some figures of pressure mapping and the distribution of shear forces.
7. The elderly and patients are the users of wheelchair and you chose the healthyand younger participants, how should this point be considered for analysis?
8. Please modify the sentence of “Additionally, to evaluate body displacement, photographs were taken from the sagittal plane at the start and end of each measurement to assess how much the body slide from this planeto assess how much the body does slide in this plane (Figure 3).”and check the whole article.

Author Response

The manuscript investigates the effects of correcting wheelchair seat sagging on ischial pressure, shear and posture in a healthy population in seated position. The data were collected through pressure mapping systems, specialized sensors and accelerometers. It was found that the wheelchairs with correction are effective in reducing shear forces and sliding to decrease the risk of potential injury.

1. The effects of shear and sliding on pressure injuries in the introduction section are not comprehensive and needed to add references(e.g. https://doi.org/10.1016/j.cmpb.2025.108648).

Response & Revised Manuscript

Thank you for your insightful suggestion. To provide a more comprehensive overview of the effects of shear force and sliding on pressure injuries, we have incorporated the recommended reference (Zhang et al., 2025) into the manuscript. In consideration of the overall coherence of the argument, we have included only this reference among those you kindly suggested. We would be grateful if you could review the updated content.

Line 56: Pressure injuries are induced not only by vertical pressure but also by friction and shear forces, which can cause deep tissue deformation and ischemia, especially under prolonged loading conditions [12].

 

2. Why only the anterior and posterior (wheelchair center and patella) were considered but not the left and right sides of the posture and pelvic height change?

Response & Revised Manuscript

Thank you for your valuable feedback. In this study, we limited our investigation to shear forces in the anterior-posterior direction. This decision was based on the hypothesis that seat sagging leads to asymmetrical loading on the ischial tuberosities, resulting in postural instability. To compensate for this instability, users are likely to posteriorly tilt the pelvis and lean against the backrest, thereby increasing anterior shear forces.

We acknowledge that this rationale was insufficiently explained in the original manuscript; therefore, we have revised and expanded the Introduction to clarify this point.

At the same time, as you rightly pointed out, it would have been beneficial to also assess parameters in the lateral direction. Accordingly, we have addressed this limitation in the Discussion section and identified it as an important direction for future research. We sincerely appreciate your thoughtful and constructive comments.

Line 58: Occupying a sagging seat encourages posterior or lateral pelvic tilt, thereby resulting in uneven loading on the ischial tuberosities [9]. As a result, the postural control system of wheelchair users may attempt to minimize instability by tilting the pelvis posteriorly and leaning against the backrest. This compensatory strategy increases loading on the backrest and may lead to increased forward sliding of the buttocks. Such a posture compromises postural stability alters pressure distribution [13,14], increases anterior shear forces [8], and ultimately elevates the risk of pressure injury development.

Line 82: While a few studies have investigated how sling seats affect posture and seating pressure, few have thoroughly explored the specific impact of seat sagging on shear forces. Therefore, the aim of this study was to investigate the effects of wheelchair seat sagging on pressure, shear force (specifically, anterior-posterior shear force, which contributes to posterior pelvic tilt), and posture, in order to inform the development of effective strat-egies for the prevention of pressure injuries.

Line 396: Although we measured tilt angles of the iliac crests, we did not directly assess vertical displacement or asymmetry between the left and right sides. Future studies should con-sider incorporating pelvic height measurements to better understand lateral instability and its contribution to shear forces.

 

3. Line 201, you chose Shapiro-Wilk test to assess the normality of PPI or the differences of PPI between the with correction and no correction? Please make it clearer.

Response & Revised Manuscript

Thank you very much for your valuable comments. We have clarified the purpose of using the Shapiro–Wilk test and specified its application in assessing the normality of the data prior to selecting the appropriate statistical tests. The corresponding revisions have been made in the main text as follows. We kindly ask you to review them.

Line 241: The Shapiro-Wilk test was employed to assess the normality of each variable (PPI, shear force, slide, and angle data) prior to selecting the appropriate statistical test for comparing the With Correction and No Correction conditions.

 

4. Is the peak of pressure and the maximum shear force occurring at the same moment? The sampling frequencies for pressure and shear force are different, will this affect the accuracy of the maximum values?

Response & Revised Manuscript

Thank you for your valuable comments. We explicitly stated that different sampling frequencies for pressure and shear forces do not compromise the analysis, as maximum values were independently determined within the 10-minute measurement window. The corresponding revisions have been made in the main text as follows. We kindly ask you to review them.

Line 203: Although pressure and shear forces were sampled at different frequencies (20 Hz vs. 4 Hz), each outcome was expressed as the maximum value observed within the 10-min window; therefore, differences in sampling frequency do not compromise the validity of the analysis.

 

5. You described the use of a specialized sensor to capture shear force, more details could be suppled in 2.3 equipment.

Response & Revised Manuscript

Thank you for your valuable comments. Additional details regarding the specialized shear force sensor (iShear) have been included in the Equipment section.

Line 140: The sensor sheet’s specifications included dimensions of 471 mm (length) × 471 mm (width), 1024 sensors (32 rows × 32 columns), a thickness of 1.8 mm, and a resolution of 14.7 mm.

Shear force was recorded using the iShear system (Invacare Inc., Aesch, Switzerland). The sensor measures 27 × 690 × 615 mm, weighs 1.7 kg, and accommodates users weighing 45–120 kg. It consists of a lightweight aluminum sensor bar attached to a PU-coated tri-cot/nylon fabric mat, a construction that minimizes interference with seat immersion and posture (Supplementary Figure 1, Supplementary Table 1).

 

6. Please add some figures of pressure mapping and the distribution of shear forces.

Response & Revised Manuscript

Thank you for your valuable comments. Representative figures depicting pressure mapping and shear force distributions have been added to visually clarify our findings.

Figure 5. Line 308: Figure 5. Representative distribution maps of pressure and shear force: (a) Pressure distribution without correction, (b) Pressure distribution with correction, (c) Shear force without correction, and (d) Shear force with correction. While no notable differences were observed in pressure dis-tribution between conditions, shear force was reduced when seat sagging was corrected.

 

7. The elderly and patients are the users of wheelchair and you chose the healthyand younger participants, how should this point be considered for analysis?

Response & Revised Manuscript

Thank you for your valuable feedback. As suggested, we have added a statement in the abstract to clarify that the study was conducted on healthy adults. In the Discussion section, this limitation had already been acknowledged in the previous version of the manuscript, so we have retained it as is. We have revised the abstract accordingly, and kindly ask you to review the changes.

Line 34: However, because this study targeted healthy adults, further research involving older or at-risk populations is necessary.

 

8. Please modify the sentence of “Additionally, to evaluate body displacement, photographs were taken from the sagittal plane at the start and end of each measurement to assess how much the body slide from this planeto assess how much the body does slide in this plane (Figure 3).”and check the whole article.

Response & Revised Manuscript

Thank you for your valuable feedback. The sentence concerning body displacement evaluation has been clearly revised for better readability and accuracy.

Lines 207: Additionally, to evaluate body displacement, photographs were taken from the sagittal plane at the start and end of each measurement to assess how much the body slid along this plane (Figure 4).

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

The authors conducted a study to investigate "Effects of Wheelchair Seat sagging on Seat Interface Pressure and Shear, and Its Relationship with Changes in Sitting Posture.".

However, I think the authors are not prepared enough to submit their papers. First, the manuscript is not well written. I think the yellow shading or underlining in the text indicates that the authors have not followed the basic requirements for paper submission. Please revise all these appropriately in the Revised manuscript and be sure to consider my comments when submitting your papers in the future.

Comments for author File: Comments.pdf

Author Response

The authors conducted a study to investigate "Effects of Wheelchair Seat sagging on Seat Interface Pressure and Shear, and Its Relationship with Changes in Sitting Posture.".

However, I think the authors are not prepared enough to submit their papers. First, the manuscript is not well written. I think the yellow shading or underlining in the text indicates that the authors have not followed the basic requirements for paper submission.

Please revise all these appropriately in the Revised manuscript and be sure to consider my comments when submitting your papers in the future.

Response: Thank you very much for taking the time to review our manuscript. We have revised the manuscript based on your comments, as detailed below, and kindly ask you to review the changes.

Please note that this manuscript was previously submitted to this journal, received a rejection decision, and was subsequently encouraged to be resubmitted. In accordance with the editor’s instructions, we have highlighted and underlined the revisions made since the previous version. We would appreciate your understanding in this regard.

 

Abstract

1. Line 19-20: 'Twenty-four individuals were 19 recruited, and twenty-two who met the study requirements participated in the study'.

This is an unnecessary description. Abstracts usually present the number of people who were ultimately selected and studied.

2. Please provide specific information about the tools for measurement.

 

Response & Revised Manuscript

Thank you for your valuable comments. We have revised the abstract to clearly state the final number of participants and to explicitly specify the measurement tools used (CONFORMat, iShear, and accelerometers). The revised section is provided below for your review.

Line 19: A total of twenty-two participants who met the study requirements were included in the study.

Line 22: Ischial pressure was measured using a pressure-mapping system (CONFORMat), shear force with a specialized sensor (iShear), and posture with accelerometers (TSND151).

 

3. Methods: Subgroup analysis is an inappropriate technique.

It is recommended that information on measurement and analysis be clearly described, even in the Abstract.

Response & Revised Manuscript

Thank you for your insightful comments. In accordance with your suggestion, we have explicitly described the subgroup analysis as an exploratory analysis. The revised section is provided below for your review.

Line 26: The subgroup analysis was conducted as an exploratory approach to assess potential variation among participants with elevated shear forces.

 

4. Results: Please provide a p-value numerical value.

Response & Revised Manuscript

Thank you for your valuable feedback. We have added the p-values to the Results section of the abstract. The revised portion is provided below for your review.

Line 27: Results: There was no statistically significant difference in ischial pressure between the No Correction and With Correction conditions(p=0.37). However, shear force and slide were significantly reduced when seat sagging was corrected(p<0.05). Accelerometer data showed no significant difference in postural changes between conditions(p≧0.05), although the With Correction condition displayed a slight trend toward greater positional variability over time.

 

Keywords

1. Use MeSH terms.

 

Response & Revised Manuscript

Thank you for your helpful comments. We have updated the keywords to align with standard MeSH terms relevant to the content of the manuscript. The revised keywords are listed below.

Line 38: Keywords: Pressure Ulcer, Wheelchairs, Seating, Posture, Biomechanics

 

Introduction

1. Does the yellow shaded part have any special meaning?

Response :

Regarding the yellow highlighting and underlining in the manuscript, please kindly note that this manuscript was previously reviewed and subsequently rejected with a recommendation to resubmit. Based on the editor’s instructions at that time, we included yellow highlights and underlined text to clearly indicate the revised sections in our resubmission. Therefore, the current formatting reflects those editorial requirements.

2. I checked the reference #8 and it does not match what the authors suggested.

And, reference #9 is also an inappropriate citation. Authors are encouraged to recheck that references are cited appropriately throughout the manuscript.

 

Response & Revised Manuscript

Thank you for your valuable comments. Reference 8 was indeed inappropriate and has been replaced accordingly. However, Reference 9 cites a clinical guideline, supporting the use of pressure redistribution cushions for prolonged wheelchair sitting. We respectfully request your confirmation regarding the appropriateness of this citation.

For the point you indicated, we have cited the following paper.

8. Kamegaya, T. Influence of sacral sitting in a wheelchair on the distribution of contact pressure on the buttocks and back and shear force on the ischial region. J. Phys. Ther. Sci. 2016, 28, 2830–2833. doi.org/10.1589/jpts.28.2830
9. Harms, M. Effect of Wheelchair Design on Posture and Comfort of Users. Physiotherapy 1990, 76, 266–271. doi.org/10.1016/S0031-9406(10)62219-5

 

3. Studies from 67 to 69 are important information related to the topic of this study. Background research on the seat of the wheelchair should be provided first, but a lot of information on cushions, etc. was provided. Please supplement the information on the seat.

Response & Revised Manuscript

Thank you for your valuable comments. As you rightly pointed out, information regarding the seat surface was insufficient. We have added recent literature on seat structure and its biomechanical implications to the Introduction section. The revised content is provided below for your review.

Line 73: Recent research has further highlighted the critical impact of wheelchair seat structure on interface pressure and shear. Shirogane et al. [18] quantitatively measured pressure and shear stress using a flexible sheet-type sensor, highlighting how variations in seat in-clination influence shear forces. Barks et al. [19] observed significant associations between wheelchair seat fit and seated posture, focusing on health outcomes such as pain and risk of pressure injuries in older wheelchair users. Additionally, Koda et al. [20] examined the effects of tilt-in-space and reclining angles of wheelchairs on normal and shear forces in the gluteal region, confirming substantial influences of seat adjustments on pressure and shear distributions.

 

Methods

1. Present an experimental flow diagram.

Response & Revised Manuscript

Thank you for your valuable comments. We have created a flowchart of the experimental procedure.

Line 104: An experimental flow diagram has been included in the Methods section, as recommended, to visually clarify the study procedures (Figure 1).

 

2. Please provide a basis for estimating the sample size.

For example, what is the basis for setting the effect size to 0.5?

After checking the #18 references, it is difficult to confirm the basis for setting it to 0.5.

Response & Revised Manuscript

Thank you for your valuable comments. We have clarified the rationale for the selected effect size (0.5) and the basis for the sample size calculation in the Methods section. The revised portion is provided below for your review.

Line 118: The effect size of 0.5 was calculated using Cohen's d formula, where the mean difference between groups (25.9 − 23.4 = 2.5 mmHg) was divided by the pooled standard deviation [√((4.7² + 5.4²)/2), which is approximately 5.07], resulting in d of approximately 0.49, which was rounded to 0.5 for power analysis.

 

3. For each measurement tool, provide validity and reliability.

Response & Revised Manuscript

Thank you for your valuable comments. All measurement devices used in this study were selected based on their use in previous research. Accordingly, we have cited relevant literature that employed the same instruments. The revised portion is provided below for your review.

Line 150: Furthermore, the three measurement devices used in this study (CONFORMat, iShear, and TSND151) have been utilized in prior studies, and their measurement methodologies are well-established [22-25].

 

4. I recommend that authors describe their ethical considerations at the beginning of the Methods section.

Also provide additional information about clinical trial registration.

Response & Revised Manuscript

Thank you for your valuable comments. Details regarding ethical approval and informed consent have been explicitly stated at the beginning of the Methods section.

As this study involved healthy adult participants, it was not registered as a clinical trial. The study commenced only after receiving approval from the ethics committee. Information related to ethical approval, informed consent, and privacy protection has been moved to the beginning of the Methods section, as shown below.

Line 97: 2) Ethical Considerations

This study received approval from the Ethics Committee of the Graduate School of Nara Gakuen University (approval number: 5-002). Written informed consent was ob-tained from all participants. All data were managed to preserve anonymity, and partici-pant privacy was rigorously protected.

 

5. Provide information about the clinical experience and academic degrees of the measurers.

Response & Revised Manuscript

The clinical experience and educational background of the measurers are as follows.

Measurements were conducted by three experienced therapists: one occupational therapist with 30 years of experience, and two physical therapists with 18 and 13 years of experience, respectively. Among the physical therapists, the one with 18 years of experience holds a master's degree, while the other two hold bachelor's degrees. We have added this information to the manuscript as shown below.

Line 166: In this study, the measurers and evaluators were different individuals. Measure-ments were conducted by an occupational therapist with 30 years of experience, a physical therapist with 18 years of experience (who holds a master’s degree), and a physical therapist with 13 years of experience.

 

Also, were all measurements performed under the blinded condition?

Yes, all outcome measurements were conducted under blinded conditions where applicable. Specifically, the evaluation of slide distance using photographic images and ImageJ was performed by a separate assessor who was blinded to the seating condition (With Correction or No Correction). The images were anonymized and coded before analysis to ensure blinding. Other measurements (pressure and shear force) were recorded using objective instruments and did not involve subjective interpretation, thereby minimizing the risk of observer bias.

 

Revised Manuscript

Line 216: To minimise observer bias, data collection and image analysis were carried out by differ-ent individuals. All photographs were captured by the measurer, whereas slide distance was quantified in ImageJ by a separate evaluator. The evaluator received only de-identified image files renamed with anonymised codes and was therefore blinded to whether each image corresponded to the With-Correction or No-Correction condition; the code key was opened only after all measurements had been completed.

 

6. Underlining and erasing the text with yellow shading is highly inappropriate.

Response:

Regarding the yellow highlighting and underlining in the manuscript, please kindly note that this manuscript was previously reviewed and subsequently rejected with a recommendation to resubmit. Based on the editor’s instructions at that time, we included yellow highlights and underlined text to clearly indicate the revised sections in our resubmission. Therefore, the current formatting reflects those editorial requirements.

 

Results & Tables

7. Insert the pace between the letter/number and symbol.
8. Be careful with capitalization within the text, especially Table 1.
9. Table 1 should also present information about the number of subjects, gender, age, etc..

 

Response & Revised Manuscript

Thank you for your comments. In response, we have made all the necessary corrections:

Spaces have been inserted appropriately between letters/numbers and symbols.

Capitalization within the text, especially in Table 1, has been revised.

Table 1 has been updated to include information on the number of subjects, gender, age, and other relevant demographic data.

Line 260: Table 1,

Line 291: Changes in the angles of the head, chest, left iliac crest, and right iliac crest (expressed as median [interquartile range]) were assessed. The head angle changes were –0.15 [–3.82 – 9.61] ° in the No Correction condition and –1.08 [–5.37 – 7.96] ° in the With Correction condition. The chest angle changes were 0.19 [–4.25 – 8.13] ° under No Correction and –0.08 [–5.93 – 21.26] ° under With Correction. For the left iliac crest, the change was –0.16 [–1.37 – 1.18] ° in the No Correction condition and –0.74 [–5.52 – 5.52] ° in the With Correc-tion condition. For the right iliac crest, the change was –0.24 [–1.36 – 0.81] ° under No Correction and –1.27 [–8.62 – 2.58] ° under With Correction. Although there were no sig-nificant differences between the two conditions, there was a tendency toward greater pos-tural variation under With Correction (Table 2).

Line 302: Table 2.

 

Discussion

1. Insert the pace between the letter and symbol.

Response

Thank you for your valuable comments. We apologize for the oversight in the original manuscript. Appropriate spacing has been inserted between letters/numbers and symbols as suggested.

 

References

1. The papers presented in References are generally old. This means that background research on the research topic may be inadequate. To reflect recent research trends, authors are encouraged to cite recent papers.

Response

Thank you for your comment. We have added the most recent references where possible.

Author Response File: Author Response.pdf

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors

The manuscript entitled "Effects of Wheelchair Seat sagging on Seat Interface Pressure and Shear, and Its Relationship with Changes in Sitting Posture" has been reviewed. The study investigates the effects of wheelchair seat sagging on ischial pressure, shear force, and posture in healthy adults. The topic is clinically relevant in the context of long-term wheelchair use among older adults or individuals with mobility impairments.

The study population comprises only healthy young adults, which limits the relevance of the findings to clinical populations. The lack of inclusion of at-risk groups is a major limitation that should be highlighted more strongly in both the abstract and conclusion.

There is no mention of blinding the assessors to the seating conditions, which could introduce observer bias, particularly when measuring slide using photographs and ImageJ.

The manuscript contains frequent grammatical errors, redundancy, and awkward phrasing that hinder comprehension.

Author Response

The manuscript entitled "Effects of Wheelchair Seat sagging on Seat Interface Pressure and Shear, and Its Relationship with Changes in Sitting Posture" has been reviewed. The study investigates the effects of wheelchair seat sagging on ischial pressure, shear force, and posture in healthy adults. The topic is clinically relevant in the context of long-term wheelchair use among older adults or individuals with mobility impairments.

Response:

Thank you very much for taking the time to review our manuscript. We have revised the manuscript based on your comments, as detailed below, and kindly ask you to review the changes.

 

The study population comprises only healthy young adults, which limits the relevance of the findings to clinical populations. The lack of inclusion of at-risk groups is a major limitation that should be highlighted more strongly in both the abstract and conclusion.

Response & Revised Manuscript

We fully agree with this important point. In the Abstract, we revised the final sentence to explicitly acknowledge the study’s limitation and the need for further research in at-risk populations. Similarly, in the Conclusion, we added a clear statement emphasizing the importance of investigating the effects of seat sagging in elderly and mobility-impaired individuals in future studies. These revisions help clarify the limited generalizability of our findings and outline directions for subsequent research.

Line 34: However, because this study targeted healthy adults, further research involving older or at-risk populations is necessary.

Line 429: One limitation of this study is that all participants were healthy adults, whereas older individuals and those who use wheelchairs daily often exhibit different load-bearing pat-terns [38], as well as differences in muscle mass and skin integrity. Older adults, whose physical functions have declined, not only experience greater instability in seated balance but are also more prone to muscle fatigue and posterior pelvic tilt during prolonged wheelchair sitting.

 

There is no mention of blinding the assessors to the seating conditions, which could introduce observer bias, particularly when measuring slide using photographs and ImageJ.

Response & Revised Manuscript

Thank you for pointing this out. We have added the following sentence to the Measurement Procedure and Analysis section in the Methods:

“The assessor who analyzed the sagittal plane photographs using ImageJ was different from the measurer and was blinded to the seating conditions.”

This clarification indicates that a blinded evaluation protocol was implemented to reduce potential bias during image-based measurements.

Line 216: To minimise observer bias, data collection and image analysis were carried out by differ-ent individuals. All photographs were captured by the measurer, whereas slide distance was quantified in ImageJ by a separate evaluator. The evaluator received only de-identified image files renamed with anonymised codes and was therefore blinded to whether each image corresponded to the With-Correction or No-Correction condition; the code key was opened only after all measurements had been completed.

 

The manuscript contains frequent grammatical errors, redundancy, and awkward phrasing that hinder comprehension.

Response

We appreciate your concern regarding the clarity of the manuscript. To address this, we have thoroughly revised the manuscript for grammar, style, and conciseness. We believe the revised version significantly improves readability and scientific presentation.

Round 2

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

I have no other question.

Reviewer 4 Report (New Reviewer)

Comments and Suggestions for Authors

The authors replied satisfactorily to reviewers’ comments and took into account the suggestions given. The updates were appropriate and I have nothing further to suggest.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The submitted manuscript studied how wheelchair seat sagging affects pressure, shear, and posture – an important question to drive facilities to either update their wheelchair supply or consider the addition of inserts. Ultimately, this works towards improved pressure injury prevention and ideally improved posture and function as well. The study has the potential to add new and important information to the field, but some missing information from the methodology limits my ability to complete a thorough review.

 

Major Concerns

Methods

• More information is needed about the use of the iShear. The device is large and fairly rigid. Where was it placed relative to the sling/cushion/insert/pressure mat? How would this impact the participants’ seating? This impacts the interpretation of the findings.
• Please provide more details about the wheelchair setup. You state that arm and foot supports were adjusted for each participant. How was the ideas setup defined? (For example, did you try to make the thigh horizontal? What position did you seek for the arm support?). Was it adjusted separately for the no correction and the with correction condition? This also impacts the interpretation of the findings.
• At what time point was the 5N shear cutoff selected? Introduce this in the methods, and explain why the absolute shear force value was used to create subgroups, despite the fact that the normalized value was studied elsewhere.

Results

• Provide more data about the absolute shear force values at the time point contributing to the ≥5N cutoff – this would clarify whether the data distribution was bimodal or if this was simply an arbitrary cutoff.

Discussion

• There are a number of limitations that need more attention:
  • On average, the participants were not sized appropriately for the wheelchair. As described, the wheelchair was approx. 40x40cm, while the average participant was 36x44cm. making the chair a bit wide and short. This might be typical for a facility owned chair supporting your choice, but the implications should be discussed nonetheless.
  • The authors bring up the use of healthy adults instead of older adults. However, this warrants greater attention in terms of the ability of older adults to maintain posture without adequate muscle strength.
  • The manuscript reports on postural changes, but not the actual posture itself. Could you report on pelvic posture to provide a comparison to typical seated postures of older adults? The introduction mentions that posterior pelvic tilt is typical, but we don't know if these healthy adults initially sat with the posterior pelvic tilt typically seen in older adults, and how that might have impacted the findings, as shear forces and sliding would be increased with such a tilt.
  • The longer sitting times >10 minutes should also be elaborated on.
• Line 251 – calling the reduction of slide “marked” seems a bit strong, as the difference was 3mm. While I appreciate the statistical significance, and that the clinical significance may be apparent in its relation to shear force and the fact that over time, this may translate to greater sliding, 3mm in and of itself likely has limited clinical significance.

 

Minor Concerns

Introduction

• Line 47 – While trying to communicate the importance of wheelchairs for getting out of bed, the language appears slightly misleading. I read this as playing a role in transfers themselves, such as a transfer board, or other transfer aid. This is minor, but could confuse some novice readers, so I would consider rewording.
• Line 53-54 – Consider adding that placing a cushion on a sling seat only compromises the effectiveness of some cushions, as it may be dependent on the rigidity of the cushion.
• Line 60 – I don’t recall the Harms reference clearly, but did this refer to sling seats without a cushion? If so, please clarify.

Methods

• It may be helpful to clarify that the normalized shear force values are reported in N/N.
• Was any validation completed to confirm posture measurements at the iliac crest on participants with more soft tissue?

Results

• Line 225-226 – Numbers should be reported with consistent decimal precision throughout.

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Pressure injuries are a severe problem in wheelchair users and the contribution of shear forces are not well known yet. This study aims to investigate how wheelchair seat sagging affects pressure, shear, and posture. Gaining this understanding can help shape pressure injury prevention strategies, making it a valuable contribution to reducing the incidence of pressure injuries among wheelchair users.

The paper is well written and mostly clear. My biggest open question is related to the iShear and the measurement of shear forces: does iShear measure shear forces in all directions (and do you have information on the direction of the resulting shear force) or does it take into account only shear forces related to forward slide in the seat? This is relevant for the interpretation of the results and needs clarification.

Besides this general remark, the detailed comments and questions are listed below:

 

Abstract:

• Line 19: you state " Twenty-four healthy adults, meeting specific anthropometric requirements for proper wheelchair fit". This is not correct since two participants did not meet the requirement (hip width was less than the requested 34cm). Please correct this.

 

Introduction:

• Line 43-44 / 47-48: on line 43 you write that wheelchairs are often used to transfer from bed to a sitting position. As I understand this, persons are using the wheelchair only to drive / being pushed from the bed to a chair / couch. This is a very short period of time. Later on, you write that musculoskeletal pain and discomfort arise from wheelchair use. However, musculoskeletal pain usually does not manifest during such a short period of use. Please rephrase the statement on wheelchair use and maybe focus more/additionally on long-term wheelchair users.
• Line 71-72: why do you restrict your overarching goal to pressure injury prevention of older adults? Also, young wheelchair user do profit a lot from pressure injury prevention.

 

Methods:

• Line 82: "buttock–popliteal length, sitting elbow height, sitting axillary height, and lower leg length". It's too unspecific how you measured it, especially for sitting elbow and axillary height I don't know how this is measured. If I look at the results table 1 elbow height is 22cm and axillary height is 41cm. For me it's not clear what this is. On the other hand, what do you need this data for? Is it needed to for this publication since you don't use it for the analysis. Therefore, either be more specific on what the variables mean and how they're measured or consider to not include it in this paper.
• The information on how the measurements are performed and with what devices are spread over the subchapters Equipment, Measurement Procedure and Data Management and Analysis. The subchapters make sense, however the information is not always in the right subchapter and there are repetitions. This makes it difficult to the reader to find the information. Examples are:
  • "Shear force was assessed using “iShear” (Vicair B.V., Wormer, the Netherlands)" is mentioned in Equipment and Data Measurement. The same accounts to seat pressure / interface pressure (here please use always the same wording consistently throughout the documents).
  • Line 151: "First, participants sat in the wheelchair without the cushion to establish a baseline shear force value. The wheelchair cushion and seat base (if used) were then installed, and participants were reseated." This belongs in my view to measurement procedure. Please restructure these parts to make easier for the reader to follow.
• Line 104: when you introduce the seat base include a reference to figure 2.
• CONFORMat line 105 and 144:
  • When I checked this mat I only found CONFORMat from Tekscan. Please check whether your information on the producer (NITTA) is really correct.
  • Include additional information on the measurement frequency of the mat
• iShear line 108 and 151:
  • When I checked this mat I only found iShear from Invacare. Please check whether your information on the producer (Vicair) is really correct.
  • Give more details on the measurement and output of the mat: Does it measure shear forces only in one direction? That's relevant for the analysis/interpretation of the results.
  • do you get an average number of shear force (sum of all forces) or do you get individual values from different sensors, as for the CONFORMat?
  • what is the sample frequency?
• Line 124: it's Figure 3 not Figure 1.
• Line 135: did you standardize how the photograps were taken? Always the same distance angle etc.? Please give more information on this.
• Line 144, interface pressure: you state that you analyzed ischial pressure. Did you verify that it pressure was measured at ischial tuberosity or did you just take the highest value? That's not clear from the description. If you verified it, add a description on how you verified that the interface pressure you analyzed was located at the ischial tuberosity.
• Line 148: It is not clear how you calculated PPI. You write that highest average value derived from the peak pressure cell and its adjacent three cells (four cells in total) is the PPI. If the sensors are placed in a grid, the peak pressure cell has 8 adjacent cells. Why did you take only three and how are they selected?
• Line 155: for calculating shear force you take the maximum of the 10 min, for the pressure you take the value at 10min. Is this comparable? Why is this discrepancy and why did you not do it the consistently for both devices?
• Line 167, tilt angle of forehead: why did you include the head tilt? Head position is very variable and will change a lot over the 10 minutes, depending fore example on where you look, what you do etc. What conclusion can you draw from it?
• Line 167-168: you attached the accelerometers with straps to the manubrium and iliac crest. How feasible was it and did this attachment allow for a reliable detection of movement?
• Line 162-163: Can you give more information on how accurate the method for measuringof slide is? What is the minimal detectable change? Is it below the 3mm of slide you indicated in the results?
• Line 176: Please add more information on what you compared with the t-test and the Wilcoxon test (compare between correction and no correction). Of course this is clear from the text before but should be mentioned in this section.
• Line 178: give a brief explanation why you did an additional subgroup analysis, it's not mentioned before.

 

Results

• Line 187: it's not correct that you had 24 participants. 2 of the participants did not fulfill inclusion criteria.
• Table 2 and corresponding text:
  • include unit for all tilt angles
  • always use the same number of digits after the comma, especially for data with the same unit (tilt angles)
  • I assume the differences of tilt angles are given in degrees? If this is the case, I'm very surprised that the difference in head tilt is only 0.15 degrees. And that all the differences in tilt in the no correction are less than 1°.
• Line 231-233: you state that there is a tendency towards greater postural variation under With Correction. However, this difference usually below 1°. Is this clinically relevant?
• Table 4: This data is a repetition of the values in the text. I would therefore delete this table, which consists only one line.
• Table 5: title is not correct, and also here this table could be omitted since it's already mentioned in the text.

Discussion

• Line 258: you discuss Braden scores. Please give a short description what it is or what a score of 18 means. Otherwise the reader does not now the population and can't judge the statement.
• Line 288-293: So far you talked about anterior/posterior tilt, in this part it's about pelvis tilt to one side/"lateral tilt". This part is difficult to understand, please rephrase. In addition for lateral tilt it's relevant to know whether shear forces are measured only in anterior/posterior direction or also in the frontal plane.
• Line 302-304: "Earlier studies have indicated that posterior pelvic tilt generates shear force [13,24] and that seat correction can influence lumbar alignment [14]. Hence, we hypothesized that seat correction would lessen postural changes and diminish shear force production." Related to my previous comment: also here it's important to know which shear forces are include, only in one or in two directions. Seat correction could also directly reduce the shear force in the frontal plane.
• Line 327: so far you did not mention that the methods you used are not accurate or not standardized. Please give more information here / discuss in more detail.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors thoroughly addressed the majority of the comments from the previous review, leading to an improved manuscript. However, the explanation of the use of the iShear identifies a critical flaw in the methodology. By placing a rigid object on top of the wheelchair cushion, they are negating multiple important effects that they are trying to study:

1. The effect of the contour of the wheelchair cushion created by the presence or absence of the sagging of the wheelchair sling seat
2. The immersion of the participant into the wheelchair cushion

Furthermore, they are introducing a new artifact: A change in seat height relative to the height adjusted for the sagging seat condition, as the iShear will span the highest points of the cushion or seat pan, leading to a higher seat height and potential challenges reaching the footrest.

As a result, interpretation of all findings related to shear measurements cannot be clearly attributed to the sling seat as much as the presence of the iShear itself. While the current manuscript faces significant challenges in its full form, I believe there is still valuable work worth sharing from your research. A focused manuscript that presents your interface pressure and posture results would provide a meaningful contribution to the field, even if more modest in scope than originally envisioned. This approach allows you to publish the sound portions of your research while maintaining scientific integrity.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript has improved a lot and especially the methods section is not much clearer and more specific. I only have some minor changes to be adapted for the final manuscript:

 

Line 47: small error in the sentence "Nevertheless, although wheelchairs are convenient for living away from bed, but musculoskeletal pain and discomfort have been reported": the "but" is not needed in the sentence. Please rephrase.

Line 94: add the unit to the values from the experimental and control group.

Figure 1 (a): seat sagging is missing an i.

Line 168: this sentence is not needed and does not fit perfectly anymore after rewriting this section. Please consider deleting it.

Line 170: the sentence "to assess how much the body slide from this plane" is not correct. Suggestions "to assess how much the body does slide (or) slid in this plane."

In addition, if you know the minimal detectable change, please also add this information to the manuscript. It helps the reader to contextualize your results.

Line 181-185: writing these sentences in bold is not needed, please use normal font.

Line 195: Please specify what EZR is.

Line 196 and 197: sometimes you write ischial pressure with an upper-case I and sometimes with a lower-case i. Please write it consistently throughout the manuscript, preferably with lower-cases. The same accounts for shear force, slide, seat sagging or axillary height. 

Line 197: it is not clear what you mean with data amount in the sentence "to determine whether there were ... data amount with or without deflection correction. Please rephrase. 

Line 231: I believe that "on the ischial" is not correct. Either use "ischial tuberosity" or "ischium".

Line 243: Specify that these values are measured in the subgroup with high shear forces. Add something like "in this subgroup, mean shear force..."

Table 3: Description: it's confusing if your write "changes in shear force", it implies that values in the table are changes from the participants with elevated shear forces to the whole cohort. Use the same title as in Table 2, like "Shear force among participants with elevated shear force." In addition, include the (mean +- SD) in the header of the table, like in table 2. And also add the information which test you used as in Table 2.

Line 363: In my view "While" is not needed in this sentence or it has to be rephrased.

Line 369: I would not call it "hip sensation". Either only sensation or something like sensation in the sitting area.

Line 376: this was not a subgroup analysis but performed with all participants.

Line 383: The sentence on the methodology is not well placed, it's in the middle of the discussion on older/younger adults as participants. I suggest moving this sentence to Line 391, before "Moreover, ...".