Investigating Kinematics and Electromyography Changes in Manual Handling Tasks with an Active Lumbar Exoskeleton

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper describes an evaluation of a trunk exoskeleton by measuring muscle activity and kinematic data during manual handling tasks. The exoskeleton itself is a novel device and the topic is interesting for the reader. The major limitation of the study is the evaluation being limited to only tasks with very light loads where the exoskeleton effects aren’t needed nor detected.

Comments:

- First paragraph (lines 33-44): The introduction gives a reader a false sense that this study will solve for the MSDs (which can certainly be a long-term goal) but this research is about evaluation of an exoskeleton for manually handling tasks that are common in physically demanding jobs.

MSD diagnosis and physical demands are two different problems. There are other disabilities and diagnosis (like back pain mentioned in the later paragraph) that would also affect how a person can perform in physically demanding jobs, and so you can either include many of them as an example of how the exosuit could potentially help people in the future or remove the MSDs all together (which I believe would make more sense). This could be a part of a future work in the discussion section if authors plan to focus on testing the exoskeleton with people diagnosed with MSD.

- The purpose of the study (line 64-68): Limiting the range of motion itself isn’t a positive outcome. It could mean that it simply restricts the movement which could prevent a person from completing a task. But if it means limited time in or limited motion to risky positions/end range positions, that would be something the reader is interested in. Similar to that, decreasing muscle activity of the trunk sounds like a dangerous feature. Engaged trunk muscles are important for safety and stability when performing tasks with arms. The introduction needs to be more clear on why this hypothesis is important to test or the hypothesis needs to be rephrased.

- Figure 1: labels for different parts of the exoskeleton are in a light gray color, make them in black so they are more visible as the font is already small.

- 2.2 Belt – subsection title needs to be aligned left

- Marker placement labels on Figure 3 are too small and the meaning of the labels need to be described in the caption and in the text. Exact anatomical position of the markers should be listed in the text for each marker set. Marker placement needs to be described in a way that another researcher can replicate the study.

- The same comment for the EMG, what was the exact placement protocol you used for each muscle? SENIAM recommendations can have multiple options for certain muscles and some muscles are missing on the website, so there needs to be a clear description on what you did specifically.

- Line 119-122: As mentioned above, all marker cluster labels in “{ASP_CL1,}” need to be explained earlier in the text and with the Figure 3. The study needs to be replicable.

Based on the design of the exoskeleton, I would not expect to see a decrease the EMG of the trunk. In fact, if tightened, the passive belt could be used as a bracing device (as used in Olympic lifting for example) and increase activity of the trunk muscles to make the movement more stable for the user (and protective of their spine). A decrease would make sense if the loading is transferred to the device or distributed to other muscles (as done with other exoskeletons). What is the proposed mechanism that this device provides the benefit to the user?

Limitation: Larger ROM could be a positive thing – more trunk flexibility, especially with a lighter weight. If heavier weight was lifted, subjects could lean towards a more conservative movement on their own without the belt to increase strength and stability.

This study needs another condition with a heavier load as done in other exoskeleton studies (10 and/or 20kg). With a 5 kg load, the impact of the load is so little that the effects of the exoskeleton can’t even be effectively observed.

Conclusion: You hypothesized that the exoskeleton would decrease muscle activity as if that is a wanted outcome of the study. Now you are saying the exoskeleton will not cause muscle atrophy as if reduction of the muscle activity would be a negative outcome. Seems like you adjusted the narrative to fit with the results.

Author Response

Object: Responses to Reviewer #1

First, I would like to thank you for your comments and suggestions on my manuscript. All the requests have been considered in the revision of this manuscript.  Please find my point-by-point responses to your report.

Reviewer #1 request:  - First paragraph (lines 33-44): The introduction gives a reader a false sense that this study will solve for the MSDs (which can certainly be a long-term goal) but this research is about evaluation of an exoskeleton for manually handling tasks that are common in physically demanding jobs. MSD diagnosis and physical demands are two different problems. There are other disabilities and diagnosis (like back pain mentioned in the later paragraph) that would also affect how a person can perform in physically demanding jobs, and so you can either include many of them as an example of how the exosuit could potentially help people in the future or remove the MSDs all together (which I believe would make more sense). This could be a part of a future work in the discussion section if authors plan to focus on testing the exoskeleton with people diagnosed with MSD.

Answer to the Reviewer #1:  The authors thank the reviewer for constructive remarks and for giving us the opportunity to improve our manuscript. We have taken the reviewer's suggestions into consideration, and as a result:

we have revised the introduction to include the following statement: "In this context, the utilization of exoskeletons has been advocated to reduce work-related musculoskeletal stress (Flor-Unda et al., 2023)"

In the conclusion section, we have incorporated additional perspectives as follows: "Future studies conducted under real working conditions and over a longer duration would bolster these findings and offer a deeper understanding of the productivity of operators using exoskeletons. Furthermore, the impact of exoskeletons on the prevention of musculoskeletal disorders (MSD) remains open and requires dedicated investigations."

Added reference :

Flor-Unda, O., Casa, B., Fuentes, M., Solorzano, S., Narvaez-Espinoza, F., & Acosta-Vargas, P. (2023). Exoskeletons : Contribution to Occupational Health and Safety. Bioengineering, 10(9), 1039. doi: 10.3390/bioengineering10091039

Reviewer #1 request:  - The purpose of the study (line 64-68): Limiting the range of motion itself isn’t a positive outcome. It could mean that it simply restricts the movement which could prevent a person from completing a task. But if it means limited time in or limited motion to risky positions/end range positions, that would be something the reader is interested in. Similar to that, decreasing muscle activity of the trunk sounds like a dangerous feature. Engaged trunk muscles are important for safety and stability when performing tasks with arms. The introduction needs to be more clear on why this hypothesis is important to test or the hypothesis needs to be rephrased.

Answer to the Reviewer #1:  :  The authors express their appreciation to the reviewer for their remark. In response, we have modified the text as follows: "The objective of this study is to objectively quantify the biomechanical impact of an active lumbar exoskeleton. By conducting handling tasks in a motion capture laboratory and analyzing kinematics and EMG data, we hypothesized that the active exoskeleton would influence the range of motion and modify the muscular activity of the trunk muscles. These two components are crucial for objectively categorizing the prescription for the future use of the active exoskeleton."

In the discussion, we have also added: "The clinical relevance of reductions in muscle activity concerning the prevention of musculoskeletal diseases remains an open question. Some authors advocate for reducing muscle activities to prevent intervertebral disc compression(Walter, Stutzig, & Siebert, 2023), while others endorse muscle activities to prevent injury by enhancing trunk stability (Huxel Bliven & Anderson, 2013)or to contribute to the rehabilitation process of low back pain(Macedo et al., 2012)"

Added reference

Huxel Bliven, K. C., & Anderson, B. E. (2013). Core Stability Training for Injury Prevention. Sports Health: A Multidisciplinary Approach, 5(6), 514‑522. doi: 10.1177/1941738113481200

Macedo, L. G., Latimer, J., Maher, C. G., Hodges, P. W., McAuley, J. H., Nicholas, M. K., … Stafford, R. (2012). Effect of Motor Control Exercises Versus Graded Activity in Patients With Chronic Nonspecific Low Back Pain : A Randomized Controlled Trial. Physical Therapy, 92(3), 363‑377. doi: 10.2522/ptj.20110290

Walter, T., Stutzig, N., & Siebert, T. (2023). Active exoskeleton reduces erector spinae muscle activity during lifting. Frontiers in Bioengineering and Biotechnology, 11, 1143926. doi: 10.3389/fbioe.2023.1143926

Reviewer #1 request:  - Figure 1: labels for different parts of the exoskeleton are in a light gray color, make them in black so they are more visible as the font is already small.

Answer to the Reviewer #1:  the reviewer’s remark is pertinent, and we modified the figure as follow.

Reviewer #1 request:  - 2.2 Belt – subsection title needs to be aligned left

Answer to the Reviewer #1:  Correction done

Reviewer #1 request:  - Marker placement labels on Figure 3 are too small and the meaning of the labels need to be described in the caption and in the text. Exact anatomical position of the markers should be listed in the text for each marker set. Marker placement needs to be described in a way that another researcher can replicate the study.

Answer to the Reviewer #1:  To address the reviewer's remark, we have included a complementary file that precisely details our marker set. This additional file offers the advantage of providing comprehensive information without overloading the main publication. We have accordingly modified the legend of Figure 3 to align with these changes.

Complementary file : Detail of the marker set.

Figure 3 has been extended to make it easier to read.

Reviewer #1 request:  - The same comment for the EMG, what was the exact placement protocol you used for each muscle? SENIAM recommendations can have multiple options for certain muscles and some muscles are missing on the website, so there needs to be a clear description on what you did specifically.

Answer to the Reviewer #1: To address the reviewer's remark, we have added the following: "Before applying the surface EMGs to the skin, the skin was prepared according to SENIAM recommendations The subjects' skin was rubbed with abrasive paper and then cleaned with alcohol. The EMG sensor for the longissimus dorsi (LD) was placed 25mm lateral to the L1 spine. The EMG sensor for the rectus abdominis (RA) was placed 25mm above the umbilicus and 40mm lateral to the midline. The EMG sensor for the external oblique abdominus (OE) was placed 20mm above and 20mm anterior to the iliac crest. (Chino et al., 2024). "

Added reference

Chino K, Ohya T, Suzuki Y. Association between expiratory mouth pressure and abdominal muscle activity in healthy young males. Eur J Appl Physiol. 2024 Mar 1. doi: 10.1007/s00421-024-05430-5. Epub ahead of print. PMID: 38427101.

Reviewer #1 request:  - Line 119-122: As mentioned above, all marker cluster labels in “{ASP_CL1,}” need to be explained earlier in the text and with the Figure 3. The study needs to be replicable. Answer to the Reviewer #1: The detail of marker labels have been added in the supplementary File .

Reviewer #1 request:  Based on the design of the exoskeleton, I would not expect to see a decrease the EMG of the trunk. In fact, if tightened, the passive belt could be used as a bracing device (as used in Olympic lifting for example) and increase activity of the trunk muscles to make the movement more stable for the user (and protective of their spine). A decrease would make sense if the loading is transferred to the device or distributed to other muscles (as done with other exoskeletons). What is the proposed mechanism that this device provides the benefit to the user?

Answer to the Reviewer #1:  The reviewer's remark is pertinent, and to address it, we have added the following text to the discussion: "This observation does not contradict the primary design objective of the exoskeleton used in this study, which aimed to apply an external traction force to the lumbar spine through SEA, rather than reducing muscle activities to mitigate intervertebral disc compression (Zaïri et al., 2021)"

Added reference :

Zaïri, F., Moulart, M., Fontaine, C., Zaïri, F., Tiffreau, V., & Logier, R. (2021). Relevance of a novel external dynamic distraction device for treating back pain. Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 235(3), 264‑272. doi: 10.1177/0954411920971401

Reviewer #1 request:  Limitation: Larger ROM could be a positive thing – more trunk flexibility, especially with a lighter weight. If heavier weight was lifted, subjects could lean towards a more conservative movement on their own without the belt to increase strength and stability.

Answer to the Reviewer #1:  We thank the reviewer for this comment, and to address it, we have included the following text in the revised version: "Moreover, RULA range of motion areas should be used only as a rough indicator, as it is designed for postural analysis in quasi-static situations and not for rapid, significant changes in posture(Kee, 2022)"

Added reference :

Kee, D. (2022). Systematic Comparison of OWAS, RULA, and REBA Based on a Literature Review. International Journal of Environmental Research and Public Health, 19(1), 595. doi: 10.3390/ijerph19010595

Reviewer #1 request:  This study needs another condition with a heavier load as done in other exoskeleton studies (10 and/or 20kg). With a 5 kg load, the impact of the load is so little that the effects of the exoskeleton can’t even be effectively observed.

Answer to the Reviewer #1: we thank the reviewer for this comment, and we corrected the text as follow “In our case, the load to be handled was 5 kg, requiring a light effort with a low-risk lifting situation [5] . In comparison, in Luger's study [37], where the load handling was 9.6 kg, which is considered as a medium risk lifting situation [5], the exoskeleton resulted in a 10.5% reduction in back muscle activity. Consequently, in our case, we observed only a slight reduction in muscle activity.”

Reviewer #1 request:  Conclusion: You hypothesized that the exoskeleton would decrease muscle activity as if that is a wanted outcome of the study. Now you are saying the exoskeleton will not cause muscle atrophy as if reduction of the muscle activity would be a negative outcome. Seems like you adjusted the narrative to fit with the results.

Answer to the Reviewer #1:  The reviewer's remark is pertinent, and we have revised it as follows: "In the situation studied, the exoskeleton did not reduce or increase the muscle activity of the abdominal-lumbar region. Therefore, further studies should be conducted to evaluate the potential muscle atrophy or overstrain in this area."

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for inviting me to review this article for your journal. I also appreciate the authors for their noteworthy research work and methodology. I have some relevant questions to clarify before I can make a positive decision on this manuscript:

1. I suggest that the authors work further on the introduction section. The type of technology employed and the evaluated tasks are not better explained than in the title. In this section, a more detailed overview of the state-of-the-art is expected, highlighting the main contributions of this technology in the selected application area and justifying the interest of the topic to be addressed, as well as the need for the presented work.

2. The phrase "The null hypothesis was no significance difference between the three conditions. The null hypothesis is rejected if the p-value (level of significance) the Friedman test is less than 0.05. In this case, the alternative hypothesis (significant difference between the three conditions) was supported" is repeated three times in the statistical analysis section. Please find a way to incorporate it only once.

3. Figure 6 is very small and almost illegible. There is too much space between the graphs. Try making them larger, even if they end up a bit closer together.

4. I don't fully understand the practical utility of this study or its rationale. What is the usefulness of comparing the passive and active components of an exoskeleton? Are they typically used separately? What are the main points of the article? My suggestion is that the authors work more on providing practical meaning to the study, delving into its practical applications and its definitive contributions to current knowledge.

5. Keywords should be different from those in the title

Minor comments:

Line 51: can you explain what does transparency mean in this context?

Line 216: The expression "back risk areas" must be introduced and justified in the introductory section.

Line 222: This result must be presented in the introductory section, as it an expected outcome

Line 249: Please report the effect size of the small reduction or remove this sentence. I assume that if you define a free-lifting condition you should expect for large inter-subject variations.

Comments on the Quality of English Language

it is fine

Author Response

Object: Responses to Reviewer #2

First, I would like to thank you for your comments and suggestions on my manuscript. All the requests have been considered in the revision of this manuscript.  Please find my point-by-point responses to your report

Reviewer #2 request:  1. I suggest that the authors work further on the introduction section. The type of technology employed and the evaluated tasks are not better explained than in the title. In this section, a more detailed overview of the state-of-the-art is expected, highlighting the main contributions of this technology in the selected application area and justifying the interest of the topic to be addressed, as well as the need for the presented work.

Answer to the Reviewer #2:  The authors express gratitude to the reviewer for their constructive review and for affording us the opportunity to publish our manuscript. We have carefully considered the reviewer's suggestions and revised the introduction accordingly. We have included the following statement: "Additionally, owing to the heterogeneity of exoskeleton designs, predicting physical human-exoskeleton interactions accurately to determine the appropriate prescription for use in industrial sectors requires specific investigation (Massardi et al., 2022)."

Added reference :

 Massardi, S., Rodriguez-Cianca, D., Pinto-Fernandez, D., Moreno, J. C., Lancini, M., & Torricelli, D. (2022). Characterization and Evaluation of Human–Exoskeleton Interaction Dynamics : A Review. Sensors, 22(11), 3993. doi: 10.3390/s22113993

Reviewer #2 request:  2. The phrase "The null hypothesis was no significance difference between the three conditions. The null hypothesis is rejected if the p-value (level of significance) the Friedman test is less than 0.05. In this case, the alternative hypothesis (significant difference between the three conditions) was supported" is repeated three times in the statistical analysis section. Please find a way to incorporate it only once.

Answer to the Reviewer #2:  In accordance with the reviewer's remarks, the revised version has been modified accordingly.

Reviewer #2 request:  3. Figure 6 is very small and almost illegible. There is too much space between the graphs. Try making them larger, even if they end up a bit closer together.

Answer to the Reviewer #2:  Figure 6 has been extended to make it easier to read. Abbreviations have been added for each muscle and are explained in the legend.

Figure 6. RMS values in percentage of maximum of the “Control” condition (MCC) of EMG for the Left Longissimus Dorsi (LLD), Right Longissimus Dorsi (RLD), Left Rectus Abdominis (LRA), Right Rectus Abdominis (RRA), Left Obliquus Externus abdominis (LOE) and Right Obliquus Externus abdominis (ROE) during the FREE LIFTING, SQUAT LIFTING and LOAD TRANSFER sessions.

Reviewer #2 request:  4. I don't fully understand the practical utility of this study or its rationale. What is the usefulness of comparing the passive and active components of an exoskeleton? Are they typically used separately? What are the main points of the article? My suggestion is that the authors work more on providing practical meaning to the study, delving into its practical applications and its definitive contributions to current knowledge.

Answer to the Reviewer #2:   The authors express their appreciation to the reviewer for their remark. In response, we have modified the text as follows: "The objective of this study is to objectively quantify the biomechanical impact of an active lumbar exoskeleton. By conducting handling tasks in a motion capture laboratory and analyzing kinematics and EMG data, we hypothesized that the active exoskeleton would influence the range of motion and modify the muscular activity of the trunk muscles. These two components are crucial for objectively categorizing the prescription for the future use of the active exoskeleton."

  Reviewer #2 request:  5. Keywords should be different from those in the title

Answer to the Reviewer #2:  We appreciate the reviewer's suggestion; however, we have used common keywords related to the topic of our study.

  Reviewer #2 request:  Line 51: can you explain what does transparency mean in this context?

Answer to the Reviewer #2: To address the reviewers' comments, we have rephrased the sentence as follows: "However, the daily use of exoskeletons in companies has raised questions about their direct effect or transparency [9], defined as their neutrality of biomechanical impact on humans [10] [11], in terms of ranges of motion and the muscular activity of surrounding muscles [12]."

  Reviewer #2 request:  Line 216: The expression "back risk areas" must be introduced and justified in the introductory section.

Answer to the Reviewer #2:  we appreciate the reviewer's comment, and we have modified the text as follows: "During handling, our results showed that both the passive and active parts of the exoskeleton reduced the time spent in the risk range of motion, as defined by the RULA method (McAtamney et al., 1993)."

  Reviewer #2 request:  Line 222: This result must be presented in the introductory section, as it an expected outcome

Answer to the Reviewer #2:  As previously mentioned, we have modified the text as follows: "The objective of this study is to objectively quantify the biomechanical impact of an active lumbar exoskeleton. By conducting handling tasks in a motion capture laboratory and analyzing kinematics and EMG data, we hypothesized that the active exoskeleton would influence the range of motion and modify the muscular activity of the trunk muscles. These two components are crucial for objectively categorizing the prescription for the future use of the active exoskeleton."

  Reviewer #2 request:  Line 249: Please report the effect size of the small reduction or remove this sentence. I assume that if you define a free-lifting condition you should expect for large inter-subject variations.

Answer to the Reviewer #2:  We thank the reviewer for the suggestion, and the sentence has been removed in the revised version.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors did a great job addressing all my comments and suggestions. I think the paper is much clearer and concise. Figures are improved and the supplementary table makes the study more replicable and therefore useful for other researchers.

I highly recommend using higher load conditions when conducting future studies with the exoskeleton when the actual usability comes into play.

Author Response

Object: Responses to Reviewer #1

The authors would like to thank the editor for taking into account the corrections, and for the additional remarks which will further improve the quality of the document. The author has taken them into account as follows and they have been added to the revised text.

 Reviewer #1 request:  The authors did a great job addressing all my comments and suggestions. I think the paper is much clearer and concise. Figures are improved and the supplementary table makes the study more replicable and therefore useful for other researchers.

Answer to the Reviewer #1:  The authors thank the reader for this encouragement  

Reviewer #1 request:  I highly recommend using higher load conditions when conducting future studies with the exoskeleton when the actual usability comes into play.

Answer to the Reviewer #1:  To take in account the reviewer’s remark we rephrase the conclusion as follow “Future studies conducted under real working conditions , over a longer duration and with higher load conditions would bolster these findings , and offer a deeper understanding of the productivity of operators using exoskeletons.”

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

I appreciate the revisions made by the authors to enhance the document. However, certain aspects still lack clarity, and there remains a dearth of data regarding effect size as previously requested. Therefore, I suggest that the authors further delve into their document revision or withdraw their publication request.

I recommend that the authors dedicate additional effort to refining the introduction section of the manuscript. Currently, the exposition of the technology utilized and the tasks under evaluation lacks sufficient elaboration beyond what is already conveyed in the title. Within this section, a more comprehensive overview of the state-of-the-art is anticipated, elucidating the principal advancements facilitated by this technology within the designated application domain and substantiating the significance of the addressed topic, as well as the necessity for the presented research.

I find myself lacking a complete grasp of the pragmatic significance of this study or its underlying rationale. What are the practical implications of contrasting the passive and active components of an exoskeleton? Are they conventionally employed in isolation? What constitutes the primary focus of the article? I propose that the authors dedicate more attention to articulating the practical implications of the study, delving into its real-world applications and its definitive contributions to existing knowledge.

Author Response

Object: Responses to Reviewer #2

The authors would like to thank the editor for taking into account the corrections, and for the additional remarks which will further improve the quality of the document. The author has taken them into account as follows and they have been added to the revised text.

 Reviewer #2 request:  I recommend that the authors dedicate additional effort to refining the introduction section of the manuscript. Currently, the exposition of the technology utilized and the tasks under evaluation lacks sufficient elaboration beyond what is already conveyed in the title. Within this section, a more comprehensive overview of the state-of-the-art is anticipated, elucidating the principal advancements facilitated by this technology within the designated application domain and substantiating the significance of the addressed topic, as well as the necessity for the presented research.

Answer to the Reviewer #2: We thanks the reviewers for the remarks. The current paper is focused on the biomechanics impact  of an active lumbar exoskeleton as expressed in the title. Concerning the state of the art, we are cited numerous recent publications which propose review and systematic review of the topic of the use of  exoskeleton in industry. 

However to take in account the reviewer’s remark first we added in the revised text the following  phrase in the first paragraph : “ More precisely, the back is the area most affected by musculoskeletal stress in various industries i.e. construction (Flor-Unda et al., 2023), nursing (Farah et al., 2023), farming (Thansuwan et al., 2020), and manufacturing (Inoue et al., 2020). In this context, the utilization of exoskeletons has been advocated to reduce work-related musculoskeletal stress. Additionally, spinal traction devices offer opportunities for preventing low back pain (Rabal-Pelay et al., 2020). However, designing lower-back exoskeletons with such spinal traction functions presents challenges in terms of potential side effects on adjacent levels, which could globally limit the efficiency of the exoskeleton (Moon et al., 2022). “

Added references :

Flor-Unda, B. Casa, M. Fuentes, S. Solorzano, F. Narvaez-Espinoza, et P. Acosta-Vargas, « Exoskeletons: Contribution to Occupational Health and Safety », Bioengineering, vol. 10, no 9, p. 1039, sept. 2023, doi: 10.3390/bioengineering10091039.

Farah, D. Roll, A. Sorais, et A. Vallée, « Assessment of Exoskeletons on Nurses’ Quality of Work Life: A Pilot Study at Foch Hospital », Nurs. Rep., vol. 13, no 2, p. 780‑791, mai 2023, doi: 10.3390/nursrep13020068.

Thamsuwan, S. Milosavljevic, D. Srinivasan, et C. Trask, « Potential exoskeleton uses for reducing low back muscular activity during farm tasks », Am. J. Ind. Med., vol. 63, no 11, p. 1017‑1028, nov. 2020, doi: 10.1002/ajim.23180.

Inoue et al., « Occupational Characteristics of Low Back Pain Among Standing Workers in a Japanese Manufacturing Company », Workplace Health Saf., vol. 68, no 1, p. 13‑23, janv. 2020, doi: 10.1177/2165079919853839.

Rabal-Pelay, C. Cimarras-Otal, M. Macia-Calvo, C. Laguna-Miranda, et A. V. Bataller-Cervero, « Use of a Spinal Traction Device during Work Shift in Assembly Line Workers », Int. J. Environ. Res. Public. Health, vol. 18, no 14, p. 7708, juill. 2021, doi: 10.3390/ijerph18147708.

Moon, J. Bae, J. Kwak, et D. Hong, « A Lower-Back Exoskeleton With a Four-Bar Linkage Structure for Providing Extensor Moment and Lumbar Traction Force », IEEE Trans. Neural Syst. Rehabil. Eng., vol. 30, p. 729‑737, 2022, doi: 10.1109/TNSRE.2022.3159178.

Reviewer #2 request:  I find myself lacking a complete grasp of the pragmatic significance of this study or its underlying rationale. What are the practical implications of contrasting the passive and active components of an exoskeleton? Are they conventionally employed in isolation? What constitutes the primary focus of the article? I propose that the authors dedicate more attention to articulating the practical implications of the study, delving into its real-world applications and its definitive contributions to existing knowledge.

Answer to the Reviewer #2:  In response to the reviewer the point raised about the rational of our study is explicated in introduction in the  the sentence : “ The main objective of exoskeletons is to prevent injuries, while maintaining the mobility of workers . However, the daily use of exoskeletons in companies has raised questions about their direct effect or transparency, defined as their neutrality of biomechanical impact on humans , in terms of ranges of motion and the muscular activity of surrounding muscles. Additionally, owing to the heterogeneity of exoskeleton designs, predicting physical human-exoskeleton interactions accurately to determine the appropriate prescription for use in industrial sectors requires specific investigation”

However to take in account the reviewer remark we also added the following sentence. “ However, evaluating the effectiveness of industrial exoskeletons is a challenging issue (Li-Baboud et al., 2023; Golabchi et al., 2023). Additionally, since an exoskeleton requires a classification as a medical device by EU regulation (2017/745), rigorous evaluation of each active and passive component of the product are necessary. This is particularly critical in the case of exoskeletons that combine active and passive components because a sophisticated control system is required to optimize performance and demonstrate the benefits of these designs (Presenti et al., 2021). “ 

Added references :

Y.-S. Li-Baboud et al., « Evaluation Methods and Measurement Challenges for Industrial Exoskeletons », Sensors, vol. 23, no 12, p. 5604, juin 2023, doi: 10.3390/s23125604.

Golabchi, A. Chao, et M. Tavakoli, « A Systematic Review of Industrial Exoskeletons for Injury Prevention: Efficacy Evaluation Metrics, Target Tasks, and Supported Body Postures », Sensors, vol. 22, no 7, p. 2714, avr. 2022, doi: 10.3390/s22072714.

European Parliament, « Regulation (EU) 2017/745 of the European Parliament and of the Council of 5 April 2017 on medical devices ». Eur-Lex, 20 mars 2023. [En ligne]. Disponible sur: http://data.europa.eu/eli/reg/2017/745/oj

European Agency for safety and health at work (OSHA), « The impact of using exoskeletons on occupational safety and health ». EU-OSHA, 27 août 2019. Consulté le: 17 avril 2024. [En ligne]. Disponible sur: https://osha.europa.eu/sites/default/files/2021-11/Exoskeletons%26OSH.pdf

Pesenti, A. Antonietti, M. Gandolla, et A. Pedrocchi, « Towards a Functional Performance Validation Standard for Industrial Low-Back Exoskeletons: State of the Art Review », Sensors, vol. 21, no 3, p. 808, janv. 2021, doi: 10.3390/s21030808.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

I appreciate the efforts made by the authors to enhance the quality of the study and its scientific significance. I see that they have incorporated relevant information and citations into the introduction and addressed some redundancies in the methodology. However, my main concern regarding the

My requests (in previous rounds) for calculation of effect size have not been addressed, nor has an explanation been provided for why it is not reported.

Additionally, the proposed questions have not been answered:

• What are the practical implications of contrasting the passive and active components of an exoskeleton?
• Are they conventionally employed in isolation?
• What constitutes the primary focus of the article?

Could you please elaborate on the practical implications of the study, delving into its real-world applications and its definitive contributions to existing knowledge?

Given this lack of response, my opinion is that the article should not proceed further in the publication process. However, I defer the final decision to the editors.

Author Response

Here, we provide our argumentation (and sometimes our understanding of the comment). We hope that the following answers we have provided will assist you in making a decision.

-New comment of the reviewer was : “My requests (in previous rounds) for calculation of effect size have not been addressed, nor has an explanation been provided for why it is not reported.”

Respond : in the round 1, the reviewer wrote :” Line 249: Please report the effect size of the small reduction or remove this sentence. I assume that if you define a free-lifting condition you should expect for large inter-subject variations.”. In response, we stated: “We thank the reviewer for the suggestion, and the sentence has been removed in the revised version.” As you can see, we fully addressed the reviewer's remark. It is worth noting that in round 2, the reviewer did not bring up this point again. We believe this matter was resolved.

-New comment of the reviewer was : “What are the practical implications of contrasting the passive and active components of an exoskeleton?”

Respond : this point was already taken in account in the round 2 and we responded : “ However, evaluating the effectiveness of industrial exoskeletons is a challenging issue (Li-Baboud et al., 2023; Golabchi et al., 2023). Additionally, since an exoskeleton requires a classification as a medical device by EU regulation (2017/745), rigorous evaluation of each active and passive component of the product are necessary. This is particularly critical in the case of exoskeletons that combine active and passive components because a sophisticated control system is required to optimize performance and demonstrate the benefits of these designs (Presenti et al., 2021).”-New comment of the reviewer was : Are they conventionally employed in isolation?

Respond : We believe that this point was clarified by the sentence “ The device consists of two sub-elements, a passive part with the textile belt and the ac-tive part with two series elastic actuators (SEA) sets positioned on both sides of the body (Figure 1-A)” in the materals and methods sections.

Respond : To clarify, we have now added it “ The device consists of two sub-elements, a passive part with the textile belt and the ac-tive part with two series elastic actuators (SEA) sets positioned on both sides of the body (Figure 1-A). These two parts are never used in isolation.”

-New comment of the reviewer was : “What constitutes the primary focus of the article?”

Respond : The point was already addressed in round 1, and our response was as follows “ The objective of this study is to objectively quantify the biomechanical impact of an active lumbar exoskeleton. By conducting handling tasks in a motion capture laboratory and analyzing kinematics and EMG data, we hypothesized that the active exoskeleton would influence the range of motion and modify the muscular activity of the trunk muscles. These two components are crucial for objectively categorizing the prescription for the future use of the active exoskeleton.”

-New comment of the reviewer was : Could you please elaborate on the practical implications of the study, delving into its real-world applications and its definitive contributions to existing knowledge?

Respond : According the remark of the reviewer 1 in the round 1, We believe that this point was clearly stated in the conclusion by :“In the situation studied, the exoskeleton did not reduce or increase the muscle activity of the abdominal-lumbar region. Therefore, further studies should be conducted to evaluate the potential muscle atrophy or overstrain in this area. Future studies conducted under real working conditions, over a longer duration and with higher load conditions would bolster these findings and offer a deeper understanding of the productivity of operators using exoskeletons.”

However, to make it more explicit we propose to complete by : “ In the situation studied, the exoskeleton did not reduce or increase the muscle activity of the abdominal-lumbar region. Our study contributes to defining the optimal prescriptions for the utilization of active exoskeletons as medical devices. Therefore, further studies should be conducted to evaluate the potential muscle atrophy or overstrain in this area. Future studies conducted under real working conditions, over a longer duration and with higher load conditions would bolster these findings and offer a deeper understanding of the productivity of operators using exoskeletons.”

Best regards

Round 4

Reviewer 2 Report

Comments and Suggestions for Authors    After carefully reading the authors' new responses and the modified manuscript, I believe I have gained a better understanding of the corrections they had previously sent. While it is true that I would like the authors to more clearly identify the practical implications of their project, as the core of the discussion revolves around a reduction in time spent in high-risk positions according to RULA, they may need to delve deeper in this direction to add value to their conclusions. Nevertheless, I consider that they have made a significant effort to improve the manuscript and its current form may be considered for publication. Comments on the Quality of English Language

it is fine.

Author Response

Object: Responses to Reviewer #2

Reviewer #2 request:  “After carefully reading the authors' new responses and the modified manuscript, I believe I have gained a better understanding of the corrections they had previously sent. While it is true that I would like the authors to more clearly identify the practical implications of their project, as the core of the discussion revolves around a reduction in time spent in high-risk positions according to RULA, they may need to delve deeper in this direction to add value to their conclusions. Nevertheless, I consider that they have made a significant effort to improve the manuscript and its current form may be considered for publication.”

Answer to the Reviewer #2: We thank the reviewers for their remarks. The reviewers' feedback was very valuable in enhancing the quality of the publication.