Reclined Seating Postures on Passive Safety Performance in Automotive Seats: A Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

It is a good and well-prepared paper containing comprehensive knowledge about the subject of the OOP test and the problem of the reclined position during the impact. Therefore, I recommend this paper for publication.

Author Response

Comment: It is a good and well-prepared paper containing comprehensive knowledge about the subject of the OOP test and the problem of the reclined position during the impact. Therefore, I recommend this paper for publication.

Response: We thank the reviewer for the positive assessment of our manuscript and for recognizing its contribution to the understanding of reclined occupant safety and OOP-related challenges. We appreciate the recommendation for publication and have carefully addressed all comments to further improve the clarity and overall quality of the paper.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript provides an overview of experimental and numerical studies in terms of occupant biomechanics, restraint system performance, and injury risk in reclined seating. The authors claim this manuscript as a systematic review, but they do not clearly describe the methodology used for literature selection and analysis. The scientific databases used, search keywords, and time window should be clearly indicated in the manuscript. 

Moreover, the paper lacks information regarding literature selection. How many papers were initially identified?  How many were included in the final review and why? 

Figure 1 is unclear, particularly regarding the red feedback line. The interaction pathway between "Injury Mechanisms," "Restraint System Interaction," and "Regulatory Assessment" is difficult to interpret. As currently depicted, a double feedback loop appears in the figure, but the workflow is not sufficiently explained. The authors must clarify the intended information flow and provide a more detailed explanation of this relationship in the figure caption and/or the main text.

The authors should consider completely restructuring the paper. Adding tables that summarize key parameters used for literature comparison could be very useful for the readers.

Author Response

Comment 1: The manuscript provides an overview of experimental and numerical studies in terms of occupant biomechanics, restraint system performance, and injury risk in reclined seating. The authors claim this manuscript as a systematic review, but they do not clearly describe the methodology used for literature selection and analysis. The scientific databases used, search keywords, and time window should be clearly indicated in the manuscript. 

Moreover, the paper lacks information regarding literature selection. How many papers were initially identified?  How many were included in the final review and why? 

Response 1: We thank the reviewer for this important observation and apologize for the lack of clarity. The manuscript was incorrectly described as a systematic review; it is, in fact, a narrative review intended to provide a structured synthesis of the current state of research.

The manuscript has been revised to remove any reference to a systematic review. As a narrative review, it does not follow a formalized systematic methodology. However, the scope and rationale of the literature considered have been clarified in the manuscript to better reflect the intended approach and ensure transparency regarding the selection of relevant studies.

 

Comment 2: Figure 1 is unclear, particularly regarding the red feedback line. The interaction pathway between "Injury Mechanisms," "Restraint System Interaction," and "Regulatory Assessment" is difficult to interpret. As currently depicted, a double feedback loop appears in the figure, but the workflow is not sufficiently explained. The authors must clarify the intended information flow and provide a more detailed explanation of this relationship in the figure caption and/or the main text.

Response 2: We appreciate this comment and agree that the clarity of Figure 1 required improvement.

The figure and its corresponding description in the Introduction have been revised as follows:

• The diagram now clearly presents the current workflow for passive safety assessment, distinguishing standard procedures from new seating challenges.
• The "red feedback line" has been replaced with a dashed red arrow to highlight the regulatory gap regarding reclined seating postures.
• The right side of the figure now illustrates how reclined seating impacts three key assessment pillars: (i) testing methodologies, (ii) occupant kinematics and restraint system interaction, and (iii) injury mechanisms.
• The caption has been expanded to serve as a standalone guide, linking visual elements to core themes in the review.

 

Comment 3: The authors should consider completely restructuring the paper. Adding tables that summarize key parameters used for literature comparison could be very useful for the readers.

Response 3: We agree that structured summaries are valuable for improving readability. The manuscript has been revised to improve its overall structure and clarity. In particular, Table 1 has been reorganized to provide a clearer synthesis of the reviewed studies. The revised table categorizes restraint strategies according to their primary biomechanical objective, explicitly highlighting the relationship between identified safety challenges and proposed solutions. Additional refinements throughout the text further improve coherence and reduce redundancy.

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript constitutes a comprehensive and timely review addressing the critical intersection of automotive passive safety and reclined seating postures. There are some comments.
1. The Introduction should more explicitly define the specific "novelty" or "contribution" of this review compared to existing literature on occupant safety and posture.
2. In Section 2 (Testing Protocols), there is a lack of in-depth discussion regarding the specific "Regulatory Gap," such as how current standards (e.g., FMVSS, Euro NCAP) technically circumvent testing reclined seats or the specific barriers to implementing reclined testing.
3. Section 3 (Biomechanical Foundations) remains somewhat theoretical; it lacks a specific sub-analysis on how recline physically alters the "Load Path" of the seatbelt from the pelvis to the abdomen.
4. Section 4 (Experimental and Numerical Studies) is descriptive but lacks a critical comparative analysis of the discrepancies between ATD, PMHS, and HBM results, particularly regarding tissue-level injury prediction in reclined positions.
5. Table 1 (in Section 5) is disorganized in the current submission; the categorization of "Strategy Type" is unclear, and the table requires restructuring to effectively convey the "Problem-Solution" relationship rather than just listing studies.
6. Section 5.2 (Adaptive Strategies) mentions Active Seatback Positioning (ASPA) but does not critically address the physical time constraints and feasibility of fully repositioning a seat within the short duration of pre-crash emergency braking.
7. The Future Perspectives section is generic; it lacks forward-looking insights into the integration of Artificial Intelligence or Machine Learning for real-time posture-adaptive restraint control systems.
8.  There is a lack of consistency and critical analysis regarding the cited literature; the manuscript includes many references from 2025 and 2026, which requires verification of their publication status and integration into the narrative.
9. The terminology is inconsistent, frequently oscillating between terms like "Reclined," "Relaxed," "Non-standard," and "Non-conventional" to describe the seating posture, which dilutes the precision of the text.

Author Response

This manuscript constitutes a comprehensive and timely review addressing the critical intersection of automotive passive safety and reclined seating postures. There are some comments.

Response: We thank the reviewer for their constructive and insightful feedback. The comments have been instrumental in improving the clarity, structure, and technical depth of the manuscript. All modifications are highlighted in red in the revised version and are addressed in detail below.

 

Comment 1: The Introduction should more explicitly define the specific "novelty" or "contribution" of this review compared to existing literature on occupant safety and posture.

Response 1: We appreciate the reviewer’s comment regarding the need to clarify the novelty and contributions of this review. The final paragraphs of the Introduction have been revised to highlight the novelty of this review, which includes three key aspects:

• This work introduces a conceptual framework (Figure 1) that identifies the "regulatory gap" caused by applying traditional upright seating assumptions to reclined postures.

• It connects biomechanical principles with the limitations of current restraint systems, synthesizing experimental findings and occupant kinematics to guide future research.
• The review discusses occupant protection in the context of automated and comfort-driven vehicle interiors, emphasizing the need for adaptation to non-standard configurations.

 

Comment 2: In Section 2 (Testing Protocols), there is a lack of in-depth discussion regarding the specific "Regulatory Gap," such as how current standards (e.g., FMVSS, Euro NCAP) technically circumvent testing reclined seats or the specific barriers to implementing reclined testing.

Response 2: Section 2 has been revised to clarify that current regulatory and consumer testing frameworks focus primarily on standardized upright seating conditions. These protocols rely on fixed seat designs and specific ATD positioning, along with injury criteria for upright postures, limiting evaluations of reclined configurations.

The text also addresses the technical and methodological challenges of including reclined postures in testing, and the lack of agreed-upon definitions for reclined seating configurations. These changes aim to clearly outline the regulatory gap and the limitations hindering the implementation of safety assessment protocols that include varied postures.

Comment 3: Section 3 (Biomechanical Foundations) remains somewhat theoretical; it lacks a specific sub-analysis on how recline physically alters the "Load Path" of the seatbelt from the pelvis to the abdomen.

Response 3: We thank the reviewer for this important observation. Section 3 has been revised to provide a more explicit biomechanical analysis of how reclined seating alters the load transfer pathway of the seatbelt.

The revised text explains how increased seatback recline induces posterior pelvic rotation and a more horizontal lap belt orientation, reducing effective engagement with the pelvic structure. As a result, the load path shifts from the pelvis toward the abdominal region, leading to a redistribution of forces to soft tissues and altered load transmission through the lumbar spine.

 

Comment 4: Section 4 (Experimental and Numerical Studies) is descriptive but lacks a critical comparative analysis of the discrepancies between ATD, PMHS, and HBM results, particularly regarding tissue-level injury prediction in reclined positions.

Response 4: We appreciate the reviewer’s comment. Section 4.3 has been revised to provide a clearer comparative analysis of ATDs, PMHS, and HBMs in reclined seating. The updated section details each surrogate's complementary roles and limitations. ATDs ensure consistent kinematics, while PMHS reveal injury mechanisms. Finite element HBMs connect for tissue analysis. While consistent global kinematic trends are observed across surrogate types, the revised discussion emphasizes that significant discrepancies persist in predicted injury metrics, particularly in the lumbar spine and abdominal region.

 

Comment 5: Table 1 (in Section 5) is disorganized in the current submission; the categorization of "Strategy Type" is unclear, and the table requires restructuring to effectively convey the "Problem-Solution" relationship rather than just listing studies.

Response 5: We appreciate the reviewer’s comment regarding the organization and clarity of Table 1. In response, the table has been completely restructured to move beyond a descriptive listing of studies toward a problem–solution-oriented synthesis. The categorization now reflects the primary biomechanical objectives, such as pre-crash repositioning and adaptive restraint deployment, linking safety challenges with mitigation strategies. Additionally, Section 5.3 has been revised to explain the table, highlighting how different restraint concepts address specific failure mechanisms. This improves readability and clarifies the link between biomechanical issues and engineering solutions, aligning the table with the review's goal of offering a biomechanically grounded synthesis rather than a descriptive literature compilation.

 

Comment 6: Section 5.2 (Adaptive Strategies) mentions Active Seatback Positioning (ASPA) but does not critically address the physical time constraints and feasibility of fully repositioning a seat within the short duration of pre-crash emergency braking.

Response 6: We thank the reviewer for highlighting the importance of real-world implementation constraints. In response, Section 5.2 has been revised to include a more critical assessment of the feasibility of ASPA under pre-crash conditions. The revised text highlights the challenges of fully repositioning occupants from reclined to upright during emergency braking, suggesting that partial repositioning with adaptive restraint deployment is more feasible. It emphasizes the need for coordination among pre-crash sensing, control algorithms, and restraint activation timing, framing occupant protection in reclined positions as a coupled control problem rather than just a purely mechanical repositioning solution.

 

Comment 7: The Future Perspectives section is generic; it lacks forward-looking insights into the integration of Artificial Intelligence or Machine Learning for real-time posture-adaptive restraint control systems.

Response 7: We thank the reviewer for emphasizing forward-looking perspectives. In response, we revised the Future Perspectives section to include the role of artificial intelligence and machine learning in posture-adaptive restraint systems. This update highlights AI's potential in occupant protection through state estimation, injury risk prediction, and adaptive restraint parameters, while addressing challenges like model robustness, validation under safety-critical conditions, and integration within real-time control architectures, providing a more balanced and technically grounded perspective.

 

 

Comment 8:  There is a lack of consistency and critical analysis regarding the cited literature; the manuscript includes many references from 2025 and 2026, which requires verification of their publication status and integration into the narrative.

Response 8: We appreciate the reviewer’s feedback regarding the consistency and currency of the cited literature. All references have been carefully reviewed to verify their publication status and accuracy. All contributions, including conference proceedings and early-access publications, have been updated where necessary. Furthermore, the manuscript has been revised to improve the integration and critical discussion of recent studies, ensuring that they are properly contextualized within the broader body of literature rather than simply listed.

 

 

Comment 9: The terminology is inconsistent, frequently oscillating between terms like "Reclined," "Relaxed," "Non-standard," and "Non-conventional" to describe the seating posture, which dilutes the precision of the text.

Response 9: We agree that consistent terminology is essential for clarity. The terminology used in the manuscript is intentional and reflects different levels of abstraction. "Reclined seating" describes specific seatback configurations, while "non-conventional" and "non-standard" refer to a broader range of occupant postures, including rotated, relaxed, and zero-gravity positions.

To address this concern, the manuscript has been revised to ensure consistent use and a clearer definition of these terms, thereby improving precision and readability.

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed the comments; the paper can now be accepted for publication.

Reviewer 3 Report

Comments and Suggestions for Authors

No further comments.