Review Reports - Agreement-Based Validation of ISOMETRO for Upper-Limb Isometric Tension Measurements

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper reports a calibration study of the ISOMETRO device for measuring isometric tension of the upper limb in a vertical laboratory configuration. The study used a force table as an independent calibration standard, and internal consistency verification was performed using a series of weighing sensors. The results showed excellent consistency, indicating that ISOMETRO can effectively measure the vertical tension of the upper limb under this specific experimental configuration. However, the paper has several issues that require clarification, supplementation, or revision regarding methodological details, result interpretation, graphs and data presentation, depth of discussion, and the rigor of the conclusions.

The text only states that the participants were physically active, but does not describe their specific sports activities, training frequency, or intensity. Given that the study was conducted within the framework of the rock climbing research group, this information is crucial for generalizing the results and should be supplemented.
Introduction Lines 77-86, “Isometric strength (IS) testing is widely used because it can be implemented…”, to provide more effective evidence, the authors may consider referring to the following updated relevant studies: New insights optimize landing strategies to reduce lower limb injury risk (https://doi.org/10.34133/cbsystems.0126).
The text mentions that ISOMETRO has undergone factory calibration, but does not specify whether it was recalibrated before this experiment, nor does it describe the calibration status and cycle of the force stage and the series load cells. Furthermore, the time synchronization of the three systems only mentions being based on a shared sampling frequency and a synchronization start flag, but does not specify the specific synchronization method (hardware triggering or software post-alignment). A detailed explanation is recommended.
The author correctly points out that this comparison is only used to verify internal consistency, not as an independent calibration. However, it should be explained in more detail in the discussion section: under shared mechanical pathways, even if the readings are highly consistent, they may still be affected by systematic errors (installation deviations, friction) and cannot fully represent ISOMETRO's absolute measurement accuracy for external loads.
The text mentions that the model diagnostics indicate the key assumptions are fully met and cites figures S1-S3, but these figures are not provided. Furthermore, while the text mentions the use of Shapiro-Wilk and Breusch-Pagan tests, specific test statistics and p-values are not reported. It is recommended that the key diagnostic results be fully reported in the main text or supplementary materials.
Given that the study sample consisted of 21 healthy, young, active adults and was conducted in a highly controlled, vertical laboratory configuration, the reported near-perfect concordance may not generalize to other populations (patients, older adults), other joint angles, non-vertical force directions, or non-laboratory environments. It is recommended that this limitation be more explicitly emphasized in the abstract, discussion, and conclusion.
The authors note that this study did not assess potential frictional effects associated with non-perpendicular or multi-plane loading configurations and suggest future research to explore this. This is a reasonable limitation in itself. However, it should be considered to briefly mention in the discussion that even in vertical configurations, minute static friction may exist between the guide rail and the slider, which could introduce errors at very low force levels, although this may be insignificant under the maximum force conditions of this study.
The text mentions that the test order and phase order are randomized, but it doesn't explain how randomization was achieved (whether a computer-generated random sequence, a random number table, or subjective arrangement by the researcher was used). It is recommended to provide additional details to enhance the reproducibility of the method.
The article mentions that any attempt to show visible compensatory motion or detect off-axis force on the force measuring platform will be repeated immediately until a valid test is obtained, but no objective criteria for judging off-axis force (the percentage threshold of force in the front-back or left-right direction relative to the vertical force) are given.
The discussion cites other studies based on load cells or force tables, but it would be more specific to compare ISOMETRO’s rail-slider design with the mechanical design differences of other portable or stationary devices (compared to handheld force gauges that rely on inspector stability, or to other wall-mounted systems) and analyze how this design specifically contributes to reducing variability and improving consistency.

Author Response

Please see the attached document for our detailed point-by-point responses to the reviewers’ comments.

All suggested revisions have been carefully addressed, and the corresponding changes have been incorporated into the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a carefully designed agreement-based validation of the ISOMETRO system under a clearly defined and mechanically constrained vertical traction configuration. The study is methodologically rigorous, statistically well-structured, and commendably transparent in distinguishing between independent criterion validation (force plate) and internal measurement-chain verification (in-series load cell). The authors demonstrate appropriate restraint in their conclusions and provide a thoughtful discussion of the device’s scope and limitations. Overall, the manuscript reflects strong experimental control, analytical maturity, and conceptual clarity.

Below are several minor comments intended to further strengthen the manuscript.

Introduction

The introduction provides a comprehensive overview of isometric strength assessment tools and clearly positions the need for mechanically standardized upper-limb tensile testing.

The authors may also consider acknowledging recent work applying self-supervised learning approaches to sensor-derived performance signals in sports science, such as the study Self-Supervised Gait Event Detection from Smartphone IMUs for Human Performance and Sports Medicine (Appl. Sci., 2025), for further contextualization within emerging sensor-based performance analytics frameworks.

Materials and Methods

The experimental setup is described in sufficient technical detail, particularly regarding mechanical alignment and calibration procedures. The use of mixed-effects modeling to account for nested data structure is appropriate and well justified.

The manuscript states that the highest peak-force value (rather than the average of trials) was retained for analysis. Although this approach is common in maximal voluntary contraction testing, a brief clarification supporting this choice would enhance methodological transparency.
Given the near-unity regression slopes observed in the results, a short clarification acknowledging the mechanically constrained vertical configuration and its implications for strong collinearity between devices could pre-empt potential interpretative concerns.

Statistical Analysis

The statistical framework is robust and appropriately implemented. The combination of mixed-effects regression, Bland–Altman analysis, CCC, ICC (2,1), SEE, and MAE provides a comprehensive assessment of agreement.

The reporting of R² values equal to 1.000 may benefit from additional decimal precision, if available, to avoid misinterpretation of perfect determinism.
The rationale for using Bland–Altman plots with proportional bias testing is well executed; no further comments here.

Results

The results are clearly structured and logically organized across overall agreement, test-specific agreement, and force-magnitude stratification. The presentation of Tables 1–3 is clear and consistent.

Figures 5 and 6 effectively illustrate agreement patterns. No major concerns are identified in this section.

Discussion

The discussion appropriately interprets the findings within the limits of the controlled laboratory configuration and avoids overgeneralization. The distinction between independent criterion validity and internal consistency is particularly well articulated.

The limitations section is thorough and appropriately acknowledges the absence of test–retest reliability assessment. No additional concerns are noted here.

Conclusions

The conclusions are appropriately conservative and remain strictly within the tested configuration. The scope limitations are clearly stated.

Overall Recommendation

The manuscript is technically sound, well written, and methodologically rigorous. The suggested revisions are minor and primarily aimed at enhancing clarity and contextual positioning. With these adjustments, the paper would represent a strong contribution to device validation research in sports biomechanics.

Author Response

Please see the attached document for our detailed point-by-point responses to the reviewers’ comments.

All suggested revisions have been carefully addressed, and the corresponding changes have been incorporated into the revised manuscript.