Validity of Force and Power Measures from an Integrated Rotary Encoder in a HandyGym Portable Flywheel Exercise Device

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript, titled " Validity of force and power measures from an integrated rotary encoder in a HandyGym portable flywheel exercise device " aims to evaluate the validity of HandyGym's portable flywheel equipment in measuring strength and power during iso-inertial training compared to conventional reference system. The study analyzed the measurement bias and error of HandyGym's rotary encoder under different load configurations by comparing its measurements with those of a standard system (MuscleLab 6000 strain gauge and linear encoder). The results of the study show that the HandyGym has some validity in force measurements, but suffers from large deviations in power measurements, especially under high load conditions, limiting its use in accurate assessment.

However, there are still some problems with this study; the paper does not clearly state the objectives of the study in the introduction and lacks elaboration on the importance of the HandyGym system and the significance of the study; the lack of background explanation of the technical details of the equipment tends to confuse the reader; the selection of the sample size, the rationale for the load configuration, and the randomization process are not sufficiently explained; and the causes of the equipment's underperformance at low loads and the suggestions for improvement are yet to be explored in depth.

Specific comments are shown below:

Lines 31-39: Exercise monitoring has become more and more important in sports training, which can effectively improve sports performance and reduce sports injuries. Among them, exercise monitoring including the risk of ACL injury is also highly valued by researchers. The authors may consider citing the following relevant studies in the description of relevant evidence: Accurately and effectively predict the ACL force: Utilizing biomechanical landing pattern before and after-fatigue (https://doi.org/10.1016/j.cmpb.2023.107761)

Lines 59-72: While the introduction touches on the importance of monitoring training loads and the potential of isoinertial training systems, it would be beneficial to clearly outline the objectives of this particular study earlier in the introduction. Clearly state why evaluating the HandyGym system is important, and what gap it fills in the existing literature.

Lines 73-77: Some technical descriptions, like the distinction between cylindrical and conical shafts, need additional context to make it clear why these details are relevant to the study. Ensure that the audience, especially those less familiar with isoinertial systems, can follow these points.

Lines 100-110: While the participants’ characteristics are outlined, it would be beneficial to specify inclusion and exclusion criteria in more detail, such as any specific physical or health conditions that were considered. Additionally, justify the sample size used (n=10), particularly in terms of its statistical power and whether it is adequate to detect meaningful differences between the devices.

Lines 157-161: Although the load configurations are listed, provide context or reasoning behind selecting these specific configurations. Explain why these loads represent the full range of resistances and how they relate to practical applications in training scenarios.

Lines 170-174: You mention that load configurations were tested in a randomized order. Clarify the randomization process used (e.g., how the randomization was conducted) to ensure there was no bias in the order of load testing, which could affect performance.

Lines 200-215: The description of data processing in R software is concise but could benefit from further explanation, particularly regarding how phases of movement were detected and verified. Consider specifying any thresholds or criteria used in the custom R routine for phase identification.

Lines 170-174: The article mentions the poor accuracy of the HandyGym under low load conditions, especially in force and power measurements. It is suggested that the authors delve into possible physiological or mechanical causes, such as increased control difficulty due to lower inertia and imprecise phase transitions, and suggest possible improvements.

Lines 324-368: Specific optimization suggestions for the deviation patterns of power measurements under different load conditions are suggested in the discussion, e.g. improving the encoder design of the device or optimizing the data processing using algorithms to improve the reliability of the measurements.

Comments on the Quality of English Language

none

Author Response

A point by point response has been added in "word" .docx format (attached).
We greatly appreciate your time and effort to review our work.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for submitting your manuscript entitled "Validity of force and power measures from an integrated rotary encoder in a HandyGym portable flywheel exercise device". The objective of your study to validate a portable, affordable exercise device for measuring force and power during exercise is timely given the growing interest in real-time performance monitoring.

The manuscript focuses on the validation of an exercise technology (HandyGym) used to measure force and power during iso-inertial exercise, which is consistent with the journal's focus on Applied Sciences, including applied physics and biomechanics. It fits well with the multidisciplinary approach of the journal. In addition, it aligns with bioengineering, biomechanics, and biosignal processing, particularly with its focus on using technology to measure aspects of performance, which fits with the section's focus on new developments in bioengineering applications. Finally, this study contributes to the understanding of performance aspects by evaluating force and power in a sports training device, which fits well with the special issue on biomechanics and technology in sports.

While your manuscript has many strengths, several areas require refinement to fully meet the journal's standards and the goals of the special issue. By addressing the concerns outlined below, the manuscript could be significantly improved and positioned as a state-of-the-art review. The key areas for revision are as follows:
A. While the manuscript provides adequate background on isoinertial training and flywheel systems, it would benefit from a deeper exploration of competing devices and technologies. Expanding the literature review to include comparisons with similar wearable devices or technologies would more clearly contextualize HandyGym's novelty and potential market positioning. Along the same lines, adding more recent references to advances in sports technology and validation studies would also enhance the scientific depth of the manuscript.

B. The authors correctly identify systematic biases in the device's power and force measurements but could provide more detail on why these discrepancies occur. For example, a more detailed discussion of the mechanical limitations of the HandyGym (e.g., friction, gear ratios, internal calibration issues) would provide a clearer understanding of how these biases could be mitigated in future device iterations.

C. In addition, potential user-induced variability (e.g., differences in braking techniques during the eccentric phase) should be discussed more thoroughly, especially given its significant impact on force and power measurements. This would be critical for readers intending to implement this device in professional or rehabilitation settings.

D. The practical applications section could be expanded to provide more concrete recommendations on how users (e.g., coaches, and therapists) should interpret the device's results given its biases. Currently, the manuscript suggests the use of force measures rather than power, but it could provide more actionable advice for real-world applications, such as suggested correction factors or specific scenarios in which the device would be appropriate.

E. The implications for athletes and coaches in terms of accuracy limitations should be clearly stated to avoid misinterpretation of the device's results, especially in high-performance settings where accuracy is critical.

F. Although the sample size of 10 participants is acceptable for an initial validation study, the generalizability of the findings is somewhat limited. The authors should acknowledge that a larger sample size, including participants from different athletic backgrounds, could strengthen the external validity of the results. This limitation could be highlighted in the discussion and suggestions for future research.

G. While the results are clearly presented, additional visual aids or improved labeling of existing graphs would improve clarity. For example, figures could benefit from clearer axis labels and explanatory notes that guide the reader through the data interpretation process.

H. The Bland-Altman plots, while informative, could be accompanied by a more intuitive explanation of the biases and errors they reveal. This would be helpful to readers who may not be familiar with these statistical tools.

I. The authors mention the potential for regression-based correction equations to improve the instrument's measurement validity. However, providing a preliminary correction formula or suggestion would greatly enhance the practical utility of the manuscript.

J. In addition, suggesting areas for future research, such as improvements in device calibration or studies comparing the HandyGym to other portable devices, would round out the discussion and signal the manuscript's contribution to ongoing technological development in the field.

K. Other aspects of the manuscript require attention and correction to ensure scientific rigor and clarity. I provide detailed feedback on these points below:
1. In several instances throughout the manuscript, you report p-values as p=0.000. This is not appropriate because it suggests a level of precision that is unrealistic. Instead, when p-values are extremely small, they should be reported as <0.001. This is a widely accepted standard in statistical reporting and ensures that results are accurately reported without implying an exact value of zero.
2. The manuscript mentions the use of the R software package (v. 4.4.1) for statistical analysis, but this is not properly cited according to International Committee of Medical Journal Editors (ICMJE) guidelines. When referencing software or computational tools in a scientific manuscript, it is important to provide a formal citation.
3. Throughout the manuscript, figure captions or section headings may appear at the bottom of one page while the corresponding figure or section begins on the next page ("orphaned" titles). Ensure that all figure captions and section headings appear on the same page as the associated content (figure or text). This may require reformatting the document to eliminate orphaned titles and improve the overall readability of the manuscript.
4. The tables in the manuscript are critical to understanding the results, but may require additional clarification to ensure that readers can easily interpret the data. Some of the column headings, such as "Bias," "TEE," and "Correlation," may not be immediately clear to all readers, especially those less familiar with these metrics. Please consider adding explanatory footnotes to each table, defining key terms and explaining how certain metrics (e.g., "Typical Error of Estimation") should be interpreted. This will help make the tables more accessible to a broader audience and enhance understanding.
5. It should be noted that the manuscript reports 90% confidence intervals in several places. While confidence intervals provide valuable information about the precision of the estimates, it is more common in scientific studies to use 95% confidence intervals because they provide a more conservative and widely accepted measure of uncertainty. Unless there is a specific justification for using 90% confidence intervals, it is recommended that you recalculate and present the results using 95% confidence intervals, which is the standard in most scientific research. If 90% confidence intervals were chosen for a specific reason, please explain the manuscript to clarify this choice.

L. Additional suggestions for improvement: the manuscript follows appropriate ethical guidelines and informed consent was obtained from participants. However, the transparency of the data analysis could be improved by making the raw data or the custom R code used for the analysis available in a public repository. This would be in line with modern standards of scientific transparency and reproducibility.

Attention to the above will greatly enhance the manuscript's scientific rigor, presentation quality, and adherence to established publication standards. Addressing these issues will ensure that the manuscript meets the high standards expected by the journal and its readership.

Comments on the Quality of English Language

Overall, the quality of the English is quite solid, with no major errors, but a few refinements would make the manuscript more polished and easier to read.
Some sentences, while grammatically correct, could be rephrased for better readability. Some sections are dense and could benefit from simpler sentence structures to improve flow. Shortening some sentences or breaking them into smaller ones could make the manuscript easier to follow, especially for international readers. For example, in the Methods section, some sentences describing the experimental setup are long and technical. Breaking these into smaller, more digestible pieces would improve readability.
There are occasional instances of inconsistent formatting (e.g., bold text in line 43) or minor typographical errors that should be corrected for consistency. In addition, the manuscript frequently uses the passive voice, which is acceptable in scientific writing but can sometimes obscure the clarity of the actor. Changing some of these sentences to active voice, where appropriate, could make the manuscript more direct and engaging.
Some word choices may benefit from refinement for precision or clarity. For example, in some cases, synonyms could be replaced with terms more commonly used in scientific discourse.
Finally, I recommend a final round of professional English editing to ensure that the manuscript flows smoothly and that any minor grammatical or typographical issues are resolved. This could also help to polish the language and eliminate any awkward phrasing.

Author Response

A point by point response has been added in "word" .docx format (attached).
We greatly appreciate your time and effort to review our work.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Specific comments: The article presents an interesting opportunity to expand information about the context. Nevertheless, it is imperative to take into account a number of variables:

The Abstract is competently written and provides a lucid overview of the study's methodology and findings.

The Introduction is well-written and presents a clear definition of the problem. Nevertheless, I propose the deletion of the sentence in lines 91-93: “To this end, the measurements obtained with the device were compared with those from a criterion reference system, which includes an electrodynamometer and a linear encoder” as it represents a description of a methodological step.

 

Material and Methods

Participants

Line 100 states that “Ten young volunteers (3 women and 7 men …)”. Has the sample number or power of the sample been calculated? Please include this information.

It would be beneficial to provide further clarification regarding the inclusion criteria. For instance, it would be helpful to know why the volunteers were recruited from the TecnoCampus-Mataró (Pompeu Fabra University) and why they had to be students.

It is recommended that the phrases in lines 105-107 (“…Detailed written information and verbal instructions were provided to all participants prior to the commencement of the testing, and each participant signed an informed consent form.) and 109-110 (“The study protocol was approved by the Ethics Committee of the Tecnocampus Mataró-Maresme Foundation (CEI 5/2022)”) be combined and placed in the sequence of the method, or alternatively, an Ethics item be inserted.

Furthermore, I propose that the sentence in lines 107 to 109 (A familiarization session, lasting approximately 15 minutes, was conducted before data collection to ensure proper execution technique and understanding of the measurement systems) be incorporated into the item "Study design."

It would be prudent to eliminate the sentence in lines 140-141 from the text (“The authors were unable to find further technical details regarding the encoder”).

Line 167 indicates that the evaluations were conducted at the Laboratory of Technological Innovation, strength and functional assessment (LabIT). It would be advisable to specify whether the conditions were established at the time of testing, such as temperature, humidity, and the time of day.

Should the entire name of the laboratory not be presented in capital letters?

Line 169 states that “The session began with a standardized warm-up and familiarization period (10-15 minutes)...”. Please provide more details on how the warm-up was carried out.

 

Results:

The results are well presented and described but could be improved.

It would be reasonable at table 2, to place the unit of measurement (N) adjacent to the row of the variable (Criterion measure (MuscleLab) and (Practical measure (HandyGym)) rather than in every row of the table. The same recommendation applies to table 3, unit of measurement (W).

It appears that the third line of Table 2 has a different font color. Please review and confirm.

It is recommended that the title of table 2 should just be “Comparative analysis between criterion (MuscleLab) and practical (HandyGym) force measures”. The remaining text (lines 234-239) should be incorporated into the Results section, rather than appearing as a table title. The same recommendation applies to table 3, line 264.

Figures 3 and 4 require reformatting, as the current presentation hinders the ability to discern the written information.

 

Discussion:

          Discussion offers valuable insights and reflections on the findings presented. However I have some notes.

It would be advisable to commence the discussion with the primary findings, including the first sentence within the sequence (“A certain level of bias … parameters being assessed [24,26,37]”. Furthermore, I propose the removal of the aim, given that it is already established.

 

Conclusions and Practical applications: are well described and consistent with the evidence and arguments presented

 

References: Most of them are current and relevant to the topic.

Author Response

A point by point response has been added in "word" .docx format (attached).
We greatly appreciate your time and effort to review our work.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All comments have been addressed.

Comments on the Quality of English Language

none

Author Response

Dear reviewer,

Thank you very much for your valuable feedback and insightful comments. We sincerely appreciate the time and effort you dedicated to reviewing our work, which have undoubtedly helped improve the quality and clarity of the manuscript.

Best regards,
The Authors

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

First, I would like to congratulate you on the substantial improvements made to your manuscript entitled "Validity of force and power measures from an integrated rotary encoder in a HandyGym portable flywheel exercise device". Your efforts to address the feedback provided have greatly improved the overall quality and clarity of the study.

The expanded literature review and detailed discussion of the discrepancies in force and power measurements, as well as the adjustments to the Bland-Altman plots, are particularly commendable. These changes help to contextualize your findings and provide a clearer understanding of the strengths and limitations of the device. However, I would like to request a few final adjustments to further refine the manuscript:
1. Practical Applications section: While this section has been expanded, it would benefit from more concrete recommendations for practitioners. Specifically, adding correction factors or practical advice on how to adapt the results in real-world settings would improve the applicability of the manuscript.
2. Correction formulas: Since you mention the possibility of regression-based corrections to improve measurement accuracy, providing a preliminary correction formula or suggestion would significantly increase the practical utility of your work for coaches, therapists, and researchers alike.
3. Language Review: Although the manuscript is written in clear English, a final review for minor grammatical issues and sentence flow would ensure even better readability and overall presentation.

Again, congratulations on your work so far. With these minor revisions, I believe your manuscript will be an excellent contribution to the field. Please feel free to contact me if you have any questions, and I look forward to seeing the final version.

Comments on the Quality of English Language

The English used in the manuscript is generally clear and understandable, but there are areas where readability and flow could be improved. Some sentences are overly complex and could be simplified for clarity. There are also occasional minor grammatical issues, such as missing articles or inconsistent verb tenses. Proofreading the manuscript for smoother transitions between ideas and correcting minor errors would improve its overall quality.

I recommend a thorough revision of grammar, sentence structure, and style to ensure a more polished and professional presentation of the content. It may be helpful to have a native English speaker or professional language editing service review the manuscript before final submission.

Author Response

Dear reviewer,

Thank you very much for your valuable feedback, which has undoubtedly helped to further improve the quality and clarity of our work. In response to your comments, we have added more specific instructions in the Practical Applications section, allowing readers to utilize the regression equations to calculate criterion force values. These changes have been highlighted in red.

Additionally, a native English-speaking colleague has thoroughly reviewed the language throughout the manuscript. While these language revisions are not marked in color, they have improved the consistency and simplified overly complex sentences.

We hope that with these revisions, we have addressed all your suggestions, and we sincerely appreciate your help in enhancing our manuscript.

Best regards,
The Authors

Reviewer 3 Report

Comments and Suggestions for Authors

I am grateful for the opportunity to provide further information and for my initial comments to have been taken into account.

The changes and clarifications made by the authors have considerably enhanced the quality and presentation of the article.

Author Response

Dear reviewer,

Thank you very much for your valuable feedback and insightful comments. We sincerely appreciate the time and effort you dedicated to reviewing our work, which have undoubtedly helped improve the quality and clarity of the manuscript.

Best regards,
The Authors