-->PONE-D-25-62980-->-->Understanding the “how” and “why”: a mixed methods process evaluation for the PRO-HIIT intervention-->-->PLOS One

Dear Dr. Liu,

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Academic Editor

PLOS One

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Reviewers' comments:

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Reviewer #1: Partly

Reviewer #2: Yes

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Reviewer #1: N/A

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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-->5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1:  General comments to the authors

The manuscript is nicely written, and the topic is valuable and important. However, I have a few major concerns which should be addressed.

First, and the most important one, is the definition of the training program studied. Namely, HIIT is rather strictly defined training program which is used with the main purpose of increasing VO2max (Buchheit & Laursen, 2013). The main acute physiological stimulus required to enable adaptation is time spent ≥90% VO2max/HRmax (Buchheit & Laursen, 2013). To enable attainment and maintenance of intensity which would elicit VO2 and HR responses above 90% of their respective maximal values, the exercises used are often cyclic in nature and the intensity is strictly prescribed through velocity (for running) or power (for cycling) defined through some kind of progressive incremental test. While other body weight cyclic exercises (like the ones you used in your study) can lead to high level of intensities, the intensity is hard to prescribe and control (monitor) for. Therefore, these exercises are not used for HIIT as they are usually not able to elicit the appropriate level of intensity nor they can enable maintenance of that intensity for, for example, 5 minutes (which is proposed as the low threshold for acute physiological response to HIIT). Of course, your other references (like #19), point out that you very well know all this stuff. My main suggestion here is, therefore, to “rename” the training program so it is clear from the get-go that body-weight cyclic exercises were used in the training program, and not the actual HIIT. This could be addressed in the title and throughout the manuscript.

Secondly, it is unclear whether you have and how you assessed HRmax? The 20 m shuttle run test was mentioned in the Discussion section; however, it was not mentioned in the Methods. So, did you perform the 20mSRT or any other maximal incremental aerobic test to establish HRmax?

Thirdly, some of the instruments used to assess, for example, enjoyment, were not supported by references. So, what instruments were used? Were they validated? References to support their validity and reliability. Overall, there are number of variables presented in the manuscript for which we do not know how they were measured.

Finally, I think that the manuscript can be defined as professional paper at best, as no quantitative or appropriate qualitative analysis was performed. It was probably due to the low number of participants included in the focus groups and interviews. Unfortunately, this is the main drawback of the study. Even though you conducted a large-scale intervention which engaged large number of participants, the overall data collected was just not enough for making and firm conclusions. We did not learn much from the study.

Specific comments to the authors

1. Line 129: Something is wrong here.

2. Line 233: Remove “is” or “was” from the sentence.

3. Line 303: “May be too long” should be here.

4. Line 425-427: I would disagree that there is no consensus reached about the main acute parameter which would serve as the HIIT target. Namely, time spent above 90% HRmax is currently used as proxy measure to achieve optimal cardiorespiratory stimulus during HIIT (Buchheit & Laursen, 2013).

5. One of the conclusions was that dose fell slightly below the minimum. How did you select the minimum (i.e., 5 times/week)? Why would you think that this is the minimum? Reference?

6. Results section should be shortened drastically as no firm conclusions can be made based on all these individual responses presented.

Buchheit, M. & Laursen, P.B. (2013). High-intensity interval training, solutions to the programming puzzle. Part 1: Cardiopulmonary emphasis. Sports Medicine, 43(5), 313-338.

Buchheit, M. & Laursen, P.B. (2013). High-intensity interval training, solutions to the programming puzzle. Part 2: Anaerobic energy, neuromuscular load and practical applications. Sports Medicine, 43(10), 927-954.

Reviewer #2:  Dear Authors,

Thank you for submitting this manuscript that presents a mixed methods process evaluation of the PRO-HIIT intervention within a Chinese secondary school setting. I commend the authors for moving beyond simple efficacy testing to explore the "black box" of intervention implementation. The application of the Medical Research Council (MRC) guidance provides a robust theoretical framework for this study, and the honesty regarding implementation barriers, such as weather and conflicting school schedules—adds significant ecological validity to the work. The findings regarding the trade-off between intervention fidelity and student autonomy are particularly insightful for the field of pediatric exercise science. However, to strengthen the manuscript and ensure it meets the highest standards of reporting, I have identified specific areas requiring clarification and refinement.

In the Methods section, regarding the qualitative component, you note on lines 214–218 that two student focus groups (n=9 total) and one teacher focus group (n=2) were conducted. While mixed methods research often relies on smaller qualitative samples, you must explicitly address whether data saturation was achieved with this sample size. With only two teachers interviewed, it is crucial to justify how this represents the broader experience of the staff involved, or acknowledging this as a limitation in capturing the full breadth of the "teacher experience." Furthermore, on line 148, you mention peer coaches were trained to lead sessions. Given that "peer coaches" emerged as a facilitator in your results, the Methods section requires more detail on the specific content and duration of their training. Did the peer coaches receive specific instruction on the SAAFE principles? Providing this detail is essential for replication.

Regarding the data analysis and results, there is a minor typographical error on line 233 stating "The coding is was initially deductive," which requires correction. More substantially, in the Fidelity section (lines 262–267), the presentation of heart rate (HR) data requires precision. You state that 18% of HR measures met the 80% HRmax threshold, yet the mean peak HR was 85% HRmax. It is important to clarify if the "18%" refers to the total time spent above the threshold or the percentage of individual data points collected that were above the threshold. If students are reaching a peak of 85% but the average is 71%, this suggests the interval peaks are high but recovery is substantial. Please ensure the distinction between "time spent at intensity" versus "peak intensity achieved" is explicit, as this speaks directly to the physiological stimulus delivered.

In the Discussion section, the interpretation of the results is generally sound and well-contextualized. However, the discussion regarding the "Repetition of HIIT workouts" (Line 372) as a barrier could be deepened. You mention that students found it monotonous, yet retention was high. It would be valuable to discuss this paradox further. Does the social element or the peer-coaching aspect mitigate the boredom of repetitive exercises? Additionally, on line 424, you suggest the intensity might be "slightly lower than expected." I would argue that for a school-based, peer-led intervention, a mean HR of 71% HRmax is actually quite successful. You might frame this more positively as a demonstration of feasibility in a non-laboratory setting, rather than a failure to meet strict laboratory HIIT criteria which are often unrealistic in schools.

Finally, regarding the "Unintended Consequences" (Line 196 and 363), you list the school-wide sports event disrupting dosage as an unintended consequence. In the context of process evaluation, this is perhaps better categorized strictly as a contextual barrier or implementation failure rather than an "unintended consequence" of the intervention itself (which usually refers to adverse events or unexpected positive side effects). Reconsidering this categorization might align better with the MRC framework's intent. Addressing these points will clarify the contribution of this work to the field of implementation science in youth physical activity.

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Reviewer #2: Yes:  Alston Choong

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-->PONE-D-25-62980R1-->-->Understanding the “how” and “why”: a mixed methods process evaluation for the PRO-HIIT intervention-->-->PLOS One

Dear Dr. Williams,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by May 21 2026 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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We look forward to receiving your revised manuscript.

Kind regards,

Esedullah Akaras

Academic Editor

PLOS One

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1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.-->

Reviewer #1: (No Response)

Reviewer #2: (No Response)

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #1: Yes

Reviewer #2: Yes

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-->5. Is the manuscript presented in an intelligible fashion and written in standard English?

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-->6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1: Thank you very much for your response to my comments and for making certain amendments to the new version of the manuscript with the aim of accepting my suggestions. I understand that some of my suggestions were hard to accept, considering the fact that you already have extensive list of publications in which this type of training has been designed and investigated. However, I do not agree with some of your comments made. Anyway, I recommend acceptance of the manuscript as you probably would not be willing to change your mind in accordance with my proposals.

1. The control of intensity during HIIT (but real HIIT) in school-based settings is not unfeasible. I do it all the time and it works perfectly if running is the exercise modality.

2. The fact that “body-weight, multi-joint, cyclic activities are commonly adopted in school interventions and have been widely used in previous school-based HIIT research” does not mean that they are better or that they are optimal.

3. The criterium of time spent ≥90% VO2max is widely accepted criterium and it is recognized as a key physiological stimulus with physiological rationale backing it up (Odden et al., 2024; Molmen & Ronnestand, 2024). There are other references as well, of course. Other criteria are arbitrarily defined and that is why they are inferior to the one mentioned above.

Odden, I., Nymoen, L., Urianstad, T., Kristoffersen, M., Hammarström, D., Hansen, J., Mølmen, K.S., & Rønnestad, B.R. (2024). The higher the fraction of maximal oxygen uptake is during interval training, the greater is the cycling performance gain. European Journal of Sport Science, 24(11), 1583-1596.

Mølmen, K.S. & Rønnestad, B.R. (2024). A narrative review exploring advances in interval training for endurance athletes. Applied Physiology, Nutrition, and Metabolism, 49(7), 1008-1013.

4. Even though your primary aim was not to assess physiological adaptations, the training program investigated needs to be properly prescribed. If the program is not prescribed properly, then everything else is false. All results presented in your study are basically not related to HIIT, but to some other type of training.

5. Claiming that this type of HIIT (which is not HIIT) is more feasible, or only feasible, in school-setting is wrong. Real HIIT sessions, which are optimal for improvement of VO2max which is the main health-related physical fitness component, are very easily incorporated withing school settings. Studies which claim that inferior types of HIIT are more feasible and optimal are creating “noise” in the literature and offer inferior practical solutions. HIIT is HIIT. There is no school-based HIIT literature. Or there shouldn’t be school-based HIIT literature.

6. The fact that you used 220-age to assess HRmax is unacceptable for scientific publication. Check the variability in such estimation, please. I understand that estimation is more feasible, but some things need to be done properly.

7. You claim that “It is also not feasible to retain children and adolescent participants under such high exercise intensity”. It is feasible, you just need to prescribe exercise better to make it happen. That is the main purpose of being a coach or a PE teacher. And to add to that, intensity has been recognized as the key variable for health enhancement (Schwendinger et al., 2025), so trying to make students work at higher intensity, but with keeping the RPE low, is the ultimate goal in finding the right HIIT design.

Schwendinger, F., Infanger, D., Lichtenstein, E., Hinrichs, T., Knaier, R., Rowlands, A. V., & Schmidt-Trucksäss, A. (2025). Intensity or volume: the role of physical activity in longevity. European Journal of Preventive Cardiology, 32(1), 10–19.

8. The fact that Buchheit and Laursen’s paper is over a decade old does not make it obsolete. It does not change the fact that the propositions presented do not still stand. Again, saying that there is heterogeneity in HIIT studies is making “noise” and creating confusion. However, the main issue is that no optimal practical solutions are provided when poor program designs are labeled as HIIT.

9. The ≥90% VO2max/HRmax should be accepted as the main criterium and, as I pointed out earlier, we need to find the exercise design in which time ≥90% HRmax would be maximized but lowest levels of RPE and blood lactate and highest level of enjoyment and affect. Choosing the right exercises is the first step. And the choice should not be left to students to decide.

Reviewer #2: Dear Authors,

Thank you for your revised manuscript that shows substantive efforts made to address the methodological and interpretative concerns raised during the previous peer review process. The clarification of the high-intensity interval training definition within a school-based context, as opposed to a strictly controlled laboratory environment, significantly elevates the practical relevance of the work. Furthermore, the improved reporting of the heart rate intensity thresholds and the recategorization of the school sports event as a contextual barrier rather than an unintended consequence enhance the precision and transparency of the process evaluation narrative. The expanded limitations section appropriately contextualizes the small qualitative sample size, ensuring the findings are interpreted with suitable academic caution.

Addressing the methodological descriptions of the intervention delivery, the decision to omit the SAAFE principles from the peer coach training is adequately justified in the rebuttal. However, this creates a minor gap in the fidelity assessment narrative that warrants brief discussion. If peer coaches are responsible for demonstrating and leading the exercises but are not formally trained in the supportive or autonomous principles, this lack of training directly influences the "unknown" or "low" compliance scores for those specific SAAFE domains observed in Table 1. Adding a brief sentence in the discussion section that explicitly connects the limited scope of the peer coach training to these specific fidelity outcomes would provide a more cohesive and comprehensive interpretation of the implementation barriers.

Finally, while the main text is written in clear and standard English, a meticulous review of the bibliography reveals several formatting inconsistencies and metadata extraction errors indicative of unverified reference management software output. Submitting a manuscript at this advanced stage without a thorough manual proofread of the references does not align with the rigorous publication standards expected by the journal. For instance, Reference 5 displays the journal name in all capital letters and lacks standard page numbers. Reference 37 contains a formatting anomaly in the author name, listing "K BO" instead of the correct format. Reference 35 utilizes inconsistent capitalization for the journal title, and Reference 41 is missing volume and page numbers entirely. A manual, line-by-line proofread of the entire reference list is required to ensure all citations strictly adhere to the formatting guidelines, presenting a polished and professional final manuscript. Implementing these minor adjustments will ensure the manuscript perfectly reflects the high quality of the underlying research.

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Reviewer #1: No

Reviewer #2: Yes:  Alston Choong

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-->PONE-D-25-62980R2-->-->Understanding the “how” and “why”: a mixed methods process evaluation for the PRO-HIIT intervention-->-->PLOS One

Dear Dr. Williams,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Jul 19 2026 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:-->

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• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

-->

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

As the corresponding author, your ORCID iD is verified in the submission system and will appear in the published article. PLOS supports the use of ORCID, and we encourage all coauthors to register for an ORCID iD and use it as well. Please encourage your coauthors to verify their ORCID iD within the submission system before final acceptance, as unverified ORCID iDs will not appear in the published article. Only  the individual author can complete the verification step; PLOS staff cannot  verify ORCID iDs on behalf of authors.

We look forward to receiving your revised manuscript.

Kind regards,

Esedullah Akaras

Academic Editor

PLOS One

Journal Requirements:

1. If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise.

2. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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Reviewer's Responses to Questions

-->Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.-->

Reviewer #2: (No Response)

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-->2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. -->

Reviewer #2: Yes

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-->3. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #2: Yes

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-->4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #2: Yes

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-->5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #2: Yes

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-->6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #2: Dear Authors,

Thank you for submitting the revised manuscript that has presented a highly valuable, pragmatic, and rigorously evaluated school-based health promotion study. Conducting a process evaluation using the Medical Research Council (MRC) guidance is an excellent methodological choice that provides critical context to the trial outcomes. The authors provide a robust, evidence-based rebuttal to the previous reviewer regarding the definition of High-Intensity Interval Training (HIIT) in a school setting, which is highly commendable. From the perspective of sports and exercise medicine, the assertion that pedagogical feasibility, student enjoyment, and pragmatic adaptations (such as bodyweight resistance exercises and age-based heart rate estimations) are vital for the real-world translation and scalability of public health interventions is fully supported. The authors' defense was scientifically sound and professionally articulated. The manuscript is in excellent shape; however, to ensure full compliance with the highest international reporting standards, a few minor methodological refinements have been identified that will further elevate the quality of this work.

In the Introduction, the research gap has been effectively and clearly defined. Process evaluations are indeed frequently undervalued in sports science, and the rationale for adopting the MRC framework is compelling. The transition from the overarching concept of school-based HIIT to the specific need for evaluating the PRO-HIIT implementation is logical and well-justified.

In the Methods section, the detailed mapping of the process evaluation measures to the MRC framework is a significant strength. However, a minor methodological flaw remains regarding the explicit classification of the mixed methods approach. While it is correctly stated that both quantitative and qualitative data were collected, the manuscript lacks a formal declaration of the specific mixed methods design typology employed (for instance, a convergent parallel design, an explanatory sequential design, or an exploratory sequential design). To align with the Good Reporting of A Mixed Methods Study (GRAMMS) framework, it is recommended that the authors explicitly define their mixed methods design in the Data Analysis section. A brief explanation of how and at what stage the quantitative and qualitative data were integrated to formulate the conclusions should be provided.

Furthermore, while the qualitative methodology involving focus groups and thematic analysis (using the Braun and Clarke approach) is sound, there is no explicit mention of adherence to the Consolidated Criteria for Reporting Qualitative Research (COREQ), which is the standard EQUATOR Network guideline for qualitative studies. As an actionable recommendation, the authors should insert a brief statement confirming adherence to the COREQ guidelines. In doing so, the concept of data saturation within the qualitative data subsection must be briefly addressed. Given the small qualitative sample size (nine students and two teachers), it is important to explicitly state whether thematic saturation was reached or if the findings represent an exploratory thematic overview rather than an exhaustively saturated dataset. This transparency will protect the manuscript from future methodological critiques regarding qualitative sample size adequacy.

The Results and Discussion sections are meticulously constructed. The integration of the quantitative dose-delivered metrics with the qualitative contextual barriers provides a rich, nuanced picture of school-based intervention realities. The incorporation of the previous reviewer's suggestion regarding the lack of Supportive, Active, Autonomous, Fair, and Enjoyable (SAAFE) principle training for the peer coaches is greatly appreciated. This addition provides a highly transparent and cohesive explanation for the fidelity outcomes observed in Table 1. The discussion appropriately balances the physiological ideals of HIIT with the sociological and pedagogical realities of the school environment.

In conclusion, this is a highly commendable manuscript that makes a significant contribution to the literature on physical activity interventions in adolescents. The recommendation for a minor revision is strictly to allow the authors to explicitly align their methodology section with the GRAMMS and COREQ reporting guidelines, specifically by naming their mixed methods design typology and clarifying qualitative thematic saturation, thereby ensuring full compliance with the EQUATOR Network's international reporting standards.

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-->7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Reviewer #2: Yes:  Alston Choong

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Understanding the “how” and “why”: a mixed methods process evaluation for the PRO-HIIT intervention

PONE-D-25-62980R3

Dear Dr. Williams,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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PLOS One

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-->Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.-->

Reviewer #2: All comments have been addressed

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-->2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. -->

Reviewer #2: Yes

**********

-->3. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #2: Yes

**********

-->4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #2: Yes

**********

-->5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #2: Yes

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-->6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #2: Dear Authors,

Thank you for submitting the revised manuscript that investigates the process evaluation of a school-based high-intensity interval training intervention using a mixed methods approach. It is a pleasure to evaluate this revised manuscript. The authors are commended for their thorough, rigorous, and professional responses to the previous peer review concerns. The methodological and interpretative enhancements have significantly enhanced the manuscript's scientific integrity, bringing it into full alignment with the highest international standards for sports and performance science publications.

The reviewer notes that the explicit identification of the convergent parallel mixed-methods design within the Data Analysis section successfully meets the requirements of the Good Reporting of A Mixed Methods Study (GRAMMS) framework. Furthermore, the detailed explanation of how quantitative and qualitative findings were integrated and triangulated during the interpretation stage provides excellent methodological clarity. This addition firmly establishes the rigorous analytical framework utilized to derive the study's conclusions.

The authors are also commended for their transparent handling of the constraints in qualitative reporting. By explicitly acknowledging the small qualitative sample size in the Strengths and Limitations section and by clearly framing the thematic findings as an exploratory overview rather than claiming exhaustive thematic saturation, the manuscript now accurately reflects the scope and intent of the qualitative data. This careful contextualization effectively preempts methodological critiques regarding strict adherence to the Consolidated Criteria for Reporting Qualitative Research (COREQ) guidelines, ensuring that the qualitative insights are interpreted with the appropriate academic caution.

The manuscript is now methodologically robust and scientifically sound, and it addresses a highly relevant topic in public health and physical education. The pragmatic adaptations explored within this process evaluation provide highly valuable insights for the real-world translation and scalability of school-based interventions. No further revisions are required.

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-->7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Do you want your identity to be public for this peer review?  For information about this choice, including consent withdrawal, please see our Privacy Policy.-->

Reviewer #2: Yes:  Alston Choong

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