All reviews of published articles are made public. This includes manuscript files, peer review comments, author rebuttals and revised materials. Note: This was optional for articles submitted before 13 February 2023.
Peer reviewers are encouraged (but not required) to provide their names to the authors when submitting their peer review. If they agree to provide their name, then their personal profile page will reflect a public acknowledgment that they performed a review (even if the article is rejected). If the article is accepted, then reviewers who provided their name will be associated with the article itself.
Thank you for your revised submission. I am satisfied that you have addressed the concerns of the reviewers, and am happy to accept your paper for publication.
[# PeerJ Staff Note - this decision was reviewed and approved by Celine Gallagher, a PeerJ Section Editor covering this Section #]
**PeerJ Staff Note:** Although the Academic and Section Editors are happy to accept your article as being scientifically sound, a final check of the manuscript shows that it would benefit from further editing. Therefore, please identify necessary edits and address these while in proof stage.
Apologies for the duplicate email, we are troubleshooting your inability to resubmit.
**PeerJ Staff Note:** Please ensure that all review, editorial, and staff comments are addressed in a response letter and that any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.
**Language Note:** The review process has identified that the English language must be improved. PeerJ can provide language editing services - please contact us at [email protected] for pricing (be sure to provide your manuscript number and title). Alternatively, you should make your own arrangements to improve the language quality and provide details in your response letter. – PeerJ Staff
This is a well-informed review. However, please illustrate how the articles were filtered down to 37 using a flowchart.
-
-
To improve the transparency and reproducibility of the review, it is recommended to clearly define the search keywords used to identify relevant literature.
This manuscript provides a significant and comprehensive contribution to the literature on multi-component exercise in diabetes management. With the recommended enhancements in clarity, interpretation of heterogeneity, and practical implications, this manuscript will be well-prepared for submission to PeerJ. These amendments will enhance scientific rigor and ensure better alignment with the journal's publication standards and expectations.
Section-by-Section Comments:
Abstract
1) Line 32: To clearly indicate the study design, add the phrase “randomized controlled trials (RCTs)” after “systematically searched”.
2) Line 38: Include a brief statement about the clinical significance or implications, such as “These findings could inform practical exercise recommendations for diabetes management.”
Introduction
1) Lines 50-52: Provide a brief summary by citing recent systematic reviews or meta-analyses that specifically address multi-component exercises in diabetes, highlighting existing research gaps.
2) Lines 65-67: Explain why multi-component exercise is beneficial; describe how different exercise modalities can work together to produce a synergistic effect when compared to single-exercise modalities.
Methods
1) Lines 102-104: Clearly state the nature of "Comparison" in the PICOS criteria, and define the control or minimal activity groups.
2) Line 125: Include a sentence outlining how discrepancies between independent researchers during data extraction were resolved.
3) Lines 140-142: Briefly describe the criteria used for sensitivity analysis, such as the exclusion of low-quality studies or studies with significant heterogeneity.
Results
1) Lines 178-182: Provide a brief explanation of the high heterogeneity observed in fasting blood glucose results.
2) Line 204: To ensure clarity and completeness, specify the exact number of studies involved in each subgroup analysis.
3) Lines 215-217: Verify the consistency of abbreviations (e.g., HDL, LDL, TG) throughout all figures and tables.
Discussion
1) The discussion of mechanisms (e.g., GLUT-4, mitochondrial adaptations) is extensive; however, provide brief commentary on practical implications, particularly patient adherence and the feasibility of multi-component exercise interventions.
2) Lines 265-268: Increase practical relevance by discussing potential barriers or facilitators of patient adherence to multi-component exercises.
3) Line 290: Clearly acknowledge the limitations of differences in exercise intensity reporting across included studies and recommend standardization in future research.
4) Line 312: Provide specific recommendations for future research, such as “Future trials should clearly report exercise intensity and adherence measures to improve study comparability.”
Figures and Tables
1) Figure 4 (Forest Plot): To improve readability, clearly label subgroup analyses as "(A) Exercise frequency" and "(B) Exercise duration" within the plot.
2) Figure 11 (Funnel Plot): Clarify the legend by including a brief sentence summarizing the implications for publication bias.
References
Lines 400–520: Verify and correct inconsistencies in reference formatting to adhere strictly to PeerJ guidelines (e.g., correct journal abbreviations, punctuation consistency).
Overall, the English language used in the manuscript is sufficient. However, the background and context could be expanded to better highlight the novelty and rationale of the study. Additionally, tables and figures would benefit from improved consistency/formatting, as there are several discrepancies in style and reporting. Finally, based on the PROSPERO registration, there appear to be some slight deviations from the original protocol that should be clarified.
The research question is defined, although somewhat broad, and the inclusion of quality of life as an outcome, mentioned in both the PROSPERO registration and manuscript text, is not presented in the analysis. The authors should emphasize how this work fills a specific knowledge gap in the existing literature in the introduction. Additionally, the quality of the methods used for this SRMA could be improved, particularly regarding the search strategy and justification of statistical analyses.
I believe this work remains valuable, but the novelty is not as strong as it could be. The data are clearly presented, and the conclusions are generally well supported by the findings.
General comments:
This meta-analysis explored the effects of multi-component interventions on various health outcomes in people living with type 2 diabetes, including 37 articles and more than 3,200 individuals. Overall, this is an interesting contribution, but the authors may need to better highlight the novelty of their research. It is well established from various RCTs and/or SRMA that exercise improves several cardiometabolic health components (e.g., A1c, VO2 max, blood pressure, etc.). Therefore, adding more “volume” or different types of exercise would be expected to lead to similar or even greater improvements. I believe that including a comparison between multimodal and unimodal interventions could have added more value to the present study. I still find this work valuable, but the authors need to ensure that the greater impact of multimodal interventions is not simply due to higher total exercise volume. This could be addressed in the introduction, through additional subgroup analyses and meta-regressions, and discussed in more detail in the discussion section.
Specific comments:
At line 303, the authors use the term non-diabetic individuals. I suggest using more inclusive, person-first language, such as: “…higher than in people not living with type 2 diabetes.”
There is also some inconsistency in the formatting of citations. In most cases, there is no space between the reference and the preceding word. Additionally, some references—for instance, the first one in the introduction (line 42)—do not include the authors’ names, only the year. I recommend that the authors carefully revise all references to ensure accuracy/consistency.
Abstract
The abstract is overall well written and to the point. I understand that by presenting the 95% confidence intervals, the reader can infer that each outcome is statistically significant, as the intervals do not cross zero. However, some clinicians and healthcare providers may not be familiar with this concept.
Therefore, I suggest adding a brief statement at the beginning of the results section in the abstract indicating that all outcomes presented are statistically significant, or alternatively, including the individual p-values for each outcome.
At line 24, there is no space between Standard mean difference and (SMD)—this should be corrected.
Introduction:
The introduction is well written and follows a clear funnel structure. One question that readers might ask themselves is whether the benefits of multi-component programs are truly due to the combination of modalities or simply driven by a greater total volume of exercise. When total volume is matched, are multi-component interventions still superior to single-component programs? While I understand that addressing this question is beyond the scope of the present SRMA, including a sentence acknowledging that the observed benefits might be independent of total volume could help strengthen the rationale.
Methods
I appreciate that the research team registered their meta-analysis on PROSPERO. However, in the PROSPERO registration, the population is listed as individuals living with diabetes. Why were individuals with type 1 diabetes excluded from the review? Was this an intentional decision or a mistake during registration?
Additionally, quality of life is listed as an outcome in the PROSPERO registration but is not consistently addressed across the manuscript’s methods and results sections. For example, Table 2 indicates that some studies (e.g., Macdonald 2021) did include quality of life as an outcome. Please ensure that the quality of life is reported consistently throughout all sections of the manuscript.
The authors provide the search strategy in Table 1. Was this search strategy developed or verified by an experienced librarian? According to PRISMA guidelines, search strategies should be tailored for each database, as MeSH terms and Boolean operators can differ. If this was done, please clarify and provide the individual search strategies per database. If not, consider acknowledging this as a potential limitation.
Regarding the flow diagram (Figure 1), although most key information appears to be included, following the PRISMA flow diagram template more closely could improve clarity and help the reader follow the screening process more easily.
Lines 128 to 130: The authors wrote, “Additionally, I² was used to assess the degree of heterogeneity; if I² > 50%, a random-effects model was used, otherwise a fixed-effects model was applied if the heterogeneity was low or unclear.” Model selection should be guided by conceptual reasoning first, rather than relying solely on statistical thresholds. A random-effects model accounts for between-study variability, which is almost always present, especially in exercise interventions, where study duration, intervention type, and population characteristics (e.g., sex, age, comorbidities) differ considerably. I would argue that a random-effects model should be applied to all analyses unless there is a strong justification for assuming homogeneity. Moreover, I² = 50% is only a rule of thumb, and using a strict cutoff (e.g., 49% = fixed effects; 50% = random effects) may not always be appropriate.
While the authors report the I² to assess heterogeneity, this metric primarily indicates the proportion of variance due to between-study differences rather than providing a direct measure of true heterogeneity. A more informative approach would be to include prediction intervals as well, which offer valuable context regarding the expected range of true effects. I highly recommend considering this addition to improve the interpretability of the findings. For further guidance, Dr. Borenstein provides an excellent explanation in this video:
https://www.youtube.com/watch?v=kXGY0_pKc8w&ab_channel=Meta-Analysis.
That said, I am unsure whether this flexibility is possible within RevMan.
Line 143–144: The manuscript states that “gender proportion” was reported, but refers to male and female categories. This appears to reflect reporting of sex, not gender. Please revise accordingly.
Results
Overall, the results section is well written. It could be more succinct in some areas, but it includes all necessary information. Lines 169–170: The authors state that significance is determined because the forest plot does not cross the zero line. Please also report the p-values to clearly support this.
For the A1c outcome, please double-check the values reported for Kadoglou 2012. The SMD is listed as 3.02, which is markedly higher than in all other studies.
Minor formatting issues remain in the forest plots: a) Inconsistencies in spacing between authors’ names and the publication year; b)Differences in capitalization (e.g., some author names are fully capitalized, some not); c) Some references include first names, while others don’t. Please revise all references for consistency and proper formatting.
I appreciate that the authors explored the influence of intervention frequency and duration. Estimating total exercise volume (frequency *session duration) could offer an even clearer understanding of the intervention’s impact. Although not mandatory, this would be a valuable addition. A meta-regression using total volume would offer a more nuanced, continuous analysis compared to subgroup comparisons based on frequency alone.
Similarly, meta-regression analyses exploring the influence of age, time since diagnosis, and BMI would strengthen the manuscript. These factors may influence the effect of exercise on cardiometabolic outcomes in people with T2D.
As mentioned earlier, quality of life is identified as an outcome in the PROSPERO registration, introduction, and methods, but it is not reported in the results section. If no included studies assessed this outcome, it should still be mentioned explicitly in the results, as this highlights a gap in the literature.
Discussion
The discussion is generally well organized and covers a wide range of outcomes. However, it could benefit from deeper interpretation and explanation of findings. Currently, the authors relate their results to the existing literature but rarely explore potential mechanisms/reasons for the observed effects. For example, a more in-depth discussion about the role of total exercise volume would strengthen the rationale and better contextualize the finding.
Along those lines, the authors cite the study by Sigal et al. (2007), stating that the combined intervention had twice the impact on A1c compared to aerobic training, and attribute this to greater muscle mass activation and GLUT4 translocation. However, in Sigal’s study, the combined group performed double the total exercise volume, which likely contributed to the greater A1c reduction. This should be clarified, as the volume difference may be a more likely explanation than the activation of additional muscle groups alone.
Conclusion
Overall, the conclusion supports the findings of the present study. The conclusion notes that age should be considered in intervention design. Since age data are available, I recommend conducting a meta-regression on age. If age significantly moderates the effect of the intervention on certain outcomes (e.g., a1c), the conclusion could be more impactful.
All text and materials provided via this peer-review history page are made available under a Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.