The Effects of High-Intensity Interval Training (HIIT) on Sleep Quality in Obese Patients: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear corresponding Author, thank you for submitting your work to Obesities journal and congratulations on your research.

Brief Summary

The manuscript presents a systematic review and meta-analysis on the effects of HIIT on sleep quality in obese patients. Eight studies were analyzed in the review and six in the meta-analysis (191 participants), evaluating the effects on PSQI, ESS and AHI. The results show significant improvements in total PSQI score, in some subscales and in AHI.

General Comments

The topic is relevant and the methodology follows PRISMA guidelines but doesn't have registration in Prospero. The introduction requires more depth on the physiological mechanisms that connect obesity, poor sleep quality and HIIT.

The results present some inconsistencies, particularly in the discussion of PSQI subscales. The risk of bias assessment highlights that several studies have "some concerns" or "high risk", a limitation that would deserve a more thorough discussion, as well as the moderate-high heterogeneity in some analyses.

Specific Comments

• Lines 44-53: Elaborate on the mechanisms of obesity that influence sleep quality, it's not clear and it's a key topic of your review.
• Lines 54-67: Improve the connection between HIIT and pathophysiological alterations of sleep in obese subjects. Also specify better "which" HIIT because in this form it is definitely too generic
• Lines 232-247: Better explain the exclusion criteria of the two studies from the meta-analisys.
• Lines 269-271: Resolve the inconsistency between the forest plots of PSQI subscales and what is discussed in the text.
• Lines 309-314: Explain the high heterogeneity in the analysis of daytime sleepyness.
• Lines 343-375: Include an analysis of different HIIT protocols to identify the most effective ones, indicate if they have active or passive recoveries and the intervention time.
• Lines 394-404: Expand the discussion of methodological limitations which are not minimal.
• Lines 405-414: Add concrete recommendations for clinical practice.

The manuscript addresses an important topic but needs revisions to improve clarity, consistency and interpretation of results. I remain curious to read an improved version to give a second review

Author Response

Reviewer 1:

General Comments

The topic is relevant and the methodology follows PRISMA guidelines but doesn't have registration in Prospero. The introduction requires more depth on the physiological mechanisms that connect obesity, poor sleep quality and HIIT.

The results present some inconsistencies, particularly in the discussion of PSQI subscales. The risk of bias assessment highlights that several studies have "some concerns" or "high risk", a limitation that would deserve a more thorough discussion, as well as the moderate-high heterogeneity in some analyses.

• We would like to clarify that the review protocol has been registered with PROSPERO since 18 November 2024, under the registration number CRD42024611322. The registration record can be accessed at the following link: https://www.crd.york.ac.uk/PROSPERO/view/CRD42024611322 (Line 118-121)
• The suggestions regarding the depth of the introduction and the physiological mechanisms involved will be addressed in the corresponding specific comment
• These concerns regarding the inconsistencies in the PSQI subscales and the moderate-to-high heterogeneity in certain analyses will be addressed in the corresponding specific comments
• Regarding the risk of bias assessment, we have revised the manuscript to provide a more detailed discussion of the domains assessed using the Cochrane RoB 2 tool. Specifically, we have elaborated on studies that were judged as having "some concerns" or "high risk" in key domains such as randomization, deviations from intended interventions, missing outcome data, measurement of outcomes, and selective reporting. The revised discussion emphasizes how these methodological limitations may influence the overall certainty of the synthesized results. (Line 219-239)

Specific Comments

Lines 44-53: Elaborate on the mechanisms of obesity that influence sleep quality, it's not clear and it's a key topic of your review.

• We have revised the introduction to provide a more detailed explanation of the physiological and psychological mechanisms by which obesity influences sleep quality, including pathways involving OSA, inflammation, hormonal dysregulation, circadian disruption, and mental health comorbidities. Relevant references have also been added to support these points. (Line 44-66)

Lines 54-67: Improve the connection between HIIT and pathophysiological alterations of sleep in obese subjects. Also specify better "which" HIIT because in this form it is definitely too generic

• We have revised this section to clarify the connection between HIIT and sleep-related pathophysiological mechanisms in obesity, including its effects on adiposity, inflammation, hormonal regulation, circadian rhythm, and psychological stress. We have also specified the nature of HIIT used in the included studies, which commonly involved aerobic or resistance-based exercises performed at 80 to 95% of maximum heart rate with recovery at 50 to 70%, across various modes such as cycling, treadmill running, or circuit training. These revisions aim to avoid overly generic descriptions and provide a clearer context for the physiological rationale behind HIIT’s impact on sleep. (Line 67-90)

Lines 232-247: Better explain the exclusion criteria of the two studies from the meta-analisys.

• We have clarified that Delgado-Floody et al. (2020) was excluded due to its single-group pre-post design without a control group. Lins-Filho et al. (2024) was excluded due to participant overlap with another included publication from the same trial. Only the more comprehensive report was retained to avoid data duplication. (Line 243-252)

Lines 269-271: Resolve the inconsistency between the forest plots of PSQI subscales and what is discussed in the text.

• Lines 269–271 (in version 1) serve only to introduce Figure 5, describing it as a meta-analysis of the mean difference in PSQI subscales between the experimental (HIIT) and control groups. The detailed interpretation of the results is provided in Lines 282-300 (in version 2), which accurately reflect the data presented in Figure 5, including the direction, significance, and heterogeneity of each PSQI subscale.

Lines 309-314: Explain the high heterogeneity in the analysis of daytime sleepyness.

• We have added an explanation that the high heterogeneity observed in the ESS analysis may be attributed to differences in baseline sleepiness and HIIT protocols across the included studies. (Line 314-319)

Lines 343-375: Include an analysis of different HIIT protocols to identify the most effective ones, indicate if they have active or passive recoveries and the intervention time.

• Based on our review, the included studies applied a wide variety of HIIT protocols differing in exercise type, intensity, duration, frequency, and recovery mode. Due to this heterogeneity, we did not conduct a subgroup analysis. Moreover, we believe that the effectiveness of a given HIIT protocol likely depends on individual characteristics such as baseline fitness, comorbidities, and exercise tolerance, and therefore no single protocol can be considered universally “most effective.” Nevertheless, we have added a paragraph to the Discussion section summarizing typical features of standard HIIT routines to enhance clarity. (Line 349-355)

Lines 394-404: Expand the discussion of methodological limitations which are not minimal.

• We acknowledge that the methodological limitations in the included studies are not minimal. In response, we have expanded the discussion to more thoroughly address key limitations, including small sample sizes, heterogeneity in participant characteristics, variation in HIIT protocols (frequency, intensity, recovery type), differences in outcome measurement tools, and lack of long-term follow-up. These factors may have contributed to the variability in results and should be carefully considered when interpreting the findings. The revised paragraph now reflects these points in greater detail. (Line 411-424)

Lines 405-414: Add concrete recommendations for clinical practice.

• Concrete recommendations for clinical practice have been added to the conclusion, including suggested HIIT frequency, duration, intensity, recovery intervals, and safety considerations. (Line 426-439)

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Interesting study for the exercise method used, very topical

Introduction

Within the application, the type of HIIT referred to must be indicated, as the effect will not be the same in those short ones of about 30 s as in those whose duration is longer. The type of exercise used should also be commented on (analytical or integrated), as each exercise has different objectives.

The authors should compare this practice with others, differentiating between lighter and more adherent ones, explaining their differences, and the reasons for choosing HIIT. Otherwise, a biased view was provided.

Discussion

The participants were selected from 18 to 75 years of age. Differentiation between the types of HIIT with respect to the various ages of the sample and the differentiation by gender is necessary to clarify the results and discern which methodology corresponds in each case.

These elements should be included in the limitations section at the end of the Discussion.

Author Response

Reviewer 2:

Introduction

Within the application, the type of HIIT referred to must be indicated, as the effect will not be the same in those short ones of about 30 s as in those whose duration is longer. The type of exercise used should also be commented on (analytical or integrated), as each exercise has different objectives.

• We have clarified the characteristics of the HIIT protocols included in this review. Specifically, we noted that most studies utilized moderate-to-long intervals lasting between 2 to 4 minutes and employed integrated exercise modalities such as cycling or treadmill walking, which engage multiple muscle groups simultaneously. This information has been added to the Introduction section to address the distinction between short and longer HIIT formats, as well as the type of exercise used. (Line 67-75)

The authors should compare this practice with others, differentiating between lighter and more adherent ones, explaining their differences, and the reasons for choosing HIIT. Otherwise, a biased view was provided.

• In response, we have added a comparative discussion between HIIT and moderate-intensity continuous training (MICT) to the final part of the Introduction section. This includes distinctions in intensity, time efficiency, physiological outcomes, and adherence profiles. We have also justified the rationale for focusing on HIIT in this review, particularly its relevance to obese individuals due to its shorter duration and potential for greater cardiometabolic benefits. The added content can be found in Lines (Line 99-113)

Discussion

The participants were selected from 18 to 75 years of age. Differentiation between the types of HIIT with respect to the various ages of the sample and the differentiation by gender is necessary to clarify the results and discern which methodology corresponds in each case.

These elements should be included in the limitations section at the end of the Discussion.

• The included studies did not consistently report subgroup analyses by age or gender, nor did they differentiate HIIT protocols based on these characteristics. We acknowledge this limitation and have added it to the revised manuscript under the “Limitations” section of the Discussion. (Line 411-424)

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have carefully reviewed the authors' revisions and I appreciate the significant contribution and the effort they made to improve this version of the manuscript. I believe that, in its current form, the study can be recommended for publication.