Effects of Functional Training on Body Composition in Adults with Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript “Effects of Functional Training on Body Composition in Adults with Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Clinical Trial” is a noteworthy review article detailing the current evidence on the effects of functional resistance training, specifically on body composition among individuals with excess body weight. The focus of functional training on body composition outcomes among individuals with overweight and obesity is a novel topic, one that a clear recommendation does not exist, and a major strength of this manuscript. This manuscript thus represents an important contribution and should be considered high impact.

One big picture suggestion would be to display similar body composition results from reviews that asked the same question in adults with overweight/obesity for aerobic training, resistance training, and HIIT, maybe in a table or chart, to demonstrate how FT compares.

Also, the title should close with “Trials” , not “Trial”.

 

Introduction:

Line 50: the term “calorie” is a unit of measurement for energy, and thus should only be used when referring to a specific amount of energy. For example, I ate 500 calories yesterday. Other instances, such as calorie/caloric restriction, should be replaced with “energy”.

Materials and Methods:

Study criteria, definitions, literature search, data synthesis, and processes for assessing methodological quality and certainty of the evidence were detailed very well.  

Results:

In table 2, are the effect sizes listed the cohen d? it seems they do not align with the observed outcomes or we are missing details… the Sperlich study states a positive effect size for fat and fat free mass, but the observed outcomes column states that fat mass was reduced and fat free mass was increased. It also seems that some of these effect sizes were very large but were not deemed significant, and some were very small and deemed significant. This makes the effect sizes hard to interpret. It may be better to state absolute results (change scores) and detail what was significant between groups and overtime.

Section 3.4 and 3.5 of the results seem to paint the picture that results cannot be interpreted with any confidence. However, it seems much of the issues highlighted would be consistent across most exercise interventions. I would recommend putting this in context, maybe in the conclusions, that all free-living exercise studies carry risk of bias, and all body composition assessments have limitations.

Table 4 is difficult to read, likely just needs to be resized or reformatted.

Discussion

Line 405: I’m assuming MM is muscle mass? This was not defined prior

Line 416: regarding the claim that BIA overestimates FFM among individuals with higher BMI because of more extracellular water… since water would be considered lean mass, is this accurate? I agree that BIA is far less robust than DXA, but this could be stated, and referenced, better.

Line 418: seems to state that DXA provides muscle mass data, which it does not. Bone-free, fat-free mass cannot be assumed to be muscle mass.

Line 439-441: although I have no issue and would probably agree, it seems statements such as this, that white women are under more pressure regarding body image, should be better referenced.

Line 456 and 465: both paragraphs start with the same sentence, and say essentially the same thing, which seems to discount the findings. I would suggest recognizing the limitations, putting them in context with other exercise interventions (as mentioned before), while highlighting the results. Maybe leading with “the current evidence suggests that FT can reduce body fat percentage” with the caveats noted afterwards. It appears the conclusion states this well, so those these two paragraphs could be cut substantially.

Author Response

Manuscript Title: Effects of Functional Training on Body Composition in Adults with Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials (Manuscript ID: jfmk-4367104)

Dear Reviewer,

We sincerely appreciate the time, effort, and expertise devoted to the evaluation of our manuscript. We are grateful for your thorough and constructive comments, which greatly contributed to improving the scientific quality, methodological transparency, and overall clarity of our work.

We have carefully considered each of your suggestions and have revised the manuscript accordingly. All modifications are highlighted in the revised manuscript file.

1. Reviewer Comment: One big picture suggestion would be to display similar body composition results from reviews that asked the same question in adults with overweight/obesity for aerobic training, resistance training, and HIIT, maybe in a table or chart, to demonstrate how FT compares.

Response: We sincerely thank the reviewer for this insightful suggestion. We agree that placing the findings of functional training (FT) into the context of other well-established exercise modalities improves the clinical interpretation of our results. Although we chose not to include a separate comparative table or figure, as this would extend beyond the primary scope of the present systematic review, we incorporated a broader discussion comparing the body composition outcomes observed after FT with those reported in recent systematic reviews and meta-analyses of aerobic training, resistance training, combined training, and high-intensity interval training (HIIT) in adults with overweight or obesity. Specifically, we incorporated evidence from Khalafi et al. and Wang et al., demonstrating that the reductions in body fat percentage observed following FT are consistent with those reported for other exercise modalities commonly recommended for weight management. This comparison provides a broader clinical perspective while maintaining the primary focus of the review on functional training.

Modification Performed in the Manuscript: A new comparative paragraph was added to the Discussion to contextualize the effects of functional training on body composition relative to other established exercise modalities (Page 22 starting from line 465).

 

 

2. Reviewer Comment: Also, the title should close with “Trials”, not “Trial”.

Response: We thank the reviewer for noting this issue. Accordingly, the title was revised to use the plural form “Trials.”

Modification Performed in the Manuscript: The manuscript title was corrected from “Randomized Clinical Trial” to “Randomized Clinical Trials.”

3. Reviewer Comment: The term "caloric restriction" should be "energy restriction", because "calorie" is a measure of energy and should only be used when referring to a specific amount. Other uses, such as "caloric restriction", should be changed to "energy".

Response: We sincerely thank the reviewer for this important observation. We fully agree that the term "energy restriction" is scientifically more appropriate, as "calorie" represents a unit of energy rather than a physiological concept. Accordingly, the terminology was revised throughout the manuscript to ensure consistency with current scientific nomenclature.

Modification Performed in the Manuscript: The term "caloric restriction" was replaced with "energy restriction" in the Introduction to ensure the use of appropriate scientific terminology (Page 2 - line 59).

4. Reviewer Comment: In Table 2, are the effect sizes listed Cohen’s d? They do not appear to align with the reported outcomes, or some detail is missing. Sperlich reports a positive effect size for fat mass and lean mass, but the results column states fat mass decreased and lean mass increased. It also appears that some effect sizes were very large but non-significant, while others were very small but significant. It may be preferable to report the absolute results and specify what was significant between groups and over time.

Response: We sincerely thank the reviewer for this valuable and insightful suggestion. We fully agreed that the original version of Table 2 did not clearly distinguish within-group changes from between-group differences and relied excessively on the presentation of effect sizes, which could lead to ambiguity in the interpretation of the findings. To address this concern, Table 2 was completely redesigned. The effect size column was removed, and the table was reconstructed to present the original body composition outcomes reported by each study as absolute values (pre–post values or change scores, when only these were available). In addition, the statistical interpretation was substantially expanded to explicitly distinguish within-group changes (time effect) from between-group differences or time × intervention interactions whenever these analyses were reported in the original studies. This revised format allows readers to directly visualize the magnitude and direction of changes in fat mass, body fat percentage, lean mass, and fat-free mass, while clearly identifying whether the reported effects reflected significant changes over time within the intervention groups or significant differences between intervention groups. We believe that the revised table substantially improves the clarity, transparency, and clinical interpretability of the evidence presented.

Modification Performed in the Manuscript: Table 2 was completely reconstructed.

The following modifications were implemented:

• The effect size column was removed.
• Absolute body composition outcomes (pre–post values or reported change scores) were incorporated for all included studies.
• Within-group statistical significance (time effect) was explicitly reported.
• Between-group differences and time × intervention interactions were explicitly described whenever available.
• The presentation of fat mass, body fat percentage, lean mass, and fat-free mass outcomes was standardized across all included studies.
• The statistical descriptions were carefully revised to ensure complete consistency with the original results reported by each clinical trial.

As a result, Table 2 now directly addresses the reviewer's recommendation by providing a clearer, more transparent, and clinically meaningful summary of the body composition outcomes reported in the included studies (pages 13-15).

5. Reviewer Comment: Results Sections 3.4 and 3.5 seem to indicate that the results cannot be interpreted. It seems to me, however, that many of the highlighted issues would apply to most exercise interventions. I would recommend contextualizing this somehow, perhaps in the conclusions, noting that all exercise studies in the wild have a risk of bias, and all body composition assessments have limitations.

Response: We sincerely thank the reviewer for this thoughtful and constructive suggestion. We agree that the methodological limitations identified in the included studies should be interpreted within the broader context of exercise science research rather than as limitations unique to functional training. Because Sections 3.4 and 3.5 are intended to objectively report the findings of the risk of bias (RoB 2.0) and GRADE assessments, these sections were retained without substantial modification. However, to directly address the reviewer's concern, we expanded the Conclusions by adding a paragraph that places these limitations into perspective. Specifically, we emphasize that challenges such as the inability to blind participants, variability in intervention implementation, adherence to exercise protocols, and the inherent limitations of body composition assessment methods (including DXA and bioelectrical impedance analysis) are common features of exercise-based research conducted under real-world conditions and are not exclusive to functional training interventions. We believe that this addition provides a more balanced interpretation of the findings by acknowledging the methodological limitations without implying that the available evidence is not interpretable.

Modification Performed in the Manuscript: A new paragraph was added to the Conclusions to contextualize the methodological limitations identified in the included studies within the broader field of exercise science research. The revised text emphasizes that limitations related to participant blinding, intervention implementation, adherence monitoring, and body composition assessment methods represent common methodological challenges in exercise-based research rather than issues specific to functional training (page 25 starting from line 621).

6. Reviewer Comment: Table 4 is difficult to read. It likely just needs resizing or reformatting.

Response: We thank the reviewer for this helpful suggestion. We agree that the original formatting of Table 4 affected its readability. Accordingly, the table was reformatted to improve its visual presentation and readability in accordance with the MDPI formatting guidelines. The column widths and overall layout were adjusted to facilitate interpretation while preserving all original content. This issue was also raised by Reviewers 2 and 3, and the revised formatting has been incorporated into the updated manuscript.

Modification Performed in the Manuscript: Table 4 was reformatted to improve readability. The column widths and overall layout were adjusted in accordance with the MDPI formatting guidelines, resulting in a clearer presentation of the GRADE assessment while preserving all original content (page 18-20).

7. Reviewer Comment: Line 405: I presume MM is muscle mass? This was not previously defined.

Response: We sincerely thank the reviewer for this careful observation. Upon revisiting the manuscript, we identified that the use of the term muscle mass in the referenced passage resulted from a terminological inconsistency rather than an undefined abbreviation. As correctly pointed out, the included studies assessed body composition using measures such as lean mass or fat-free mass, rather than directly measuring muscle mass. To improve terminological accuracy and ensure consistency with the outcomes reported in the included studies, we revised the manuscript by replacing muscle mass with lean mass in the relevant section of the Discussion. This revision ensures that the terminology accurately reflects the variables evaluated in the original studies.

Modification Performed in the Manuscript: The term "muscle mass" was replaced with "lean mass" in the Discussion to ensure terminological accuracy and consistency with the body composition outcomes reported in the included studies (line 516).

8. Reviewer Comment: Line 416: Regarding the statement that BIA overestimates fat-free mass (FFM) in people with higher BMI due to increased extracellular water—wouldn’t the water be considered lean mass? I agree that BIA is much less robust than DXA, but this statement could be better worded and referenced.

Response: We sincerely thank the reviewer for this valuable observation. We agree that the original wording was overly simplified and could lead to an inaccurate interpretation of the mechanisms underlying potential errors in body composition estimates obtained by BIA. To address this concern, the relevant paragraph in the Discussion was substantially revised to provide a more physiologically accurate explanation. Rather than attributing the potential bias exclusively to increased extracellular water, the revised text emphasizes that the accuracy of BIA-derived estimates may be influenced by alterations in body water distribution, particularly changes in the intracellular-to-extracellular water ratio, as well as by the assumptions incorporated into the prediction equations used by BIA devices. We also clarified that lean mass estimation is highly dependent on total body water and that alterations in fluid distribution, commonly observed in individuals with obesity, may affect impedance measurements and consequently influence the estimation of fat mass and fat-free mass. In addition, appropriate references were incorporated to support this revised explanation.

Modification Performed in the Manuscript: The paragraph discussing the limitations of BIA in the Discussion was substantially revised. The revised text now provides a more accurate physiological explanation of how alterations in body water distribution may influence BIA-derived body composition estimates and includes additional references to support this interpretation (page 23 starting from line 525).

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9. Comment: Line 418: This seems to indicate that DXA provides muscle mass data, which it does not. Fat-free mass and bone cannot be considered muscle mass.

Response: We agree with the reviewer that the original wording could inadvertently suggest that DXA directly measures muscle mass. Therefore, the paragraph was revised to adopt terminology that is fully consistent with both the outputs provided by DXA and the current body composition literature. The description of the body composition variables assessed by DXA was also revised to clarify that this technique provides estimates of fat mass, lean mass, bone mineral density, and visceral fat distribution, without implying a direct measurement of skeletal muscle mass. These revisions ensure conceptual accuracy and improve consistency with the outcomes reported in the included studies.

Modification Performed in the Manuscript: The paragraph describing body composition assessment methods in the Discussion was revised. References to muscle mass were replaced with LM, and the description of the body composition variables assessed by DXA was updated to accurately reflect the compartments measured by this technique (page 23 starting from line 535).

10. Reviewer Comment: Lines 439–441: While I don't necessarily have a problem and likely agree, it seems like statements such as this, that white women experience more body image pressure, should be better referenced.

Response: We agree that the previous text was unnecessarily specific and could require additional evidence to support the statement adequately. To improve scientific accuracy and avoid overgeneralization, the text was revised by removing the reference to a specific racial subgroup and adopting a broader statement better supported by the available literature on sociocultural influences on body image and weight management. The revised paragraph now focuses on the well-documented social pressures experienced by women regarding body image, body weight, and thinness ideals, without making demographic-specific claims that are not essential to the objectives of the present review. This revision improves the balance of the discussion while maintaining the rationale for the predominance of women in the included studies.

Modification Performed in the Manuscript: The paragraph discussing the predominance of women in the included studies was revised in the Discussion. The reference to a specific racial subgroup was removed, and the sociocultural explanation for participation patterns in weight-management research was reformulated using broader, evidence-based terminology supported by the appropriate references (page 23 starting from line 540).

 

11. Reviewer Comment: Lines 456 and 465: Both paragraphs begin with the same sentence and essentially state the same thing, seeming to disregard the findings. I would recommend acknowledging the limitations, contextualizing them with other exercise interventions, and highlighting the findings. Maybe start with "Current evidence suggests FT may reduce body fat percentage", with the caveats noted after.

Response: Following the reviewer's recommendation, the Discussion was reorganized to improve both its structure and interpretability. We agreed that the previous version placed excessive emphasis on methodological limitations before adequately presenting the principal findings, resulting in unnecessary repetition and an overly negative interpretation of the available evidence. The revised Discussion now begins by highlighting the main finding of the review, namely that current evidence suggests FT may be associated with reductions in body fat percentage among adults with overweight or obesity. These findings are subsequently contextualized alongside evidence from other established exercise modalities commonly used in weight-management programs. Only after presenting the principal findings are the methodological limitations, sources of heterogeneity, and certainty of the evidence discussed. This restructuring provides a more balanced interpretation of the available evidence while preserving an appropriately cautious interpretation of the results.

Modification Performed in the Manuscript: The corresponding section of the Discussion was substantially reorganized. Redundant introductory statements were removed, the principal findings were presented before discussing methodological limitations, and the results were contextualized alongside other established exercise modalities. The previous repetitive paragraphs were consolidated into a single, more coherent discussion that better reflects both the strengths and limitations of the available evidence.

 

Dear reviewer, we hope the revisions satisfactorily address the concerns raised. We remain available for any further clarification that may be required.

 

Sincerely,

The authors.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a systematic review and meta-analysis of randomized controlled trials evaluating the effects of functional training (FT) on body composition in adults with overweight or obesity. Seven RCTs involving a total of 296 participants were included in the review, and an additional meta-analysis of two studies was conducted for body fat percentage. Strengths of the manuscript include adherence to PRISMA guidelines, assessment of risk of bias using RoB 2, and evaluation of the certainty of evidence using the GRADE approach. However, the manuscript requires revisions regarding the definition of functional training, consistency in intervention classification, the rationale and methodology of the meta-analysis, and the interpretation of findings. Detailed comments are provided below.

Abstract

A1. The conclusions presented in the abstract are more definitive than warranted by the quality of the available evidence. The statement that “FT appears to be a promising strategy” should be more carefully balanced by noting that the meta-analysis was based on only two studies and that the certainty of evidence was rated as low.

A2. The abstract states that the analysis focused on FT; however, later sections of the manuscript classify some interventions as HIIT-F or mixed training programs. It would be helpful to clarify already in the abstract that functional forms of HIIT were also included in the review.

Introduction

I1. The authors provide an extensive discussion of potential psychosocial benefits of FT, such as enhanced self-esteem and improved health behaviors, whereas the review focuses exclusively on body composition outcomes. This section should either be shortened or more clearly linked to the primary objective of the study.

I2. The manuscript lacks a clear rationale for analyzing FT separately from multicomponent training, CrossFit, or functional HIIT interventions. Since the boundaries between these intervention types become an important methodological issue later in the manuscript, this distinction should be introduced more explicitly in the Introduction.

Methods

M1. The criteria used to classify interventions as FT are highly restrictive and include six eligibility conditions. However, the manuscript does not indicate which included studies fulfilled each specific criterion. A summary table showing the classification process for each intervention would improve transparency.

M2. The meta-analysis was conducted using post-intervention values rather than change scores from baseline. The authors should justify this methodological choice and demonstrate that the intervention and control groups were comparable at baseline.

Results

R1. Of the seven included studies, only two were incorporated into the meta-analysis. The authors should provide a more detailed explanation as to why the remaining studies could not be quantitatively synthesized, particularly since some of them also reported body composition outcomes.

R2. Table 2 reports “effect size” values; however, the specific effect size metric used (e.g., Cohen’s d, η², or another measure) is not clearly identified. This information should be specified either in the Methods section or in the table footnote.

R3. The presentation of results frequently focuses on within-group changes, even though some studies did not demonstrate statistically significant between-group differences. The authors should more clearly distinguish within-group effects from comparative treatment effects. The interpretation of the study by Feito et al. (2019) is one example where this distinction should be improved.

R4. The GRADE summary table (Table 4) is difficult to read and appears incomplete in its current form. The formatting should be carefully checked before publication.

Discussion

D1. The authors repeatedly imply causal relationships, for example by suggesting that longer intervention duration “amplifies improvements” or that specific program components “enhance” body composition outcomes. Based on seven heterogeneous studies, it is not possible to reliably determine the contribution of individual intervention characteristics.

D2. The statement that six studies demonstrated statistically significant increases in lean body mass (LBM) appears overly categorical. In the Results section, not all studies clearly reported significant improvements in LBM. The authors should verify and refine this synthesis.

D3. The extended discussion regarding socio-cultural factors influencing female participation in exercise interventions goes beyond the scope of the evidence presented in the included studies and is largely speculative. In its current form, this section should either be shortened or supported with stronger evidence.

D4. The final section of the Discussion (lines 455–480) contains partially repetitive statements regarding low certainty of evidence, study heterogeneity, and the need for further research. Merging these paragraphs may improve clarity and conciseness.

Conclusions

C1. The statement suggesting that FT may reduce fat mass and increase lean body mass is somewhat too definitive given the low or very low certainty of evidence according to GRADE. The uncertainty surrounding these estimates should be emphasized more clearly.

C2. The conclusions should more clearly distinguish findings derived from the meta-analysis (%BF) from those based solely on the qualitative synthesis of other body composition outcomes. At present, all effects are presented with a similar level of certainty despite differences in the underlying evidence base.

Author Response

Manuscript Title: Effects of Functional Training on Body Composition in Adults with Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials (Manuscript ID: jfmk-4367104)

Dear Reviewer,

We sincerely appreciate the time, effort, and expertise devoted to the evaluation of our manuscript. We are grateful for your thorough and constructive comments, which greatly contributed to improving the scientific quality, methodological transparency, and overall clarity of our work.

We have carefully considered each of your suggestions and have revised the manuscript accordingly. All modifications are highlighted in the revised manuscript file.

1. Reviewer Comment: The conclusions presented in the abstract are more definitive than warranted by the quality of the available evidence. The statement that “FT appears to be a promising strategy” should be more carefully balanced by noting that the meta-analysis was based on only two studies and that the certainty of evidence was rated as low.

Response: Dear reviewer, we agree that the conclusions presented in the Abstract should accurately reflect the strength and limitations of the available evidence. To address this concern, we revised the Conclusions section of the Abstract to adopt a more cautious interpretation and avoid overly definitive statements regarding the effectiveness of functional training. Specifically, stronger statements were replaced with wording indicating that the current evidence only suggests a potential association between FT/HIIT-F and reductions in body fat percentage. We also explicitly acknowledged the very low certainty of the evidence according to the GRADE assessment, the methodological limitations of the included studies, the fact that the quantitative synthesis was based on only two randomized controlled trials, and the predominance of female participants, which limits the generalizability of the findings.

Modification Performed in the Manuscript: The Conclusions section of the Abstract was revised to adopt a more cautious interpretation of the findings. Overly definitive language was removed, and explicit statements were added regarding the very low certainty of the evidence, the limited number of studies included in the meta-analysis, the methodological limitations of the available evidence, and the restricted generalizability of the findings.

 

2. Reviewer Comment: The abstract states that the analysis focused on FT; however, later sections of the manuscript classify some interventions as HIIT-F or mixed training programs. It would be helpful to clarify already in the abstract that functional forms of HIIT were also included in the review.

Response: Dear reviewer, we humbly agree that the scope of the interventions included in the review should be clearly presented in the Abstract to ensure consistency with the manuscript’s main text. Accordingly, the Methods section of the Abstract was revised to explicitly state that, in addition to traditional FT, interventions classified as HIIT-F, multicomponent training programs, and CrossFit-like interventions were also considered eligible when they fulfilled the predefined functional training classification criteria adopted in this review. This revision provides a clearer description of the intervention framework evaluated and improves consistency between the Abstract and the methodological sections of the manuscript.

Modification Performed in the Manuscript: The Methods section of the Abstract was revised to clarify that HIIT-F, multicomponent training programs, and CrossFit-like interventions were included when they met the predefined eligibility criteria for classification as functional training.

3. Reviewer Comment: The authors provide an extensive discussion of potential psychosocial benefits of FT, such as enhanced self-esteem and improved health behaviors, whereas the review focuses exclusively on body composition outcomes. This section should either be shortened or more clearly linked to the primary objective of the study.

Response: To better align the Introduction with the primary objective of the review, we substantially revised this section by reducing the discussion of psychosocial outcomes that were not directly related to the scope of the study. Because the present review was specifically designed to evaluate the effects of functional training on body composition outcomes in adults with overweight or obesity, we considered it appropriate to streamline the background information and maintain the focus on the scientific rationale supporting this objective. The revised Introduction now emphasizes the role of functional training as an exercise strategy for improving body composition while retaining only the essential contextual information regarding obesity management and exercise interventions. This revision improves the focus and coherence of the Introduction and more closely aligns it with the objectives and outcomes evaluated in the review.

Modification Performed in the Manuscript: The Introduction was revised to reduce the discussion of psychosocial benefits associated with functional training. The section now focuses primarily on the rationale for investigating the effects of functional training on body composition in adults with overweight or obesity, thereby improving consistency between the background and the objectives of the review (Page 2 starting from line 84).

4. Reviewer Comment: The manuscript lacks a clear rationale for analyzing FT separately from multicomponent training, CrossFit, or functional HIIT interventions. Since the boundaries between these intervention types become an important methodological issue later in the manuscript, this distinction should be introduced more explicitly in the Introduction.

Response: We appreciate the reviewer's important observation and agree that the conceptual boundaries between FT, multicomponent training, CrossFit-like interventions, and functional forms of HIIT should be introduced more clearly at the beginning of the manuscript. To address this issue, we revised the Introduction by incorporating a conceptual framework based on the recent international consensus on functional training. Specifically, we clarified that FT should not be viewed as a rigidly defined exercise category but rather as a continuum of functionality encompassing different training approaches that share common functional characteristics. We also explained that multicomponent programs, CrossFit-like interventions, and functional forms of HIIT were considered within the scope of FT when they incorporated multi-joint movement patterns, integrated multiple physical capacities, and aimed to promote transferable adaptations relevant to activities of daily living.

Modification Performed in the Manuscript: The Introduction was revised to include a clearer conceptual definition of FT and to explain the rationale for including multicomponent programs, CrossFit-like interventions, and HIIT-F within the scope of FT when they met the predefined eligibility criteria adopted in this review (Page 2 starting from line 73).

5. Reviewer Comment: The criteria used to classify interventions as FT are highly restrictive and include six eligibility conditions. However, the manuscript does not indicate which included studies fulfilled each specific criterion. A summary table showing the classification process for each intervention would improve transparency.

Response: We appreciate the reviewer's valuable suggestion and fully agree that greater transparency in the classification of interventions is essential. To address this issue, we created a supplementary table (Supplementary Table S1) detailing the classification process for all included studies. Specifically, the table presents each of the six predefined eligibility criteria for FT and indicates how each of the seven included studies fulfilled these requirements. This addition allows readers to clearly understand the rationale underlying study inclusion, facilitates the reproducibility of the classification process, and provides greater methodological transparency regarding the operational definition of functional training adopted in this review. In addition, we included an explicit reference to Supplementary Table S1 in the Methods section, immediately after the description of the FT eligibility criteria.

Modification Performed in the Manuscript: A Supplementary Table S1 was created showing the classification of all included studies according to the six predefined FT eligibility criteria. In addition, a direct reference to Supplementary Table S1 was added to the Methods section (page 4 starting from line 164).

Table S1. Classification of the Included Studies According to the Predefined Functional Training Eligibility Criteria.

Study	C1	C2	C3	C4	C5	C6	Overall Decision	Classification
Sperlich et al., 2017	✓	✓	✓	✓	✓	✓	Eligible	HIIT-F
Batrakoulis et al., 2018	✓	✓	✓	✓	✓	✓	Eligible	FT
Feito et al., 2019	✓	✓	✓	✓	✓	✓	Eligible	HIIT-F
Teixeira et al., 2020	✓	✓	✓	✓	✓	✓	Eligible	FT
Cavaggioni et al., 2021	✓	✓	✓	✓	✓	✓	Eligible	FT
Cao et al., 2024	✓	✓	✓	✓	✓	✓	Eligible	HIIT-F
Ameur et al., 2024	✓	✓	✓	✓	✓	✓	Eligible	HIIT-F

Note: FT = Functional Training; HIIT-F = High-Intensity Functional Training.

Eligibility criteria:

C1 = Predominance of multi-joint and/or multi-planar movement patterns.

C2 = Intentional integration of at least two physical capacities within training sessions.

C3 = Presence of a documented progression scheme (intensity, volume, complexity, or training load).

C4 = Inclusion of neuromuscular challenges beyond isolated resistance exercises.

C5 = Clear reporting of exercise dose and monitoring procedures (frequency, session duration, work-to-rest ratio, and/or validated intensity metrics).

C6 = Explicit justification or evidence distinguishing the intervention from conventional resistance training and pure HIIT.

Note: Studies were classified as eligible when all six predefined criteria were satisfied.

6. Reviewer Comment: The meta-analysis was conducted using post-intervention values rather than change scores from baseline. The authors should justify this methodological choice and demonstrate that the intervention and control groups were comparable at baseline.

Response: To improve methodological transparency, the meta-analysis was revised to clarify the rationale underlying the quantitative synthesis. The quantitative synthesis was restricted to studies comparing FT or HIIT-F with a non-exercising control group and reporting comparable post-intervention body fat percentage data. Two studies fulfilled these criteria. In the primary analysis, the final assessment available from each study was used (40 weeks in Batrakoulis et al. and 12 weeks in Cao et al.). The pooled estimate favored FT/HIIT-F (MD = −4.44 percentage points; 95% CI −7.08 to −1.80; p = 0.001; I² = 0%). We also clarified that post-intervention values were used because standard deviations for change scores and adjusted between-group estimates were not consistently available across the included studies. Baseline comparability between the intervention and control groups was verified before conducting the quantitative synthesis. In addition, the interpretation of the findings was revised to adopt a more cautious approach, considering the small number of included studies, the risk of bias, the limited sample size, and the use of different body composition assessment methods.

Modification Performed in the Manuscript: In the Data Synthesis subsection, we clarified the eligibility criteria for inclusion in the meta-analysis, justified the use of post-intervention values, described the primary pooled analysis, and explicitly stated that baseline comparability was verified before conducting the quantitative synthesis (page 6 starting from line 246).

7. Reviewer Comment: Of the seven included studies, only two were incorporated into the meta-analysis. The authors should provide a more detailed explanation as to why the remaining studies could not be quantitatively synthesized, particularly since some of them also reported body composition outcomes.

Response: Dear reviewer, to improve methodological transparency, we revised the Methods and Results sections to provide a more explicit explanation of why only two studies were eligible for quantitative synthesis. Specifically, we clarified that a meta-analysis was performed only when at least two studies reported comparable numerical data for the same outcome and comparison. Although other included studies assessed body composition, only Batrakoulis et al. and Cao et al. compared FT/HIIT-F with a non-exercising control group and reported post-intervention body fat percentage as mean ± standard deviation, allowing calculation of a pooled mean difference. The remaining studies could not be quantitatively synthesized because they differed substantially in comparator groups (e.g., resistance training, combined training, interdisciplinary therapy, intermittent fasting), intervention designs, follow-up duration, body composition assessment methods, outcome definitions, and reporting formats. In several studies, the comparable numerical data required for meta-analysis were not available. To further improve methodological transparency, we added a subsection describing the quantitative synthesis and included a sensitivity analysis using the alternative follow-up time point from Batrakoulis et al. The Discussion was also expanded to explain why the meta-analysis was restricted to body fat percentage and why the remaining body composition outcomes were synthesized narratively.

Modification Performed in the Manuscript: The Data Synthesis subsection (Methods) was expanded to describe the eligibility criteria for quantitative synthesis and to explain why only body fat percentage could be pooled (page 6 starting from line 246). New Quantitative Synthesis and Sensitivity Analysis subsections were added to the Results (page 21 starting from line 427). In addition, the Discussion now explicitly states that the remaining body composition outcomes could not be meta-analyzed because of differences in comparator groups, intervention characteristics, follow-up duration, assessment methods, outcome reporting, and the incomplete availability of comparable numerical data (page 24 starting from line 590).

8. Reviewer Comment: Table 2 reports “effect size” values; however, the specific effect size metric used (e.g., Cohen’s d, η², or another measure) is not clearly identified. This information should be specified either in the Methods section or in the table footnote.

Response: We appreciate the reviewer's important observation and agree that the presentation of effect size values in the original version of Table 2 could create ambiguity regarding the metric used and make the results more difficult to interpret. To address this issue, and in response to a related recommendation from Reviewer 1, we decided to remove the effect size column from Table 2. Instead, we revised the table to present absolute changes in the body composition outcomes (change values) and expanded the description of the results to clearly indicate whether statistically significant effects were observed within groups (over time) and/or between groups. We believe that this approach provides a more transparent presentation of the findings, facilitates comparisons across studies, and avoids potential misinterpretations associated with effect size estimates derived from heterogeneous outcome measures and reporting formats.

Modification Performed in the Manuscript: The effect size column was removed from Table 2. The table was revised to present absolute changes in body composition outcomes and to explicitly report the statistical significance of within-group and between-group comparisons whenever available (pages 13-15).

9. Reviewer Comment: The presentation of the results often focuses on within-group changes, even when some studies did not demonstrate statistically significant between-group differences. The authors should more clearly distinguish within-group effects from comparative treatment effects. The interpretation of the study by Feito et al. (2019) is an example where this distinction should be improved.

Response: Dear reviewer, we acknowledge this important methodological observation and agree that within-group changes should not be interpreted as evidence of comparative treatment effectiveness. To address this issue, we revised both the Results section and Table 2 to more clearly distinguish changes observed within the intervention groups over time from statistically significant between-group differences. Particular attention was given to the interpretation of the study by Feito et al. In the revised manuscript, we clarified that no significant between-group differences were observed for the DXA-derived body composition outcomes and that the significant finding reported for lower-limb lean mass occurred only within the HIIT-F group. Therefore, this result is now presented as a within-group change rather than as evidence of the superiority of HIIT-F over the comparator intervention.

Modification Performed in the Manuscript: The Results section and Table 2 were revised to explicitly distinguish whether statistically significant findings represented within-group changes or comparative treatment effects. The description of Feito et al. (2019) was revised to avoid implying comparative effectiveness when only within-group changes were observed (page 11 starting from line 334/pages 13-15).

10. Reviewer Comment: The GRADE summary table (Table 4) is difficult to read and appears incomplete in its current form. The formatting should be carefully checked before publication.

Response: Following the reviewer's recommendation, we thoroughly revised Table 4 to improve both its readability and the completeness of the information presented. We agreed that the original version of the table could compromise readability and did not clearly present all relevant information from the GRADE assessment. To address this issue, we comprehensively revised Table 4 in terms of both its content and presentation. Specifically, we reconstructed the table following the format recommended by GRADEpro GDT, reorganizing the layout to improve visual clarity and facilitate interpretation of the findings. The revised table now includes all outcomes evaluated in this review. Body fat percentage is presented based on the pooled estimate from the meta-analysis, whereas the remaining body composition outcomes (fat mass, lean mass/fat-free mass, body weight, body mass index, central adiposity, and visceral fat area) were assessed through narrative synthesis, together with their corresponding certainty-of-evidence ratings. In addition, we carefully reviewed all GRADE judgments and explicitly reported the reasons for downgrading the certainty of the evidence across the applicable domains, including risk of bias, inconsistency, indirectness, and imprecision. Formatting issues were also corrected to improve the overall readability of the table. We believe these revisions have made the table more complete, transparent, and consistent with GRADE recommendations.

Modification Performed in the Manuscript: Table 4 was completely revised and reformatted. Its layout was redesigned following the GRADEpro GDT format to improve readability, all body composition outcomes assessed in the review were incorporated, and the reasons for downgrading the certainty of the evidence were explicitly reported for each applicable GRADE domain (pages 18-20).

11. Reviewer Comment: The authors repeatedly imply causal relationships, for example by suggesting that longer intervention duration “amplifies improvements” or that specific program components “enhance” body composition outcomes. Based on seven heterogeneous studies, it is not possible to confidently determine the contribution of individual intervention characteristics.

Response: Dear, we recognize your relevant concern and agree that causal inferences regarding specific intervention characteristics cannot be supported by the limited number of heterogeneous studies included in this review. To address this issue, we carefully revised the Discussion and replaced language implying causality with more cautious and descriptive interpretations. Throughout the manuscript, statements suggesting that specific intervention characteristics were responsible for the observed outcomes were reformulated to indicate potential associations or possible explanations rather than causal relationships. We also emphasized that the included interventions varied substantially in duration, exercise content, intensity, comparator conditions, and body composition assessment methods, precluding reliable conclusions regarding the independent contribution of any individual training component. In addition, we included explicit statements acknowledging that the interventions represent different manifestations along a continuum of functionality and that the observed findings should be interpreted in light of the substantial heterogeneity across protocols rather than being attributed to isolated intervention characteristics.

Modification Performed in the Manuscript: Several statements throughout the Discussion were revised to avoid causal interpretations. The revised text now uses more cautious language, emphasizing potential associations rather than cause-and-effect relationships and acknowledging the heterogeneity of the included interventions (page 21 starting from line 457).

12. Reviewer Comment: The statement that six studies demonstrated statistically significant increases in lean mass appears overly categorical. In the Results section, not all studies clearly reported significant improvements in lean mass. The authors should verify and refine this summary.

Response: Dear reviewer, we appreciate your attentive observation and agree that the original text could be interpreted as overstating the consistency of the findings regarding lean mass and fat-free mass. To address this issue, we revised the Discussion to provide a more balanced interpretation of the available evidence. Specifically, we replaced statements suggesting a uniform increase in lean mass across all studies with wording emphasizing that some studies reported favorable changes in lean mass or fat-free mass, but that these findings were not consistent across all trials and often reflected within-group changes rather than statistically significant between-group differences. We also reinforced the substantial heterogeneity in intervention protocols, comparator groups, and body composition assessment methods, which limits direct comparisons across studies.

Modification Performed in the Manuscript: The Discussion was revised to provide a more balanced summary of the evidence regarding lean mass and fat-free mass. Statements implying consistent improvements across studies were replaced with more cautious wording that acknowledges the variability of the findings, distinguishes within-group changes from between-group differences, and recognizes the methodological heterogeneity among the included studies (page 21 starting from line 457).

13. Reviewer Comment: The extended discussion of sociocultural factors influencing female participation in exercise interventions goes beyond the evidence presented in the included studies and is largely speculative. In its current form, this section should either be shortened or supported by stronger evidence.

Response: We appreciate the reviewer's important observation and agree that the discussion should remain focused on the implications of the sex distribution observed in the included studies rather than on speculative explanations. To address this issue, we revised this section to emphasize the methodological implications of the predominance of female participants, particularly its impact on external validity and the generalizability of the findings. The revised text now prioritizes the discussion of sex-related physiological differences that may influence responses to exercise interventions and explicitly highlights the limited applicability of the current findings to men. In addition, sociocultural considerations were retained only as a potential contextual factor and are now presented in a more cautious manner. We also reinforced the recommendation that future randomized controlled trials should recruit more balanced samples and consider hormonal status in their analyses.

Modification Performed in the Manuscript: The section of the Discussion addressing the predominance of female participants was revised to place greater emphasis on external validity, sex-related physiological differences, and the limited generalizability of the findings. Sociocultural explanations were retained only as a potential contextual factor and are now presented in a more cautious and balanced manner (page 23 starting from line 553).

14. Reviewer Comment: The final section of the Discussion (lines 455–480) contains partially repetitive statements regarding the low certainty of the evidence, study heterogeneity, and the need for further research. Merging these paragraphs may improve clarity and conciseness.

Response: We appreciate the reviewer's suggestion and agree that some sections of the Discussion and Conclusion contained overlapping statements regarding methodological limitations and intervention heterogeneity. To improve readability and reduce redundancy, we carefully revised these sections and consolidated repetitive concepts while preserving the scientific interpretation of the findings. Specifically, repeated references to intervention heterogeneity, methodological limitations, and the cautious interpretation of the available evidence were streamlined. These revisions improved the flow of both the Discussion and the Conclusion while retaining all information necessary for an accurate interpretation of the available evidence.

Modification Performed in the Manuscript: The Discussion and Conclusion were revised to reduce repetition of concepts related to intervention heterogeneity, methodological limitations, and the certainty of the evidence, thereby improving readability and the overall narrative flow (pages 24 and 25).

15. Reviewer Comment: The statement suggesting that FT may reduce fat mass and increase lean mass is somewhat categorical, considering the low or very low certainty of the evidence according to the GRADE framework. The uncertainty surrounding these estimates should be emphasized more clearly.

Response: We appreciate the reviewer's important observation and agree that the conclusions should accurately reflect both the strength and the limitations of the available evidence. To address this issue, we revised the Conclusion section to adopt more cautious language and align the interpretation of the findings with the certainty of the evidence assessed using the GRADE approach. Specifically, we replaced definitive statements regarding the effects of FT with wording emphasizing potential associations rather than causal effects. We also explicitly incorporated the very low certainty of the evidence for the assessed outcomes, acknowledged that causal inferences cannot be established based on the currently available studies, highlighted the predominance of female participants and the resulting limitations in the generalizability of the findings, and reinforced the need for additional high-quality randomized controlled trials. These revisions ensure that the conclusions are proportionate to the available evidence and consistent with the methodological limitations identified throughout the review.

Modification Performed in the Manuscript: The Conclusion section was revised to emphasize the very low certainty of the evidence for the assessed outcomes, avoid causal interpretations, acknowledge the limited generalizability of the findings, and strengthen the recommendations for future research (page 25 starting from line 622).

16. Reviewer Comment: The conclusions should more clearly distinguish findings derived from the meta-analysis (%BF) from those based solely on the qualitative synthesis of other body composition outcomes. At present, all effects are presented with a similar level of certainty despite differences in the underlying evidence base.

Response: We appreciate the reviewer's valuable observation and agree that the Conclusion should more clearly distinguish findings supported by the meta-analysis from those derived exclusively from the narrative synthesis. To address this issue, we revised the Conclusion section to clearly separate the evidence for body fat percentage from the remaining body composition outcomes. Specifically, we clarified that the evidence suggesting reductions in body fat percentage is based on the pooled estimate obtained from the meta-analysis, whereas the findings for fat mass, lean mass/fat-free mass, body weight, body mass index, central adiposity, and visceral fat area are based exclusively on the narrative synthesis because these outcomes could not be quantitatively pooled. We also emphasized that these findings should be interpreted according to the certainty of the underlying evidence, avoiding the impression that all outcomes are supported by the same level of evidence. These revisions ensure that the conclusions are fully consistent with the quantitative and qualitative syntheses presented throughout the manuscript.

Modification Performed in the Manuscript: The Conclusion section was revised to explicitly distinguish findings derived from the meta-analysis from those based on the narrative synthesis. Body fat percentage is now presented as the only outcome supported by quantitative synthesis, whereas the remaining body composition outcomes are described separately based on the qualitative evidence available (page 25 starting from line 622).

 

Sincerely,

The authors.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for the opportunity to review this manuscript. The study addresses a relevant topic regarding the effects of functional training on body composition in adults with overweight or obesity and makes an important effort by conducting a systematic review with PROSPERO registration. However, several aspects of the manuscript require clarification and substantial revision.

1. The authors conducted a meta-analysis on body fat percentage using only two studies. Moreover, these studies used different body-composition assessment methods, namely dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA). Although both methods can assess body fat percentage, they are not equivalent in terms of validity, precision, and measurement assumptions. Therefore, a meta-analysis based on only two studies using different body-composition assessment methods requires a stronger methodological justification and a more cautious interpretation.

In addition, the manuscript states in the Results section that “The diversity of instruments (BIA vs. DXA) and outcome definitions limited direct comparability between studies and precluded quantitative synthesis,” yet a meta-analysis was subsequently performed for body fat percentage. This creates an internal inconsistency that should be resolved. The authors should either revise this statement or clearly explain why body fat percentage was considered sufficiently comparable for quantitative pooling.

2. The authors should justify the use of post-intervention values rather than change scores or adjusted between-group differences in the meta-analysis. In randomized trials with small sample sizes, baseline differences may meaningfully influence post-intervention comparisons. If available, change-from-baseline data or adjusted estimates would provide a more appropriate synthesis and improve the interpretability of the pooled effect.

3. En la evaluación de la calidad metodológica, Batrakoulis et al. se clasificó como con un alto riesgo de sesgo. Sin embargo, este estudio se incluyó en el metaanálisis sin realizar un análisis de sensibilidad. La sección Métodos indica explícitamente que no se realizaron análisis de sensibilidad. Aunque el análisis de sensibilidad puede ser limitado cuando solo se incluyen dos estudios, esta limitación debilita aún más la robustez de la estimación agrupada. Los autores deben justificar la inclusión de este estudio en el metaanálisis de manera más rigurosa, realizar un análisis de sensibilidad apropiado si es posible, o evitar sobreinterpretar el resultado agrupado.

4. The classification of interventions requires further clarification. Although the review focuses on functional training, the included studies involve heterogeneous modalities such as functional high-intensity interval training, combined training, resistance training, running-based HIIT, interdisciplinary therapy, and intermittent fasting combined with exercise. This heterogeneity makes it difficult to determine whether the observed effects are attributable to functional training itself or to combined/multicomponent interventions. The authors should clarify how each intervention was classified as functional training or functional HIIT and explain how this heterogeneity affects the interpretation of the findings.

5. The GRADE approach can be applied to both quantitative and narrative syntheses; however, for outcomes without pooled estimates, the manuscript should clearly explain how inconsistency and imprecision were judged. In particular, for lean mass/fat-free mass and fat mass, no pooled effect estimate or confidence interval is provided, yet certainty ratings are assigned. Please clarify the criteria used to downgrade these domains in the absence of meta-analytic estimates.

6. The manuscript reports a clear predominance of female participants. Therefore, the generalizability of the findings to men should be interpreted with caution. The title, abstract, and conclusions refer broadly to adults with overweight or obesity, but the evidence base is mainly composed of women. This limitation should be more explicitly reflected when discussing external validity and applicability of the findings.

7. The conclusions should be revised to adopt a more cautious tone consistent with the limitations of the evidence. Statements such as “The evidence indicates that FT can reduce body-fat percentage” imply a causal or intervention-oriented interpretation that is not fully supported by the available evidence, particularly considering the low certainty of evidence, the high risk of bias in some included studies, the small number of studies included in the meta-analysis, and the heterogeneity of interventions and assessment methods. I recommend revising the conclusion to avoid strong causal language and to align more closely with the methodological limitations and uncertainty of the findings.

8. The in-text citations are occasionally not presented in the correct MDPI format. According to the journal’s guidelines, references should be cited using square brackets in order of appearance. For example, the reference to “Review Manager software, version 5.4.1, using a random-effects model (18)” uses parentheses instead of brackets. Similarly, “RT programs (17,18)” should be corrected. Please review and correct all in-text citations throughout the manuscript.

9. In Table 1, the footnotes contain typographical errors. For example, the abbreviation for RPE is listed as “Rated perceived exertio” instead of “Rated perceived exertion.” Please carefully check the table footnotes and ensure that all acronyms used in the tables are accurately defined. Each table should be self-contained and understandable without requiring the reader to search for definitions elsewhere in the manuscript.

10. Table 4 presents several formatting problems that reduce readability. In the “Fat mass (kg)” row, the certainty rating appears as “Verylow” instead of “Very low.” In addition, the table layout is difficult to read, with narrow columns and fragmented words. Please revise the formatting of Table 4 to improve clarity and presentation according to MDPI standards.

11. Several statements throughout the manuscript are not adequately supported by citations. For example, at the beginning of the Introduction, the authors state that “Obesity is a chronic and progressive condition, widely recognized as a global health epidemic, and is characterized by excessive accumulation of body fat” without providing a direct citation for this specific statement. Similar unsupported or insufficiently referenced statements appear in other sections of the manuscript. Please review the entire text and ensure that all epidemiological, conceptual, methodological, and interpretative claims are appropriately supported by relevant and up-to-date references.

Author Response

Manuscript Title: Effects of Functional Training on Body Composition in Adults with Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials (Manuscript ID: jfmk-4367104)

Dear Reviewer,

We sincerely appreciate the time, effort, and expertise devoted to the evaluation of our manuscript. We are grateful for your thorough and constructive comments, which greatly contributed to improving the scientific quality, methodological transparency, and overall clarity of our work.

We have carefully considered each of your suggestions and have revised the manuscript accordingly. All modifications are highlighted in the revised manuscript file.

1. Reviewer Comment: The authors conducted a meta-analysis on body fat percentage using only two studies. Moreover, these studies used different body-composition assessment methods, namely dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA). Although both methods can assess body fat percentage, they are not equivalent in terms of validity, precision, and measurement assumptions. Therefore, a meta-analysis based on only two studies using different body-composition assessment methods requires a stronger methodological justification and a more cautious interpretation. In addition, the manuscript states in the Results section that “The diversity of instruments (BIA vs. DXA) and outcome definitions limited direct comparability between studies and precluded quantitative synthesis,” yet a meta-analysis was subsequently performed for body fat percentage. This creates an internal inconsistency that should be resolved. The authors should either revise this statement or clearly explain why body fat percentage was considered sufficiently comparable for quantitative pooling.

Response: We appreciate the reviewer's important observation. We agree that the original wording could create an apparent inconsistency between the rationale for the quantitative synthesis and the discussion of methodological heterogeneity. To clarify this point, we revised the Methods section and the interpretation of the results. The meta-analysis was restricted exclusively to body fat percentage (%BF), as only two studies compared FT/HIIT-F with a non-exercising control group and reported directly comparable post-intervention data (means, standard deviations, and sample sizes). Although these studies used different body composition assessment methods (DXA and BIA), both assessed the same outcome (%BF), allowing quantitative synthesis using the mean difference. At the same time, we explicitly stated that this methodological difference represents a source of indirectness and constitutes a limitation of the meta-analysis, which was considered in the GRADE assessment and in the cautious interpretation of the findings. The remaining body composition outcomes were not pooled because of heterogeneity in comparator groups, intervention protocols, data reporting formats, and the lack of comparable numerical data.

Modification Performed in the Manuscript: The Data Synthesis (page 6 starting from line 246), Quantitative Synthesis (page 21 starting from line 427), Discussion (page 24 starting from line 590) and Certainty of the Evidence (page 16 starting from line 388), sections were revised to clarify that the meta-analysis was restricted to body fat percentage, justify its methodological feasibility, and explicitly acknowledge that the use of different body composition assessment methods (DXA and BIA) constitutes a limitation considered in the certainty of the evidence assessment.

2. Reviewer Comment: The authors should justify the use of post-intervention values rather than change scores or adjusted between-group differences in the meta-analysis. In randomized trials with small sample sizes, baseline differences may meaningfully influence post-intervention comparisons. If available, change-from-baseline data or adjusted estimates would provide a more appropriate synthesis and improve the interpretability of the pooled effect.

Response: Dear reviewer, we kindly appreciate your relevant observation. To increase methodological transparency, we included an explicit justification for the use of post-intervention values in the meta-analysis. Post-intervention values were used because the eligible studies did not consistently report standard deviations for change-from-baseline values or adjusted between-group estimates. Under these circumstances, the use of final values is a methodologically accepted approach, provided that baseline comparability exists between the randomized groups. Before conducting the quantitative synthesis, we verified this baseline comparability and acknowledged that small residual differences between groups cannot be completely excluded. This limitation is now explicitly acknowledged in the Discussion.

Modification Performed in the Manuscript: The Data Synthesis section (page 6 starting from line 246) was revised to justify the use of post-intervention values and to state that baseline comparability between the groups was verified before the quantitative synthesis. The Discussion was also expanded to acknowledge this methodological choice as a limitation of the quantitative synthesis (page 24 starting from line 590).

3. Reviewer Comment: Batrakoulis et al. was classified as having a high risk of bias but was included in the meta-analysis without a sensitivity analysis. Although sensitivity analysis may be limited when only two studies are included, this limitation further weakens the robustness of the pooled estimate. The authors should provide a more rigorous justification for including this study in the meta-analysis, perform an appropriate sensitivity analysis if possible, or avoid overinterpreting the pooled result.

Response: Dear reviewer, thank you for your valuable suggestion. We agree that assessing the robustness of the pooled estimate strengthens the interpretation of the meta-analysis. To address this concern, we performed a sensitivity analysis using the 20-week assessment point from Batrakoulis et al. instead of the 40-week assessment point adopted in the primary analysis. In the primary analysis, the last available follow-up from each study was used (40 weeks for Batrakoulis et al. and 12 weeks for Cao et al.). The pooled analysis demonstrated a significant reduction in body fat percentage in favor of FT/HIIT-F (MD = −4.44 percentage points; 95% CI −7.08 to −1.80; p = 0.001; I² = 0%). The sensitivity analysis also favored FT/functional HIIT, demonstrating a significant reduction in body fat percentage (MD = −3.40 percentage points; 95% CI −6.00 to −0.80; p = 0.01; I² = 0%). The direction and statistical significance of the effect remained consistent, indicating that the pooled estimate was not substantially influenced by the choice of the follow-up time point from Batrakoulis et al. We also maintained the high risk-of-bias judgment for Batrakoulis et al. and explicitly considered this limitation in both the GRADE assessment and the interpretation of the findings.

Modification Performed in the Manuscript: A new Sensitivity Analysis subsection (Section 3.7) and an additional forest plot (Figure 3) were included to evaluate the influence of the selected follow-up time point from Batrakoulis et al. The Methods section was also updated to describe the sensitivity analysis (page 6 starting from line 246) and the Discussion now explicitly acknowledges that the certainty of the pooled estimate remains limited because only two studies were included, one of which was classified as having a high risk of bias (page 24 starting from line 590).

4. Reviewer Comment: The classification of interventions requires further clarification. The included studies involve heterogeneous modalities such as functional HIIT, combined training, resistance training, treadmill HIIT, interdisciplinary therapy, and intermittent fasting combined with exercise. This heterogeneity makes it difficult to determine whether the observed effects are attributable to functional training itself or to combined/multicomponent interventions.

Response: We appreciate the reviewer's important observation and agree that greater transparency regarding the classification of the interventions was needed. To address this concern, we revised the Introduction to provide a clearer conceptual definition of functional training (FT). Specifically, we incorporated a recent international consensus defining FT as a physical intervention approach aimed at improving human performance according to individual goals, while considering task specificity and individual responses. We also clarified that FT should be understood as a continuum of functionality rather than as a rigidly distinct exercise category. In this context, we explained that multicomponent programs, CrossFit-like interventions, and functional forms of high-intensity interval training (HIIT-F) were considered within the scope of FT when they incorporated multi-joint movement patterns, integrated multiple physical capacities, and aimed to produce transferable adaptations relevant to activities of daily living. To increase transparency, we created a supplementary table (Supplementary Table S1) detailing how each of the seven included studies fulfilled these predefined criteria. This table documents the classification process and demonstrates that all included interventions met the operational definition of FT adopted in this review. Finally, we revised the Discussion section to explicitly acknowledge that the included interventions represent different manifestations along a continuum of functional training, including traditional FT, high-intensity functional training (HIIT-F), and functionally oriented multicomponent programs. Therefore, although all included studies fulfilled the predefined eligibility criteria for FT, the heterogeneity of the intervention designs limits the ability to attribute the observed effects to any isolated component of functional training and should be considered when interpreting the findings.

Modification Performed in the Manuscript: The Introduction was revised and expanded (page 2 starting from line 73). Supplementary Table S1 was added (page 4 starting from line 164) and a new paragraph was included in the Discussion acknowledging the heterogeneity of the intervention modalities and its implications for the interpretation of the findings (page 24 starting from line 585).

Table S1. Classification of the Included Studies According to the Predefined Functional Training Eligibility Criteria.

Study	C1	C2	C3	C4	C5	C6	Overall Decision	Classification
Sperlich et al., 2017	✓	✓	✓	✓	✓	✓	Eligible	HIIT-F
Batrakoulis et al., 2018	✓	✓	✓	✓	✓	✓	Eligible	FT
Feito et al., 2019	✓	✓	✓	✓	✓	✓	Eligible	HIIT-F
Teixeira et al., 2020	✓	✓	✓	✓	✓	✓	Eligible	FT
Cavaggioni et al., 2021	✓	✓	✓	✓	✓	✓	Eligible	FT
Cao et al., 2024	✓	✓	✓	✓	✓	✓	Eligible	HIIT-F
Ameur et al., 2024	✓	✓	✓	✓	✓	✓	Eligible	HIIT-F

Note: FT = Functional Training; HIIT-F = High-Intensity Functional Training.

Eligibility criteria:

C1 = Predominance of multi-joint and/or multi-planar movement patterns.

C2 = Intentional integration of at least two physical capacities within training sessions.

C3 = Presence of a documented progression scheme (intensity, volume, complexity, or training load).

C4 = Inclusion of neuromuscular challenges beyond isolated resistance exercises.

C5 = Clear reporting of exercise dose and monitoring procedures (frequency, session duration, work-to-rest ratio, and/or validated intensity metrics).

C6 = Explicit justification or evidence distinguishing the intervention from conventional resistance training and pure HIIT.

Note: Studies were classified as eligible when all six predefined criteria were satisfied.

5. Reviewer Comment: The GRADE approach: For outcomes without pooled estimates (lean mass and fat mass), the manuscript does not explain how inconsistency and imprecision were assessed.

Response: We appreciate your attention for highlighting this important methodological aspect. We agree that the previous version of the manuscript did not explain with sufficient clarity how the GRADE domains were applied to outcomes that could not be included in the meta-analysis. To address this issue, we revised the Certainty of the Evidence Assessment section and completely reformulated Table 4. We clarified that, for outcomes without pooled estimates, including fat mass, lean mass/fat-free mass, body weight, body mass index, central adiposity, and visceral fat area, the certainty of the evidence was assessed based on the narrative synthesis. In this assessment, the GRADE domains were judged by considering the risk of bias of the included studies, the consistency in the direction of effects, the clinical and methodological heterogeneity across interventions and comparators, the sample sizes, the body composition assessment methods, and the availability of comparable data. We also explicitly reported, both in the text and in Table 4, the rationale for each downgrade in the certainty of the evidence, thereby increasing the transparency of the assessment process.

Modification Performed in the Manuscript: The Certainty of the Evidence Assessment section was expanded to describe how the GRADE domains were applied to outcomes evaluated through narrative synthesis. Table 4 was completely revised to explicitly present the judgments for risk of bias, inconsistency, indirectness, and imprecision for each outcome, together with the corresponding rationale for downgrading the certainty of the evidence (pages 18-20).

6. Reviewer Comment: The manuscript reports a clear predominance of female participants. Therefore, the generalizability of the findings to men should be interpreted with caution. The title, abstract, and conclusions refer broadly to adults with overweight or obesity, but the evidence base is mainly composed of women. This limitation should be more explicitly reflected when discussing external validity and applicability of the findings.

Response: Dear reviewer, thank you for the important observation, and we fully agree that the predominance of female participants limits the generalizability of the findings to men. To address this issue, we revised the Abstract conclusion to explicitly acknowledge that the available evidence is derived predominantly from women and that extrapolation of the findings to men should be interpreted with caution. In addition, we expanded the Discussion to address more explicitly the implications of this sex imbalance for external validity. The revised text now emphasizes that most of the available evidence comes from studies involving women with overweight or obesity, that physiological and body composition differences between the sexes may influence responses to exercise interventions, and that future randomized controlled trials with a more balanced representation of men and women are needed to strengthen the certainty, applicability, and generalizability of the evidence.

Modification Performed in the Manuscript: The Abstract (Conclusion section) and the Discussion were revised to explicitly acknowledge the predominance of female participants and the limited generalizability of the findings to men (page 23 starting from line 542).

7. Reviewer Comment: The conclusions should be revised to adopt a more cautious tone consistent with the limitations of the evidence. Statements such as “The evidence indicates that FT can reduce body-fat percentage” imply a causal or intervention-oriented interpretation that is not fully supported by the available evidence, particularly considering the low certainty of evidence, the high risk of bias in some included studies, the small number of studies included in the meta-analysis, and the heterogeneity of interventions and assessment methods. I recommend revising the conclusion to avoid strong causal language and to align more closely with the methodological limitations and uncertainty of the findings.

Response: We appreciate your important observation and agree that the conclusions should reflect the very low certainty of the available evidence. To address this issue, we revised both the Abstract conclusion and the Main text’s Conclusions section to adopt a more cautious tone. Specifically, we replaced causal or definitive language with wording emphasizing that functional training may be associated with favorable changes in body composition, particularly in body fat percentage, but that these findings should be interpreted with caution because of the very low certainty of the evidence, the methodological limitations, the small number of studies included in the meta-analysis, the heterogeneity of the interventions and body composition assessment methods, and the predominance of female participants.

Modification Performed in the Manuscript: The Conclusion was revised to avoid strong causal language and to better align with the very low certainty of the evidence assessed using the GRADE approach, as well as with the methodological limitations identified throughout the review (page 25 starting from line 623).

8. Reviewer Comment: The in-text citations are occasionally not presented in the correct MDPI format. According to the journal’s guidelines, references should be cited using square brackets in order of appearance. For example, the reference to “Review Manager software, version 5.4.1, using a random-effects model (18)” uses parentheses instead of brackets. Similarly, “RT programs (17,18)” should be corrected. Please review and correct all in-text citations throughout the manuscript.

Response: We appreciate the reviewer's observation and agree with this recommendation. The entire manuscript was carefully reviewed to ensure that all in-text citations comply with the MDPI guidelines by using square brackets instead of parentheses.

Modification Performed in the Manuscript: All in-text citations were reviewed, and parentheses were replaced with square brackets wherever necessary. A complete verification of the manuscript was performed to ensure consistency with the MDPI reference formatting requirements.

9. Reviewer Comment: In Table 1, the footnotes contain typographical errors. For example, the abbreviation for RPE is listed as “Rated perceived exertio” instead of “Rated perceived exertion.” Please carefully check the table footnotes and ensure that all acronyms used in the tables are accurately defined. Each table should be self-contained and understandable without requiring the reader to search for definitions elsewhere in the manuscript.

Response: We thank the reviewer for identifying this issue. The footnotes of Table 1 were thoroughly reviewed and corrected. All abbreviations used in the tables were also verified and properly defined in the corresponding table footnotes.

Modification Performed in the Manuscript: The footnotes of Table 1 were corrected, including the definition of RPE (page 10). In addition, all abbreviations used throughout the tables were verified and properly defined in the corresponding footnotes to ensure that each table is self-contained and can be understood without referring to other sections of the manuscript.

10. Reviewer Comment: Table 4 presents several formatting problems that reduce readability. In the “Fat mass (kg)” row, the certainty rating appears as “Verylow” instead of “Very low.” In addition, the table layout is difficult to read, with narrow columns and fragmented words. Please revise the formatting of Table 4 to improve clarity and presentation according to MDPI standards.

Response: We thank the reviewer for identifying these presentation issues. We agree that the original version of Table 4 had limitations affecting its readability. To address this issue, we completely reconstructed the table using the format recommended by GRADEpro GDT. In addition to correcting typographical errors, such as changing "Verylow" to "Very low," we reorganized the table structure and adjusted the column widths, spacing, and overall layout to substantially improve readability. The revised table now also includes all outcomes evaluated in this review, clearly distinguishing those synthesized by meta-analysis from those evaluated through narrative synthesis, while presenting the GRADE judgments and the rationale for downgrading the certainty of the evidence in a clearer and more transparent manner.

Modification Performed in the Manuscript: Table 4 was completely revised and reformatted, including the correction of typographical errors, reorganization of the layout, and improvements to the overall visual presentation, making the table more comprehensive, readable, and consistent with the GRADE recommendations and MDPI formatting standards (pages 18-20).

11. Reviewer Comment: Several statements throughout the manuscript are not adequately supported by citations. For example, at the beginning of the Introduction, the authors state that “Obesity is a chronic and progressive condition, widely recognized as a global health epidemic, and is characterized by excessive accumulation of body fat” without providing a direct citation for this specific statement. Similar unsupported or insufficiently referenced statements appear in other sections of the manuscript. Please review the entire text and ensure that all epidemiological, conceptual, methodological, and interpretative claims are appropriately supported by relevant and up-to-date references.

Response: We thank the reviewer for pointing out this issue. References [1,2] were added to the first sentence of the Introduction, supporting the definition and characterization of obesity as a chronic and progressive condition. In addition, we conducted a comprehensive review of the entire manuscript to ensure that all epidemiological, conceptual, methodological, and interpretative statements are appropriately supported by relevant and up-to-date references.

Modification Performed in the Manuscript: A comprehensive review of the manuscript was conducted to ensure the appropriate use of citations throughout the text. References were added wherever necessary to support epidemiological, conceptual, methodological, and interpretative statements that previously lacked adequate bibliographic support.

 

Sincerely,

The authors.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I would like to thank the authors for their careful revision of the manuscript. I recommend acceptance of the manuscript in its current form.