Influence of Oestradiol Fluctuations in the Menstrual Cycle on Respiratory Exchange Ratio at Different Exercise Intensities: A Systematic Review, Meta-Analysis and Pooled-Data Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This reviewer would like to commend the authors on their effort on this project. The meta-analysis sought to assess the impact of the menstrual cycle phase on measures of exercise respiratory exchange ratio. The findings of the meta-analysis suggest there are no differences in RER between menstrual cycle phases except when considering maximal intensities. The pooled analysis suggests that there may be differences in RER at lower intensities as well. However, I have some concerns about the interpretation of the data that must be addressed prior to publication.

 

The authors repeat their findings throughout the discussion in multiple different ways that make it difficult to follow. On figure 3, the low intensity studies clearly have no change or favor the luteal phase. Figure 4 clearly demonstrates that the high intensity (100% VO2max) exercise has a moderate effect on RER favoring the follicular phase. Yet, there was no correlation between the change in estrogen across the phases and RER. It would be most helpful for the authors to revise the discussion to reflect the way the results are presented. As it stands now, the authors prioritize the pooled data analysis findings because there was significance there. I must caution the authors about putting so much weight on a pooled analysis because of the inherent limitations to the method (Bravata DM, Olkin I. Simple pooling versus combining in meta-analysis. Eval Health Prof. 2001 Jun;24(2):218-30. doi: 10.1177/01632780122034885. PMID: 11523387). The differences between the phases while significant were extremely small and have little clinical relevance to the field of exercise research. As such, the discussion emphasis and abstract conclusion need to be updated to reflect the limitations of the approach and to fairly present the results of the meta-analysis. While it is interesting that maximal intensities may be impacted by the menstrual cycle, most females do not exercise or train at that level. Additionally, the authors do not fully present how the findings compare and contrast to previous literature. The findings of the meta-analysis demonstrate that there may not be phase differences in RER, which aligns with much of the recent research demonstrating small effects on exercise outcomes.  

 

It is recommended the authors proofread the manuscript. There were quite a few misinterpretations of cited papers, grammatical errors, and possible switches of the terms “anaerobic” and “aerobic.” Please see below for a few examples:

 

Line 88: double period

 

Line 88 to 89: “When blood glucose con-centrations are high, use of glucose as a fuel is prioritised, but this is limited by the actions of oestradiol [16,17].” Please clarify what you mean by this sentence. As it is written now, it seems like you are suggesting estrogen blunts the utilization of blood glucose, which is not true and not the correct interpretation of the studies you have cited.

 

Alemany M. Estrogens and the regulation of glucose metabolism. World J Diabetes. 2021 Oct 15;12(10):1622-1654. doi: 10.4239/wjd.v12.i10.1622. PMID: 34754368; PMCID: PMC8554369.

 

Line 324: missing a period

 

Line 354: Do the authors mean “aerobic” since they are referring to carbohydrate oxidation?

 

Line 256: A low I2 value demonstrates that there was low heterogeneity meaning that the studies were homogenous

 

Figure quality is poor in figure 3 and in figure 4 the axis cut off.

 

 

Author Response

Comment 1

The authors repeat their findings throughout the discussion in multiple different ways that make it difficult to follow. On figure 3, the low intensity studies clearly have no change or favor the luteal phase. Figure 4 clearly demonstrates that the high intensity (100% VO2max) exercise has a moderate effect on RER favoring the follicular phase. Yet, there was no correlation between the change in estrogen across the phases and RER. It would be most helpful for the authors to revise the discussion to reflect the way the results are presented. As it stands now, the authors prioritize the pooled data analysis findings because there was significance there. I must caution the authors about putting so much weight on a pooled analysis because of the inherent limitations to the method (Bravata DM, Olkin I. Simple pooling versus combining in meta-analysis. Eval Health Prof. 2001 Jun;24(2):218-30. doi: 10.1177/01632780122034885. PMID: 11523387).

Response 1

 Thank you for taking the time to review our manuscript, we are grateful for your feedback, and below we detail how we have amended it accordingly.

Lines 381-382 [but the results must be considered with caution due to the possibility of a type 1 error] and lines 411-412 [However, effects were not supported by the meta-analysis, therefore should be interpreted with caution] now highlight the limitations of pooled-analyses.

 

Comment 2

The differences between the phases while significant were extremely small and have little clinical relevance to the field of exercise research. As such, the discussion emphasis and abstract conclusion need to be updated to reflect the limitations of the approach and to fairly present the results of the meta-analysis. While it is interesting that maximal intensities may be impacted by the menstrual cycle, most females do not exercise or train at that level. Additionally, the authors do not fully present how the findings compare and contrast to previous literature. The findings of the meta-analysis demonstrate that there may not be phase differences in RER, which aligns with much of the recent research demonstrating small effects on exercise outcomes.

 

Response 2

 Thank you for this comment. We agree that meta-analyses are the most robust comparison however the pooled-analysis does hold value by inclusion of larger samples. Inclusion of both provides a greater overview of current literature whilst also highlighting the variability in menstrual cycle research. We agree that the effects of the menstrual cycle on exercise during submaximal exercise are minimal, however the pooled-analysis does present differences of up to 0.04 in RER between phases. As illustrated by Goedeke et al., 2000 [Goedecke et al., 2000] changes of 0.02 to 0.04, as evidenced in the pooled-analysis, between 0.70 and 0.94 RER reflect changes in fat oxidation of up to 13% which is likely to have significant implications for fuelling in extended duration events.

Additionally, in the meta-analyis, the effect size towards a higher RER in the follicular phase at maximum was 0.60 indicating a moderate effect of menstrual cycle at maximum intensity. Recent research has evidenced a large majority of athletes reaching VO_2max across various running distance events [Molinari et al., 2020]. In fact, it has been reported that women spend a larger amount of training time in high-intensity zones than men [van Erp et al., 2019]. Therefore, across competitions and training of varying distances, women are likely to be exercising at maximal intensity; should the menstrual cycle have an effect on maximum RER, as suggested by this meta-analysis, this implies an altered metabolic response to exercise during tasks that are often used in training and competition.

A variety of different running workouts will also achieve this level of intensity in both untrained and trained women, for example, tempo runs or maximal intervals. Additionally, high intensity interval training is used frequently in both sexes as an exercise choice but also in research at intensities at or above 95%VO_2max  [Flockhart et al., 2021;  Helgerud J et al., 2007] therefore if the menstrual cycle is influential on maximal RER, these research studies may need to consider its impact on the outcome variables of interest, and take into account menstrual cycle phase in future research protocols.

 

We have compared and contrasted to the current literature in menstrual cycle and substrate utilisation from line 377 through to 408 for below maximal exercise followed by line 421 for maximal. If this is not sufficient, please could the reviewer provide further clarification on where or in regard to which finding more comparison is required.

 

 

Comment 3

It is recommended the authors proofread the manuscript. There were quite a few misinterpretations of cited papers, grammatical errors, and possible switches of the terms “anaerobic” and “aerobic.” Please see below for a few examples:

Line 88: double period

Line 88 to 89: “When blood glucose con-centrations are high, use of glucose as a fuel is prioritised, but this is limited by the actions of oestradiol [16,17].” Please clarify what you mean by this sentence. As it is written now, it seems like you are suggesting estrogen blunts the utilization of blood glucose, which is not true and not the correct interpretation of the studies you have cited.  - Alemany M. Estrogens and the regulation of glucose metabolism. World J Diabetes. 2021 Oct 15;12(10):1622-1654. doi: 10.4239/wjd.v12.i10.1622. PMID: 34754368; PMCID: PMC8554369.

Line 334: missing a period

Line 354: Do the authors mean “aerobic” since they are referring to carbohydrate oxidation?  

Line 256: A low I2 value demonstrates that there was low heterogeneity meaning that the studies were homogenous

Figure quality is poor in figure 3 and in figure 4 the axis cut off

 

Response 3

Thank you for your helpful feedback, we have made some edits to the manuscript as requested. Missing periods or double periods rectified; we have also rephrased line 88-89 to avoid confusion in line with your recommendations [When blood glucose concentrations are high, use of glucose as a fuel is prioritized; this glucose homeostasis is reported to be partly mediated by oestrogen whereby estrogen acts to enhance uptake into the muscles and liver].

Line 354: We are unsure which line this is in reference to but if in reference to line 381 [At high intensities (75%-99%), exercise involves mixed substrate utilisation with a greater contribution of glucose utilisation, but once again RER may be higher in the follicular phase which may indicate an earlier switch to anaerobic metabolism and more pronounced shift towards reliance on carbohydrates]. In this instance, an increased RER may indicate anaerobic metabolism when above 1 [Solberg et al.,2005].  and this is also an indicator of mainly carbohydrate utilisation [Jeukendreup et al., 2005]. Please could the reviewer clarify if this is the line to which they are referring, and we will endeavour to rectify.

Line 256: In regard to the I2 values and homogeneity, apologies, we are again unsure where this refers to as the line numbers do not seem to align. If this is in reference to line 281, the I2 value stated here and the wording around heterogeneity not being altered meaningfully is related to the I2 of 9.94% when sedentary groups were removed from analysis, and is not a statement of heterogeneity/homogenous groups. Please could the reviewer elaborate on where this error has occurred.

The missing axis was the result of a formatting error, now corrected. We have re-exported and re-formatted the graphics. Figure 3 now as a 900 × 900 resolution and Figure 4 a 600 × 450 resolution, both PDF files.

 

References

Flockhart M, Nilsson LC, Tais S, Ekblom B, Apró W, Larsen FJ. Excessive exercise training causes mitochondrial functional impairment and decreases glucose tolerance in healthy volunteers. Cell Metab. 2021;33(5):957-970.e6. doi:10.1016/j.cmet.2021.02.017

Goedecke JH, St Clair Gibson A, Grobler L, Collins M, Noakes TD, Lambert EV. Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes. Am J Physiol Endocrinol Metab. 2000;279(6):E1325-E1334. doi:10.1152/ajpendo.2000.279.6.E1325

Helgerud J, Høydal K, Wang E, Karlsen T, Berg P, Bjerkaas M, Simonsen T, Helgesen C, Hjorth N, Bach R, Hoff J. Aerobic high-intensity intervals improve V˙ O2max more than moderate training. Medicine & science in sports & exercise. 2007 Apr 1;39(4):665-71

Jeukendrup AE, Wallis GA. Measurement of substrate oxidation during exercise by means of gas exchange measurements. Int J Sports Med. 2005;26 Suppl 1:S28-S37. doi:10.1055/s-2004-830512

Molinari CA, Edwards J, Billat V. Maximal Time Spent at VO_2max from Sprint to the Marathon. Int J Environ Res Public Health. 2020;17(24):9250. Published 2020 Dec 10. doi:10.3390/ijerph17249250

Solberg G, Robstad B, Skjønsberg OH, Borchsenius F. Respiratory gas exchange indices for estimating the anaerobic threshold. J Sports Sci Med. 2005;4(1):29-36. Published 2005 Mar 1.

van Erp T, Sanders D, de Koning JJ. Training Characteristics of Male and Female Professional Road Cyclists: A 4-Year Retrospective Analysis. Int J Sports Physiol Perform. 2019;15(4):534-540. Published 2019 Nov 5. doi:10.1123/ijspp.2019-0320

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Editor,

Thank you for inviting me to review the manuscript entitled “Influence of Oestradiol Fluctuations in the Menstrual Cycle on Respiratory Exchange Ratio at Different Exercise Intensities: A Systematic Review, Meta-Analysis and Pooled-Data Analysis.”

I believe the manuscript aligns with the journal’s aims and demonstrates an acceptable level of quality. However, I feel it necessary to suggest several improvements:

ABSTRACT

• Lines 14-15: Please revise to clarify that PRISMA guidelines are intended for reporting, not for conducting reviews.
• Line 16: A systematic review should broadly map the available literature. Why was the Embase database not included, and why was gray literature not considered? This could represent an important limitation to the findings.

INTRODUCTION

• Lines 66-72: I suggest adding further citations to support this paragraph.
• Lines 81-83: "Therefore, when these hormone levels are lower during the follicular phase, there might be a greater reliance on anaerobic ATP production due to reduced efficiency of mitochondrial respiration." Please add a citation here.
• Lines 111-115: It may improve clarity to more explicitly define the objective of the review by creating a subsection titled "1.1 Objective of the Review." This will help readers more easily identify the review’s goal.

METHODS
There are some methodological limitations in the Methods section that should be addressed:

• Line 118: "This systematic review and analysis were conducted (reported) based on the PRISMA statement guidelines [26]" – Please rephrase for accuracy.
• Line 120 (Eligibility Criteria): Specify that the PICOS methodology was used and briefly describe it. There’s no need for an in-depth breakdown of each PICOS element; typically, descriptions in this context are more concise. For example, in the “S” component, simply stating “primary studies” may suffice.
• Table 1: This table belongs in the Results section under a heading like “Description of Included Studies.” It currently lacks a legend explaining acronyms and contains minor formatting errors (e.g., "(n)"). In individual studies, the number of participants should ideally be reported as "(n=xx)." Please review and revise the table accordingly.
• Section 2.2: The search strategy for each database is not provided, which could limit the reproducibility of the search strings.

RESULTS
The results are generally well-presented with high methodological quality.

• Figures 2 and 3: These figures, especially Figure 3, lack adequate graphic quality.
• Table 4: Please add a legend for acronyms.

DISCUSSION
I commend the authors on a well-written and interpretable discussion section. However, it is quite lengthy. I suggest dividing the final part into two subsections: "4.1 Limitations Addressed" and "4.2 Implications for Clinical Practice." I believe these changes would enhance readability and overall quality.

REFERENCES
Please ensure that references adhere to the journal’s style guidelines, including italicization and bold formatting where required.

FINAL CONSIDERATIONS
In my view, this manuscript has the potential to be publishable once the suggested revisions are implemented, offering a high-quality secondary evidence source on this topic.

Author Response

ABSTRACT

Comment 1

Lines 14-15: Please revise to clarify that PRISMA guidelines are intended for reporting, not for conducting reviews.

Response 1

Thank you to the reviewer for your time and comments. This has been corrected.

 

Comment 2

Line 16: A systematic review should broadly map the available literature. Why was the Embase database not included, and why was gray literature not considered? This could represent an important limitation to the findings.

 

Response 2

Thank you for this feedback, the databases utilised were those supported and available by institutional access. Grey literature was not utilised due to the aim of including high quality peer-reviewed papers for which we used a detailed quality appraisal process. This is to improve the overall quality of menstrual cycle research and reviews available as poor quality has been highlighted as a limitation of current menstrual cycle research by McNulty et al., 2020

 

INTRODUCTION

Comment 3

Lines 66-72: I suggest adding further citations to support this paragraph

 

Response 3

A further citation has been added. [Bellar et al., 2012]

 

Comment 4

Lines 81-83: "Therefore, when these hormone levels are lower during the follicular phase, there might be a greater reliance on anaerobic ATP production due to reduced efficiency of mitochondrial respiration." Please add a citation here.

 

Response 4

A citation has been added [Irwin et el., 2008]

 

Comment 5

Lines 111-115: It may improve clarity to more explicitly define the objective of the review by creating a subsection titled "1.1 Objective of the Review." This will help readers more easily identify the review’s goal. –

 

Response 5

Thank you for this suggestion, we added in a line to outline the objective of the review more clearly on line 120 [Subsequently the objective of this review was to evaluate the impact of both menstrual cycle phase and oestradiol levels on RER with consideration for substrate utilisation.]

 

METHODS
There are some methodological limitations in the Methods section that should be addressed:

Comment 6

Line 118: "This systematic review and analysis were conducted (reported) based on the PRISMA statement guidelines [26]" – Please rephrase for accuracy.

Response 6

This has been rephrased in line with comment [This systematic review and analysis were conducted and reported based on the PRISMA statement guidelines [27] and registered protocol (CRD42024524091)].

Comment 7

Line 120 (Eligibility Criteria): Specify that the PICOS methodology was used and briefly describe it. There’s no need for an in-depth breakdown of each PICOS element; typically, descriptions in this context are more concise. For example, in the “S” component, simply stating “primary studies” may suffice. –

Response 7

Thank you for this comment, we have added the methodology in line 127 [The PICOS method was utilised to enable formulation and search for the research question.]. We would like to keep the PICOS breakdown, as we believe it provides clarity to the reader for the process of study selection which supports replication.

 

Comment 8

Table 1: This table belongs in the Results section under a heading like “Description of Included Studies.” It currently lacks a legend explaining acronyms and contains minor formatting errors (e.g., "(n)"). In individual studies, the number of participants should ideally be reported as "(n=xx)." Please review and revise the table accordingly.

 

Response 8

In agreement, we have moved Table 1 to the results section. We have also changed in individual studies to the (n-x) format as suggested. Explanation of acronyms has been provided in the Table 1 caption.

 

Comment 9

Section 2.2: The search strategy for each database is not provided, which could limit the reproducibility of the search strings.

Response 9

The search strategy was suitable for all the included databases and the search terms utilised are listed in line 153-157. Extra wording to confirm the search terms were used in all databases has been added [The following search terms were used in all databases:]

 

RESULTS

Comment 10

Figures 2 and 3: These figures, especially Figure 3, lack adequate graphic quality.

Table 4: Please add a legend for acronyms. – VO2max and RER

 

Response 10

Thank you for this comment, we have re-exported and re-formatted the graphics. They have a 900 × 900 resolution for Figure 3 and 600 × 450 resolution for Figure 4, both have been submitted in PDF format as required in journal guidelines. Font sizes have been increased where possible without disrupting the figure. Explanation of VO2max and RER has been provided in the Table 4 caption.

 

DISCUSSION

Comment 11
I commend the authors on a well-written and interpretable discussion section. However, it is quite lengthy. I suggest dividing the final part into two subsections: "4.1 Limitations Addressed" and "4.2 Implications for Clinical Practice." I believe these changes would enhance readability and overall quality.

Response 11

We appreciate your feedback; we have split the discussion as suggested to help improve the readability.

REFERENCES

Comment 12
Please ensure that references adhere to the journal’s style guidelines, including italicization and bold formatting where required.

 

Response 12

 Thank you for highlighting this, we have reviewed all formatting of references.

 

References

Bellar D, Judge LW. Modeling and relationship of respiratory exchange ratio to athletic performance. J Strength Cond Res. 2012;26(9):2484-2489. doi:10.1519/JSC.0b013e31823f271d

Irwin RW, Yao J, Hamilton RT, Cadenas E, Brinton RD, Nilsen J. Progesterone and estrogen regulate oxidative metabolism in brain mitochondria. Endocrinology. 2008;149(6):3167-3175. doi:10.1210/en.2007-1227

McNulty KL, Elliott-Sale KJ, Dolan E, Swinton PA, Ansdell P, Goodall S, et al. The Effects of Menstrual Cycle Phase on Exercise Performance in Eumenorrheic Women: A Systematic Review and Meta-Analysis. Sports Med. 2020; 50:1813. Available from: /pmc/articles/PMC7497427/22.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Response 2- Please add this rationale and evidence into the discussion. "We agree that the effects of the menstrual cycle on exercise during submaximal exercise are minimal, however the pooled-analysis does present differences of up to 0.04 in RER between phases. As illustrated by Goedeke et al., 2000 [Goedecke et al., 2000] changes of 0.02 to 0.04, as evidenced in the pooled-analysis, between 0.70 and 0.94 RER reflect changes in fat oxidation of up to 13% which is likely to have significant implications for fuelling in extended duration events."

I still feel strongly that the authors should clarify the difference between recreational and elite athletes and the potential impact for each IN the manuscript. The current comparison discussion on lines 337-413 discusses mainly VO2max, not RER. My original comment was to request RER be the main focus not VO2max or at least present the RER findings from the literature so the reader can compare results from table 4 specifically. 

Line 354: We are unsure which line this is in reference to but if in reference to line 381 [At high intensities (75%-99%), exercise involves mixed substrate utilisation with a greater contribution of glucose utilisation, but once again RER may be higher in the follicular phase which may indicate an earlier switch to anaerobic metabolism and more pronounced shift towards reliance on carbohydrates]. In this instance, an increased RER may indicate anaerobic metabolism when above 1 [Solberg et al.,2005]. and this is also an indicator of mainly carbohydrate utilisation [Jeukendreup et al., 2005]. Please could the reviewer clarify if this is the line to which they are referring, and we will endeavour to rectify.--- Yes, I was referring to this sentence. Please add your explanation into the manuscript.

Line 256: In regard to the I2 values and homogeneity, apologies, we are again unsure where this refers to as the line numbers do not seem to align. If this is in reference to line 281, the I2 value stated here and the wording around heterogeneity not being altered meaningfully is related to the I2 of 9.94% when sedentary groups were removed from analysis, and is not a statement of heterogeneity/homogenous groups. Please could the reviewer elaborate on where this error has occurred.--- I was referring actually to this sentence: The analysis of 11 submaximal exercise studies provided a minimal mean effect size (ES = -0.09 [CI: -0.35 – 0.17], p = 0.5). There was also evidence of low heterogeneity between studies (I2 = 3.58%, p =0.4) highlighting variation between studies (Fig 4). Eggers regression test did not suggest a significant effect of publication bias (Egger = 0.37, p= 0.71).

Author Response

Comment 1: Response 2- Please add this rationale and evidence into the discussion. "We agree that the effects of the menstrual cycle on exercise during submaximal exercise are minimal, however the pooled-analysis does present differences of up to 0.04 in RER between phases. As illustrated by Goedeke et al., 2000 [Goedecke et al., 2000] changes of 0.02 to 0.04, as evidenced in the pooled-analysis, between 0.70 and 0.94 RER reflect changes in fat oxidation of up to 13% which is likely to have significant implications for fuelling in extended duration events." 

Response 1: Thank you for this comment, we agree, and we have added in this rationale on line 350 "Subsequently, the effects of the menstrual cycle on exercise during submaximal exercise are minimal, however the pooled-analysis does present differences of up to 0.04 in RER between phases. As illustrated by Goedeke et al. [64] changes of 0.02 to 0.04, between 0.70 and 0.94 RER reflect changes in fat oxidation of up to 13% which is likely to have significant implications for fuelling in extended duration events." 

  

Comment 2: I still feel strongly that the authors should clarify the difference between recreational and elite athletes and the potential impact for each IN the manuscript. The current comparison discussion on lines 337-413 discusses mainly VO2max, not RER. My original comment was to request RER be the main focus not VO2max or at least present the RER findings from the literature so the reader can compare results from table 4 specifically.  

Response 2: Thank you for this comment, we have added in some of the response regarding trained and untrained women utilising these intensities in line 432 - 442 "This has implications in athletic populations as recent research has evidenced a large majority of athletes reaching VO2max across various running distance events [Molinari et al., 2020]. In fact, it has been reported that women spend a larger amount of training time in high-intensity zones than men [van Erp et al., 2019]. Therefore, should the menstrual cycle have an effect on maximum RER as suggested by this meta-analysis, this implies an altered metabolic response to exercise during training and competition. In both untrained and trained women, a variety of different running workouts will also achieve intensities of at or above 95%VO2max such as tempo runs or maximal intervals [Flockhart et al., 2021; Helgerud J et al., 2007]. If the menstrual cycle is influential on maximal RER, future research studies may need to consider its impact of the outcome variables of interest, and account for menstrual cycle phase."  which we hope demonstrates the importance of this finding for both trained and untrained women.   

Regarding your comment about VO2max discussion between lines 340-419; these paragraphs are focused on RER as a measure of substrate utilisation, discussing RER in relation with the wider literature, including referring to Table 4 on line 391. VO2max is mentioned here only as a measure of intensity, as percentage of VO2max was used to group the studies as part of the review. The review is centred on presenting the RER findings from the literature and summarises the current available literature on RER at differing exercise intensities on line 334 and in Table 1. 

  

Comment 3: Line 354: We are unsure which line this is in reference to but if in reference to line 381 [At high intensities (75%-99%), exercise involves mixed substrate utilisation with a greater contribution of glucose utilisation, but once again RER may be higher in the follicular phase which may indicate an earlier switch to anaerobic metabolism and more pronounced shift towards reliance on carbohydrates]. In this instance, an increased RER may indicate anaerobic metabolism when above 1 [Solberg et al.,2005]. and this is also an indicator of mainly carbohydrate utilisation [Jeukendreup et al., 2005]. Please could the reviewer clarify if this is the line to which they are referring, and we will endeavour to rectify. --- Yes, I was referring to this sentence. Please add your explanation into the manuscript. 

Response 3: Thank you to the reviewer for this clarification, we have added in further explanation on line 373: 'once again RER may be higher in the follicular phase which may indicate an earlier reliance onto anaerobic metabolism due to the likelihood of reaching an RER of 1 earlier [Solberg et al.,2005] and more pronounced shift towards reliance on carbohydrates, reflected by greater RER values [Jeukendreup et al., 2005].' 

  

Comment 4: Line 256: In regard to the I2 values and homogeneity, apologies, we are again unsure where this refers to as the line numbers do not seem to align. If this is in reference to line 281, the I2 value stated here and the wording around heterogeneity not being altered meaningfully is related to the I2 of 9.94% when sedentary groups were removed from analysis and is not a statement of heterogeneity/homogenous groups. Please could the reviewer elaborate on where this error has occurred. --- I was referring actually to this sentence: The analysis of 11 submaximal exercise studies provided a minimal mean effect size (ES = -0.09 [CI: -0.35 – 0.17], p = 0.5). There was also evidence of low heterogeneity between studies (I2 = 3.58%, p =0.4) highlighting variation between studies (Fig 4). Eggers regression test did not suggest a significant effect of publication bias (Egger = 0.37, p= 0.71). 

Response 4: Thank you for highlighting this, we have added in the missing word on line 269 "highlighting little variation between studies". 

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have made appropriate changes to the manuscript, it can be published

Author Response

Thank you to the reviewer for their final review, we greatly appreciate your time and constructive feedback on our manuscript.