The Effects of L-Citrulline and Malic Acid on Substrate Utilisation and Lactate Elimination
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsL-citrulline and malic acid are both natural-sourced supplements that has been widely used (usually together as citrulline malate) in hope to improve athletic performance. Numerous studies have been conducted to research their effectiveness and potential mechanisms of action, yet the results of those studies are often equivocal. This manuscript by Baráth et al. contributed another insight to the field, focusing on the effects of L-citrulline and malic acid separately, and using RER, RPExHeart rate and blood lactate level as readout. This study was double-blind with placebo controls in design, and the data were analyzed and presented with suitable statistical tools, making this manuscript easy to read and scientifically sound.
Below are a few questions and comments for the authors:
1. The authors advocate the use of RPExHeart rate as a measure of fatigue, which is interesting. However, the author should include the data showing RPE and heart rate separately to give a clear comparison and to better showcase the benefits of using RPExHeart rate combination.
2. The number on the y-axis of the Figure 2A need to be revised (add another decimal, I assume).
3. What statistical criterial was used to determine the outliners that were present in many figures? Can authors comments on how why so many outliners were seen?
4. Line 305-307 and Figure 5 should be in the section 3.3, not before.
5. On line 333, the authors wrote: “Considering the low cost and accessibility of these supplements everybody should at least give it a thought”. It is beyond the scope of this scientific article to advocate everybody to use the citrulline/malate. Consider changing it to something like “people who wish to improve…may consider it” or similar.
6. In the discussion section, the authors should provide some discussion on single dose (as in this study) versus long-term doses (as in the study highlighted by the authors, reference [15]).
7. Line 87, what is “the reviewed literature” referring to? Is that all the previous works mentioned above agree on the statement, or just a subset of them (in that case citations needed). Kind of confusing here.
8. For the introduction section, it is suggested that more original literature should be cited (if possible) rather than just citing review articles. (For example, line 59).
9. “L-citrulline” please check with the journal guideline if L needs to be capitalized (which is usually the case in chemical names).
Comments on the Quality of English LanguageThere are a number of grammar issues throughout the manuscript, although they didn't influence the understanding of the content.
Author Response
Dear Reviewer,
first of all, thank you for your valuable feedback! Please find or responses below.
Comment 1: The authors advocate the use of RPExHeart rate as a measure of fatigue, which is interesting. However, the author should include the data showing RPE and heart rate separately to give a clear comparison and to better showcase the benefits of using RPExHeart rate combination.
Answer 1: We agree, therefore we provided seperate heart rate and RPE data in table 4 and 5, lines 316-320.
Comment 2: The number on the y-axis of the Figure 2A need to be revised (add another decimal, I assume).
Answer 2: We agree, therefore we changed the figure and corrected the mistake.
Comment 3: What statistical criterial was used to determine the outliners that were present in many figures? Can authors comments on how why so many outliners were seen?
Answer 3: Due to the small sample size, we decided to not use statistical analysis to identify outliers.
Comment 4: Line 305-307 and Figure 5 should be in the section 3.3, not before.
Answer 4: We agree, therefore we moved this part to section 3.3.
Comment 5: On line 333, the authors wrote: “Considering the low cost and accessibility of these supplements everybody should at least give it a thought”. It is beyond the scope of this scientific article to advocate everybody to use the citrulline/malate. Consider changing it to something like “people who wish to improve…may consider it” or similar.
Answer 5: We agree, therefore we changed the text line 389-391.
Comment 6: In the discussion section, the authors should provide some discussion on single dose (as in this study) versus long-term doses (as in the study highlighted by the authors, reference [15]).
Answer 6: In the literature review (lines 57-87) we attempted to focus on the fact that although there are many studies regarding this topic broadly, there is not a single study examining the effects of acute and separate citrulline and malic acid supplementation on aerobic endurance. The present study is the first one which targets all of these aspects at the same time. Hence, we are unable to make comparisons, as the referenced study used a citrulline-malate blend.
Comment 7: Line 87, what is “the reviewed literature” referring to? Is that all the previous works mentioned above agree on the statement, or just a subset of them (in that case citations needed). Kind of confusing here.
Answer 7: We agree, therefore we added the required references line 85-87.
Comment 8: For the introduction section, it is suggested that more original literature should be cited (if possible) rather than just citing review articles. (For example, line 59).
Answer 8: Out of the 21 references used in the introduction only two are meta-analysis or reviews. Moreover, we used multiple of the individual studies used in the meta-analysis but found the manuscript to be understood easier with only citing the review article.
Comment 9: “L-citrulline” please check with the journal guideline if L needs to be capitalized (which is usually the case in chemical names).
Answer 9: We agree, therefore we changed it to capital letters.
Reviewer 2 Report
Comments and Suggestions for AuthorsFirstly, thank you for providing me an opportunity to review this interesting article. This study aimed to explore the influence of different supplements on performance of the athletes in terms of endurance. I want to emphasize that this topic is valuable and interesting in terms of the endurance capacities of athletes. For better clarity of the article please see my comments below:
INTRODUCTION
The introduction is written poorly, it does not flow between topics (e.g., endurance athletes, supplements, the importance of supplement use in endurance sports, and aim).
Lines 87-89 – this part is divided but does not represent the topic on its own, should be connected to the previous or following part.
Lines 91-99 – this part is about your ideas and will to research this topic but it is out of context when placed in the middle of the introduction, either remove it or connect it to the aim paragraph.
There are a lot of typos – reference numbers, extra spaces, etc..., please revise.
Revise the type of reference writing in the text, the numbers should be placed before dots, and within brackets not separated by them.
In my opinion, the introduction should changed throughout, with different paragraphs. Also, there is no need to explain all measured variables in the introduction that could be done in methods or discussion to connect it to the results obtained.
Lines 124-130 – Hypothesis 1 includes all other hypotheses, therefore, there is no need to place all of them. Consider writing fewer hypotheses.
METHODS
Table 1 is messed up and it interferes with line numbers.
Why the authors did not measure VO2 max to provide more informative demographics on participants?
Why is RER measured with a Polar strap, and not with Jaeger? The measurement with a gas analyzer should be a more precise method.
Figures 1a and 1b are small and not visible enough, please enlarge them.
Did all participants use all supplements or were they divided into groups? This part is not included in the methods.
DISCUSSION
Consider starting the discussion with a listing of all the important findings of this study.
Would you consider a higher RER in the placebo group before the test, to be important for the results.
Include the limitations and strengths section in the discussion.
Author Response
Dear Reviewer,
first of all, thank you for your valuable feedback! Please find or responses below.
Comment 1: Lines 87-89 – this part is divided but does not represent the topic on its own, should be connected to the previous or following part.
Answer 1: We agree, therefore we connected it to the paragraph prior line 85-87.
Comment 2: Lines 91-99 – this part is about your ideas and will to research this topic but it is out of context when placed in the middle of the introduction, either remove it or connect it to the aim paragraph.
Answer 2: We agree, therefore we moved it to the aims paragraph lines 126-134.
Comment 3: There are a lot of typos – reference numbers, extra spaces, etc..., please revise.
Answer 3: We revised the text and corrected reference numbers and spelling mistakes.
Comment 4: Revise the type of reference writing in the text, the numbers should be placed before dots, and within brackets not separated by them.
Answer 4: We changed the reference writing according to the guidelines.
Comment 5: In my opinion, the introduction should changed throughout, with different paragraphs. Also, there is no need to explain all measured variables in the introduction that could be done in methods or discussion to connect it to the results obtained.
Answer 5: We made adjustments where possible. We decided to keep the explanation of the variables, as we also want readers to understand our paper who are not familiar with exercise physiology expressions. Moreover, considering we are obligated to type out the words of an abbreviation used the first time (e.g. RPE [rate of perceived exertion]), it seems logically consistent to also give a brief explanation regarding these niche expressions.
Comment 6: Lines 124-130 – Hypothesis 1 includes all other hypotheses, therefore, there is no need to place all of them. Consider writing fewer hypotheses.
Answer 6: We agree, therefore we deleted the first hypothesis.
Comment 7: Table 1 is messed up and it interferes with line numbers.
Answer 7: We adjusted table 1.
Comment 8: Why the authors did not measure VO2 max to provide more informative demographics on participants?
Answer 8: We included VO2 max into the description of participants lines 150-151.
Comment 9: Why is RER measured with a Polar strap, and not with Jaeger? The measurement with a gas analyzer should be a more precise method.
Answer 9: It was a typo mistake that we corrected. We moved the RER-value to line 207 where we list parameters recorded by the Jaeger.
Comment 10: Figures 1a and 1b are small and not visible enough, please enlarge them.
Answer: We agree, therefore we enlarged figures 1a and 1b.
Comment 11: Did all participants use all supplements or were they divided into groups? This part is not included in the methods.
Answer 11: “Participants completed the protocol three separate times on three separate days at the same time of the day with 48 hours of recovery in between. The supplementation was either 6000 mg of L-citrulline + 300 ml of water, 3000 mg of malic acid + 300 ml of water or a placebo + 300 ml of water.” (lines 179-182). In our opinion, this clarifies this topic sufficiently.
Comment 12: Consider starting the discussion with a listing of all the important findings of this study.
Answer 12: We agree, therefore we added a few sentences to provide some extra information lines 364-368.
Comment 13: Would you consider a higher RER in the placebo group before the test, to be important for the results.
Answer 13: The RER-values in the placebo group before the test were not significantly higher, thus we did not include it.
Comment 14: Include the limitations and strengths section in the discussion.
Answer 14: We included a strengths and limitations section lines 433-439.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
Thank you for revising your manuscript according to my comments and suggestions.
