Analysis of Cyclist’s Drag on the Aero Position Using Numerical Simulations and Analytical Procedures: A Case Study

Round 1

Reviewer 1 Report

I think this paper is unique because it makes full use of biomechanics research methods. It may not be worth mentioning here, but given the interest of the readers of this paper, it may be submitted to a journal specializing in sports science. 

I know that one subject is standard in biomechanics research, but from the perspective of public health research, I wonder if it can be generalized by the result of only one person, so I am specialized in public health. Please describe the reason why one subject is enough for readers to understand.

The research in this paper is an excellent attempt to clarify cyclist drag by focusing on CFD and analytical procedure. There is no problem from the perspective of sports science, and it is possible to publish almost as it is. I think that it can be adopted because of the novelty of measurement and analysis methods. In biomechanics research, one subject is normal, so I am wondering if it should be pointed out, but I am wondering whether only one subject can assert the validity and reliability of this analysis method, so I can solve that point I think that the description will be a better paper. From a more nasty point of view, I think it would be helpful for readers to add a description so that they can understand how this research will contribute to the fields of Environmental Research and Public Health.

Author Response

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Reviewer 2 Report

This is an interesting study comparing two methods (numerical simulation and analytical procedures) of evaluation of cyclist's drag on the aero position. The methods of research are correct, although in my opinion the conclusions are too general - only one athlete was examined and no conclusions can be drawn about the usefulness of these methods. I suggest that we increase the number of particpants and change the title of the work to emphasize that paper is about comparing two assessment methods.

Author Response

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Reviewer 3 Report

This paper compared a cyclist drag force estimated by two different methods including the computational fluid dynamics (CFD) and analytical procedures. Both methods were used to compute drag, frontal area and drag coefficient at different speeds ranging 1 m/s and 22 m/s. The authors concluded that the drag force values obtained by analytical procedures appear to be overestimated compared to the CFD method, but there was no significant difference between the two methods. The topic may be interesting for the potential readers in the relevant fields, but there are some major issues to be addressed:

1. Abstract: Background part does not inform background.
2. Line 119–122: What is the variable to be tested? The drag force? If this reviewer understood correctly, the drag force is determined by either CFD or the analytical procedures, and thus, the distribution cannot be determined. This reviewer agrees that the Bland–Altman analysis is appropriate method to compare one method (analytical procedures for here) with the traditional (or gold-standard) method (CFD for here). Please clarify how the paired t-test can be used to compare the two methods.
3. In the Results section, there are many redundant figures. If this reviewer understood correctly, main messages would be: (1) the difference in the drag force between CFD and analytical procedures becomes greater, as the speed increases; (2) At a higher speed, the analytical procedures underestimate the drag force compared to CFD; and (3) The drag force estimated by the two methods is not statistically different. Please clarify data presentation.
4. Technically, Figure 4 is not a Bland–Altman plot.
5. Line 162: The authors described that CFD is considered as gold standard, while there is approximately 7–11% error between CFD and wind tunnel methods. This reviewer thinks that the wind tunnel method is gold standard and the CFD approach is one of alternatives. Please clarify this.
6. Line 172–173: Can the authors calculate drag coefficient as a function of speed in the CFD approach? This would be more powerful to support the authors’ statements.
7. In general, this reviewer would suggest that the authors may want to add the potential effects of subject’s body mass, surface area on the drag force estimation. This sensitivity analysis would provide a general agreement for a reasonable range of such factors to estimate the drag force accurate enough compared to the CFD approach.
8. There are many errata and grammatical mistakes. This reviewer strongly recommends an extensive English correction.

Author Response

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Round 2

Reviewer 2 Report

The authors have significantly improved the text, especially by making it clear that it is a case study and that it is necessary to be careful in the interpretation of data. I hope that in the future the authors will prepare a similar work with the participation of more respondents.

Author Response

Thank you very much for your kind suggestions and commentaries to improve our manuscript.

Reviewer 3 Report

Thank the authors for the effort to address the previous comments. The revised manuscript is now more clear. I have a few comments:
1. This reviewer still wonder if the paired t-test is appropriate, although the authors described the rationale by citing the previous papers. This is because there are two factors: one is the method and the other is the speed. The authors consider only one factor (i.e., the method) to have distribution by ignoring the effect of the speed, but this does not sound reasonable because the experimental design is to see how the drag forces are different between the methods at different speeds. Please clarify it.
2. This reviewer would suggest adding a figure for drag coefficients for both methods as a function of speed.
3. Is there any ways to modify the current analytical equation from this study? For example, the drag coefficient in the current analytical equation is not a function of speed, but the authors learned that the drag coefficient from CFD is a function of speed. If the authors could modify the current equation and provide the performance by comparing the CFD results, this paper would be more helpful for potential readers who do not access to the CFD technique that has huge computation costs, and thus is potentially not practical.

Author Response

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