Functional Exercise Induces Adaptations in Muscle Oxygen Saturation in Division One Collegiate Butterfly Swimmers: A Randomized Controlled Trial

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper uses wearable near-infrared spectroscopy (NIRS) electronic devices to examine the effects of a 5-week exercise program designed to enhance the endurance of the posterior shoulder musculature of swimmers, and mitigate shoulder fatigue and injury. The devices measure SmO2, which is a metric of the muscle oxygenation. Four out of six swimmers that applied the exercise program saw a decrease of their muscle oxygen saturation (SmO2) over the duration of a 100-yard butterfly sprint. Also, Posterior Shoulder Endurance Test (PSET) scores (a metric inversely related to the pain that athletes feel) taken throughout the 5 weeks show that the exercise program reduces pain and thus improves endurance.

On the positive side, this is one of the few available studies that measures SmO2 in-situ (during swimming) and the first randomized control trial that assesses the role of wearable NIRS sensors in optimizing athlete training. However, there are multiple points to consider. As the authors themselves acknowledge, the sample size is very small (12 athletes), and a weekly 100-yard butterfly sprint is perhaps not the best metric of endurance. In my opinion, the PSET scores are stronger evidence of the exercise program’s benefits than the SmO2 data. It seems that there are different trends in the SmO2 data within the 5 weeks (see comments). Also, the SmO2 data constitute a key piece of the manuscript, since it is these data that were acquired using the wearable sensors. Hence, I would recommend to perform additional experiments in order to enlarge the sample size and clarify the SmO2 data trends, unless the authors are somehow able to explain the SmO2 trends with the existing data.

Comments:

·         How is the sensor used in this study dealing with issues commonly affecting wearable devices, such as the attenuation of wireless signals in water, motion artifacts, and suboptimal skin contact?

·         Figure 2, panel (e): It seems that there are massive variations of SmO2 in Week 1. Any ideas as to why? Could the sensor have been damaged?

·         In Figure 3, it actually seems to me like the only cases where there is a clear downward trend of the median SmO2 over time in the exercise group are panels (c), (d) and (e). In panels (a), (b), (f) the median SmO2 value in Week 5 is higher than that of Week 1. Can the authors comment on this?

·         In four out of six athletes in the exercise group (panels a, d, e, f), the median SmO2 value increases from Week 1 to Week 2. Do the authors have an explanation for this?

Author Response

We appreciate your feedback and agree that the SmO2 data presents challenges in identifying consistent patterns due to the noise observed in certain weeks for specific individuals. This noise, as reflected in both the graphs and the Point of Inflection (POI) R^2 values, has indeed skewed our results, leading to artificially higher medians during these problematic weeks.

To address this, we had created the secondary analysis grouping based on "chosen weeks," selected according to the POI R^2 value. This grouping highlights the weeks where SmO2 plots more closely follow the hypothesized "desaturation-sustained" pattern, providing a clearer picture of the trends we observed. Since this is not currently clear in the median plots, we decided to add an asterisk above the weeks that were designated as the chosen weeks to aid in clarity.

We recognize that a 200-yard butterfly test would likely provide a more thorough assessment of the athletes' endurance compared to the 100-yard distance we employed. However, regardless of the distance, the posterior deltoid and rotator cuff muscles primarily play a supportive role, contributing minimally to the swimmer's propulsion. While a longer distance might offer deeper insights as the swimmer becomes more fatigued, we believe the fatigue onset for these muscles likely follows a fairly similar pattern regardless of the distance. Our SmO2 data indicates that four out of six athletes in the EX group experienced a decrease in overall SmO2 during their swim, while all six EX group athletes showed significant improvements in their PSET scores—outcomes not observed in the CTRL group.

Furthermore, this is the first study to evaluate how a dryland exercise program translates to in-water SmO2 characteristics. We believe that the SmO2 data reflects an alteration in the onset of fatigue, which might not be accurately reflected in their swimming performance due to the “sprint” nature of the 100 yard distance. However, the increase in PSET score reflects improvements in muscular endurance, by quantifying the increased delay in muscular failure.

 

Comments 1: How is the sensor used in this study dealing with issues commonly affecting wearable devices, such as the attenuation of wireless signals in water, motion artifacts, and suboptimal skin contact?

Response 1: The wearable sensor we used in our experiments (MOXY Monitor) records and stores the SmO2 data on the device itself. This eliminates the issues regarding wireless signal attenuation due to water interference. 

However, motion artifacts and suboptimal skin contact are issues that were much more pertinent to our study. We used a double-sided adhesive on the underside of the device to secure it to the athlete. Strips of waterproof athletic tape were applied over the device, further securing it to the athlete and minimizing both vertical and horizontal translation of the device. Over the duration of the study, we continued to adapt and refine the adhesive placement such that it was slightly tailored to each athlete’s individual structure. An additional panel has been added to Figure 1 displaying the sensor and adhesive placement.

Comment 2: Figure 2, panel (e): It seems that there are massive variations of SmO2 in Week 1. Any ideas as to why? Could the sensor have been damaged?

Response 2: We believe that the more generalized adhesive patterns we applied at the start of the experiment led to noise due to issues with skin contact or motion artifacts. We know that the sensor itself was not the issue, due to the fact that other data collected that week and over the duration of the experiment used the same sensor.

Comment 3: In Figure 3, it actually seems to me like the only cases where there is a clear downward trend of the median SmO2 over time in the exercise group are panels (c), (d) and (e). In panels (a), (b), (f) the median SmO2 value in Week 5 is higher than that of Week 1. Can the authors comment on this?

Response 3: 

Panel A: There was significant noise present in the data for Week 1 (Shown in Figure 2a), although even when looking at the chosen weeks, the decrease in SmO2 is still nonsignificant.

Panel B: There was significant noise present in the data for Week 5 (Shown in Figure 2b), artificially inflating the Median SmO2 value. If looking at the data between the chosen weeks (Weeks 1&4), the negative trend becomes apparent. 

Panel F: Athlete 6’s data was consistently in the 0-10% SmO2 range throughout the entire experiment. This makes it difficult to make any claims about his data, outside the PSET score improvement.

Comment 4: In four out of six athletes in the exercise group (panels a, d, e, f), the median SmO2 value increases from Week 1 to Week 2. Do the authors have an explanation for this?

Response 4: 

Panel A: Similar to last comment, Week 1 had significant noise.

Panel D: Week 1 also had significant noise for Athlete 4 (Shown in Figure 2d), and showed a poor fit to the desaturation-sustained pattern (R^2=0.481).

Panel E: Resting values of SmO2 can fluctuate due to a variety of factors (hydration, body fat levels, muscle fatigue, etc.) This increase likely reflects one of these variables, since Athlete 5’s SmO2 did not desaturate during either week 1 or week 2, and isn’t reflective of any adaptation.

Panel F: Similar to the last comment, it is difficult to make any definitive conclusions from Athlete 6’s SmO2 data alone.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In your abstract, you can refer to the statistical analysis that you used

24. Add a reference.

37. Please, refer to them.

57. Describe the abbreviation

91. Please, give more information about the way that you split the participants. Also, the differences between groups should presented clearly.

95. I suggest to demonstrate participants’ World Aquatic points. Check this reference: https://doi.org/10.1080/24748668.2024.2333612. Also, refer to their performance.

100. Please, check if the table’s units are suitable for this journal.

105. Was it a controlled pace for all participants?

121. Why did you choose these degrees? I expected to implement this exercise at 0 degrees.

134. Please, explain these positions.

139. Was this process under the consideration of any coach?

148. It would be useful to include a photo. It is very crucial for the swimmers to feel comfortable with the tape.

150. If you conducted measurements each week; why did you conduct repeated measures ANOVA?

165. Begin with text and not numbers. “Forty – eight”

174. Explain the abbreviations under the table.

Please, modify the tables’ format.

 221. Any reference?

248. How did this happen? Were there technical corrections during the exercise?

 

280. It is not necessary to include statistical indexes.

Author Response

We appreciate your feedback, and have addressed your comments to the best of our ability. We have uploaded a marked-up copy of the manuscript in the non-published materials, highlighting the changes made.

Please see the attachment for our responses to your comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I would like to thank the authors for their response and provided explanations. I understand the notion of "chosen weeks" much better now. I believe the paper can be published in its current form.

Author Response

Thank you again for your suggestions during the previous round.

Reviewer 2 Report

Comments and Suggestions for Authors

The World Aquatic points should be included to depict the swimming level of the participants

Please, explain in the text the reasons that you used the 15 degrees.

How can you ensure the proper execution during the dry land training?

In statistical analysis, I did understand your answer. Please, re-write it. You split your sample into two teams (Control and Exercise) and you measured them 5 times. 

I asked about the tables' format so as not to split the table. Check the tables in this article https://doi.org/10.3390/sports11090186 

Please, address your comments referring to the number of lines that you modified.

Comments on the Quality of English Language

Please do a final check on the English language.

Author Response

Thank you again for your comments. Please see the attachment for the edits made.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

My comments were explained, moving to the necessary modifications in the manuscript.