Study on the Effect of Different Transcranial Pulse Current Stimulation Intervention Programs for Eliminating Physical Fatigue

Round 1

Reviewer 1 Report

• In this study, authors aimed to examine the optimal parameters (intensity and duration) of tPCS, which is a relatively a new NIBS modality, by investigating the effect of these parameters on the fatigue level after treadmill running in 30 healthy adults, who were allocated either in moderate or severe fatigue group. Using 5 tPCS programs and analyzing fatigue specific measures, they found that the effect on each group depends on the intensity and in less extent on duration of tPCS.

Present findings might be of great interest to the readership of Applied Sciences. Though, the present study is within Applied Sciences' scope of the interests, I do have some major concerns/comments/suggestions. Please see below.  

 

• Major Concerns:
• In the introduction, the gap of knowledge and the rationale of conducting this study is not well presented and discussed. Authors should elaborate more on why testing tPCS and no other NIBS/TES modalities is important. Also, why fatigue elimination is important, in either healthy and clinical cohorts.
• There are parts in the Methods section, such as 2.2 - 2.5, that require more details and information.  

 

• Minor Concerns (still important but may not impact conclusions):
• Title
• As the title currently is, it does not fully reflect to the present study.
• Authors should consider revision.
• Abstract
• It requires some revisions.
• Line 9: "eliminating fatigue" = please elaborate in ()
• Line 11: the right number should be 30 and not 40, right?
• Lines 14-15: add the intervention programs in ()
• All dependent variables should be listed (eg, LF, HF, etc).
• Line 20: "had the best effect" - elaborate on this. Best implies the lowest p-val or biggest change?
• Introduction
• Lines 38-40: please add the appropriate references at the end of the sentence.
• Line 40: "Williams" - wrong format, please correct it
• Line 41: "elimination effects" - please elaborate more on this
• Line 44: appropriate ref should be cited.
• Line 72: RR should be spelled out.
• Line 74: HbO2 - please spell it out.
• Lines 80-81: Per table 2, program III is different for what is stated in these lines. Please correct accordingly. 
• Methods
• Line 88: (no distinction between sports) - why is that? Does this imply that the fatigue level is similar across sports?
• Lines 91-93: how these inclusion criteria were determined? Scales, questionnaires?
• Line 97: why three rounds of screening? Is it typical?
• Line 100: "recovery time": please elaborate on this. Does it imply that fatigue level must be fallen below a certain level? If so, which one?
• Line 111: "duty cycle" - please elaborate
• Lines 134-135: 2.2.5 - please add more details about the treadmill (speed range, inclination, etc)
• Line 140: "correlation coefficient" - do you mean ICC, the reliability index?
• Line 152: "20 or 30 min" - the selection of these durations was based on what?
• Lines 161-162: how were these sensations controlled?  
• Lines 173-178: 2.4 section
• For all measures, authors should elaborate on the directionality of each measure (i.e., increase of variable A implies what?) That will help with better interpretation of the results.
• Also, authors should add the units for each measure. Usually frequency measures are in Hz, but in certain figures the those units are in m/s2. Please elaborate.
• Line 195: Figure 2 - has no captions - please add it.
• Lines 196-197: please convert seconds to minutes
• Results
• Line 239: please do the same of all change rates - just one decimal point.
• Table 3: what are the T and P stand for? t-test and p-val?
• Discussion/Conclusion
• Line 293: "all five programs" - based on figure 4 this is not the case. Please elaborate.
• Line 297: "HF decreased" - Per figure 4 (see C1 and C2), LF decreased after intervention.
• Line 299: "overall worst effect" - based on what results, please elaborate?
• Line 306: "NIBS" - which one?
• Line 332: "current stimulation" - what type of NIBS? 
• Lines 390-394: please add refs
• Lines 450-451: somewhere in the text, authors should elaborate on both the similarities and differences between tDCS and tPCS.
• Line 460: "The objective of this study was to …." - was it? Based on the introduction, the aim of the study was different. Please elaborate.
• References
• Please double check the refs
• Some of the are duplicates, like 7-40 & 13-18.

Author Response

Point-by-point Responses to Reviewer 1 Comments

Dear reviewer,

Thank you for the time and effort that you have dedicated to providing your insightful and valuable comments on our manuscript. Although I do not know the situation around you, please stay healthy and keep safe. Following are the point-by-point responses to your comments, and I hope that the responses address your concerns effectively.

Sincerely,

On behalf of all authors

                                                                           

Major Concerns:

In the introduction, the gap of knowledge and the rationale of conducting this study is not well presented and discussed. Authors should elaborate more on why testing tPCS and no other NIBS/TES modalities is important. Also, why fatigue elimination is important, in either healthy and clinical cohorts.

Response: Thank you for your suggestions. Your suggestions are of great significance to improve the quality of this manuscript. I have added the reasons for conducting this study in the introduction. This paper explains the harm of fatigue from three aspects of society, physiology and psychology, and proves the significance and value of eliminating fatigue. In addition, I also elaborate the similarities and differences between tDCS and tPCS in detail according to the requirements of experts, and stated the reasons why tPCS was tested. Finally, we made appropriate modifications to the introduction to make the structure more rigorous and the content more abundant, so as to meet the theme and expert opinions. I would like to thank the experts again for your suggestions.

 

 

Title

Point 1: As the title currently is, it does not fully reflect to the present study. Authors should consider revision.

Response1: Thank you for your valuable advice. Indeed, this title does not fully reflect our study. After careful consideration, we changed the title to Study on the effect of different transcranial pulse current stimulation intervention program for eliminating physical fatigue.

 

 

ABSTRACT

Point 2: Line 9: "eliminating fatigue" = please elaborate in ()

Response 2: Thank you for your specific comments. The fatigue eliminated here refers to cognitive fatigue, which has been explained in the manuscript.

 

 

Point 3: Line 11: the right number should be 30 and not 40, right?

Response 3: Thank you for your careful review. Sorry, we didn't express our meaning clearly. The total number of participants in the experiment was 40, and 40 participants were randomly divided into two groups of 20. However, after exercising on treadmills, only 15 participants in each group met the fatigue standard, so in the end, only 30 participants fully participated in the experiment. On this point, we have revised the original manuscript.

 

 

Point 4: Lines 14-15: add the intervention programs in ()

Response 4: Thanks for your specific suggestion, we have added the intervention program as your requested.

 

 

Point 5: All dependent variables should be listed (eg, LF, HF, etc).

Response 5: Thank you for your specific suggestions. We have made modifications.

 

 

Point 6: Line 20: "had the best effect" - elaborate on this. Best implies the lowest p-val or biggest change?

Response 6: Thank you for this comment, your observation is very detailed, "had the best effect" means the biggest change.

 

 

Introduction

Point 7: Lines 38-40: please add the appropriate references at the end of the sentence.

Response 7: Thank you for this suggestion. We have added references according to your suggestions.

 

 

Point 8: Line 40: "Williams" - wrong format, please correct it

Response 8: Thank you for this suggestion. We have modified this in the manuscript.

Reference:

 

 

Point 9: Line 41: "elimination effects" - please elaborate more on this

Response 9: Thank you for your comments. The elimination effect of tDCS means that the exercise time can be prolonged after using tDCS. The elimination effect of tACS means that tACS can promote corticospinal excitation, improve motor function and improve motor stability.

 

 

Point 10: Line 44: appropriate ref should be cited.

Response 10: Thank you for this suggestion. We have added references according to your suggestion.

Reference:

Moreno-Duarte I, Gebodh N, Schestatsky P, et al. Transcranial electrical stimulation: Transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), transcranial pulsed current stimulation (tPCS), and transcranial random noise stimulation (tRNS)[M]//The stimulated brain. Academic Press, 2014: 35-59.

 

 

Point 11: Line 72: RR should be spelled out.

Response 11: Thank you for this suggestion. RR refers to the interval between R peaks in the heartbeat cycle, the change has been made.

 

 

Point 12: Line 74: HbO₂ - please spell it out.

Response 12: Thank you for this suggestion. We have made modifications according to your requirement, HbO₂ means oxygenated hemoglobin concentration.

 

 

Point 13: Lines 80-81: Per table 2, program III is different for what is stated in these lines. Please correct accordingly. 

Response 13: Thank you for your comment. Indeed, stimulation time of program III is wrong, and it has been modified to 20 minutes.

 

 

Methods

Point 14: Line 88: (no distinction between sports) - why is that? Does this imply that the fatigue level is similar across sports?

Response 14: Thank the expert for giving me the opportunity to explain. This means we didn't distinguish between athletes' sports, so that the athletes' sports have trained before are different. The focus of this study is to make sure the fatigue degree of the Participants met the experimental requirements, and whether the fatigue degree between different sport is similar is not considered at present. However, according to another experiment, we found that the fatigue level between different sport is related to the intensity and time of exercise, but has little to do with the project.

 

 

Point 15: Lines 91-93: how these inclusion criteria were determined? Scales, questionnaires?

Response 15: Thank the experts for giving me the opportunity to explain. These inclusion criteria are determined based on a large number of our previous investigations. The main purpose is to exclude the risk of accidents and factors affecting the degree of fatigue. Therefore, before the formal experiment, we require participants to have ECG examination to ensure that there are no accidents in the experiment; then use the questionnaire to investigate the subjects' living habits to ensure that the participants' living habits will not affect the fatigue level.

 

 

Point 16: Line 97: why three rounds of screening? Is it typical?

Response 16: Thank the expert for giving me the opportunity to explain. The purpose of three screening is to exclude those who do not meet the experimental requirements during the experiment. Our decision is based on the following considerations：

• For example, in the experiment, we found that when using the same severe fatigue program, most athletes had an RPE score of 9 and three athletes had an RPE score of 6; Under the same level of fatigue (RPE 8 - 10), the recovery time of two athletes is much longer than the average (5 minutes more).
• Because the fatigue degree and recovery time of these athletes are quite different from the average value when they carry out the same fatigue program, the fatigue elimination effect of the same tPCS intervention program on these athletes is quite different from others. If the experimental data of these athletes are included, it will affect the evaluation of the fatigue elimination effect of tPCS. Therefore, for the sake of the preciseness of the experiment, we conducted three screening. After the third screening, it was found that there was no significant difference in their fatigue degree and natural recovery time when the remaining athletes carried out the same fatigue program. So, it is necessary to conduct three screening, and the athletes left in the end meet the experimental requirements.

As considered by experts, this is not a typical operation paradigm, but an additional step to make this experiment more rigorous.

 

 

Point 17: Line 100: "recovery time": please elaborate on this. Does it imply that fatigue level must be fallen below a certain level? If so, which one?

Response 17: Thanks for your question. As the expert said, there is a falling standard. In this experiment, the RPE score of all athletes should be reduced to less than 2 points. In the experiment, we found that when the RPE of subjects was 9 points, the time for most people to fall to 2 was about 11 minutes. When the RPE of subjects fell to 2 for more than 16 minutes, we judged that the recovery time of these subjects was too long.

 

 

Point 18: Line 111: "duty cycle" - please elaborate

Response 18: Duty cycle refers to the percentage of the time that the circuit is connected to the whole working cycle of the circuit. For example, if a circuit is connected for half of its working cycle, its duty cycle is 50%. For the tPCS instrument used in this experiment, the circuit on time is 29.7%, so the duty cycle is 29.7%.

 

 

Point 19: Lines 134-135: 2.2.5 - please add more details about the treadmill (speed range, inclination, etc)

Response 19: Thank you for this suggestion. We have added these details to the manuscript according to your suggestion.

Running area of running platform: 150 cm long and 50 cm wide

Speed range: 0 to 22.0 km / h (0 to 6.1m / s)

Slope: 0 to 25.0% (0 to 14.0 °)

 

 

Point 20: Line 140: "correlation coefficient" - do you mean ICC, the reliability index?

Response 20: Yes, as the experts say.

 

 

Point 21: Line 152: "20 or 30 min" - the selection of these durations was based on what?

Response 21: Thank you for your inquiry. The choice of stimulation duration is based on the following reasons.

1.        Yang et al. Summarized the stimulation duration of all TES instruments in the past. It was found that 77.82% of the stimulation duration was between 16 minutes and 30 minutes [1].
2. Moreover, we found that in the stimulation of tPCS, the experiment with the stimulation duration of 20 minutes was the most [2-6].
3. In the current tPCS intervention program, the longest stimulation duration is 30 minutes [7].

Based on the above three points, we choose 20 minutes and 30 minutes as the stimulation duration of our experiment.

Reference:

• Jaberzadeh S, Bastani A, Zoghi M, et al. Anodal transcranial pulsed current stimulation: the effects of pulse duration on corticospinal excitability[J]. PLoS One, 2015, 10(7): e0131779.
• Alon G, Yungher D A, Shulman L M, et al. Safety and immediate effect of noninvasive transcranial pulsed current stimulation on gait and balance in Parkinson disease[J]. Neurorehabilitation and neural repair, 2012, 26(9): 1089-1095.
• Wang W J, Zhong Y B, Zhao J J, et al. Transcranial pulse current stimulation improves the locomotor function in a rat model of stroke[J]. Neural Regeneration Research, 2021, 16(7): 1229.
• Morales-Quezada L, Leite J, Carvalho S, et al. Behavioral effects of transcranial pulsed current stimulation (tPCS): Speed-accuracy tradeoff in attention switching task[J]. Neuroscience Research, 2016, 109: 48-53.
• Vasquez A C, Thibaut A, Morales-Quezada L, et al. Patterns of brain oscillations across different electrode montages in transcranial pulsed current stimulation[J]. Neuroreport, 2017, 28(8): 421.
• Vasquez A, Malavera A, Doruk D, et al. Duration dependent effects of transcranial pulsed current stimulation (tPCS) indexed by electroencephalography[J]. Neuromodulation: Technology at the Neural Interface, 2016, 19(7): 679-688.

 

 

Point 22: Lines 161-162: how were these sensations controlled?

Response 22: Thank you for your question. Your question points out the key steps of the experiment. The control of sensations is also the focus of our experimental operation. Before the experiment, we will explain to the subjects what is the sensory intensity and what are the feelings when the sensory intensity is generated (for example, there is tremor in the nasal root, the sense of acupuncture under the electrode is tolerable, no light vertigo and other abnormal feelings). Then let each subject experience the sensory intensity with their eyes closed and remember this feeling. At this time, we will record the sensory intensity of each subject.

In the formal experiment, we will ask the subjects how they feel while increasing the current intensity. Once the subject has the above feeling, we stop increasing the intensity and wrote down the magnitude of the sensory intensity at this time. The final data showed that the average sensory intensity of moderate physical fatigue was 1.13mA and that of severe physical fatigue was 1.52mA.

 

 

Point 23: Lines 173-178: 2.4 section. For all measures, authors should elaborate on the directionality of each measure (i.e., increase of variable A implies what?) That will help with better interpretation of the results. Also, authors should add the units for each measure. Usually frequency measures are in Hz, but in certain figures the those units are in m/s2. Please elaborate.

。

Response 23: Thank the experts for their specific opinions. According to your requirements, we have explained the directionality of each measure t in manuscript and added units for each measure. Indeed, as you said, the frequency measurement unit is usually Hz, but HRV is a special measurement, we generally choose to express the frequency in ms², which is also used by many scholars [1,2].

Reference:

• [2]. Biel R, Danieli C, Shekarrizfard M, et al. Acute cardiovascular health effects in a panel study of personal exposure to traffic-related air pollutants and noise in Toronto, Canada. Sci Rep. 2020;10(1):16703.

 

 

Point 24: Line 195: Figure 2 - has no captions - please add it.

Response 24: Thanks for the expert's reminder. We have added a caption to figure 2.

 

 

Point 25: Lines 196-197: please convert seconds to minutes

Response 25: Thanks for the specific advice of the experts, we have made changes.

 

 

Results

Point 26: Line 239: please do the same of all change rates - just one decimal point.

Response 26: Thank you for your advice. We have revised the manuscript according to your requirements.

 

 

Point 27: Table 3: what are the T and P stand for? t-test and p-val?

Response 27: Yes, as the experts say. T-value is the statistical value of t-test, and P-value is probability.

 

 

Discussion/Conclusion

Point 28: Line 293: "all five programs" - based on figure 4 this is not the case. Please elaborate.

Response 28: Thank you for your observation of the details. Your observation is very insightful. All five intervention programs had effects on the elimination of moderate physical fatigue, which means that all five programs can eliminate physical fatigue to some extent, but it does not mean that the intervention effects of all five programs are significant, these are two completely different meanings. This statement is also reflected in the following text . For example, the reason why program V had effects on eliminating physical fatigue is that human physical functions will natural recovery themselves when not exercising, so it can eliminate fatigue to some extent (reflected in the change rate of each index), but the effect is not significant.

 

 

Point 29: Line 297: "HF decreased" - Per figure 4 (see C1 and C2), LF decreased after intervention.

Response 29: Thank the experts for pointing out my mistakes. We are very sorry for our incorrect writing. Indeed, LF decreased after the intervention. We have revised the manuscript according to your requirements.

 

 

Point 30: Line 299: "overall worst effect" - based on what results, please elaborate?

Response 30: Thank you for your questions. Our conclusion is based on the following considerations;

1. Among the five indicators we measured, the effect of programs I on indicators RMSSD and LF was not significant, however, the effects of other true stimulus programs are significant.
2. RMSSD is an most important indicator representing HRV level, and the change rate of RMSSD is the lowest in program I.

Therefore, we determined that the elimination effect of program I on moderate physical fatigue was the worst among all true stimulation programs.

 

 

Point 31: Line 306: "NIBS" - which one?

Response 31: Thank you for your questions. NIBS refers to tDCS.

 

 

Point 32: Line 332: "current stimulation" - what type of NIBS? 

Response 32: Thank you for your questions. Current stimulation refers to tDCS

 

 

Point 33: Lines 390-394: please add refs

Response 33: Thanks for your specific comments. We have added references in the manuscript.

 

 

Point 34: Lines 450-451: somewhere in the text, authors should elaborate on both the similarities and differences between tDCS and tPCS.

Response 34: We agree with you. According to the suggestion of you, we added this part to the introduction

 

 

Point 35: Line 460: "The objective of this study was to …." - was it? Based on the introduction, the aim of the study was different. Please elaborate.

Response 35: Thank you for your careful observation. Your suggestions have greatly improved the quality of this manuscript. This is our negligence in expression. What we want to express is that this study tentatively analyzes the changes of HRV and concentration of HbO₂ after tPCS stimulation of the frontal lobe and explore the possible pathway of tPCS affecting HRV and the concentration of HbO₂. We have revised in the manuscript.

 

 

References

Point 36: Please double check the refs. Some of the are duplicates, like 7-40 & 13-18.

Response 36: Thank you for your careful observation. We checked all the references again, deleted the duplicate, added the missing, and made sure that all the expressions in the manuscript are consistent with the references. Because there are many changes in references, they cannot be displayed one by one.

 

 

Thank you for your careful review. Your careful review has helped to make our study clearer and more comprehensive. We really appreciate your efforts in reviewing our manuscript during this unprecedented and challenging time. We wish good health to you, your family, and community.

Author Response File: Author Response.docx

Reviewer 2 Report

A convincing and very well written manuscript on eliminating physical fatigue by transcranial pulsed current stimulation. I have just a few minor notes for the authors:

•  Line 40: et. al. (please correct throughout the entire manuscript)
• Please optimize table 1 - the numbers must not be so close together in order to record the values immediately.
• Line 110: 60 - 80 Hz, a space before and after the hyphen. (please correct throughout the entire manuscript)

 

Author Response

Point-by-point Responses to Reviewer 2 Comments

 

Dear reviewer,

Thank you for the time and effort that you have dedicated to providing your insightful and valuable comments on our manuscript. Although I do not know the situation around you, please stay healthy and keep safe. Following are the point-by-point responses to your comments, and I hope that the responses address your concerns effectively.

Sincerely,

On behalf of all authors

                                                                         Comments and Suggestions for Authors

A convincing and very well written manuscript on eliminating physical fatigue by transcranial pulsed current stimulation. I have just a few minor notes for the authors:

 

Point 1: Line 40: et. al. (please correct throughout the entire manuscript)

Response 1: Thank you for your careful observation, we have revised it in the manuscript.

 

 

Point 2: Please optimize table 1 - the numbers must not be so close together in order to record the values immediately.

Response 2: Thanks to the specific comments of experts, we have optimized the table 1，See Figure 1.

Figure 1 Optimized basic information of participants

 

 

Point 3: Line 110: 60 - 80 Hz, a space before and after the hyphen. (please correct throughout the entire manuscript)

Response 3: Thank you for your attention to detail. The change has been made.

 

 

Thank you for your careful review. Your careful review has helped to make our study clearer and more comprehensive. We really appreciate your efforts in reviewing our manuscript during this unprecedented and challenging time. We wish good health to you, your family, and community.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors evaluated the changes in heart rate variability and oxyhemoglobin concentration in the frontal lobe after different transcranial pulsed current stimulation (tPCS) conditions to distinguish which intervention condition has the greatest intervention effects on eliminating moderate and severe physical fatigue. This topic is novel, however, I have following major concerns :

• The rational for choosing the different stimulation conditions (sensory intensity+0.2 mA at 30 or 20 minutes and sensory intensity at 30 or 20 minutes) has not been stated adequately. The authors have referred to studies on tDCS and TES for using 0.2 mA and 20-30 minutes. Referring to evidence specific to tPCS would be useful.
• It is unclear what sensory stimulus intensity is and why it was chosen. The reference provided by the author is not relevant to the statement made (Page 2, Ln 55-59) .
• It is unclear why the authors applied the exclusion criteria after randomizing the participants into moderate and severe fatigue groups. Such post-randomization exclusions may threaten to bias intervention comparisons .
• From the information provided in the methods, it appears that all the five stimulation conditions were given on the same day without any washout period. Thus, carry-over effects cannot be ruled out.
• Consider rechecking the references to make sure they are relevant to the statements made. For eg., Page 1 Ln 42; Page 2 Ln 59; Page 4 Ln 149 (couldn't find Yang and Chew et al in the reference), Page 12 Ln 425-428 etc.

 

Author Response

Point-by-point Responses to Reviewer 3 Comments

Dear reviewer,

Thank you for the time and effort that you have dedicated to providing your insightful and valuable comments on our manuscript. Although I do not know the situation around you, please stay healthy and keep safe. Following are the point-by-point responses to your comments, and I hope that the responses address your concerns effectively.

Sincerely,

On behalf of all authors

                                                                           

Comments and Suggestions for Authors

The authors evaluated the changes in heart rate variability and oxyhemoglobin concentration in the frontal lobe after different transcranial pulsed current stimulation (tPCS) conditions to distinguish which intervention condition has the greatest intervention effects on eliminating moderate and severe physical fatigue. This topic is novel, however, I have following major concerns :

 

Point 1: The rational for choosing the different stimulation conditions (sensory intensity+0.2 mA at 30 or 20 minutes and sensory intensity at 30 or 20 minutes) has not been stated adequately. The authors have referred to studies on tDCS and TES for using 0.2 mA and 20-30 minutes. Referring to evidence specific to tPCS would be useful.

Response 1: Thank you for your questions. We have revised the references according to your suggestion The choice of stimulation duration is based on the following reasons:

1. Yang et al. Summarized the stimulation duration of all TES instruments in the past. It was found that 77.82% of the stimulation duration was between 16 minutes and 30 minutes [1].
2. Moreover, we found that in the tPCS intervention program, the experiment with the stimulation duration of 20 minutes was the most [2 - 6].
3. In the current tPCS intervention program, the longest stimulation duration is 30 minutes [7].

Based on the above three points, we choose 20 minutes and 30 minutes as the stimulation duration of our experiment.

The reasons why we chose sensory stimulation intensity + 0.2mA are as follows:

1. At present, more and more studies have proved that due to individual differences, such as soft tissue, skull thickness, post exercise fatigue and other factors, the fixed stimulation intensity is not suitable for all subjects [8].
2. Scholar workman has done a lot of research on the stimulation intensity of tDCS and believes that when the subjects can tolerate it, the intensity of stimulation current should be increased to improve the intervention effect of tDCS [9,10].
3. Jamilde et al. proved in the study that because the baseline of brain excitability is different, different stimulation intensity may have different maximum efficacy. Only in line with individual sensory intensity can the intervention effect of TES be maximized [11,12].

In this study, the intensity of sensory stimulation can not only approach the tolerance of subjects, but also avoid injury due to excessive intensity, which may improve the intervention effect of tPCS. Therefore, based on the above three points, we set the stimulation intensity of tPCS as the sensory intensity,

As the experts said, our stimulation intensity of 0.2mA refers to tDCS, which is mainly due to the following reasons:

At present, there is indeed a lack of research on the strength of tPCS, so we refer to the research on the intensity of tDCS belonging to TES. In tDCS, the gradient of 0.2mA can produce greater cortical excitation. In tDCS, the gradient of 0.2mA can produce greater cortical excitation, and the gradient often increased in the stimulation intensity is also 0.2mA, which is consistent with the athlete's sensory feedback collected in our experiment [12]. Therefore, we designed the sensory intensity + 0.2mA based on the sensory intensity. After that, our team will further study the stimulation time and stimulation intensity of tPCS, so as to enrich the research on the intervention program of tPCS and improve the practical application effect of tPCS.

Reference:

• [2]. Jaberzadeh S, Bastani A, Zoghi M, et al. Anodal transcranial pulsed current stimulation: the effects of pulse duration on corticospinal excitability[J]. PLoS One, 2015, 10(7): e0131779.
• [3]. Alon G, Yungher D A, Shulman L M, et al. Safety and immediate effect of noninvasive transcranial pulsed current stimulation on gait and balance in Parkinson disease[J]. Neurorehabilitation and neural repair, 2012, 26(9): 1089-1095.
• [4]. Wang W J, Zhong Y B, Zhao J J, et al. Transcranial pulse current stimulation improves the locomotor function in a rat model of stroke[J]. Neural Regeneration Research, 2021, 16(7): 1229.
• [5]. Morales-Quezada L, Leite J, Carvalho S, et al. Behavioral effects of transcranial pulsed current stimulation (tPCS): Speed-accuracy tradeoff in attention switching task[J]. Neuroscience Research, 2016, 109: 48-53.
• [6]. Vasquez A C, Thibaut A, Morales-Quezada L, et al. Patterns of brain oscillations across different electrode montages in transcranial pulsed current stimulation[J]. Neuroreport, 2017, 28(8): 421.
• [7]. Vasquez A, Malavera A, Doruk D, et al. Duration dependent effects of transcranial pulsed current stimulation (tPCS) indexed by electroencephalography[J]. Neuromodulation: Technology at the Neural Interface, 2016, 19(7): 679-688.
• [8]. Logothetis N K, Kayser C, Oeltermann A. In vivo measurement of cortical impedance spectrum in monkeys: implications for signal propagation[J]. Neuron, 2007, 55(5): 809-823.
• [9]. Workman C D, Kamholz J, Rudroff T. The tolerability and efficacy of 4 mA transcranial direct current stimulation on leg muscle fatigability[J]. Brain sciences, 2019, 10(1): 12.
• Workman C D, Fietsam A C, Uc E Y, et al. Cerebellar transcranial direct current stimulation in people with Parkinson’s disease: a pilot study[J]. Brain sciences, 2020, 10(2): 96.
• Jamil A, Batsikadze G, Kuo H I, et al. Systematic evaluation of the impact of stimulation intensity on neuroplastic after‐effects induced by transcranial direct current stimulation[J]. The Journal of physiology, 2017, 595(4): 1273-1288.
• Chen YI, Ren J, Wang FN, et al. Inhibition of stimulated dopamine release and hemodynamic response in the brain through electrical stimulation of rat forepaw. Neurosci Lett. 2008;431(3):231-235.
• Chew T, Ho K A, Loo C K. Inter-and intra-individual variability in response to transcranial direct current stimulation (tDCS) at varying current intensities[J]. Brain stimulation, 2015, 8(6): 1130-1137.

 

 

 

Point 2: It is unclear what sensory stimulus intensity is and why it was chosen. The reference provided by the author is not relevant to the statement made (Page 2, Ln 55-59).

Response 2: Thank the experts for their questions. We think about the intensity of sensory stimulation in this way:

As experts think, the sensory stimulus intensity is vague. At present, there is a lack of direct evidence for the accurate definition of sensory stimulus intensity, and there are different opinions on the level of sensory stimulus intensity. However, according to workman's point of view and a large number of our studies [1], it is indirectly proved that the sensory stimulus intensity includes the following contents: nasal root tremor, sense of pressure, tolerable sense of acupuncture, no tingling and burning sensation, no dizziness and blindness and other abnormal feelings. Under this stimulation intensity, participants feel that they are tolerable.

Our method for determining the sensory stimulus intensity is as follows:

Before the formal experiment, we defined the range of the sensory stimulus intensity, and determined the sensory stimulus intensity by stimulating the athletes and asking them how they felt. We found that when the stimulus intensity of tPCS was sensory stimulus intensity, the subjects' sensations included: nasal tremor, tolerable acupuncture under the electrodes, and no dizziness, blindness, or other abnormal sensations during the intervention. The final data show that in moderate physical fatigue, the average sensory stimulus intensity was 1.13 mA, in severe physical fatigue, the mean intensity of sensory stimulation was 1.52 mA.

At the same time, our previous research results have proved that sensory stimulation intensity has a significant effect on the elimination of physical cognitive fatigue, which has been accepted by Chinese Journal of Sports Medicine: Effects of different transcranial pulse current stimulation program on fatigue elimination in physical cognitive mixed tasks.

The reason for choosing the sensory stimulus intensity has been explained in poin1.

Finally, according to the requirements of experts, we updated the references to make them more consistent with our statements.

Reference:

• Workman C D, Kamholz J, Rudroff T. The tolerability and efficacy of 4 mA transcranial direct current stimulation on leg muscle fatigability[J]. Brain sciences, 2019, 10(1): 12.

 

 

Point 3: It is unclear why the authors applied the exclusion criteria after randomizing the participants into moderate and severe fatigue groups. Such post-randomization exclusions may threaten to bias intervention comparisons.

Response 3: Thank the experts for giving me the opportunity to explain. After hearing the opinions of experts, we found that there were problems in the experimental flow chart, which did not clearly express our meaning. The flow chart has been modified, as shown in Figure 2 below.

The purpose of this experiment is to obtain two groups of fatigue models with different degrees. In grouping, we did not randomly divide the 40 participants into moderate and severe fatigue groups. First, 40 healthy college athletes were randomly divided into two groups of 20, denoted as A and B, then select the subjects who met the requirements of moderate and severe fatigue through screening (see manuscript 2.1 for the screening method), finally, 15 subjects in each group met the experimental criteria. After the experiment was officially started, the subjects in group A were exercised to moderate physical fatigue and group B to severe physical fatigue.

In fact, the screening of the two groups is carried out at the same time, so the two groups can be regarded as two independent experiments, but the athletes in each group were obtained from 40 people at the beginning. After the third screening, each group found that there was no significant difference in the degree of fatigue and natural recovery time of the remaining subjects in the same fatigue scheme, which improved the preciseness of the experiment, and the results can better explain the effect of tPCS on the elimination of physical fatigue.

Figure 2 Modified experimental testing chart.

 

 

Point 4: From the information provided in the methods, it appears that all the five stimulation conditions were given on the same day without any washout period. Thus, carry-over effects cannot be ruled out.

Response 4: Thank you for your questions. Allow me to explain that, in fact, the five stimulation conditions are not on the same day, and each stimulation condition is separated by 48 hours to avoid the accumulation of fatigue and stimulus effects. This is explained at 2.5 in the manuscript.

 

 

Point 5: Consider rechecking the references to make sure they are relevant to the statements made. For eg., Page 1 Ln 42; Page 2 Ln 59; Page 4 Ln 149 (couldn't find Yang and Chew et al in the reference), Page 12 Ln 425-428 etc

Response 5: Thanks to the specific comments of experts, we carefully checked the literature and statements, and modified the inappropriate statements or references to ensure that the references and statements are relevant.

1. Original ln 42; The statement of page 2 is revised to: At present, although Morales et al proved the ability of tPCS to eliminate cognitive fatigue.

References are revised to: Morales-Quezada L, Cosmo C, Carvalho S, et al. Cognitive effects and autonomic responses to transcranial pulsed current stimulation[J]. Experimental brain research, 2015, 233(3): 701-709.

 

2. The original reference at page 2 ln 59 was added. From the comprehensive analysis of the two documents, it is concluded that increasing the gradient of 0.2mA is a common increase range, and 0.2mA can produce greater cortical excitability in the study of chew et al. Therefore, the stimulation intensity of 0.2mA was used in this study. The new references are as follows: Chen YI, Ren J, Wang FN, et al. Inhibition of stimulated dopamine release and hemodynamic response in the brain through electrical stimulation of rat forepaw. Neurosci Lett. 2008;431(3):231-235.

 

3. Yang and chew et al, originally page 4 ln 149, is located in 24 and 26 references in the revised manuscript.

     4.The references of the original page 12 ln 425-428 have been modified. The          revised references are as follows:     

        [1] Saavedra L C, Morales-Quezada L, Doruk D, et al. QEEG indexed frontal         connectivity effects of transcranial pulsed current stimulation (tPCS): a                 sham-controlled mechanistic trial[J]. Neuroscience letters, 2014, 577: 61-65.          [2]Gao D, Jiang JJ, Gu SH, Lu JZ, Xu L. Morphological Detection and                       Functional Assessment of Regenerated Nerve after Neural Prosthesis with          a PGLA Nerve Conduit. Sci Rep. 2017;7:46403. Published 2017 Apr 13.

         Thank you for your careful review. Your careful review has helped to make our study clearer and more comprehensive. We really appreciate your efforts in reviewing our manuscript during this unprecedented and challenging time. We wish good health to you, your family, and community.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors did great job responding to reviewers comments, yet authors should edit and proof the manuscript one more time. There are sections that transitions can be smoother, and the whole manuscript should be proofed one more time.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Thank you for providing rationale for tPCS stimulation duration. However, I still have some major concerns. The explanation and rationale on sensory intensity or sensory intensity+0.2 mA is still not justified. The references cited are not relevant to sensory intensity and are in fact for higher intensities (1 mA to 4 mA). tPCS causing abnormal sensation like blindness is odd. The explanation provided on the study design is confusing, it seems like the study has reported two separate cross-over studies. Therefore, it is unclear why the participants were randomized into two groups based on fatigue levels initially when no-between group comparisons were made. The order of the intervention conditions has not been randomized which may have added a bias. The statistical analysis method needs to be explained more clearly as in the results it looks like for each group (moderate and severe fatigue) separate two-way repeated measures were done. 

Author Response

Point 1: The explanation and rationale on sensory intensity or sensory intensity+0.2 mA is still not justified. The references cited are not relevant to sensory intensity and are in fact for higher intensities (1 mA to 4 mA).

Response 1: Thank you for your professional question. Answering this question will help to improve the quality of the manuscript.

Our team re searched the literature and listed the reasons why we chose sensory intensity:

1. Many scholars have explained that the fixed stimulation intensity is not suitable for all everyone[1-2]. Workman et al. have explained in the study that the current intensity should be increased to improve the stimulation effect on the premise that the subjects can tolerate it[3]. On the other hand, it is also proved that if the current is too large, it will inhibit the excitation of neurons and reduce the effect of intervention[4]. Therefore, an appropriate stimulus intensity should be consistent with the individual state.
2. Different stimulus intensities have different intervention effects, which has been explained in the intervention of tDCS[5].
3. At the same time, some scholars directly explained that the intensity of stimulation should adapt to the somatosensory threshold[6] (see Figure 1, the picture is derived from this reference), so we decided to take the sensory intensity as the stimulation intensity. And the stimulus intensity of sensory intensity has been used by scholar ambrus in tDCS and tRNS[7], so we have more confirmed that sensory intensity should be used. The difference is that ambrus compares sensory intensity to detection threshold, but our meaning is the same.

 

We chose to increase the stimulation intensity of 0.2mA for the following reasons:

1. 2mA stimulation can also produce excitability [8](see Figure 2, the picture is derived from the references here)
2. A stimulus gradient of 0.2mA appeared in the intervention protocol of tACS[9]. (see Figure 3, the picture is derived from the reference here)
3. In the pre experiment, we also verified that 0.2mA can change the subject's feeling. After continuing to increase the current intensity, it will cause the subject's discomfort, which may inhibit the excitation of neurons and reduce the intervention effect. Therefore, we finally chose 0.2mA for the increased intensity

Sensory intensity and sensory intensity + 0.2mA are the innovations in stimulation intensity in this study, which aims to improve the intervention effect of tPCS. There may not be much direct evidence to support our choice of sensory intensity, which is one of the limitations of this manuscript. Let you have some doubts about the choice of our intervention program, we apologize for our lack of sufficient theoretical basis. In the later stage, our team will make more study around tPCS intervention program, make more explanation and definition of sensory intensity, and we hope you can continue to put forward your insightful opinions on our research, thank you very much. Finally we have revised the references of the manuscript according to the above statement.

Reference:

• Horvath J C, Forte J D, Carter O. Quantitative review finds no evidence of cognitive effects in healthy populations from single-session transcranial direct current stimulation (tDCS)[J]. Brain stimulation, 2015, 8(3): 535-550.
• Dmochowski J P, Bikson M, Parra L C. The point spread function of the human head and its implications for transcranial current stimulation[J]. Physics in Medicine & Biology, 2012, 57(20): 6459.
• Workman C D, Kamholz J, Rudroff T. Increased leg muscle fatigability during 2 mA and 4 mA transcranial direct current stimulation over the left motor cortex[J]. Experimental Brain Research, 2020, 238(2): 333-343.
• Jamil A, Batsikadze G, Kuo H I, et al. Systematic evaluation of the impact of stimulation intensity on neuroplastic after‐effects induced by transcranial direct current stimulation[J]. The Journal of physiology, 2017, 595(4): 1273-1288.
• Herrmann C S, Rach S, Neuling T, et al. Transcranial alternating current stimulation: a review of the underlying mechanisms and modulation of cognitive processes[J]. Frontiers in human neuroscience, 2013, 7: 279.
• Ambrus G G, Paulus W, Antal A. Cutaneous perception thresholds of electrical stimulation methods: comparison of tDCS and tRNS[J]. Clinical Neurophysiology, 2010, 121(11): 1908-1914.
• Chew T, Ho K A, Loo C K. Inter-and intra-individual variability in response to transcranial direct current stimulation (tDCS) at varying current intensities[J]. Brain stimulation, 2015, 8(6): 1130-1137.
• Herrmann C S, Rach S, Neuling T, et al. Transcranial alternating current stimulation: a review of the underlying mechanisms and modulation of cognitive processes[J]. Frontiers in human neuroscience, 2013, 7: 279.

 

 

Figure 1

 

Figure 2

 

Figure 3

 

Point 2: tPCS causing abnormal sensation like blindness is odd.

Response 2: We are very sorry for our incorrect writing, thank the experts for giving me the opportunity to explain. Blindness here does not mean true blindness, but changes in visual perception caused by too high electrical stimulation intensity, which temporarily affects visual perception and damages the perception of visual stimulation by the retina. In serious cases, it can lose visual perception[1-2]. We have revised the word "blindness" in the manuscript to "decreased visual perception", and corrected the relevant references.

Reference:

• [1]. Poreisz C, Boros K, Antal A, et al. Safety aspects of transcranial direct current stimulation concerning healthy subjects and patients[J]. Brain research bulletin, 2007, 72(4-6): 208-214.
• [2]. Antal A, Kincses T Z, Nitsche M A, et al. Manipulation of phosphene thresholds by transcranial direct current stimulation in man[J]. Experimental brain research, 2003, 150(3): 375-378.

 

 

Point 3: The explanation provided on the study design is confusing, it seems like the study has reported two separate cross-over studies. Therefore, it is unclear why the participants were randomized into two groups based on fatigue levels initially when no-between group comparisons were made.

Response 3: Thank the experts for giving me the opportunity to explain. They were randomly divided into two groups, not based on the degree of fatigue. When they were randomly divided into two groups, we did not know the fatigue status of each participant. The 40 people were recruited together, then they were randomly divided into 20 people in each group. The purpose of assigning 20 people in each group is to provide subjects for two groups of fatigue experiments (moderate and severe fatigue). Then 15 people in each group were selected to participate in the whole experiment according to the experimental conditions. Therefore, this study can indeed be regarded as two independent experiments, but 20 people in each group are allocated from 40 people who have been recruited. And in the experiment, in order to shorten the experimental cycle, the two groups of experiments are carried out at the same time, and the two groups do not interfere with each other. The link between the two groups is that they are both finding the most appropriate intervention program in different degrees of physical fatigue, therefore, it can make the intervention program of physical fatigue more complete.

 

 

Point 4: The order of the intervention conditions has not been randomized which may have added a bias.

Response 4: Thank you for giving me the opportunity to explain, which improves the quality of this manuscript.

In fact, at the beginning of the experimental design, we have considered the random problem of the intervention scheme, and we use the random scale to solve this problem. After reviewing the experimental records, we will now explain the specific operation methods:

First, number the five programs in sequence, from 1 to 5. The experimental group took one digit from the first column of row 10 in the random number table until it was filled with five non repeated random numbers (5,8,7,1,9). Then the order of intervention was determined from small to large. Finally, it was found that the order of intervention was IV, I, III, II and V.

The control group took one digit from the first column of row 9 in the random number table until it was filled with five random numbers that were not repeated (1,5,3,9,2). Then, the order of intervention was determined from small to large. Finally, it was found that the order of intervention was I, V, III, II and IV.

In the experiment, each participant received five different stimuli, and each stimulus was separated by 48 hours. This ensures the reliability of the data.

Finally, we explain the randomization of the intervention program in the manuscript.

 

Point 5: The statistical analysis method needs to be explained more clearly as in the results it looks like for each group (moderate and severe fatigue) separate two-way repeated measures were done.

Response 5: As experts understand, We did use two-way repeated measurements in each group. According to your suggestion, we explained the statistical method in the manuscript, emphasizing the use of two-way repeated measurement in each group. So that readers can more fully understand our results.

 

 

 

Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

Thank you for the clarification.

Response 1: I agree with the points made in the references but I would have preferred a reference that says sensory stimulation changes cortical excitability. If there is no direct evidence to support sensory stimulation, please mention it as a limitation in the manuscript.

Page 7, LN 266: Replace experimental and control group with moderate and severe fatigue group. 

Response 3: As per response 3, the authors state that there was no link between the two groups (moderate and severe fatigue). In my opinion, if there was no link between the two groups there was no need to randomize 40 participants into groups of 20 each. The potential participants could have just been screened into moderate or severe groups and undergone the 5 conditions in a cross-over-design. Also, if there was no link between the two groups then lines 274-276 are contradictory to the explanation. Please clearly state in the manuscript that there was no link between the two groups and remove the above lines.  

Abstract:

Page 1: Ln 15, 16: It is unclear what "moderate physical fatigue of 15 and severe physical fatigue of 15" means.

Discussion: Please add limitations of the study.

Author Response

Point-by-point Responses to Reviewer 3 Comments

Dear reviewer:

Thank you for the time and effort that you have dedicated to providing your insightful and valuable comments on our manuscript. Although I do not know the situation around you, please stay healthy and keep safe. Following are the point-by-point responses to your comments, and I hope that the responses address your concerns effectively.

Sincerely,

On behalf of all authors

                                                                           

Comments and Suggestions for Authors

Point 1: I agree with the points made in the references but I would have preferred a reference that says sensory stimulation changes cortical excitability. If there is no direct evidence to support sensory stimulation, please mention it as a limitation in the manuscript.

Response 1: Thank you for your comments, we agree with you. We are also looking for such reference, but our current references are indirect support for sensory stimulation. This is not only the significance of our manuscript, but also the limitations of our manuscript. We have explained this in the limitations of the manuscript according to your comments.

 

 

Point 2: Page 7, LN 266: Replace experimental and control group with moderate and severe fatigue group.

Response 2: Thank you for your specific comments. We have made changes in the manuscript.

 

 

Point 3: As per response 3, the authors state that there was no link between the two groups (moderate and severe fatigue). In my opinion, if there was no link between the two groups there was no need to randomize 40 participants into groups of 20 each. The potential participants could have just been screened into moderate or severe groups and undergone the 5 conditions in a cross-over-design. Also, if there was no link between the two groups then lines 274-276 are contradictory to the explanation. Please clearly state in the manuscript that there was no link between the two groups and remove the above lines.

Response 3: Thank you for your suggestions, we sincerely accept your comments. We have clearly stated in the manuscript that there is no link between the two groups (written in the Experience flow). According to your suggestion, we have deleted 274-276 lines in the manuscript.

 

 

Point 4: Page 1: Ln 15, 16: It is unclear what "moderate physical fatigue of 15 and severe physical fatigue of 15" means.

Response 4: Thank you for giving me the opportunity to explain. What we want to express is that 15 people in each group have reached the fatigue standard required by this experiment. I'm sorry for my incorrect writing. we have revised it in the manuscript.

 

 

Point 5: Discussion: Please add limitations of the study.

Thank you for your careful review. Your careful review has helped to make our study clearer and more comprehensive. We really appreciate your efforts in reviewing during this unprecedented and challenging time. We wish good health to you, your family, and community.

 

 

Author Response File: Author Response.docx