Rate of Torque Development Scaling Factor Decreased Following a 6-Week Unilateral Isometric Training Using Electrostimulation or Voluntary Contractions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This article aims to evaluate changes in the rate of torque development scaling factor and maximum voluntary isometric contraction variables following six weeks of unilateral isometric electromyostimulation and voluntary exercises.

The topic is very interesting and the setting of the experimental protocol is adequate, as well as the structure of the manuscript and its reading.

In my opinion there are points that can be improved especially for a better reading and other considerations useful for improving the presentation of the work.

Line 67 following the statement "It has been shown..." It would be useful to indicate some references

Line 124 you have carried out 3 test sessions, the middle one just to adjust the intensity, but wouldn't it be interesting to analyze the data even after 3 weeks? Furthermore, in the following lines 238 to 239 you indicate that “the subjects were asked to increase the current or contraction intensity throughout the training session to maintain target torque level of 60% MVC.”, so I don't understand if the changes to maintain the 60%MVC were made during each training session or only after 3 weeks.

Line 135 How was the amount and density of training (days and hours) decided?

The authors took body mass and body fat with the Bia, but the fat is not reported, why?

Line 117 misses the dot, line 163, 206 and 245 adjust the indentation. Check for other inaccuracies throughout the manuscript, including in the abstract.

Given the enormous work done and the different phases of testing, it would also be useful to include a figure who describes the testing and training process in detail, as done for the entire experimental protocol. In addition, it would be very useful to include a figure, even schematized, of the testing and training set-up.

Lines 175 and 184 why 60 seconds of rest? Do you have any references? Also, how long did MVC last, and was this time fixed or variable?

Line 166: What was the criterion by which those knee and hip angles were established for testing?

Line 189 I think there is a repetition of "using"

Line 190 it would be advisable to indicate the version of the software if there are different ones on the market.

Line 207-208 I think there is a repetition of “difference”

Line 208 I would enter these data in the description of the two groups (in the subjects paragraph) or directly in the results

Line 209: How did you establish the 40 contractions and 20 seconds of recovery?

Line 213 "close-to-identical"? It would be better to detail in my opinion... How much has it been changed and if so, why? Has it been changed on all subjects or only on some? Was this variation significant or not?

Line 240 please, indicate which force transducer is used and related software

In the Training procedures part it is not very clear how the training exercise was carried out, for example, were the starting angles the same? Or were they free? As previously commented, it would be useful to make the training part clearer

Please adjust the formatting of the statistical analysis paragraph

Figure 2: It would be better to enlarge the graphs because the numbers and letters are not very easy to read in full size. Also, I think there is an error on the title of the ordinates of the graphs that show (%MVC/s) while, according to the descriptions, it should be (%Tmax/s). On the x-axis, on the other hand, %MVC should be reported for clarity.

Given the constant and widespread use of p-value for the analysis of significant differences, I would implement it in table 1.

In the discussions, in line 332 you indicate "a significant decrease..." then continuing with conclusions, but, in my opinion, it does not seem to me that you have made a dedicated statistical analysis to affirm this thing and then also draw conclusions.

Line 344 should remove the year in parentheses

Line 352 in my opinion this sentence should go in Materials & Methods and not in discussions.

Line 362 it is not necessary to reproduce further the citation [24] already indicated in the same sentence.

Line 367 this author does not appear in the bibliography. Please check the bibliography and consequently also this part of the discussions

Put the "." after "et al" Check on the entire manuscript

Lines 387 and 388 are missing parentheses.

 

Author Response

In my opinion there are points that can be improved especially for a better reading and other considerations useful for improving the presentation of the work.

Thank you for all the comments and suggestions, we found them very useful and valuable. We believe that our work has been improved following the introduced changes.

Line 67 following the statement "It has been shown..." It would be useful to indicate some references

We agree with this comment, references were added.

Line 124 you have carried out 3 test sessions, the middle one just to adjust the intensity, but wouldn't it be interesting to analyze the data even after 3 weeks? Furthermore, in the following lines 238 to 239 you indicate that “the subjects were asked to increase the current or contraction intensity throughout the training session to maintain target torque level of 60% MVC.”, so I don't understand if the changes to maintain the 60%MVC were made during each training session or only after 3 weeks.

Thank you for this comment, the sentence “to adjust exercise intensity” seemed confusing so we changed it to “to adjust exercise threshold”. In addition, we added the sentence in the Training procedures (now lines 229-231) to further explain the purpose of what we called mid-test: “Due to anticipated positive exercise effects on Tmax, participants were re-tested after the third week of intervention (mid-test), and these data served to adjust the exercise threshold (please see Figure 2, upper right panel).”
Also, as we outlined in Study design, for the sake of simplicity, a pre-post design with random two parallel groups (both experimental) were presented. Nevertheless, we have specified in the revised version of the manuscript that the only purpose of the mid-test was to adjust the training thresholds in the last 3 weeks of the training period.
Regarding the second part of your comment, over the course of 20 contractions fatigue would set-in therefore contraction intensity would remain below the set threshold if the participants were not instructed to increase the current of the stimulation or the voluntary activation. To avoid misunderstanding, this section was partly changed and now it reads: Depending on type of exercise, the subjects were asked to increase the current (please see Figure 2, lower left panel) or voluntary activation intensity throughout the training session to maintain target torque level of ~ 60% MVC. The exerted torque during each contraction was measured with the same force transducer and software as described in testing procedures, and real-time feedback along with individual 60% MVC threshold was provided on a computer screen. All training sessions were supervised by at least one of the researchers who conducted the experiment.

Line 135 How was the amount and density of training (days and hours) decided?

Thank you for this comment, we added a sentence to clarify and justify our decision: “Training density and intensity were selected in line with previous recommendations and knowing the limitations of EMS [24,25,36].”

The authors took body mass and body fat with the Bia, but the fat is not reported, why?

This information was added to the description of subjects’ anthropometric characteristics.

Line 117 misses the dot, line 163, 206 and 245 adjust the indentation. Check for other inaccuracies throughout the manuscript, including in the abstract.

Thank you for careful reading and the comments. We made corrections accordingly.

Given the enormous work done and the different phases of testing, it would also be useful to include a figure who describes the testing and training process in detail, as done for the entire experimental protocol. In addition, it would be very useful to include a figure, even schematized, of the testing and training set-up.

We thank the Reviewer for this kind comment. We did our best to create a figure (now Figure 2) depicting testing and training set-up and training procedures.

Lines 175 and 184 why 60 seconds of rest? Do you have any references? Also, how long did MVC last, and was this time fixed or variable?

The same rest duration was used in our previous studies where MVC was assessed. Nonetheless, we added a reference to support it.
Each MVC lasted at least 3 seconds and we added a supporting reference. This section now reads “Participants were instructed to extend the knee 'as fast and as hard as possible’ and each maximal contraction was sustained for approximately 3 s [28]. Three MVC were completed for each leg with 60-s rest between successive trials [3,4].”

Line 166: What was the criterion by which those knee and hip angles were established for testing?

The same setup was used in all previous studies from our research lab that investigated muscle strength. We added the references to support our testing set-up. Also, other small changes were made to this section which now reads: “Following the warm-up, the participants were seated in a custom-made chair with knee and hip angles fixed at 120⁰ and 100⁰, respectively (Figure 2, upper left panel). Chair was adjusted for every participant with respect to their body size. The participant’s trunk, waist, and thighs were firmly strapped to the chair and the distal part of their legs were affixed to a strain gauge force transducers (Dongguan South China Sea Electronic Co.,Ltd; load cell S- Type CZL302; range 2 kN) using rigid cuffs. The cuffs were secured with hook and loop fasteners 2 cm above the malleolus lateralis.”

Line 189 I think there is a repetition of "using".

Yes, there was an omission. Thank you for pointing at this error. We have modified the sentence to improve its readability.

Line 190 it would be advisable to indicate the version of the software if there are different ones on the market.

This was addressed along with suggestion for line 189 and now the sentence reads “Data were collected and sampled at 1,000 Hz using the commercially available software Isometrics (version 4.0.0, “Sports Medical Solutions”, Belgrade, Serbia). Signals were filtered with a low pass (5 Hz), second- order Butterworth filter.”

Line 207-208 I think there is a repetition of “difference”

Yes, there was, thank you for pointing at this omission.

Line 208 I would enter these data in the description of the two groups (in the subjects paragraph) or directly in the results

We appreciate Reviewer’s comment. We decided to keep where it was just to emphasize and justify the application of training over the “weaker” and not over the kicking-dominant leg. A small change was made and this sentence now reads: “As a note, there was a significant between-leg difference in Tmax in both groups (10±7%; p<0.01 in EMS, and 12.5±5%; p<0.01 in VOL group).”

Line 209: How did you establish the 40 contractions and 20 seconds of recovery?

This protocol was built-in with our Compex device that we used in this study. Nonetheless, we added a sentence as well as the illustration (now Figure 2) to clarify the protocol “The number of contractions and contraction-to-rest ratio (6.25/20s) were in accordance with the work-to-rest pattern produced by muscle stimulation device (Figure 1, and Figure 2 – upper and lower right panel).).”

Line 213 "close-to-identical"? It would be better to detail in my opinion... How much has it been changed and if so, why? Has it been changed on all subjects or only on some? Was this variation significant or not?

We thank the Reviewer for their comments and questions. This sentence and the section in general indeed needed improvements so we made changes to that sentence and added another one to further clarify what we meant by close-to-identical: “The stimulation intensity was determined during the familiarization when EMS was delivered at the individually maximal tolerable dose and was kept close-to-identical among the session, averaging in total ~60% MVC per subject [24]. Specifically, EMS intensity varied between 58% and 63% across sessions and subjects, depending on their daily pain tolerance.” The significance of this variation was not tested.

Line 240 please, indicate which force transducer is used and related software

We partly changed this sentence and now it reads “The exerted torque during each contraction was measured with the same force transducer and software as described in testing procedures, and real-time feedback along with individual 60% MVC threshold was provided on a computer screen.”
We also added a sentence regarding the supervision of training sessions: “All training sessions were supervised by at least one of the researchers who conducted the experiment.”

In the Training procedures part it is not very clear how the training exercise was carried out, for example, were the starting angles the same? Or were they free? As previously commented, it would be useful to make the training part clearer

We thank the reviewer for this comment since it shed light on an important aspect of the training procedure. Therefore, we added the following explanation that we hope to contribute to better understanding of this part of the study: “Participants positioning during training sessions was identical to that during testing procedures. The participant’s trunk, waist, and thighs were firmly strapped to the chair with knee and hip angles fixed at 120⁰ and 100⁰, respectively. The distal part of the trained leg was affixed to a strain gauge force transducer (Figure 2, upper left panel).”

Please adjust the formatting of the statistical analysis paragraph

Corrected.

Figure 2: It would be better to enlarge the graphs because the numbers and letters are not very easy to read in full size. Also, I think there is an error on the title of the ordinates of the graphs that show (%MVC/s) while, according to the descriptions, it should be (%Tmax/s). On the x-axis, on the other hand, %MVC should be reported for clarity.

You are correct. Again, thank you for your comments and suggestions. We will submit a revised Fig 2, hopefully better readable.
Regarding the second part of the comment, we titled the axes in line with previous studies investigating RTD-SF (please see Bellumori et al. 2010, 2011, 2013).

Given the constant and widespread use of p-value for the analysis of significant differences, I would implement it in table 1.

With all the respect, most p-values presented in this work are given in Table 1 as an asterisk or sword symbol.

In the discussions, in line 332 you indicate "a significant decrease..." then continuing with conclusions, but, in my opinion, it does not seem to me that you have made a dedicated statistical analysis to affirm this thing and then also draw conclusions.

We agree with the reviewer´s point. As you noticed, we didn’t have means to assess this statistically, so we reworded this sentence to read: “In the current study, it seems that rapid torque generation was unaffected by training intervention for intensities < 50% MVC (Figure 2). However, a visible decrease in rapid production can be observed for higher intensities (50-80%MVC) that we suspect resulted in lower RTD-SF when compared to pre-test values.”

Line 344 should remove the year in parentheses

Removed.

Line 352 in my opinion this sentence should go in Materials & Methods and not in discussions.

We agree with your point, therefore this sentence was added in part to Materials & Methods.

Line 362 it is not necessary to reproduce further the citation [24] already indicated in the same sentence.

Thank you for this comment, we deleted the redundant citation.

Line 367 this author does not appear in the bibliography. Please check the bibliography and consequently also this part of the discussions

We omitted to refresh bibliography after adding this reference. Thank you for pointing out this omission.

Put the "." after "et al" Check on the entire manuscript

Thank you for pointing out this omission. We checked throughout the manuscript.

Lines 387 and 388 are missing parentheses.

Thank you for pointing out this omission. We added parentheses as needed.

Reviewer 2 Report

Comments and Suggestions for Authors

Evaluation of manuscript applsci-3107572

 

This manuscript evaluated the chronic effect of isometric unilateral training plus electrostimulation in torque development. I would like to congratulated the authors for this research and I will write below my review, point by point aiming help the authors to improve the quality of the text.

The text is well written, I have some considerations to be made.

The title is generic. I suggest that the authors create a more specific title, which encompasses the main result of the study.

In the conclusion the authors statement that: “The VOL training failed to produce cross-education effect.” The main results indicate an absence of significative differences between the groups (i.e.; VOL vs. EMS). So, these results; do not support this conclusion. Please review.

There is a limitation not reported by the authors: the study was conducted on a sample of both sexes.

Comments on the Quality of English Language

I consider the text to be of good quality, in my opinion there are small changes to be made before publication.

Author Response

This manuscript evaluated the chronic effect of isometric unilateral training plus electrostimulation in torque development. I would like to congratulated the authors for this research and I will write below my review, point by point aiming help the authors to improve the quality of the text.

We thank the Reviewer for the kind words and appreciate all the comments and suggestions.

The text is well written, I have some considerations to be made.

The title is generic. I suggest that the authors create a more specific title, which encompasses the main result of the study.

Thank you for the suggestion, we took it into consideration, and propose new title:

Rate of Torque Development-Scaling Factor decreased following a 6-week unilateral isometric training using electrostimulation or voluntary contractions

In the conclusion the authors statement that: “The VOL training failed to produce cross-education effect.” The main results indicate an absence of significative differences between the groups (i.e.; VOL vs. EMS). So, these results; do not support this conclusion. Please review.

We appreciate Reviewer’s comment, and we partly agree. Looking into Table 1 data and Figure 3 lower right panel one may see literary no change within the VOL group. On the other hand, mostly moderate effects were observed following the EMS exercise, although main effect of factor time and time×group interaction reached significance only for RTD-SF. Nevertheless, we rewrote the sentence in question and now it reads: “Using a moderate training intensity in regularly physically active participants could explain the absence of cross-education in the VOL group”

Also, in the Conclusions paragraph we made similar changes so the sentence now reads: “Regarding the cross-education effect on the non-trained leg, the applied training intensity induced a significant decrease in the RTD-SF following the EMS exercise, whereas such changes did not reach significance in the VOL exercise group.”

There is a limitation not reported by the authors: the study was conducted on a sample of both sexes.

We appreciate Reviewer’s comment. Although we tried to eliminate some of sex-related differences by normalizing data with respect to body mass and lever length, we might have overseen other biological differences that influence the final outcomes. Therefore, we re-worded the last sentence of the limitations and now it reads: “Finally, the fact that we used a relatively limited sample that not only consisted of males and females who were regularly physically active may explain why some hypothesised effects were not observed, which may also influence the generalization of our findings.”