Effects of Plyometric Training on Surface Electromyographic Activity and Performance during Blocking Jumps in College Division I Men’s Volleyball Athletes

Round 1

Reviewer 1 Report

The authors have presented a nice manuscript consisting of the analysis of plyometric training, a form of exercise, to quantify its effects in improving vertical jump height and blocking ability. Also, the authors are interested in determining if plyometric training decreases the rate of muscle fatigue and in which hindlimb muscles are most susceptible to fatiguing after successive round of jumps/blocks. The means of quantifying readings from the athletes was done in a very unique way, via wireless communication to transmit sensor readings. The science and the results are interesting and the conclusions fair for the work that was performed. There are some limitations and comments Id like to see addressed that could improve some aspects of the study. One general statement, the use of acronyms is very overwhelming, especially since some of them are similar to others. Please see below:

 

Abstract:
Please double check the grammar and language, specifically in lines 26 and 27.

Add a brief background statement (1 or 2 sentences) to give the reader a sense of why you are performing the study.

Line 22, you say significantly but do not provide a % decrease or a p value. P value can be avoided but at least provide the % decrease since you have done so for other values.

 

Introduction: I would like to see in greater description what plyometric training entails and why was it considered as a means to assess improvement in these athletes? Specifically, this information would be beneficial around line 69. W

Why wouldnt weight training to increase muscle capacity be a consideration?

I'd like to see a hypothesis in some form towards the end of the introduction.

Line 59-60, what does this velocity indicate physiologically?

 

Methods: was average height of the athlete recorded or any other body composition parameter?

Would it have made sense to record the normal force of the athlete as they struck the surface before jump?

Line 109, is the 3-minute resting period sufficient to allow recovery? Why was it chosen?

Similar to the above, line 111, why is 8s interval between blocks sufficient?

Line 110, please explain in greater detail what a blocking agility test is.

Line 127, Why are 2 weeks and 4 weeks of medium and high-intensity, respectively used here.

Although these techniques were used before, RE: line 134, are the sensors at all a physical imposition in achieving and maximal jump height? Perhaps RE: Figure 1, it would be nice with an inset to see closer up how the sensors are connected, or at least described elsewhere to understand if players had true freedom to move.

In the subheading under 2.5 for BA test, please spell out what BA means here and if there are another paragraph titles, please make sure to include the entire word for clarity.

Was a post-hoc test performed?

Please restate line 163 regarding the 0.05 being significant. Please describe correctly.

Results: Overall, please condense and provide subtitles to sections describing different sets of data.

Line 194, "PTG was significantly higher", so provide the P-value and/or the % difference. Previously in the same sentence as well as line 189 and 190, remove p>0.05....no need for this.

Throughout the Results, please consider using % increases and decrease along with p-values to describe the data as it is less informative to see just the data.

Discussion: Would these results be applicable to non-athletes?

How does athlete height and weight play into the success of plyometric training and the results seen here?

Was athlete height or weight or even muscle dimensions used as a normalization factor?

Thsted in terms of dominant fiber type and how that play into the high frequency and low frequency velocity lead to fatigue.

Line 154-156, please provide references

Does muscle fatigue at any other muscle site caused reduced performance? (i.e. back muscles?)

In general, please organize the discussion better so that the idea of what you are trying to convey flows throughout you findings.

Line 242-243, this is a nice concluding remark, consider placing elsewhere

Can it be described somewhere the biochemical changes that are occurring plyometric training as well as from fatigue.

The discussion needs to be worked on a little more to be clear and well written.

Are any other elements of volleyball skills expected to have improved from this exercise modality?

The discussion section is missing limitations section. THis is critical. Please add important limitations to your discussion. For instance, the use of athletes to assess this effect. The lack of inclusions of athlete weight/height/age and history of playing the sport(s) which could all contribute to the performance. Authors should critically think this before resubmitting.

Please also discuss what could be happening at the NMJ during fatigue and plyometric training.

Conclusions:
A little long and some of this information should go into the discussion.

Figure 1: This is a nice picture to demonstrate the apparatus employed, however, there is no reference to anything in the frame. Please use arrows and text to point out muscles with sensors attached and the apparatus in use for the study.

Figure 2: Please change the color and make larger the "*" and the "o" because it is very difficult to see. A title above both graphs would be useful.

Is b.) just an example? IF so, demarcate the median of this spectrum.

Figure 3: please place the unit over the y-axis instead of the title

Figure 4: please place the unit over the y-axis instead of the title

Figure 5: please place the unit over the y-axis instead of the title

Table 1: please explain what the number x number indicates. Is it 10 repetitions twice or 2 repetitions 10 x. Just be clear and use units to describe, perhaps in the parentheses above each subcolumn.

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript describes the effect of plyometric training on EMG activity, vertical jump height, and blocking agility in collegiate male volleyball athletes. The authors have drafted clear, grammatically correct sentences throughout all sections. However, some technical details must be expanded on before this manuscript is suitable for publication. Additionally, the authors may consider alternative figures within the results section. Detailed comments are included below:

Introduction

This study is one of many studies that have examined the effect of plyometric training on vertical jump height in volleyball athletes. My cursory search found at least a dozen studies. The authors should highlight how this study differs from previous studies. Factors could include training intensity and duration, subject sex and age, etc.

The authors should clearly state all hypotheses within the final paragraphs of the Introduction.

Methods

There are many muscles involved in executing a vertical jump. Please explain why these 4 muscles were chosen for EMG measurements.

Instrumentation within the Data Collection section included details about joint center calculations and force plate measurements. If this data is not pertinent to the present study, it should be omitted from the methods. Similarly, only one marker is needed to calculate vertical jump height. Which of the 21 markers were used to assess jump height?

In Dependent Measurements (Section 3), the details of filetype conversion and writing a program to read the file are not needed. However, more details of the cutoff frequency and order of the low-pass filter are warranted.

In Figure 2, label all axes including units. The asterisk and “o” referenced in the Fig. 2A legend are missing from the graph. Fig. 2B shows the signal spectrum without the median being labeled. Include details of which muscle this signal spectrum was collected from.

Results

Line 175: When including many numerical values (n=8) within a single sentence, a table of these values may be easier for readers to understand.

Tests of homogeneity should be applied to the variance of residuals from the ANCOVA, not the raw data or variables. Other “basic assumptions” assessed should be listed.

Figure 3: There are 2 undefined symbols above the PTG post-test values for T2, T3 of RFM and TAM. Please define these symbols or remove them. The statistical method described an ANCOVA, but these bar graphs most commonly used to report data from a post-hoc Tukey test. The horizontal bars are confusing in this instance. It’s unclear which 2 groups are significantly different. The 2 ends of this horizontal bar should be located above the 2 groups that are significantly different. However, the pre and post groups are further subdivided into multiple time points. Are the 3 different time points significantly different, or should this data be combined? Why is this time data separated in Figure 3 and 4, but combined in Figure 5? The horizontal bar also does not acknowledge the pre-test being included in the statistical analysis. Alternatively, I’d suggest constructing a table with coefficient values (betas) from the ANCOVA. This will allow you to report all factors included in the model, as well as associated significances. You may also consider including a table comparing least square means of pertinent groups of data. If these bar graphs must stay, consider changing the groupings so pre and post bars for one muscle/subject group are adjacent to one another to aid in visual comparisons.

Figures 4 and 5: See comments above for Figure 3.

Discussion

Line 229-239: These numerical values should be reported in the Results section. The Discussion section is reserved for interpreting the meaning of reported numerical values within the Results section.

Line 248: In addition to noting that results are consistent with previous study, provide comparisons of the magnitude of change in this study and others.

Line 251: Does “not reflected in the statistical results” mean this wasn’t assessed? Or that this was assessed, but was not statistically significant? Please clarify.

Line 252-256: These numerical values should be reported in the Results section. The Discussion is reserved for interpreting the meaning of reported numerical values within the Results section.

Line 263-268: This explanation of mechanisms within muscle connected to the study results should be expanded.

Line 273: Consider rephrasing “continuous training during actual training conditions”.

Most manuscripts briefly acknowledge any weaknesses associated with the study data collection or analyses in the final paragraphs of the Discussion. Please include appropriate details.

Conclusion

Several new terms are introduced for the first time within the manuscript (i.e. 1RM%, centripetal contractions, and eccentric contractions). Please provide explanations connecting these terms to this study in the Introduction and/or the Discussion.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have addressed nearly all of my previous concerns. Prior concerns not sufficiently addressed are summarized below.

The introduction does not distinguish this work from prior studies investigating the effects of plyometric training on vertical jump height of volleyball athletes. This study's subject age and sex are unique compared to prior studies.

I appreciate the authors' description of how the 4 muscles were chosen provided in the response to reviewers. I had hoped this explanation would be included in the manuscript.

The axes of Figure 2B are still not sufficiently labeled. The x-axis is the frequency in Hz. 

In the Discussion, the authors have acknowledged potential weaknesses of the subjects and setting, but have not addressed any potential weaknesses of data collection methods.

Lastly, several of the added revisions have grammatical errors, which is a marked change from the original submission that was well written.

Author Response

Please see the attachment.

Author Response File: Author Response.docx