Dynamic Characteristics of Approach Spike Jump Tasks in Male Volleyball Players

Round 1

Reviewer 1 Report

In this paper the Authors perform a biomechanical analysis of the spike jump task (RSJ) in a group of male volleyball players. RSJ with one leg (RSJ-1L) kinematic and kinetic data are compared with those acquired during RSJ with two legs (RSJ-2L). Furthermore, the primary parameters affecting the performance of these two tasks are identified. The results show that RSJ-1L, compared to RSJ-2L, has a faster three-step approach running velocity, greater vertical GRF, greater ankle, knee and hip joint moments, less jump height, shorter last step length and push-off time, smaller knee and hip joint flexion angles at the initial foot-contact, and smaller knee range of motion. Additionally, only for the RSJ-2L, the jump height is affected by the peak knee and the hip flexion angle. The Authors conclude that “RSJ-1L and RSJ-2L employed different strategies to perform spike jump” ant that “RSJ-1L can be considered as higher loading movement for the lower extremity compared to the RSJ-2L”.

Major comments

I have two main major concerns about the paper. First of all, the manuscript is very similar to a previous one published by the same group (Tai WH, Wang LI, Peng HT. Biomechanical Comparisons of One-Legged and Two-Legged Running Vertical Jumps. J Hum Kinet. 2018, 64: 71-76). The group of subjects (identical number, mean age, body weight and height), the two tasks required, most of kinematic and kinetic variables analysed and the results are comparable. Unlike this submitted paper, the first one analyses and discuss, in more detail, the joint stiffness. In my honest opinion, the discussion described in this manuscript doesn’t add new relevant scientific contributions with respect to what illustrated in the first paper. To make more interesting the present study, I recommend to better explore and critically discuss the determinants affecting the performance of the two tasks examined (one of the aims declared by the Authors in the introduction session). This point is crucial to improve the performance of the athletes.

The second concern is a little bit more methodological. If I have understood correctly, the Authors compare the kinetic data of the left leg acquired when subject is in single stance, with all the body weight on the support leg (RSJ-1L ), with those acquired when he is in double stance, with the body weight well-balanced on the two legs (RSJ-2L). The two situations are very different in terms of GRF and, if my interpretation is correct, it’s not surprising that the kinetic data of RSJ-1L, compare to RSJ-2L, shows higher values.

Minor comments

Line 79 – What height is the volleyball? Is this position the same for all subjects? Please specify this point.

Line 84 – Please describe the clothes worn by the subjects. It is important to understand if the markers are attached on the skin or not.

Data analysis (Lines 97-121)

• Please define the “last step length” variable. This variable is reported in Tab. 1 but never defined.
• Please explain how the variables “flexion angle at contact”, the “peak flexion angle” and the “angular range of motion” are computed (e.g. manually by eye-inspection of the graph or by a custom-made software)
• It could be interesting to observe GRF and flexion angle raw and filtered data. Please insert these graphs in the manuscript.
• GRF, joint moment and power are normalised with respect body weight (Line 120). I suggest to normalise the “jump height” and the “last step length” with respect to the body heigh.

Discussion (Lines 164 - 226)

The discussion must be rewritten taking into account my major comments. Moreover, the discussion about the pre-activation of the lower limb muscles (lines 187 – 194), have to be removed because it is a simple hypothesis not supported by the results.

Author Response

On behalf of my co-authors, we would like to express our great appreciation to the reviewers. We have carefully reviewed the Editorial Office comments revised them and marked them in red in the paper. We have tried to revise the manuscript based on the comments. A revised version is enclosed for your reference.

Author Response File: Author Response.docx

Reviewer 2 Report

Thank you for receiving the manuscript on biomechanics in volleyball jumping by Tai et al.

A very similar article by Tai et al. (doi: 10.1515/hukin-2017-0185) was found. The previous publication used the identical data to answer the similar research questions.

In the present manuscript, the authors introduced some newly calculated variables and correlation analyses. They added statistical valuable information (e.g. 95% CIs). A different test was applied for the assessment of difference; it is unclear however why using previously an ANCOVA and now t-test for the same research questions. To summarize, the authors attempted to introduce new approach to handle the data, which can be valid and potentially contribute to the current literature, but there are some deficits remaining that question to value of the manuscript in its current form compared to the previous publication:

Primarily, it is unclear what new and different insights the current manuscript offers compared to the previous publication. If the authors can outline the specific deficits in the past publication and why an adapted, expended, or advanced assessment is needed and how it adds value to the current literature than this manuscript can be potentially considered for publication. Please clarify what this manuscript offers in comparison to the previous one. The manuscript must specifically refer to the previous publication in the context of what was found and which limitations shall be overcome by the new manuscript. This could include outlining more strongly the tactical differences of both spikes which reason the differences in kinematics and extensively including the briefly mentioned loads that could be a consideration in training measures. It is worth a thought to add duration from approach to striking the ball as a biomechanical criterion that relates to tactical demands. Such single changes, however, are not enough, and the authors are encouraged to seriously strengthen the added value of the manuscript across all sections of the manuscript.

Correlation analyses was something new in this manuscript. However, correlation results did not provide many insights and were barely discussed. Overall, it seems that little added value was achieved by the changes compared with the previous publication.

The reviewer suggests major revision clarifying the limitations of the previous publication and the added value of the current manuscript before further preview.

Author Response

On behalf of my co-authors, we would like to express our great appreciation to the reviewers. We have carefully reviewed the Editorial Office comments revised them and marked them in red in the paper. We have tried to revise the manuscript based on the comments. A revised version is enclosed for your reference.

Author Response File: Author Response.docx

Reviewer 3 Report

The paper titled Dynamic characteristics of approach spike jump tasks in male volleyball players is written according to the journal's guidelines. It has no illustrations and two tables. The paper is a good contribution to analysis of the kinematic and kinetic differences between the running spike-jump with one leg and with two legs. All relevant references are included, methods are adequately described and results very clearly presented. The obtained results provide detailed information’s about different strategies to perform a spike jump and can be used in volleyball training programs.

I suggest for the future studies to analyze it on a greater sample and to include subjects of the other level to confirm findings of the present paper.

Author Response

On behalf of my co-authors, we would like to express our great appreciation to the reviewers. We have carefully reviewed the Editorial Office comments revised them and marked them in red in the paper. We have tried to revise the manuscript based on the comments. A revised version is enclosed for your reference.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear authors,

the reviewer understands that this new manuscript is meant as an extension to the previous publication. The weak consideration of the previous publication in the introduction of the current manuscript, however, remains a weakness. “[…] could not fully represent the biomechanics […]” and “Knowledge of the RSJ-1L was short of the experimental kinetics combined with kinematics” (see introduction, L59-61) are not enough to clarify the limitations of the previous one and does not clarify what added value is expected by implementing the new study. Please add a clarification in the introduction.

Some of the highlighted sections contain errors or poor English.

Calculating jump height based on flight time is an imprecise method and should be seen critical for scientific purposes. Especially when like in this case a Qualisys system was used, it is recommended to calculate jump height based on vertical take-off velocity.

Specific:

Please use italics for r as it was done for p and d.

The common abbreviation of Cohen’s effect size is d. So, please do not use “EZ”; use d. Moreover, Cohen’s d does not present practical relevance but statistical magnitude. This is a very important difference. Please change in L133.

Table 1 and 2: It seems that p-values for correlation results are missing. To make more use of the space in both tables and to improve consistency within each of the tables, please report effect size of correlation (r) and underneath the significance (p), and the same for t-test (d (95%CI) for effect size; and p underneath)

Author Response

Author's Reply to the Review Report (Reviewer 2)

Comments and Suggestions for Authors

the reviewer understands that this new manuscript is meant as an extension to the previous publication. The weak consideration of the previous publication in the introduction of the current manuscript, however, remains a weakness. “[…] could not fully represent the biomechanics […]” and “Knowledge of the RSJ-1L was short of the experimental kinetics combined with kinematics” (see introduction, L59-61) are not enough to clarify the limitations of the previous one and does not clarify what added value is expected by implementing the new study. Please add a clarification in the introduction.

Response:

Thanks for your comments. We have rewrite the paragraph for the clarification in the introduction. Please refer to lines 60-63.

Some of the highlighted sections contain errors or poor English.

Response:

Thanks for your comments. They were revised accordingly. Please refer to the highlighted sections in lines 88-90, 92-96, 101-106, and 112-114

Calculating jump height based on flight time is an imprecise method and should be seen critical for scientific purposes. Especially when like in this case a Qualisys system was used, it is recommended to calculate jump height based on vertical take-off velocity.

Response:

Thanks for your comments. The method of jump height calculation in the current study was in accordance with previous scientific researches (Flanagan et al., 2008; Kobal et al., 2017; Peng et al., 2019), which has been considered a valid method for calculating jump height. Because only the lower extremity was modeled in the Qualisys system with just 21 reflective markers, we cannot obtain the center of mass of the whole body and its velocity. Moreover, the jump height was just one of variables used to evaluate the differences between RSJ-1L and RSJ-2L. The current study calculated the jump height just based on the flight time obtain from ground reaction force data. The current study focused more on the changes of joint kinematics and kinetics of the lower extremity in different RSJs. We appreciate your suggestion.  

Specific:

Please use italics for r as it was done for p and d.

Response: Thanks for your comments. We have used italics for r throughout the manuscript and tables. Please refer to the table1 and 2.

The common abbreviation of Cohen’s effect size is d. So, please do not use “EZ”; use d. Moreover, Cohen’s d does not present practical relevance but statistical magnitude. This is a very important difference. Please change in L133.

Response: Thanks for your comments. We have used d as the abbreviation of Cohen’s effect size throughout the manuscript and tables. Please refer to line: 139-140, 142155-157, and 159

Table 1 and 2: It seems that p-values for correlation results are missing. To make more use of the space in both tables and to improve consistency within each of the tables, please report effect size of correlation (r) and underneath the significance (p), and the same for t-test (d (95%CI) for effect size; and p underneath)

Response: Thanks for your comments. These have been revised. Please refer to the table1 and 2.