Jumping Side Volley in Soccer—A Biomechanical Preliminary Study on the Flying Kick and Its Coaching Know-How for Practitioners

Round 1

Reviewer 1 Report

Dear authors,

I would like to congratulate you on the novelty of the present study. Also, the use of a refreshing speech in academic writing, is a clear attempt to close the gap between academic and practical know-how and reach a wider range of potential readers. In my opinion the overall appreciation of the manuscript is fairly good, although I have some concerns about the players recruitment process and especially, regarding the presented practical implications. I think the final version of the manuscript would strongly benefit from the use of ecological approaches to motor learning, instead of the traditional and linear pedagogical approaches.

Abstract

Line 17: I believe you meant to say methods. Please correct.

Line 19: What do you mean by “…to identify elements that govern entrainment of the skill …”? Please consider changing the sentence.

Line 21: Twenty-three trials in total for all the five players? What have you considered to classify someone who has acquired this skill? Please provide a proper information to clarify the potential reader.

Line 25: “… can only be achieved through repetitive training”. Considering the more contemporary motor learning theories, I find this affirmation highly questionable or even inadequate (see Santos et al., 2016; Davids et al., 2012).

Introduction

I find it well written, with a fluent and thrilling narrative, providing the potential reader with a proper framework for understanding the problematic around the study and research question.

Line 55 and 56: I find this part of the sentence rather confusing. Please consider changing the sentence.

Material and Methods

2.1. How to establish a lab test condition for mimicking the reality?

Line 61: Please add an application-oriented investigation.

2.2.3. D Motion Capture and Biomechanical Modeling

Line 72: Was it 2.2. instead of 2.2.3.?

Line 109: “… timing) and…”. Please add space.

Line 111: Please consider changing the sentence to make it clearer.

Lines 115–116: It is not clear how were the subjects recruited. Please provide a more appropriate information about selection criteria when selecting players, particularly when classifying someone who has acquired this skill.

Line 118: Please include experience in soccer training and remove “soccer experience” from above.

Line 121: A total of 23 successful trials for the 5 subjects? How many trials in total did each one had? And which factors were observed to consider a trial as successful. I believe that these questions need to be clarified.

Results

Line 130–131: “… revealed the following…”. Please correct by adding “:” or change the sentence.

Line 141: Consider adding the confidence intervals and coefficient of variation in order to provide a clearer descriptive information.

Line 153–154: Although it comes with respect to the observed results, is this discussion?

Line 154–155: Please correct sentence.

Discussion

The authors have done a great work by providing a comprehensive view on the critical components of the jumping side volley kick. Unarguably, the knowledge about the phase identification and the key factors of this skilful movement can improve the coach’s pedagogic intervention. However, I believe that the discussion section could benefit from a further improvement. since this is a coach-oriented study, it should emphasize the ecological approaches to motor learning, besides the traditional models of repetition and application of analytical methods. Identifying the learner–environment relationship as the basis for learning design in sport intentionality captures perception and action as intertwined processes underpinning individual differences in movement behaviour (Davids et al., 2012). The use of a nonlinear pedagogy, particularly in open and complex skills such as a jumping side kick, could reinforce the authors’ intentions to help coaches to develop soccer-skills with their players.

Line 168: Please consider … and applied his/her intervention.

Line 180–182: Please reconsider placing this sentence in other part of the section, since the text fluidity is impaired.

Line 207: Please avoid such a short paragraph with only one sentence.

Line 215: Did you meant short-cut?

Line 215: It is highly questionable to argue that skill acquisition can only be achieved through repetition. I believe that the relevance of this study lies in its practical implications and it deserves a more dedicated attention to motor learning approaches, with focus on the nonlinear pedagogy implications from ecological theories (e.g., dynamic systems, or differential learning). The acquisition of open skills raises an important dichotomous question regarding the use of analytical and global methodologies.

Line 219: I find it also questionable that we must begin with phase 3. Considering the diving technique in soccer goalkeeping we do not necessary start by focusing on the landing phase, but instead, use a progression from different starting positions emphasizing other key factors. Also, different surface types can be used to promote a skill acquisition in more ecological dynamics. Please provide a rationale for this option.

Line 220–222: Again, I find this argument quite questionable.

Study limitations should also be pointed out by authors.

Conclusion

In accordance with the previous comments, I strongly suggest a redefinition of the guiding line of the discussion that can be reflected in this section, highlighting the practical implications – coaching points, training methodologies and learning stages of this skilful movement.

References

Line 241: Do you mean January? Please correct.

Please consider references suggested as follows:

Davids, K., Araújo, D., Hristovski, R., Passos, P., & Chow, J. Y. (2012). Ecological dynamics and motor learning design in sport. Skill acquisition in sport: Research, theory and practice, 112-130.

Santos, S. D., Memmert, D., Sampaio, J., & Leite, N. (2016). The spawns of creative behavior in team sports: A creativity developmental framework. Frontiers in psychology, 7, 1282.

Author Response

Please see the attachment.

Reviewer 2 Report

Brief summary

The current work investigates the biomechanics of jumping side volley in soccer. However, it is not clear how many aims there are in this study because different statements are reported in abstract, introduction and discussion. Instead, evident question/s should be indicated in the text. Five male players were recruited for this preliminary study. To collect the biomechanics (kinematics) of the players a 3D motion capture system was used fixing 42 makers on the players to assess player’s kinematics and 3 markers the ball to measure ball release speed. However, the protocol is not well described. It is not reported in detail which are the variables measured and/or calculated and to which purpose. Overall, joint angles, joints range of motion, and coordination timing were evaluated during the jumping side volley. The technical gesture was divided into three phases (jumping phase, airborne phase, and landing phase). The players’ kinematics was described qualitatively during the three phases and a table with players’ kinematics is reported in the results. However, it is not definite if the kinematics was evaluated for each phase or on the whole jumping side volley. In addition, the correlation of these variables with the ball release speed was calculated, but no statistical significance of the correlation was reported. From the results, it seems that twisting control of the upper body and instance angle between the two thighs during the jumping phase, the kick side knee minimum angle and range of motion during the airbone phase, and the arm-hand and hip landing during the landing phase are the key factors to execute a good jumping side volley and should be taught to perform safe jumping side volley.

Broad comments

The main concerns about the paper are: (1) it is not clearly indicated the purpose/s of the study (there is an inconsistency between abstract, introduction, and discussion); (2) protocol is not reported and variables are not introduced and described in the method section; (3) results are not complete (statistical significance of correlation was not calculated); (4) discussion is not supported with a comparison with existing literature, but it is only descriptive.

The abstract reports a brief background and the aim of the study; however, both the methodology and the results should be improved. Concerning the methodology, it is described that the biomechanics of three phases (jumping, kicking, and falling) was studied; however, the biomechanical parameters evaluated are not reported. Concerning the results, the main findings for the 5 key elements should be reported numerically.

The introduction explains what a jumping side volley is, how rarely can be seen in a football match, and why it is performed by a low number of athletes. However, the research question/s is not clearly outlined, but the question should be picked up from the text.

The method section gives partial information about the protocol, data acquisition, and data assessment; however, extra information should be added to the text and in order to give to the reader all the necessary information to possibly replicate the study. In particular, the following aspects should be considered:

• participants paragraph (how participants were selected and participants’ personal data) should be reported at the beginning of the method section. Does this study agree with the Declaration of Helsinki?
• Acquiring system (VICON) and acquiring set up is overall clear. However, a more detailed description of the markers position on the participants should be reported and/or if the markers set up has been previously used in another study a reference can be reported.
• Concerning the data analysis, which are the “raw data collected”? Which are the variables measured and/or calculated? How joint angles, range of motion and coordination timing were calculated? From which body segments angles were calculated? When joint angles were considered positive and when negative? How markers on the ball were used to calculate the release speed? In addition, which statistical analysis has been conducted on the data? Only descriptive statistics and correlation were used? Which type of correlation and which alpha value were set?
• It is not completely described the protocol each participant performed; does any participant perform 23 trials or does this number refer to all participants? When a trial was considered successful and when not? How the ball was pass to the participant? In the text, it has been reported “the vertically projectile ball done by each subject was applied in our lab-based data collection”, how the protocol was standardized among participants?

Form the results section appear evident that the jumping side volley can be divided into three phases (jumping phase, airborne phase, and landing phase) according to two events: take-off and ball contact. However, the rest of the paragraph is quite confusing because variables were not introduced in method section and because the three phases are described based on qualitative analysis without showing joint kinematic curves (that would help to follow the description). In particular:

• It is not definite if joints range of motion were calculated for each phase (as it seems reading the text) or during the entire jumping side volley (as it seems from table 1). Because three phases were identified, it would be interesting to assess joint range of motion for each phase. Similar considerations can be done for angles. In addition, because of the description of joints kinematic during the three phases, it would be interesting to show joints kinematics evolution over the entire jumping side volley.
• Concerning the correlation, the significance level should be reported in table 1 to identify the significant values.
• Figure 5, presenting three variables, should be reported in method section, not in the results.
• In the present form, results are complicated because there is a mix of quantitative and qualitative results. A possible solution can be to sum up quantitative results for joint range of motion, joint angle, coordination timing in table 1, clearly marking significant results. In addition, in the text qualitative results with a figure that report joint angles evolution in time. The variables description (and related figures) must be moved in the methods.

Discussion section is overall composed of three paragraphs, which interpret results from the three phases. However, the usual structure for the discussion section seems not to be respected making the section not linear. Discussion should start with a brief sum up of the aim and the results; then, interpret and discuss results comparing current findings with already existing literature; finally, a “take home message” should be given to the reader. In the present form, these parts are mixed up.

It is important to interpret the results in a practical view; however, a comparison of the current results with the literature is missing (there are no references at all in the discussion section). In addition, in discussion are introduced concepts, such as “kick power” or “accuracy”, for the first time, which is uncommon for this section.

A critical discussion of the possible limitations of the study has not been done.

The references should be in the form reported in the “Instruction for Authors” guideline. For example, books should report pages. In addition, there are studies available on this topic that are not considered.

Specific comments

Materials and methods

Line 72: Change “2.2.3. D Motion Capture and Biomechnaical Modeling” with “2.2. Motion Capture and Biomechnaical Modeling”

Lines 86-87: add a reference for the Vicon guideline for the calibration.

Lines 101: “Using basic physics” is too general.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

I commend the authors for tackling a new topic in sports biomechanics. Overall the article is well written and easy to follow. I did spot a few spelling/grammar errors  (lines 128, 215). After your final edits I suggest a an additional I have a few suggestions to improve the clarity of the article below.

Methods

Lines 80-84: Please clarify where on the scapula you placed markers. Additionally for the midsegment markers for the upper arm, forearm, thigh and shank please specify if you used a landmark for these markers or if you placed them exactly midsegment.

Line 109-110: Please explain why you ran a correlation analysis on the data – what relationships were you interested and why? Additionally, when reading the results and discussion it was not immediately evident how the correlation analysis was incorporated.  

Line 115: What skill level were the soccer players? Recreational? College players? Professional?

Line 121: Did you collect 23 trials per player? Or in total? If 23 in total, please explain why it is not an equal amount of trials per player.

Results:

The authors have done a great job summarizing the data that was created from this study. I think it would be interesting for the reader if you include some of the time series graphs in addition to Table 1 with the phases marked on the graphs.

Table 1: Please specify which shoulder is discussed in the “Max Shoulder abduction” line. Additionally, the correlation values are provided but are not discussed in the text. Please provide some context for these values.

Discussion:

I would like to see a limitations/future direction paragraph added to the discussion. There is the obvious limitation of sample size, but I am more interested in some of the less obvious limitations. Did the five players perform similarly? Was there a large amount of variability between players? Between trials within a player? What other questions are left to investigate?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

I would like to congratulate you for the provided changes. I am pleased with the contribution for the final version of the manuscript.

Author Response

Dear Reviewer,

Thank you again! Your thorough and considerate review has helped to improve the quality of the paper significantly.

Best,

Gongbing Shan

Reviewer 2 Report

I would like to thank the authors for the detailed answer in order to explain the message this article is intended to give to the reader. During the first revision, I had four main concerns about the paper: (1) the purpose/s of the study that should be clarified and be in line between introduction and discussion; (2) protocol and variables, which seem to be not clearly described in the method section; (3) in results statistical significance of correlation were missing; and (4) discussion that was not supported by existing literature and possible limitations were not considered. The authors significantly improve the manuscript addressing all these four aspects. In particular, (1) the authors clearly identify the purposes of the study in the introduction and report the purposes in the discussion; (2) method section has been improved. Details on participants and protocol have been added. Since extra technical information for data acquisition and analysis may become confusing for the reader, references have been added; (3) the authors added statistical results of correlation; (4) the authors discussed separately the two purposes: the determinants influencing the kick quality (line 218) and the two aspects that can be considered for training jumping side volley (line 245). The authors have explored possible limitations of the study and improved the conclusion.

Since the strength of this work is the strong relationship between practice and science, I would still suggest small changes to highlight this aspect in the manuscript (especially in introduction and discussion) and, thereby, to make clear the added value that this work gives to the existing literature. These small changes are:

Line 59: In the introduction, to stress more that the study is for practitioners. The authors can write some like: “To give efficient and effective information to practitioners, we have launched a preliminary study [10] to give a scientific overview of the kick, to identify key features of the skill and to formulate a scientific way of learning/training the technique.”

Line 201: In the discussion, it is possible to stress more your experience and the concept that the method adopted is widely established, the authors can write something like: “A coach-friendly study, in our vision, should use a well-established scientific method to supply explanations on…”

Line 245: when the authors discuss the two factors for training jumping side volley, they can add some text also for non-practitioners. For example, “The first one is kick power. From the practice, it is well known that is important to develop a full-body whip-like control (from trunk to KS foot) for increasing kick power….” In this way is stressed once more the link between science and practice. 

Author Response

Please see the attachment.