Relationship between Hip Abductor Muscle Strength and Frontal Plane Kinematics: A Cross-Sectional Study in Elite Handball Athletes

Round 1

Reviewer 1 Report

-       The purpose of the present study was to examine the relationship between hip abductor muscle strength and frontal plane kinematics in Handball athletes utilizing low-cost 2D analysis software (Kinovea).

-       Overall, the manuscript lacks in the justification of comparing the results of 2D analysis to the results of 3D analysis- this should really be expanded on to allow you to compare to 3D studies.  

-       While the results prove interesting, the authors make significant leaps in regards to the implications for their findings. Really, this manuscript should be about how 2D kinematics elicit similar values to 3D kinematics as would be expected from the literature. Thus, 2D kinematics could be used in future studies and in training programs to analyze risk for injury.

Introduction

-       Authors do a fine job of presenting the need for low-cost and simple methods of kinematic risk assessment

-       There is, however, no hypothesis for this present study, which is critical for any exploratory academic manuscript.

Methods

-       Please include what participants were instructed to do with the non-dominant leg during the squat with the dominant leg

-       When was the hip abductor muscular strength assessed in relation to the frontal plane kinematic analysis? Was there a rest period? Was It a different day?

-       Where the participants given a warmup prior to the strength and single-leg squat analysis? Were they trained or screened for their ability to perform a single-leg squat?

-       Test-retest reliability: the methods here are unclear. Specifically, how were the participants tested then re-tested? Typical methodology for assessing test-retest reliability is to have participants come in for a day, be tested, then come back in another day under the same conditions to be retested, to assure that the same values are obtained. Obtaining test-retest data from the same day and within minutes or even hours defeat the purpose of test-retest reliability and will skew your data towards high ICCs (as were reported).

o   Furthermore, what method was used to calculate ICCs? 2,1, or 2,k, or even 1,1? ICCs is very important data to include and provides us with great information, but it needs to be reported correctly and thoroughly. This is a key, unique feature in your study that needs to be appropriately reported.

o   Did you perform reliability between researchers analyzing the data? Or was it reliability of the measures themselves?

-       Statistical Analysis: in the present study, only HB players were assessed, and there did not seem to be an intervention. Thus, it is unclear what within-group comparisons were performed- what are you comparing? What are the two groups that are being compared and how were they determined?

Results

-       Lines 225-226 do you mean handed or legged? As in, the methods were performed to determine leg dominance for the testing. Please clarify

-       Lines 143-144: “The non-dominant lower limb was registered only for descriptive purposes” yet it was used for a within-group statistical analysis.

-       Table 2: the significance column needs to be explained- what test was performed? Are you reporting p-value or F-value? NW and the degree symbol should be defined in the abbreviations. Rather than “Dominant Side” authors should use Dominant Limb, same with non-dominant

-       Table 3: it should include what correlation variable was utilized here (i.e. Pearson Correlation Coefficient).

Discussion

-       In general, the discussion will be better served with having a hypothesis to work with

-       268-269: was the relationship with hip abductor strength like what was performed in your study?

-       276: should change to “.. may present similar results compared to a 3D system”

-       277: what correlation? Correlation between hip strength and knee valgus? Correlation between values of 2d vs 3d kinematics?

-       290-298: this is a stretch and really does not relate to the present study as it stands. The needs to independently assess and control musculoskeletal function is evident? Does Kinovea assess musculoskeletal function or kinematics? How does your study relate to musculoskeletal control? Your study assessed the kip and knee kinematics: what muscles elicit what changes in the kinematics of the lower limb? Can we control the dynamics of the frontal plane? Or do we analyze and then prescribe training/rehab to mitigate potential risk. You discuss risk factors but don’t define what risk factors can be obtained from Kinovea. To be frank I think this paragraph is either unneeded or requires substantial references to justify claims.

-       302-305: Kinovea can help with what variables? What have previous groups/researchers prescribed or recommended based on the significant relationships you’ve demonstrated in this study?

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Thank you for your submitted manuscript entitled, “Relationship between hip abductor muscle strength and frontal plane kinematics: a cross-sectional study in elite handball athletes’’.

·       Novelty of the study: What is the question being answered? What did the authors want to show? What did the authors expect? 

ABSTRACT

·       Clarify the subjects’ background, health status, time of year, day testing, nutrition etc..

·       In the conclusion, what is the new discovery? What is the major impact on practice that your study puts to the coach to personal trainer, athlete etc. 

INTRODUCTION

·       The introduction needs a bit stronger rationale for the study conduct as do we not already know all this or why is it important to know?  This information is provided in the introduction section. 

METHOD

• The procedure is rigorous and well described and the statistical analysis is correct.

DISCUSSION

• The discussion needs to reflect what you found, how it relates to the literature and each paragraph should be logical in sequence as at present it is a bit hard to follow. Make sure the paper’s importance and the need is clear to the reader.

CONCLUSION

• Finally, improve the conclusion section: it is important to suggest possible future studies.

·       Take time to check all formatting and make sure that all of the figures you have are mentioned in the text of the paper so that the reader can find them.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Overall, I appreciate the changes made in the manuscript thus far. The 2 primary issues I see currently are 1) the test-retest reliability analysis was not appropriately completed. 2) the discussion requires a more thorough touch when describing cited studies. Words like "they demonstrated a positive/negative correlation", "they reported significant/non-significant differences." Just saying "Authors reported a relationship" is not enough. 

 

Methods

-       Line 161: “test-retest reliability has shown to be excellent”. Is this from your own reliability analyses or is this from another manuscript?

-       167: Should rephrase to “was established before the Frontal plane kinematic assessments” if that’s what you mean.

-       2.3.1 It still remains unclear whether participants were given a warm up before maximal hip abductor muscle strength

-       185: if this is following a method previously proposed by Weeks et al. then it should be cited in the manuscript.

-       207-208: If this was a separate published study, it should be cited.  

-       2.4 Reliability: If they are completely different participants used for reliability, then we need more information such as their height, age, weight, etc. to compare to the participants of the present study. Did they also sign an informed consent?

o   Again, test-retest reliability helps to establish investigators obtain the same values with repeated measures. How much time from test to retest was not defined. If they were conducted back to back I do not think that the assessment can be a valid determinant of reliability unless you include citations that justify the current method utilized.

o   Koo et al. is a great source for ICC information. I would recommend citing it as well so readers understand the methods utilized to quantify test-retest

Discussion

-       273-274: what was the relationship? Was it a negative correlation like what you demonstrated? Or the opposite? Please expand/elaborate which will help to support your results. 275-276 authors did a good job of describe the outcomes of the study which aligns with your findings

-       281- A positive correlation coefficient suggests as one variable increases, the other variable increases. In this case, r = .855 for knee valgus angle and hip abduction, thus as abduction increases, knee valgus increases. This contradicts your initial statement so either statistics are unclear or how knee valgus was quantified (greater angle = less valgus?; thinking lines 201-202)

-       280-290: what are the relationships specifically? Are they positive relationships like what the authors reported? Are they negative relationships? We need specifics so that you can convince the readers that the author’s data is consistent with the findings in previous studies

o   The explination for citation 50 is vague- reported the same results? As who, your values? Or those of Sukuki [49].

-       293: “found a reasonable relationship” is not clear- was it significant or not? If it was a correlation, use the words you’ve already defined in lines 227-228

-       - 307: what should be considered? “It has turned out to be key in the dynamic balance of the lower limb” is a claim that needs to be either supported by evidence, or you should say something along the lines of, the results of the present study suggested a moderate relationship between hip strength and dynamic balance of the lower limb

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

n/a

Author Response

Thanks for reviewing the manuscript.

Round 3

Reviewer 1 Report

Overall the authors have done a great job of responding to the recommendations made. I believe these changes have allowed for a publishable manuscript. I encourage authors in the future to be thorough in the reporting of the methods and results, as these are critical portions of scientific writing. When discussing variables, there should be a consistency of language utilized, such as either valgus angle vs valgus movement, to that your ideas are not lost in confusion.