Evaluation of Voluntary Dynamic Balance through Standardized Squat-Lift Movements: A Comparison between Gymnasts and Athletes from Other Sports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

11. Avoid 1^st plural

14. Your study aims to evaluate gymnasts with other athletes, while in your title you compare gymnasts and non-athletes. Also, what do you mean with gymnasts?

15-18. Please, give a better explanation of your methodology.

30. Explain what is quiet standing.

29-117. I suggest that a comparison must be conducted between land-based sports and no gymnasts with swimmers. Also, have you searched about ski or skateboard athletes and their balance ability? I believe that in these sports, you can find comparative with your research results. Also, I suggest using a research hypothesis.

120. I suggest renaming the group as other sports athletes. The non-gymnastic gives the sense that you are talking about non-athletes.

139. Did you receive any ethical approval code from the university?  

144. I believe that your participants must have similar physical activity levels. Observing the other sports athletes with the gymnasts, they have many differences. I think that this is a strong limitation of your study.

148. Use subtitles before the description of each measurement. It is a confusing paragraph.

200. Did you utilize any cameras to record the process?

214. Now, you present other sports athletes as control. This is not correct. However, a control group would be useful.

 

220. Please, check if you have explained all of the abbreviations.

Comments on the Quality of English Language

I detected some syntax errors. I suggest that the authors must reexamine the whole manuscript. 

Author Response

Dear Reviewer #1, thank you for the comments leading to improvement of this manuscript. Your comments helped us to substantially improve the text readability and to enlighten the most relevant contributions of our research. Please, find below the itemized responses to your comments (reproduced in italics).

(1) 11. Avoid 1st plural

Authors’ reply: This passage was reworded accordingly.

(2) 14. Your study aims to evaluate gymnasts with other athletes, while in your title you compare gymnasts and non-athletes. Also, what do you mean with gymnasts?

Authors’ reply: We reworded the title to make the aim clearer. The definition of “gymnastics” was added as note 1 (lines 416-418).

(3) 15-18. Please, give a better explanation of your methodology.

Authors’ reply: We reworded different passages to make clearer the variables and procedures.

(4) 30. Explain what is quiet standing.

Authors’ reply: We improved the definition of “quiet standing” (line 30).

(5) 29-117. I suggest that a comparison must be conducted between land-based sports and no gymnasts with swimmers. Also, have you searched about ski or skateboard athletes and their balance ability? I believe that in these sports, you can find comparative with your research results. Also, I suggest using a research hypothesis.

Authors’ reply: (a) We selected athletes from sports expected to impose reduced balance demand compared to gymnastics. Comparison with swimmers or skateboarders would approach a question different from that selected in the current study. We selected athletes from different sports to prevent any sport-specific affects other than gymnastics training.

(b) In this study, we aimed to test the sensibility of two tasks for assessment of voluntary dynamic balance. Thus, this is an exploratory research, having no hypotheses.

(6) 120. I suggest renaming the group as other sports athletes. The non-gymnastic gives the sense that you are talking about non-athletes.

Authors’ reply: The non-gymnast group was renamed as suggested.

(7) 139. Did you receive any ethical approval code from the university? 

Authors’ reply: We added the approval code in the topic “2.2. Ethics” (line 141).

(8) 144. I believe that your participants must have similar physical activity levels. Observing the other sports athletes with the gymnasts, they have many differences. I think that this is a strong limitation of your study.

Authors’ reply: We highlight the last phrase of the section “4.3. Methodological strengths and weaknesses” that differences between the groups is a limitation in this investigation. This point was further addressed in the limitations’ section.

(9) 148. Use subtitles before the description of each measurement. It is a confusing paragraph.

Authors’ reply: Description of each task is now presented in a separate paragraph, with the respective subtitle (lines 156-177).

(10) 200. Did you utilize any cameras to record the process?

Authors’ reply: No cameras were used for recording the movements. This point was indicated as a limitation (lines 389-391).

(11) 214. Now, you present other sports athletes as control. This is not correct. However, a control group would be useful.

Authors’ reply: We renamed the non-gymnasts group, and reworded the passages referring to a control group throughout the manuscript.

(12) 220. Please, check if you have explained all of the abbreviations.

Authors’ reply: We made a full revision of the abbreviations and acronyms.

(13) I detected some syntax errors. I suggest that the authors must reexamine the whole manuscript.

Authors’ reply: The text was revised by a language specialist. From this review, different passages were improved in readability.

Reviewer 2 Report

Comments and Suggestions for Authors

In the present work, the authors reported the differences between gymnasts and athletes from various sports under three balance tests. Both groups performed: (1) a quiet standing task, (2) a dynamic stability task (previously presented by the same authors in https://doi.org/10.3390/biomechanics1030028), and (3) a dynamic stability task similar to a half-squat. All tasks were performed under two conditions: eyes closed and eyes open.

The introduction of the work is well structured. The aim (lines 110-113) is clear and soundness. The authors compare if the two dynamic tasks could reflect differences in voluntary dynamic balance between the evaluated groups. The proposed methodology is well aligned with the aim. The statistical tests are appropriate, and the results are correctly presented. However, this reviewer considers some issues that need to be verified by the authors.

 

Major comments:

1. In the strengths of this work, in lines 369-371, the authors state: "We highlight as the most original methodological advancement in the evaluation of voluntary dynamic balance in our study was the standardization of movement amplitude and rhythm during the performance of cyclic whole-body movements". However, this reviewer thinks this paragraph should not be understood as a strength, but rather the opposite. The kinematic variables during the dynamic tasks were not evaluated. Therefore, the lack of a prior study on the validity and reliability of this method of movement control (amplitude and rhythm) is a weakness, contrary to what the authors claim.

2. In line with the previous comment, in lines 373-375, the authors state: “With this procedure, we prevented high intra and interindividual movement variability during performance of the dynamic tasks, favoring sustainable conclusions…” What evidence do they present to support this claim? Indeed, lines 376-378 present a contradiction. In other words, the authors do not explain how they established that the execution parameters in the dynamic tasks were similar between the eyes-closed and --open conditions. This is especially critical since the guide for the end of the descendent phase was indicated by a visual reference (line 160) and auditory support (lines 172-175).

3. In the conclusions section, in lines 391-395, the authors elaborate on a speculation. This reviewer thinks this recommendation does not correspond to a conclusion, especially without prior validity and reliability studies on the presented method. The present study reports a difference between experienced gymnasts and non-gymnasts in the AP amplitude variability during the half-squat task. The subjects involved in this study are likely used to performing this movement during training and, therefore, have normal ranges of motion in the major mobile joints of the lower limbs. Consequently, strength and joint mobility limitations in the general population should not be overlooked. For example, low ankle mobility could result in significant AP variability of the CoP.

 

Minor comments:

4. Line 150 and 173: Provide fabricants’ complete information.

5. Line 188-194: Elaborate on the criteria for determining the repetition were considered valid, or not. Report how many repetitions per subject (by task and visual condition) were excluded based on the established criteria.

6. Line 196: This reviewer recommends using actual photos of the experimental setup so that the reader can have a clearer idea of the arrangement of the instruments used.

7. Line 204-207: This reviewer understands that the variables used in this work are common in the analysis of force platform data. However, the manuscript should be comprehensible as a standalone document. Elaborate and conceptualize each variable.

8. Line 298-300: This sentence is partially incorrect. The CoAP velocity did not show a significant difference, as the authors reported in lines 258-260 and Figure 4C. Please, fix the sentence.

9. Lines 378-380: This reviewer considers this sentence very important. In the present study, both groups are very different in anthropometric measures (approximately 14 kg and 11 cm differences between means). The authors could elaborate more on this limitation.

 

 

This reviewer recognizes that the manuscript is very well structured and written. Based on the comments presented above, this reviewer has some reservations about the methodology and the reliability of the results presented. It is expected that the authors will address these comments for the next round.

Author Response

Dear Reviewer #2, thank you for the comments leading to improvement of this manuscript. Your comments helped us to substantially improve the text readability and to enlighten the most relevant contributions of our research. Please, find below the itemized responses to your comments (reproduced in italics).

1. In the strengths of this work, in lines 369-371, the authors state: "We highlight as the most original methodological advancement in the evaluation of voluntary dynamic balance in our study was the standardization of movement amplitude and rhythm during the performance of cyclic whole-body movements". However, this reviewer thinks this paragraph should not be understood as a strength, but rather the opposite. The kinematic variables during the dynamic tasks were not evaluated. Therefore, the lack of a prior study on the validity and reliability of this method of movement control (amplitude and rhythm) is a weakness, contrary to what the authors claim.

Authors’ reply: Dear reviewer, from our perspective, the major limitation of previous research on voluntary dynamic balance is lack of standardization of movement amplitude and rhythm. Interindividual variability of these parameters can affect importantly the outcome of dynamic balance measurements in self-produced movements. This issue motivated the current research in the search for methodological advancement. In the current study, we tested the sensibility of the proposed dynamic tasks controlling for both movement amplitude and rhythm. The online control was made visually by the examiner to ensure that movements were performed as specified in the spatial and temporal dimensions. Our results indicate that the employed protocol is sensitive for dynamic balance evaluation through force plates without using cameras.

The fact that we had not a kinematic analysis to show a posteriori the adequateness of the performed movements regarding the specifications is declared as a limitation (lines 389-391). From these words, we understand that the methodological advancement of task standardization for evaluation of dynamic balance and lack of kinematic description of the performed movements are different issues to be considered in our investigation.

2. In line with the previous comment, in lines 373-375, the authors state: “With this procedure, we prevented high intra and interindividual movement variability during performance of the dynamic tasks, favoring sustainable conclusions…” What evidence do they present to support this claim? Indeed, lines 376-378 present a contradiction. In other words, the authors do not explain how they established that the execution parameters in the dynamic tasks were similar between the eyes-closed and --open conditions. This is especially critical since the guide for the end of the descendent phase was indicated by a visual reference (line 160) and auditory support (lines 172-175).

Authors’ reply: In this passage we are referring to a comparison between the tested tasks and conditions in which participants are allowed to perform movements at individually self-selected amplitude and rhythm. This passage was reworded to make this point clearer. To approach this issue directly, we would have compare movement variability between standardized and non-standardized conditions, requiring a different experimental design. As we have a logical argument but not factual evidence for this, the term “assumedly” (line 383) was added to the elaboration of this passage.

We agree with the comment on the difficulty of following the amplitude constraint guided by the visual reference in the condition of no vision. To address this issue, we added the following to this paragraph: “It should be acknowledged that performing the tested tasks without vision makes standardizing movement amplitude challenging due to the absence of visual reference” (lines 391-393).

3. In the conclusions section, in lines 391-395, the authors elaborate on a speculation. This reviewer thinks this recommendation does not correspond to a conclusion, especially without prior validity and reliability studies on the presented method. The present study reports a difference between experienced gymnasts and non-gymnasts in the AP amplitude variability during the half-squat task. The subjects involved in this study are likely used to performing this movement during training and, therefore, have normal ranges of motion in the major mobile joints of the lower limbs. Consequently, strength and joint mobility limitations in the general population should not be overlooked. For example, low ankle mobility could result in significant AP variability of the CoP.

Authors’ reply: Please, note that this section addresses “conclusions and implications”. In the first part of this paragraph we present the objective conclusion draw from the results, indicating that gymnasts outperformed the other athletes in the squat-lift but not in the hip flexion-extension task. In the second part, we present an overt speculation that this assessment could be possibly applicable also in the evaluation of older adults. In line with this assumption, we indicate that future studies should use the squat-lift task to evaluate dynamic balance across different age groups. From this observation, we believe to have approached your concern of undue generalization to non-athletes or older individuals.

4. Line 150 and 173: Provide fabricants’ complete information.

Authors’ reply: The requested piece of information was added (lines 152-153).

5. Line 188-194: Elaborate on the criteria for determining the repetition were considered valid, or not. Report how many repetitions per subject (by task and visual condition) were excluded based on the established criteria.

Authors’ reply: We reworded this passage to make this point clearer. In this revised version, we state that “Performance of the probing trials was visually monitored online by a single examiner. In cases that performance failed to attend the required movement amplitude or rhythm, the trial was aborted. Following extra familiarization movements, the testing was reinstated” (lines 199-203). As there were no excluded trials, we have no reports on this point.

6. Line 196: This reviewer recommends using actual photos of the experimental setup so that the reader can have a clearer idea of the arrangement of the instruments used.

Authors’ reply: Our artwork was made over real images. The advantage of using this representation rather than photos is that we prevented a noisy background with several pieces of equipment in the lab polluting the image.

7. Line 204-207: This reviewer understands that the variables used in this work are common in the analysis of force platform data. However, the manuscript should be comprehensible as a standalone document. Elaborate and conceptualize each variable.

Authors’ reply: A definition of center of pressure in posturography analysis was added as a note (#2) (lines 419-422) for the readers unfamiliar with this measurement.

8. Line 298-300: This sentence is partially incorrect. The CoAP velocity did not show a significant difference, as the authors reported in lines 258-260 and Figure 4C. Please, fix the sentence.

Authors’ reply: This statement was amended in conformity with the reported results.

9. Lines 378-380: This reviewer considers this sentence very important. In the present study, both groups are very different in anthropometric measures (approximately 14 kg and 11 cm differences between means). The authors could elaborate more on this limitation.

Authors’ reply: We developed further on this limitation, stating that anthropometric measures might affect center of pressure measurements.

10. This reviewer recognizes that the manuscript is very well structured and written. Based on the comments presented above, this reviewer has some reservations about the methodology and the reliability of the results presented. It is expected that the authors will address these comments for the next round.

Authors’ reply: The authors are grateful for the Reviewer’s recognition of the strong points of this manuscript and by indicating points that could be enhanced. We hope to have fully addressed the issues raised, leading to an improved version of our work. We expect that in the continuation of this work the generalization to other groups can be tested, including kinematic measurements in the analysis.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors improved their manuscript. 

However, in line 156, it is important to include a reference.

Author Response

Reviewer 1

We would like to thank the Reviewer for the criticisms and suggestions to improve the original version of this manuscript. These suggestions have enabled us to improve the readability of our manuscript.

1. (…) in line 156, it is important to include a reference.

Authors’ reply: Dear Reviewer, as requested, we included a reference for quiet stance evaluation.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have made corrections to address the minor comments from this reviewer. However, the major concerns were not substantially addressed. Based on this, this reviewer expects the authors to elaborate more extensively on the following comments and to incorporate these explanations into the manuscript. 

The lack of motion capture during the dynamic tasks is a significant limitation in the methodology:

1. Without motion capture (amplitude and rhythm), it is not possible to establish that the executions were similar in both vision conditions for each group. In other words, if the kinematic characteristics of task execution were not tested, it is not possible to establish that the results obtained in CoP variability are related to the condition of sports experience (primary aim) or vision (secondary aim), as stated in lines 112-119. This reviewer encourages the authors to exercise much more caution in discussing the results.

2. Lines 394-397: The anthropometric difference between groups is substantial. If the groups are so different, this is a significant methodological issue. In this regard, the differences reported in CoP variability may not be due to the type of sport (gymnasts vs. other sports). Again, if the authors intend to continue, they must elaborate more extensively and based on previous evidence why the differences found might not be affected by the anthropometric differences. This reviewer finds the response received on this comment insufficient.

3. Lines 199-203: The authors must elaborate more extensively on the exclusion criteria for invalid trials. The explanation is poor and does not allow this experiment to be replicable in future research. Additionally, "visual monitoring" by an expert is not an acceptable criterion.

 

This reviewer expects the authors to substantially improve the discussion and interpretation of their results in the next round.

Author Response

Reviewer 2

We would like to thank the Reviewer for the criticisms and suggestions to improve the original version of this manuscript. These suggestions have enabled us to improve the readability of our manuscript.

Criticisms:

1. Without motion capture (amplitude and rhythm), it is not possible to establish that the executions were similar in both vision conditions for each group. In other words, if the kinematic characteristics of task execution were not tested, it is not possible to establish that the results obtained in CoP variability are related to the condition of sports experience (primary aim) or vision (secondary aim), as stated in lines 112-119. This reviewer encourages the authors to exercise much more caution in discussing the results.

Authors’ reply: Dear Reviewer, thank you for your criticisms to methodological issues of our work. Regarding the issue of lack of kinematic measurements, we draw your attention to the point that our evaluation was based on center of pressure stability (displacement amplitude and velocity), which are universally used variables for evaluation of body balance without requirements of complementary measurements. As these variables indicate the stability of the resulting ground reaction forces, we think that it is of secondary importance whether movements had differences in kinematics between participants of the two evaluated groups. In fact, as the group of other athletes were taller than the gymnasts, it could be expected that segmental movements were somewhat distinct between the two groups. As soon as balance is maintained stable, as indicated by center of pressure, different descriptive kinematics would not affect our conclusions. From these words, we respectfully diverge from your perspective assuming that kinematics are essential for our analysis. If we had kinematic measurements, they would only provide a more detailed description of tasks performance between the groups.

2. Lines 394-397: The anthropometric difference between groups is substantial. If the groups are so different, this is a significant methodological issue. In this regard, the differences reported in CoP variability may not be due to the type of sport (gymnasts vs. other sports). Again, if the authors intend to continue, they must elaborate more extensively and based on previous evidence why the differences found might not be affected by the anthropometric differences. This reviewer finds the response received on this comment insufficient.

Authors’ reply: Dear Reviewer, please note that our aim was not making a comparison between gymnasts and athletes from other sports as it has been made in the previous research cited in the Introduction. Even if it was our purpose in this investigation, it is important to have in mind that gymnasts, by the nature of their training and sport requirements, are usually shorter than most athletes from other sports. Thus, it is virtually impractical to have one group of high-level gymnasts and another of athletes from other sports with similar anthropometric measures. This is an inherent limitation of all studies comparing gymnasts and other athletes. Further addressing this issue, in one of the few studies assessing the effect of anthropometric measurements on balance, Hue et al. (2007) showed that body weight accounted for 52% of the variance of balance stability, while body height accounted for 1% only. However, in this study BMI ranged from 17.4 to 63.8 kg/m², including thus a range of lean to very obese people. We are not aware of any investigations on the effect of anthropometrics on balance control in athletes. On the other hand, the main issue to be addressed on the posed issue is that we departed from the premise that gymnasts have better dynamic balance than athletes from other sports. From this premise, we assessed the sensibility of the two dynamic tasks tested to discriminate dynamic balance control. In this regard, whether the better balance found in the squat-lift task in the gymnasts is due to their sport training, muscular strength or some possible advantage because of their distinctive anthropometric measures is irrelevant for the purpose of our study. For the presented arguments, we did not go further on this issue in the Discussion section.

Hue, O., Simoneau, M., Marcotte, J., Berrigan, F., Doré, J., Marceau, P., ... & Teasdale, N. (2007). Body weight is a strong predictor of postural stability. Gait & posture, 26(1), 32-38.

3. Lines 199-203: The authors must elaborate more extensively on the exclusion criteria for invalid trials. The explanation is poor and does not allow this experiment to be replicable in future research. Additionally, "visual monitoring" by an expert is not an acceptable criterion.

Authors’ reply: We improved the description of this point, as it follows: “Interruption occurred in about 2% of trials; no trials were excluded from the analysis” (lines 200-1).  Please, note that visual monitoring was not used to exclude trials. It was in fact an experimental task to ensure that the task was performed as required.

4. This reviewer expects the authors to substantially improve the discussion and interpretation of their results in the next round.

Authors’ reply: The authors sincerely expect that all issues raised by the Reviewer have been satisfactorily addressed in our replies. Thank you for the thoughtful review of our work.

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

No more comments. The authors have explained their point of view.