Bilateral Strength Asymmetry in Elite Youth Soccer Players: Differences between Age Categories

Round 1

Reviewer 1 Report

The study determines the prevalence of isokinetic strength bilateral asymmetry among knee extensors and knee flexors of elite youth soccer players. The authors found a significant effect of age category on bilateral asymmetry levels in young soccer players. High incidences of increased bilateral asymmetry in the lower limbs occurred in the younger categories (U13, U15) and subsequently decreased in the later adolescent stages.

Findings of this review are in my opinion of relevance to sport science and symmetry and would fit the scope of the journal. There are, however, minor concerns which should be addressed.

 

Consider to reformulate the aim of the study (omit the word “prevalence”)

Page 1, lines 12-14: This study aimed to determine the prevalence of isokinetic strength bilateral asymmetry (BA) among knee extensors (KEs) and knee flexors (KFs) of elite youth soccer players.

 

Include the reference(s)

Page 2, lines 78-80: A reason for the lack of literature on isokinetic asymmetry in youth soccer players is undoubtedly the financial limits and the deficiency of specialised measuring equipment.

 

Remove (p < 0.05)

Page 2, lines 81-83: We hypothesise a significantly (p < 0.05) increased level of BA in the younger category (U13 and U15) compared to the older category U17.

 

Please, include the performance level of participants

Page 2, lines 93-95: The inclusion criteria were that all players were healthy, non-injured, and had no performance limitations in the pre-season measurement.

 

Specify “elite youth soccer players”

Page 5, lines 186-187: This study aimed to determine the isokinetic muscle strength and BA levels in the KEs and KFs of elite youth soccer players categorized by age.

Include % on Y-axis

Page 5: Figures 1 and 2

 

Specify the frequency of resistance training sessions in each age category of soccer players.

Pages 5-6, lines 201-202: Notably, each category in the study (U16-U21) also underwent resistance training once a week, whereas only those in U17 category underwent resistance training in our study.

Page 6, lines 200-222: We must add that only U17 players undergo strength resistance training once a week, which is reflected in the study findings.

 

The conclusion should be considerably restructured. The authors should focus only on main findings of the study and their application in practice with respect to soccer players of different ages that are not currently addressed in the literature. 

Page 7, lines 271-288: The measurement of isokinetic muscle strength provides an objective approach for the evaluation of young soccer players. These results may also serve as a novel benchmark for the expected level of asymmetry in a cohort of uninjured youth soccer players (U13, U15, and U17). Our findings showed a significant effect of AC on the level of BA in young soccer players. A high incidence of BA of the lower limbs occurred in the younger categories (U13 and U15) and subsequently decreased in the later stages of adolescence. Muscle function assessments can be used to identify specific deficiencies in apparently healthy players that could predispose them to injury. Therefore, we recommend regular monitoring of strength asymmetry from the beginning of the training process and optimization of the training load due to a higher incidence of BA. In most cases, the frequency and type of training intervention used may also be insufficient in providing an appropriate incentive to address relevant risk factors. Physiotherapists and conditioning trainers should consider that if an increased BA appears, an individualised program should be prepared for the player at least once a week, with the primary goal of reducing the detected asymmetry. Due to time constraints that exist for strength and conditioning trainers in soccer academies, they should seek to maximize the available time by adopting individualised training strategies using innovative approaches that are suitable for working with group training.

 

 

Author Response

Dear reviewer, thank you for reading and reviewing our paper. All comments as well as recommendations were helpful for us and improve quality of paper.  All changes you can find in enclosed file please. Also, you can see them in "tracked changes" version file.

Once again, thank you for your time and effort with review our paper.

Best regards,

Authors.

Author Response File: Author Response.docx

Reviewer 2 Report

This study aimed to determine the prevalence of isokinetic strength bilateral asymmetry (BA) among knee extensors (KEs) and knee flexors (KFs) of elite youth soccer players. The sample (n = 87) consisted of three age categories of under 13 (U13), under (U15), and under 17 (U17) years old. Isokinetic dynamometry was used to obtain the maximum peak torque of the KEs and KFs in the dominant and non-dominant lower limbs during concentric muscle contraction. The analysis revealed significantly lower values (p < 0.05) of BA in KEs in U17 than in younger categories, U13 and U15, and higher values (p < 0.05) of BA in KFs in category U15 than in category U17. The majority of the players in category U15 (68%) reached KFs BA higher than 10% in comparison with U13 players (50%) and U17 (28% of players) (p < 0.05). The results showed a significant effect of age category on BA levels in young soccer players. High incidences of increased BA in the lower limbs occurred in the younger categories (U13, U15) and subsequently decreased in the later adolescent stages.

In General: it's a good paper and the subject of the manuscript is applicable and useful. 

Title: the title properly explain the purpose and objective of the article

Abstract: abstract contains an appropriate summary for the article, language used in the abstract easy to read and understand, there are no suggestions for improvement.

Introduction: authors do provide adequate background on the topic and reason for this article and describe what the authors hoped to achieve.

Results: the results presented clearly, the authors provide accurate research results, there is sufficient evidence for each result.

Conclusion: in general: Good and the research provides sample data for the authors to make their conclusion.

Grammar: Need Some revision.

Finally, this was an appealing article, in its current state it adds much new insightful information to the field. Therefore, I accept that paper to be published in your journal

Author Response

Dear reviewer, thank you for reading and reviewing our paper. All changes you can find in enclosed file please. Also, you can see them in "tracked changes" version file.

Best regards,

Authors.

Author Response File: Author Response.docx