76 e-Letters

published between 2018 and 2021

  • The ACWR model presented in the IOC consensus is flawed and not validated

    The BJSM recently rejected our request of retraction or errata corrige of the editorials by Blanch and Gabbett(1) and Gabbett (2) presenting the relation between the Acute:Chronic Workload Ratio (ACWR) and likelihood of injuries. The preprint and a list of some of the errors presented in that figure can be found here: https://osf.io/preprints/sportrxiv/gs8yu/. In challenging our request, it was underlined several times by the Editor in Chief of BJSM that the “model” was presented as illustrative only, and this seems to make errors acceptable like if the editorials are a “safe zone” where for illustrative purposes it is possible to bend and even break scientific rules and methods, presenting models using unpublished and uncontrollable data.

    However, the reason of this communication is to warn the members of the consensus (and readers) that the ACWR model published in the IOC consensus(3) as a validated model has in fact not been validated at all: [page 1034] “The model has currently been validated through data from three different sports (Australian football, cricket and rugby league)(187)”. The reference 187 is one of the two editorials(1) for which we asked the retraction. So on one side the Editor in Chief insists that it is just an illustrative (flawed) model, but on the other side the same Editor in Chief, co-author (with one of the proponents of the model) of the IOC consensus wrote and published that it...

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  • Continued Question About As-Treated Analysis

    Dear Drs. McGuine, Hetzel, and Kliethermes,

    Thank you for your thorough response to my initial comment.

    I am wondering if you could help me understand the new AE-level as-treated analysis you have done in response to Point 2. This accounts for all non-compliant AEs among all athletes, correct? If I understood you correctly, there were somewhat more than the 711 non-compliant AEs reported in the paper and which you reported in your response to Point 4, correct?

    What would be very helpful to see is a.) the number of AEs and b.) the number of SRCs that occurred during those AEs for each of the following groups when considering any non-compliant AE, not just ones from athletes who suffered an SRC while non-compliant or were non-compliant >50% of the time:

    Assigned HG/Did Not Wear:
    Assigned HG/Did Wear:
    Assigned No HG/Did Not Wear:
    Assigned No HG/Did Wear:

    Thank you again for your thorough response.

  • Letter to the editor

    After careful appraisal and following our own investigations, we are concerned that the article “Is interval training the magic bullet for fat loss? A systematic review and meta-analysis comparing moderate-intensity continuous training with high-intensity interval training (HIIT)” [1] may have some data extraction and analysis errors that warrant further review by the editor and authors, and which more concerningly, may impact the original conclusions of the article.

    We were initially concerned about the reported results within the Thomas et al. paper [2], particularly the biological plausibility of a mean between-group fat-loss difference of 13.44 kg over 12 weeks. Given that the authors did not report any study-level data, we decided to investigate the effect size within this paper. However, this study [2] did not report any fat mass data, only % body fat data. Given that the authors of the review [1] reported “When studies provided insufficient data for inclusion in the meta-analysis (five studies), the corresponding authors were contacted via email to determine whether additional data could be provided; however, no corresponding authors responded.”, it is unclear how an unpublished mean difference of -13.44 kg in favour of HIIT/SIT could be presented within the fat mass analysis of this review. Furthermore, when reviewing another of the included studies [3], we found that fat mass data were reported, but not included in the current meta-analysis [1]. Given the m...

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  • Response to the comments for the paper: Does soccer headgear reduce the incidence of sport-related concussion? A cluster, randomised controlled trial of adolescent athletes.

    To: The British Journal Sports Medicine

    We are grateful for Dr. Binney’s interest in our study and his consideration of a portion of the results presented in the manuscript.

    Listed below are our responses to each of the concerns raised in the letter.

    1. In the as-treated analysis you have a very strange result. Your multivariate risk ratio (which is actually a rate ratio) is 0.63 for everyone overall, 0.64 for females, and 0.93 for males. The result for everyone should be between the results for males and females. Can you please clarify how you got these results, including the exact model(s) you used and how you calculated the rate ratios? Did you use a group*sex interaction term to get the sex-specific results?

    Response: We thank you for noticing the mathematical inconsistency in Table 4 rate ratio results for the as-treated analyses. You are correct that if these results were from one model, the overall rate ratio estimate would need to be in-between the male/female estimates. We should note that these were actually 3 separate mixed-effects models: (1) the overall model adjusting for all variables including sex, (2) female sub-group model adjusting for all variables –excluding sex, and (3) male sub-group model adjusting for all variables –excluding sex. We apologize that the footnote in the table is unclear in this regard. We did attempt to use interaction models for this analyses, but did not achieve consistent convergence. As such, we opt...

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  • Concerns About As-Treated Analysis

    Dear Dr. McGuine et al,

    I'd like to commend you on running a large RCT on such an important topic (assessing the purported effectiveness of concussion-reduction technologies). Unfortunately I have some concerns about some aspects of your data and analysis, particularly the as-treated analysis in Table 4and your reported adherence numbers. I am hoping you can clarify these concerns and re-do parts of your analysis.

    1. In the as-treated analysis you have a very strange result. Your multivariate risk ratio (which is actually a rate ratio) is 0.63 for everyone overall, 0.64 for females, and 0.93 for males. The result for everyone should be between the results for males and females. Can you please clarify how you got these results, including the exact model(s) you used and how you calculated the rate ratios? Did you use a group*sex interaction term to get the sex-specific results?

    2. How you defined the as-treated group is concerning. You state that you only re-classified a subject if they spent >50% of their time in their non-assigned group OR if they were concussed while in their non-assigned group. This approach will bias the results of your as-treated analysis as you are deliberately misclassifying the AEs of people who do not get hurt and the non-concussed AEs of those who do. You need to classify every AE, rather than each athlete, as headgear or no headgear and repeat the as-treated analysis. Otherwise this analysis is highly questionable and...

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  • Response to 'A few unanswered questions'

    Dear Dr. Anoop Balachandran

    We would like to thank you for your insightful and interesting comment.

    Regarding the first point, we presented the 28.5% to illustrate the relative difference in total absolute fat (kg) change between interventions, so the reader could have information about the relative difference between groups. We would like to highlight that it was only possible to perform this analysis using the within group changes, since the change between group analysis was showed in absolute values.

    About the second point, it was not our purpose to analyse lean body mass; however, we agree that this topic is very important for health and athletic performance purposes. This is an unanswered question and we are performing studies to test the effects of interval training on lean body mass to help shedding light in the topic.

    Best regards.

  • Accounting for Multiple Testing Calls into Question the Significance of these Results

    In this article the authors discuss their analysis of 21 female and 22 male athletic events. Testing all 43, they find 3 events significant with p<0.05. When testing 43 events, the expectation is that a well-calibrated statistical test will produce 2 false positives with random data, on average, due to the definition of the p-value. The odds of producing 3 false positives are also rather high; for normally distributed simulated data under the null, I found 3 or more false positives approximately 1/3 of the time such an analysis is performed, see here for a simulation notebook: https://github.com/davidasiegel/False-Positive-Rate-for-Multiple-Tests-i....

    This is why adjustments for multiple comparisons needs to be performed. It was neglected in their initial study and neglected again in this study. In the 2017 study they state, "These different athletic events were considered as distinct independent analyses and adjustment for multiple comparisons was not required." This doesn't make sense to me; if the analyses are distinct, then all the more reason to correct for multiple comparisons. If a Bonferroni correction were performed, none of the p-values would test significant at the level of the study (p<0.05/43 = 0.001). Therefore I do not see why there is any reason to reject the null hypothesis for any of these results.


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  • Agreed.

    For readers who are following the debate about how training load may relate to injury, Dr Johann Windt considers the implication of the correlation that is pointed out here. Thanks to all the authors. k2


  • A few unanswered questions

    The study raises two questions that one of the authors might be able to help with:

    First, the authors report both within group and between group changes in body fat in the abstract. But it is unclear why the authors chose the within-group changes (28% fat loss) as the study conclusion than the between-group change.

    The within group change showed a fat loss of 0.45 kg (28%) in favor of interval training (IT), while the between-group changes showed a large difference of 2.28 kg of fat loss in favor of IT. Considering the large difference in fat loss, and some studies recommending to avoid within group differences in meta-analysis, it would be helpful if the authors could comment on this.

    Second, maintaining lean body mass (LBM) is one of the primary reasons to include exercise as part of a weight loss strategy. So it is not clear why the authors chose not to include lean body mass as one of the outcomes. It would have certainly helped the reader to make a decision regarding the choice of exercise for weight loss.

    Finally, congratulations to all the authors for asking a very relevant question!.

  • Methodological concerns in patients with femoroacetabular impingement: is ROM deficit really absent?

    We thank Freke et al. (1) for their systematic review about physical impairments in patients with symptomatic femoroacetabular impingement, nonetheless we have some remarks about methods and results of the article, in particular for range of motion (ROM) outcome.
    A meta-analysis of ROM was performed without reporting an overall estimate. Taking into account the amount of studies included and their information, a meta-analysis should have been accomplished. Nonetheless, authors concluded that individuals with symptomatic FAI demonstrated no difference in hip ROM in any direction of movement. This conclusion was unexpected taking into account the findings reported in the primary studies included), and in the previous systematic review published in 2015 (2), that showed instead a reduced ROM.
    This discrepancy in literature is already discussed by the Warwick agreement (3), where authors stated that “the evidence on hip range of motion (ROM) in FAI syndrome is surprisingly contradictory” due to contrasting published systematic reviews (1) (2).
    Therefore, we checked the accuracy of results reported, analyzing the data reported for every movement assessed in primary studies comparing those reported in this systematic review. We noted some issues in the represented forest plots.
    Firstly, some included studies (4), (5), (6), (7) were reported twice in the meta-analysis for different times points or reporting double data of the same patients obtained by two...

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