eLetters

335 e-Letters

  • 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.

    Perfor...

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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

    https://bjsm.bmj.com/content/early/2018/05/28/bjsports-2017-098925

  • 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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  • Letter in response to: The Adductor Strengthening Programme prevents groin problems among male football players: a cluster-randomised controlled trial.

    Dear Editor,

    I would like to congratulate the British Journal of Sports Medicine for the publication of the study ‘The Adductor Strengthening Programme prevents groin problems among male football players: a cluster-randomised controlled trial’ conducted by Harøy et al.[1]. The study investigated the effect of the adductor strengthening programme on the prevalence of groin problems among football players. The findings are incredibly important for the development of sports medicine because of their clinical relevance.

    Regarding the methodology of this study, rather than giving criticism, I would like to suggest the authors if they can provide additional information or even a follow-up article on the game performance of the football teams involved in this study. As mentioned in the article, the authors have considered the groin pain causing time loss, decreasing participation or performance of the players [1]. Meanwhile, the previous study literally found that a lower incidence rate was strongly correlated with the number of goals, games won and even team ranking position [2,3]. Therefore, readers are interested whether the performance could be improved too since the results showed a significant reduction in the prevalence of groin pain in the players.

    Similar studies have been conducted to investigate the effect of a specific strength training programme on players’ injury prevalence and individuals’ performance [4]. However, no data was included to refl...

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  • BJSM encourages comments alongside papers - such as this example

    Many of you will be familiar with The BMJ and its popular 'Rapid Responses'. Because we are a sister journal to The BMJ (and part of the same publishing company of course) we have the same Platform and we encourage you to use it.

  • What's this got to do with sports medicine?

    Why is this in BJSM? In general, it is best to have papers go through peer review in the most relevant journal to their subject matter to ensure that the production team is well placed to find suitable editors and reviewers.

  • Comment and questions to Mottola et al (2019): 2019 Canadian guideline for physical activity throughout pregnancy

    Letter to the Editors
    Br J Sports Med
    J Obstet Gynecol Canada
    Oslo, Nov 23rd 2018
    Comment and questions to Mottola et al (2019): 2019 Canadian guideline for physical activity throughout pregnancy
    We have read the Canadian guideline for physical activity throughout pregnancy with great interest. We note that the guideline team have made their recommendation regarding pelvic floor muscle training (PFMT) based on evidence from a systematic review from the same research group (Davenport et al 2018). The main results of this review are in line with the latest Cochrane review (Woodley et al 2017) on the same topic; while there are some methodological differences and variations in which studies were included or not (two of the largest studies on PFMT was left out from the Davenport review; Mørkved et al 2003 and Stafne et al 2012), the findings in terms of size and precision of effect are similar, although Davenport et al used odds ratio and Woodley et al used risk ratio for their summary statistic. Davenport et al reported that PFMT gave a 50% reduction in prenatal UI and a 35% reduction in postnatal UI, but the guideline team concluded a “weak recommendation” for PFMT because UI was not rated as a "critical outcome" and the evidence was of "low quality". We find this conclusion at odds with the evidence and the interpretation of the evidence based on the guideline team’s own criteria.
    The Canadian guideline grades...

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