Re: Viana, et al “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).” British Journal of Sports Medicine 53.10 (2019): 655-664. Web. 30 May. 2019.
The eLetter was submitted by Mr Matthew Hollings, Prof. Jeff Coombes, Dr Yorgi Mavros, Dr Shelley Keating, Prof. Maria Fiatarone Singh on 30 05 2019:
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)”  may have some data extraction and analysis errors that warrant further review by the editor and authors, and which may impact the original conclusions of the article.
We were initially concerned about the reported results in one of the papers in the SR–the Thomas et al. paper . We question the biological plausibility of a mean between-group fat-loss difference of 13.4 kg over 12 weeks. Given that the SR authors did not report any study-level data, we decided to investigate the effect size as published by Thomas et al. The Thomas study  did not report any fat mass data, only % body fat data. Given that the authors of the review  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.” We authors do not understand how an unpublished mean difference of -13.44 kg in favour of HIIT/SIT could be presented within the fat mass analysis of this review.
When we reviewed another of the included studies , we found that fat mass data were reported, but not included in the current meta-analysis . Given the marginal level of significance for the fat mass outcome in the review (MD, CI; -2.28, [-4.00, -0.56]), it is possible that if these data had been excluded/included the primary conclusion of this article (that HIIT training resulted in superior fat mass loss compared to moderate intensity aerobic training), may be altered.
When we reviewed the first two data points in the % body fat plot, we are also concerned about the calculated effect sizes. We are unable to confirm whether the calculations are accurate as there are no study-level data or effect size (ES) calculation methods in either the review article or the registered protocol on PROSPERO (CRD42018089427). Whilst the Thomas et al.  paper reported % body fat data graphically, and we acknowledge there may be some minor differences in data points depending on which graph analysis tool was used, the Trapp et al.  paper reported all pre- and post- mean and standard error data, so our ES and CI calculations should be identical to those in the review if the same calculation method was used.
However, when we calculated ES using the pooled baseline SD for ES calculation (-3.30 [-13.36, 6.76]), this differed from that reported by the Viana et al (-9.59 [-16.97, -2.20]). Presuming that the authors are presenting mean difference data (as suggested in their forest plot figures), there should be no disputing this value as -3.30, based solely on study-level data.
Our analyses only examined data from these two studies, so we can neither verify nor refute the results presented for the remaining 34 included studies.
We question the inclusion of one of the studies in the review. Mr Viana and colleagues have included the study by Boer and Moss  that used 70-80% VO2peak for their moderate intensity exercise. This is outside the 40-60% VO2max ‘criteria’ for moderate intensity provided by the authors.
In conclusion, we flag 4 concerns about the accuracy of the data extraction, its analysis, as well as study selection in Mr Viana’s review . We therefore respectfully seek clarification. We appreciate that next steps would depend on the answers to our questions.
Authors: Mr Matthew Hollings1, Prof. Jeff Coombes2, Dr Yorgi Mavros1, Dr Shelley Keating2, Prof. Maria Fiatarone Singh1
 Viana RB, Naves JPA, Coswig VS, et al 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) Br J Sports Med. Published Online First: 14 February 2019.
 Thomas TR, Adeniran SB, Etheridge GL. Effects of different running programs on VO2max, percent fat, and plasma lipids. Can J Appl Sport Sci 1984;9:55–62.
 Trapp EG, Chisholm DJ, Freund J, et al. The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. Int J Obes 2008;32:684–91.
 Boer PH , Moss SJ . Effect of continuous aerobic vs. interval training on selected anthropometrical, physiological and functional parameters of adults with Down syndrome. J Intellect Disabil Res 2016;60:322–34
MATTHEW HOLLINGS | ESSAM AES
Physical Activity, Lifestyle, Ageing and Wellbeing Faculty Research Group
Faculty of Health Sciences