Vol.:(0123456789)
Sports Medicine (2022) 52:189 
https://doi.org/10.1007/s40279-021-01549-z
LETTER TO THE EDITOR
Response to: Comment on: “Sex‑Specific Differences 
in Running Injuries: A Systematic Review with Meta‑Analysis 
and Meta‑Regression”
Karsten Hollander1 · Jan Wilke2 · Astrid Zech3
Accepted: 14 August 2021 / Published online: 4 September 2021 
© The Author(s) 2021
Dear Editor,
We really appreciate the Letter to the Editor by Nnamani 
Silva et al. [1], which added valuable information and dis-
cussion to our systematic review titled “Sex-specific differ-
ences in running injuries: a systematic review with meta-
analysis and meta-regression” [2].
The unequal sample size of sexes, with more male run-
ners in road racing events and more female novice runners, 
emphasizes the need to take a closer look at moderating fac-
tors. Generally, detailed reporting of potential effect modi-
fiers is highly encouraged in primary studies to increase the 
often limited power of meta-regressions. Regardless, in our 
meta-analysis, the exclusive inclusion of studies with both 
sexes for the same running background (level) and use of 
incidences for risk ratio calculation of each study should 
have reduced the influence of unequal sample size distribu-
tion. However, we agree that the combination of studies with 
different running levels in the same pooled risk ratio calcula-
tion may have led to a greater weighting of one running level 
(towards the level with the higher number of studies). In our 
meta-regression, we quantified the running level with the 
competition distance, training duration, and training mileage 
but cannot completely rule out that a differentiation for the 
competition level (road racing vs. novice) would have led to 
different results.
In conclusion, the points raised by Nnamani Silva et al. [1] 
highlighted another important aspect in the relevant consider-
ation of sex as a variable for equal sampling in addition to the 
possible impact of sex specificity in the etiology and probably 
prevention and rehabilitation of running-related injuries.
Declarations 
Funding Open Access funding enabled and organized by Projekt 
DEAL.
Conflict of interest Karsten Hollander, Jan Wilke, and Astrid Zech 
have no conflicts of interest relevant to the content of this letter.
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long 
as you give appropriate credit to the original author(s) and the source, 
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References
 1. Nnamani Silva ON, Armijo PR, Feld LD, Mascarenhas Monteiro 
JS, Pham R, Tenforde AS. Comment on: “Sex-specific differences 
in running injuries: a systematic review with meta-analysis and 
meta-regression.” Sports Med. 2021. https:// doi. org/ 10. 1007/ 
s40279- 021- 01548-0.
 2. Hollander K, Rahlf AL, Wilke J, Edler C, Steib S, Junge A, 
Zech A. Sex-specific differences in running injuries: a system-
atic review with meta-analysis and meta-regression. Sports Med. 
2021;51:1011–39. https:// doi. org/ 10. 1007/ s40279- 020- 01412-7.
An author’s reply to this comment is available at https:// doi. org/ 10. 
1007/ s40279- 020- 01412-7.
 * Karsten Hollander 
 
karsten.hollander@medicalschool-hamburg.de
1 
Institute of Interdisciplinary Exercise Science and Sports 
Medicine, MSH Medical School Hamburg, Am Kaiserkai 1, 
20457 Hamburg, Germany
2 
Institute of Occupational, Social and Environmental 
Medicine, Goethe University Frankfurt, Frankfurt, Germany
3 
Department of Human Movement Science and Exercise 
Physiology, Institute of Sport Science, Friedrich Schiller 
University Jena, Jena, Germany

Response to: Comment on: "Sex-Specific Differences in Running Injuries: A Systematic Review with Meta-Analysis and Meta-Regression".
Hollander, Karsten,Wilke, Jan,Zech, Astrid