Funding for this research was provided by:
Deutscher Fußball Bund
Article History
Received: 28 January 2018
Accepted: 20 March 2018
First Online: 23 April 2018
Compliance with ethical guidelines
:
: C. Heim, F. Ennigkeit and M. Ullrich declare that they have no competing interests.
: This article does not contain any studies with human participants or animals performed by any of the authors.