- Correspondence to Professor Jan Ekstrand, Department of Medical and Health Sciences, Football Research Group, Linköping University, Solstigen 3, Linköping S-589 43, Sweden;
- Received 15 December 2012
- Revised 6 April 2013
- Accepted 13 April 2013
- Published in print 1 August 2013.
- Published online 11 July 2013.
- Published first 5 May 2013.
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