Statistics from Altmetric.com
Competing interests For full author disclosures and competing interests see the online supplementary folder ICMJE forms on the BJSM website (http://dx.doi.org/10.1136/bjsports-2017-097878).
Provenance and peer review Not commissioned; internally peer reviewed.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.