Received: 24 January 2019
Accepted: 26 July 2019
First Online: 19 August 2019
Ethics approval and consent to participate
: This review will gather and appraise existing data from studies for which healthy volunteer participants have previously given consent. We will not include data from any study for which participants did not give informed consent. Where raw data are requested, authors will be asked to verify that their ethical permissions allow them to release the anonymised data for ongoing research.
: Please see previous section.
: The authors declare that they have no competing interests.