Physical activity referral scheme components: a study protocol for systematic review and meta-regression - Mino, Eriselda; Geidl, Wolfgang; Naber, Inga; Weissenfels, Anja; Klamroth, Sarah; Gelius, Peter; Abu-Omar, Karim; Pfeifer, Klaus (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2021)