The German Young Olympic Athletes' Lifestyle and Health Management Study (GOAL study): design of a mixed-method study - Thiel, Ansgar; Diehl, Katharina; Giel, Katrin; Schnell, Alexia; Schubring, Astrid; Mayer, Jochen; Zipfel, Stephan; Schneider, Sven (BMC public health, 2011)