“…Considering the claims of the publishers, mobile fitness apps promise to boost fitness or health training. However, these "aggressive and exaggerated claims" (Düking et al, 2018, p.1) have rarely been sufficiently validated (e.g., Halson et al, 2016;Peake, Kerr, & Sullivan, 2018;Romeo et al, 2019). In current reviews, two aspects are criticized, i.e., lack of user or consumer integration in the development process and lack of adequate validating research (e.g., Düking et al, 2018;Peake, Kerr, & Sullivan, 2018, Warraich, 2016.…”