Validity, Accuracy, and Safety Assessment of an Aerobic Interval Training Using an App-Based Prehabilitation Program (PROTEGO MAXIMA Trial) Before Major Surgery: Prospective, Interventional Pilot Study - Sara Fatima Faqar Uz Zaman; Svenja Sliwinski; Lisa Mohr-Wetzel; Julia Dreilich; Natalie Filmann; Charlotte Detemble; Dora Zmuc; Felix Chun; Wojciech Derwich; Waldemar Schreiner; Wolf Bechstein; Johannes Fleckenstein; et al. (JMIR mHealth and uHealth)