Due to their ubiquitary distribution, smartphones might serve as an easy way/ possibility to use feedback mechanism in an app-based intervention program to increase physical activity in Multiple Sclerosis (MS) patients. Internet based cognitive-behavioral interventions have been explored as effective in the last years. In addition, smartphone-based mobility assessment and intervention might be a promising approach in other MS types and for real-life mobility assessment in observational and interventional trials. The aim is to investigate the impact of a smartphone based information and feedback program on physical activity in a 3 months, randomised waiting-group controlled trial of 40 progressive MS patients.