This study focuses on people with **iRBD** (Isolated REM Sleep Behavior Disorder), which often leads to Parkinson's disease or dementia with Lewy bodies. It aims to see if being more active can help slow down brain problems in people with iRBD. An app on your smartphone will help you be more active for one year. The study is "randomized" (participants are randomly chosen for different groups) and "double-blind" (neither the participants nor the researchers know who is in which group) to ensure fairness. The main thing being checked is changes in brain function using tests and MRI scans.

Key Points:

• The study lasts for one year and uses a smartphone app to boost physical activity.
• Participants must be aged 50-80, have basic smartphone skills, and speak German well.
• Excludes people with major heart issues or cognitive issues that make smartphone use hard.

If you're interested and meet the criteria, this study might help improve understanding of how exercise affects brain health in early stages of certain neurodegenerative diseases.