This study explores if a special phone app can help people with a sleep condition called *isolated Rapid Eye Movement (REM) sleep behavior disorder* (iRBD) exercise more. iRBD means you may be at risk for Parkinson's, a disease affecting movement. The app will encourage participants to increase their daily steps and exercise intensity for 24 months. They will use a Fitbit watch to track progress.

Key points:

• Study lasts 24 months and uses a smartphone app.
• Participants must be Dutch, aged 50+, with iRBD.
• Participants need a compatible smartphone and must not have certain health issues.

Participants will be divided into groups with different exercise goals. The success will be measured by tracking physical activity and other health markers over time. This study aims to see if exercise can help slow down symptoms before Parkinson's fully develops. The study is mainly carried out remotely, meaning most activities will be done from home.

Participants should be comfortable using a smartphone and willing to engage in regular exercise. Eligibility includes the ability to walk independently and not have heavy physical activity already. Exclusions include certain health conditions and reliance on walking aids. The study aims to better understand and possibly improve early intervention strategies for Parkinson's using digital tools.