Inclusion Criteria:  idiopathic PD Hoehn and Yahr 1-3 able to understand the Dutch language able to walk independently equal to or less than 120 minutes of sports/outdoor activities per day (question 5-28 LASA Physical Activity Questionnaire (LAPAQ)) less than 7,000 steps/day during 1-month baseline (week -4 until 0)  Exclusion Criteria:  weekly falls in the previous 3 months medical conditions that hamper mobility other than PD living in a nursing home cognitive impairments that hamper use of the motivational app (subjective evaluation by the assessor) not in the possession of a suitable smartphone (Iphone 5S or newer with iOS 10 or higher or Android 4.1 or newer)