The purpose of this study was (i) to develop a brief counseling letter intervention aiming to reduce sedentary time and to increase physical activity during leisure time among adults aged 42 to 64 years and (ii) to provide information on the feasibility.

The study aimed to assess the feasibility of a brief counseling letter intervention to increase physical activity and to reduce sedentary time in leisure time.

Following the Intervention Mapping Protocol we developed the counseling letter intervention. The intervention is based on the Health Action Process Approach, comprising 3 tailored letters based on separate assessments, delivered over 6 month.

All participants consented (i) to participate in an examination at the university hospital including standardized measurements of blood pressure, waist and hip circumference, body height and weight as well as blood sample taking, (ii) to fill in a paper-pencil questionnaire, and (iii) to wear an accelerometer for 7 days at baseline and at 12-month follow-up.

A general population sample of cardiovascular healthy adults was randomly allocated to a control and an intervention group. At 5 time points (baseline, 3-month, 6-month, 7-month, and 12-month follow-up) participants of both study groups completed standardized questionnaires.

Inclusion Criteria:

• age between 42 and 65 years
• resident in a pre-defined zip-code area

Exclusion Criteria:

• cardiovascular event (myocardial infarction, stroke) or vascular intervention
• self-reported body-mass-index over 35 kg/m²