Table 1 Description of the Join2move intervention

1. Filling out a PA Readiness Questionnaire (PARQ)

If participants answered “YES” to any of the seven PARQ, they were advised to see their GP before participation. If patients answered ‘NO’ to all of the questions, it was considered safe for them to engage in Join2move.

2. Provision of educational messages

Core elements of the program are presented on the personal website, including 1) focus on improving physical function rather than pain reduction; 2) first weeks can be accompanied by more pain;3) participant shares responsibility and has an active role.

3. Selection of a central PA

A favourite and a problematic activity are selected from an activity list, including walking, cycling, swimming etc.

4. Determination of baseline value via a 3-day self-test

To determine the baseline value, participants were requested to perform the selected activity three times a week until the pain threshold was reached. PA performances (minutes) and pain scores (1 to 10) were recorded in an online diary and stored on the website.

5. Setting a short and long term goal

In accordance with the baseline values, a range of goals is generated and presented on the website. Between the lower and upper limit of goals, patients could select a short term goal (9 weeks). Furthermore, a long term goal was set for 1 year.

6. Signing an agreement form

Participants sign an online agreement form. This form presents the short term goal and, again, core elements of the program.

7. Gradually increase selected activity (8 weekly modules)

Based on the short term goal, a tailored schedule of eight weekly modules is made on a time-contingent basis (i.e. fixed time points). The start of the schedule is slightly below the baseline value and increases incrementally towards the short term goal. Patients should not under-perform or over-perform this gradually increasing schedule. Every week, new modules and evaluation forms (pain and performance) are posted.