Fig. 1

Intervention procedure of the group exercise intervention. Dark grey boxes represent group meetings combined with supervised aerobic exercise (starting session 3) and the supporters’ session (session 14 in week 5). Session 1 contains an introduction into the intervention. Session 15 is conducted in week 12. Light grey boxes represent non-supervised exercises or resistance training, which can be conducted as participants’ first non-supervised exercise (session 6). The phone represents the weekly phone contact from week 5–12. Week 1–2 mainly aimed to increase motivation, week 2–4 mainly increase volition. Week 5–12 aimed to transfer motivation and volition for exercise into participants’ daily life routines