 The HIIT group will perform 6 sets of 30-60 second biking bouts reaching 85-100 of maximal heart rate, in combination with strength traning, three days a week for 12 weeks. The control group will perform a standardized home exercise program five days a week for 12 weeks. After 12 weeks, all assessments are preformed again. If the HIIT is well tolerated, patients in the control group will be invited to HIIT exercise according to the same protocol. Clinical assessments will be performed at 3, 6 and 9 months follow-up in a open extention. 