 This is a pilot randomized controlled trial. Muscle biopsies are taken at time of diagnosis and after 12 weeks of exercise. Muscle biopies will be analyzed as to baseline kynurenine pathway, calcium release, gene expression and inflammatory infiltrates and as to changes in these parameters following exercise.Muscle function primary outcome, maximal oxygen uptake, muscle massfat mass, disease activity, dystolic heart function, as well as quality of life and depression is measured at baseline and after 12 weeks of exercise. After all assessments, patients are randomized to HIIT or standard low-intensity home exercise. 