Effects of High-intensity Interval Training (HIIT) in Recent Onset Polymyositis and Dermatomyositis

Polymyositis and dermatomyositis are rare inflammatory systemic conditions. Reduced muscle function is a cardinal symptom and lung involvement is very common. Knowledge of heart involvement in these patients is very limited, as is knowledge of exercise effects in recent onset, active disease. The aim of this project is to investigate effects of high-intensity interval training (HIIT) compared to standard low-intensity home exercise as to tolerance, physical capacity, quality of life, depression, disease activity, inflammation, muscle mass/fat mass, muscle metabolism and heart function in patients with recent onset, active polymyositis and dermatomyositis. This is a randomized controlled trial. Muscle biopsies are taken at time of diagnosis and after 12 weeks of exercise. Muscle biopsies 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 mass/fat mass, disease activity, systolic and diastolic 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. The HIIT group will perform 6 sets of 30-60 second biking bouts reaching 85-100% of maximal heart rate, in combination with strength training, 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 an open extension. This study will improve our understanding of heart function, muscle metabolism as well as tolerance and effects of intensive exercise as well as heart