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 function early in the disease course and could also improve treatment and prognosis in patients with polymyositis and dermatomyositis.

Patients randomized to the HIIT protocol will train three days a week for 12 weeks. Before exercise start participants will rate self-reported pain and fatigue on a visual analogue scale and describe in own words information about possible changes in medication dose, any side effects from medication as well as possible negative and positive effects from previous exercise sessions, as well as physical activities performed since the previous exercise session. Each exercise session starts with a 5-minut warm-up on about 50% of maximal heart rate. Each HIIT set is between 30-60 seconds where loads are increased and the participant bikes as fast as possible with the goal of reaching >85% of maximal heart rate. During the 2-minuts rest in-between HIIT sets the participant will rate self-reported exertion using the Borg CR-10, 0-10 scale and the Borg RPE scale, 6-20.

When initiating the exercise period, participants start on three HIIT sets on a lower intensity, gradually increasing to goal intensity during the first two weeks. Then the number of sets are gradually increased to six sets.

After completing six HIIT sets the participants perform one set of 10 voluntary repetitions maximum (VRM) resistance training of the deltoids using free weights and of the quadriceps using free weights or a quadriceps curl machine, depending on degree of muscle weakness. Every other week a new 10 VRM is tested and training loads are adapted. After completing each set, the participant rates perceived muscle exertion on the Borg CR-10 scale. The program is ended with stretching of trained muscle groups and rating of overall exertion during the exercise session on the Borg RPE-scale.

Participants randomized to the control group will perform a standardized home exercise program on an easy-to moderate intensity adapted to initial muscle weakness, five days a week for 12 weeks. The program includes tasks for muscle groups targeted by myositis and takes about 15 minutes to perform. In combination with the home exercise program the participants walks 15 minutes on 60% of maximal heart rate. Participants fill out an exercise diary commenting on loads and number of repetitions for each task.

Participants in both groups ware a Polar 330A heart rate monitor during each training session. By synchronizing to a computer program all exercise data are stored in a cloud data base and can be monitored regularly by the project investigator.

Patients with polymyositis and dermatomyositis:

Inclusion Criteria:

• Probable or definite diagnosis polymyositis or dermatomyositis according to Bohand and Peter criteria, diagnosis duration between 4 weeks and 6 months, completed screening for possible concurrent cancer diagnosis and screening for lung involvement, able to performe the HIIT.

Exclusion Criteria:

• Diagnosis of inclusion body myositis, active cancer, being treated for cancer, heart- or lung involvement contraindicating HIIT, no clinical improvement with medical treatment, severe osteoporosis.

Healthy controls:

Inclusion Criteria: match a patient for age and gender, exercising not more than twice a week, no neuro- or musculoskeletal disorders.

Exclusion Criteria: Ongoing treatment for cancer, cardiovascular disease contraindicating a maximal oxygen uptake test or HIIT.

Muscle biopsies will be sent to Professor Kanneboyina Nagaraju, Professor and Founding Chair, Department of Pharmaceutical sciences, School of Pharmacy and Pharmaceutical Sciences AB-G34, Binghamton University, PO Box 6000 Binghamton, NY 13902-6000. Purpose: To analyse muscle biopsies for micro array analysis.

After completion of the project, muscle biopsies from all patients and healthy subjects will be sent to Dr Nagaraju.

The physical therapist performing assessments of muscle function (primary outcome), distributes questionnaires and who is present at maximal oxygen uptake tests and who plan all other assessments logistically is blinded to group allocation. The rheumatologists performing assessment of disease activity and the personell analysing biopsy data are also blinded to group allocation. The care provider is the only one who is not masked.