Inclusion Criteria:  diagnosis of polymyositis or dermatomyositis (Bohan and Peter criteria) age ≥18 years duration of disease since diagnosis for more than six months stable medication ≥3 months chronic inactive or mildly active but stable myositis for at least 3 months prior to observation Health Assessment Questionnaire (HAQ) ≥0.5  Exclusion Criteria:  serious cardiac or pulmonary conditions severe osteoporosis unable to exercise neoplasm cognitive disorders acute or chronic infection