Exercise Capacity of Patients with Dermatomyosis

Inclusion Criteria: * Woman or man\> 18 years, * Signature of informed consent, * Muscle biopsy for suspicion of recent inflammatory myopathy (\<6 months) or for exclusion of neuromuscular pathology. Prospectively, following the results of the muscle biopsy, the subjects will divided into three groups meeting the following criteria: * "DM" group: DM according to the ENMC criteria; * "other inflammatory myopathy" group: polymyositis, autoimmune necrotizing myopathy, non-specific myositis or inclusion myositis according to the ENMC criteria; * Group "no neuromuscular pathology": i) myalgia and / or intolerance to exercise and ii) normal neuromuscular examination, iii) no increase in blood creatine kinase level, iv) absence of electromyographic abnormality, v) histological Muscle mass. Exclusion Criteria: * \- Taking an immunomodulatory treatment within 6 months before inclusion, * Paraneoplastic form of the disease, * Presence of associated interstitial pneumonitis, * Neuromuscular pathology different from inflammatory myopathy, * Unbalanced cardiovascular disease, * Impossibility of giving the subject informed information (subject in an emergency situation, difficulty in understanding the subject, ...), * Subject under safeguard of justice, * Subject under tutelage or under curators, * Pregnancy (positive pregnancy test) * Breastfeeding.