Inclusion Criteria:  Patients aged less than 18 years old with primary or secondary impairment of respiratory muscles and followed at Necker Hospital Patients under spontaneous breathing or noninvasive or invasive mechanical ventilation Written informed consent  Exclusion Criteria:  No social insurance Significant psychomotor retardation Absence of cooperation Significant agitation Hemodynamic instability Acute condition or temporary drug treatments that may interfere with the results of the respiratory muscle explorations