Congenital myopathies are clinical and genetic heterogeneous disorders characterized by skeletal muscle weakness. Most patients experience muscle weakness and fatigue throughout their life. However, progression of symptoms is rare. There are no specific treatments for congenital myopathies. Training has been shown to benefit several other muscle diseases with weakness, but the defect in congenital myopathies involves contractile proteins of the sarcomere, why the effect of training is uncertain in these conditions. The investigators will therefore investigate the effect cycle-ergometer training for 30 minutes, three times weakly, for ten weeks in 15 patients with congenital myopathy. Another 5-10 congenital myopathy patients, who do not train, will serve as controls for the trained patients. The study starts and ends with a test day, where efficacy based on VO2max, performance in functional tests and a questionnaire will be assessed.