[A case of familial muscle weakness corrected by exercise (author's transl)].

The symptom described as muscle weakness corrected by exercise appears to be part of the recessive form of congenital myotonia, of which it can constitute the dominant clinical manifestation in some cases. This symptom coincides with decrements of the action of potentials to repetitive stimulations in the electromyogram, which may be particularly severe in these same cases. These observations contribute to the modification and precision of the description of the recessive form of Thomsen's disease, but their pathogenicity remains unclear.