Background and Objective Periodic paralyses (PP) are rare muscle channelopathies characterized by severe episodes of muscle weakness associated with variations in bloodpotassium levels.The functional consequences of ion channel mutations on muscle membrane excitability in patients can be studied by noninvasive technique of EMG.Analysis of the compound motor action potential (CMAP) amplitude before and at various times after long (5min) exercise provides information on changes in the number of active fibers, and on their ability to depolarizeand repolarize.