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Muscle weakness or myasthenia (my- from Greek μυο meaning "muscle" + -asthenia ἀσθένεια meaning "weakness") is a lack of muscle strength. The causes are many and can be divided into conditions that have either true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy and inflammatory myopathy. It occurs in neuromuscular junction disorders, such as myasthenia gravis. Muscle weakness can also be caused by low levels of potassium and other electrolytes within muscle cells. ==True and perceived muscle weakness== Muscle weakness can be classified as either "true" or "perceived" based on its cause. * True muscle weakness (or neuromuscular weakness) describes a condition where the force exerted by the muscles is less than would be expected, for example muscular dystrophy. * Perceived muscle weakness (or non-neuromuscular weakness) describes a condition where a person feels more effort than normal is required to exert a given amount of force but actual muscle strength is normal, for example chronic fatigue syndrome. In some conditions, such as myasthenia gravis muscle strength is normal when resting, but ''true'' weakness occurs after the muscle has been subjected to exercise. This is also true for some cases of chronic fatigue syndrome, where objective post-exertion muscle weakness with delayed recovery time has been measured and is a feature of some of the published definitions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Muscle weakness」の詳細全文を読む スポンサード リンク
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