Muscle disease | Description, Causes, Types, & Treatment

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class="md-content"> <div class="md-article-container template-desktop infinite-pagination"> <div class="infinite-scroll-container article last"> <article class="article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded" data-topic-id="722004"> <div class="grid gx-0"> <div class="col-auto"> <div class="topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/science/muscle-disease">muscle disease</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/muscle-disease">Introduction</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref58880"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/muscle-disease#ref58880">Indications of muscle disease</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref58881"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/muscle-disease#ref58881">Muscle weakness</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref58882"><a class="w-100 link-gray-900" href="/science/muscle-disease#ref58882">Signs and symptoms</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref58883"><a class="w-100 link-gray-900" href="/science/muscle-disease#ref58883">Assessment</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref58884"><a class="w-100 link-gray-900" href="/science/muscle-disease/Classification-of-muscle-weakness">Classification of muscle weakness</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref58885"><a class="w-100 link-gray-900" href="/science/muscle-disease/Classification-of-muscle-weakness#ref58885">Upper motor neuron disease</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref58886"><a class="w-100 link-gray-900" href="/science/muscle-disease/Classification-of-muscle-weakness#ref58886">Lower motor neuron disease</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref58887"><a class="w-100 link-gray-900" href="/science/muscle-disease/Classification-of-muscle-weakness#ref58887">Neuromuscular junction disorders</a></li></ul></li></ul></div></li><li data-target="#ref58888"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/muscle-disease/Classification-of-muscle-weakness#ref58888">Primary diseases and disorders</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref58889"><a class="w-100 link-gray-900" href="/science/muscle-disease/The-muscular-dystrophies">The muscular dystrophies</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref58890"><a class="w-100 link-gray-900" href="/science/muscle-disease/The-muscular-dystrophies#ref58890">Myasthenia gravis</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref58891"><a class="w-100 link-gray-900" href="/science/muscle-disease/The-muscular-dystrophies#ref58891">Toxic myopathies</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref58892"><a class="w-100 link-gray-900" href="/science/muscle-disease/Inflammatory-myopathies">Inflammatory myopathies</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref58893"><a class="w-100 link-gray-900" href="/science/muscle-disease/Inflammatory-myopathies#ref58893">Endocrine and metabolic myopathies</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref58894"><a class="w-100 link-gray-900" href="/science/muscle-disease/Inflammatory-myopathies#ref58894">Hormones</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref58895"><a class="w-100 link-gray-900" href="/science/muscle-disease/Inflammatory-myopathies#ref58895">Vitamin D deficiency</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref58896"><a class="w-100 link-gray-900" href="/science/muscle-disease/Inflammatory-myopathies#ref58896">Mitochondrial myopathies</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref58897"><a class="w-100 link-gray-900" href="/science/muscle-disease/Inflammatory-myopathies#ref58897">Glycogenoses</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref58898"><a class="w-100 link-gray-900" href="/science/muscle-disease/Inflammatory-myopathies#ref58898">Lipid storage myopathies</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref58899"><a class="w-100 link-gray-900" href="/science/muscle-disease/Myotonic-diseases">Myotonic diseases</a></li></ul></li></ul></div></li><li data-target="#ref58900"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/muscle-disease/Myotonic-diseases#ref58900">The periodic paralyses</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref58901"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/muscle-disease/Myotonic-diseases#ref58901">Fatigue</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/muscle-disease/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/muscle-disease">Quick Facts & Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold 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Let us know if you have suggestions to improve this article (requires login). </div> <div class="type-menu"> <label for="feedback-type" class="label mb-10">Feedback Type</label> <select id="feedback-type" class="form-select mb-30" name="feedbackTypeId" required> <option value="" selected="selected">Select a type (Required)</option> <option value="1">Factual Correction</option> <option value="2">Spelling/Grammar Correction</option> <option value="3">Link Correction</option> <option value="4">Additional Information</option> <option value="5">Other</option> </select> </div> <label for="feedback" class="label mb-10">Your Feedback</label> <textarea id="feedback" class="form-control mb-30" name="feedback" maxlength="3000" rows="7" required></textarea> <button class="btn btn-blue" type="submit">Submit Feedback</button> </form> <div class="success-messaging d-none mt-30"> <div class="title">Thank you for your feedback</div> <p>Our editors will review what you’ve submitted and determine whether to revise the article.</p> </div> </div> </div> <div class="md-websites-modal size-lg d-none"> <div class="md-modal-body"> <div class="h2 font-serif pb-15 border-bottom font-weight-bold"> External Websites </div> <div class="pb-20"> <ul class="list-unstyled mt-20 lh-lg"> <li><a class="external" href="https://www.nni.com.sg/PatientsandVisitors/Conditions-Treatments/Pages/Muscle-Diseases.aspx" target="_blank" rel="noopener ">National Neuroscience Institute - Muscle Disease</a></li> </ul> </div> </div> </div> </div> </div> <div class="toc-header-marker"></div> <button class="ai-ask-button btn border-2 js-header-ai-ask-button d-none btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10"> Ask the Chatbot a Question </button> <div class="caption alternate-titles">Also known as: muscular disease</div> <div class="md-byline module-spacing "> <div class="font-serif font-12"> <span class="written-by text-gray-700"> Written by </span> <div class="editor-popover popover p-0"> <a class="d-block p-20 gtm-byline font-12 byline-contributor" href="/contributor/Richard-Humphrey-Tudor-Edwards/3371" > <div class="editor-title font-16 font-weight-bold">Richard Humphrey Tudor Edwards</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Professor and Head, Department of Medicine, University of Liverpool; Director, Muscle Research Centre. Author of <i>Muscle Weakness.</i></div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Richard Humphrey Tudor Edwards</span>, <div class="editor-popover popover p-0"> <a class="d-block p-20 gtm-byline font-12 byline-contributor" href="/contributor/Ronald-A-Henson/1300" > <div class="editor-title font-16 font-weight-bold">Ronald A. Henson</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Physician and Neurologist, London Hospital, 1949–81. Physician, National Hospital for Nervous Diseases, 1952–81.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Ronald A. 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They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <a class="byline-edit-history" href="https://www.britannica.com/science/muscle-disease/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/science/myotonia" topicid="400566">myotonia</a></dd> <dd><a href="/science/muscular-dystrophy" topicid="398719">muscular dystrophy</a></dd> <dd><a href="/science/myopathy" topicid="400511">myopathy</a></dd> <dd><a href="/science/cramp" topicid="141697">cramp</a></dd> <dd><a href="/science/polymyalgia-rheumatica" topicid="468815">polymyalgia rheumatica</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/muscle-disease"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref524105"></span>muscle disease</strong>, any of the diseases and disorders that affect the <a href="https://www.britannica.com/science/human-muscle-system" class="md-crosslink " data-show-preview="true">human muscle system</a>. Diseases and disorders that result from direct abnormalities of the muscles are called primary <a href="https://www.britannica.com/science/muscle" class="md-crosslink autoxref " data-show-preview="true">muscle</a> diseases; those that can be traced as symptoms or <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="manifestations" href="https://www.merriam-webster.com/dictionary/manifestations" data-type="MW">manifestations</a> of disorders of the <a href="https://www.britannica.com/science/human-nervous-system" class="md-crosslink " data-show-preview="true">nervous system</a> or other systems are not properly classified as primary muscle diseases. Because muscles and nerves (<a href="https://www.britannica.com/science/neuron" class="md-crosslink " data-show-preview="true">neurons</a>) supplying muscle operate as a functional unit, <a href="https://www.britannica.com/science/disease" class="md-crosslink autoxref " data-show-preview="true">disease</a> of both systems results in muscular atrophy (wasting) and paralysis.</p><span class="marker MOD1 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref58880"> <h2 class="h1">Indications of muscle disease</h2> <span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">Muscular <span id="ref524106"></span><a href="https://www.britannica.com/science/atrophy" class="md-crosslink " data-show-preview="true">atrophy</a> and weakness are among the most common indications of muscle disease (<em>see below</em> <a href="https://www.britannica.com/science/muscle-disease#ref58881" class="md-crosslink " data-show-preview="true">Muscle weakness</a>). Though the degree of weakness is not necessarily proportional to the amount of wasting, it usually is so if there is specific involvement of nerve or muscle. Persistent weakness <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="exacerbated" href="https://www.merriam-webster.com/dictionary/exacerbated" data-type="MW">exacerbated</a> by <a href="https://www.britannica.com/topic/exercise-physical-fitness" class="md-crosslink " data-show-preview="true">exercise</a> is the primary characteristic of <span id="ref524107"></span><a href="https://www.britannica.com/science/myasthenia-gravis" class="md-crosslink " data-show-preview="true">myasthenia gravis</a>.</p><span class="marker MOD2 mod-inline"></span> <span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph"><a href="https://www.britannica.com/science/pain" class="md-crosslink " data-show-preview="true">Pain</a> may be present in muscle disease because of defects in blood circulation, injury, or <a href="https://www.britannica.com/science/inflammation" class="md-crosslink " data-show-preview="true">inflammation</a> of the muscle. Pain is rare, except as a result of abnormal posture or fatigue in <span id="ref524108"></span><a href="https://www.britannica.com/science/muscular-dystrophy" class="md-crosslink " data-show-preview="true">muscular dystrophy</a>—a hereditary disease characterized by progressive wasting of the muscles. <span id="ref524109"></span><a href="https://www.britannica.com/science/cramp" class="md-crosslink " data-show-preview="true">Cramps</a> may occur with disease of the motor or sensory neurons, with certain biochemical disorders (e.g., <span id="ref524110"></span><a href="https://www.britannica.com/science/hypocalcemia" class="md-crosslink ">hypocalcemia</a>, a condition in which the blood level of calcium is abnormally low), when the muscle tissues are affected by some form of poisoning, with disease of the blood vessels, and with exercise, particularly when cold.</p><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">Muscle enlargement (muscular <span id="ref524111"></span><a href="https://www.britannica.com/science/hypertrophy" class="md-crosslink ">hypertrophy</a>) occurs naturally in athletes. Hypertrophy not associated with exercise occurs in an unusual form of muscular dystrophy known as <span id="ref524112"></span><a href="https://www.britannica.com/science/myotonia-congenita" class="md-crosslink ">myotonia congenita</a>, which combines increased muscle size with strength and stiffness. <span id="ref524114"></span>Pseudohypertrophy, muscular enlargement through <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="deposition" href="https://www.merriam-webster.com/dictionary/deposition" data-type="MW">deposition</a> of fat rather than muscle fibre, occurs in other forms of muscular dystrophy, particularly the Duchenne type.</p><span class="marker MOD4 mod-inline"></span> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph"><span id="ref524115"></span><a href="https://www.britannica.com/science/tetany" class="md-crosslink " data-show-preview="true">Tetany</a> is the occurrence of <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="intermittent" href="https://www.merriam-webster.com/dictionary/intermittent" data-type="MW">intermittent</a> spasms, or involuntary <span id="ref524116"></span><a href="https://www.britannica.com/science/muscle-contraction" class="md-crosslink ">contractions</a>, of muscles, particularly in the arms and legs and in the larynx, or voice box; it results from low levels of <span id="ref524117"></span><a href="https://www.britannica.com/science/calcium" class="md-crosslink " data-show-preview="true">calcium</a> in the blood and from <span id="ref524118"></span><a href="https://www.britannica.com/science/alkalosis" class="md-crosslink " data-show-preview="true">alkalosis</a>, an increased alkalinity of the blood and tissues. <span id="ref524119"></span><a href="https://www.britannica.com/science/tetanus-disease" class="md-crosslink " data-show-preview="true">Tetanus</a>, also called lockjaw, is a state of continued muscle spasm, particularly of the jaw muscles, caused by toxins produced by the bacillus <em><span id="ref524120"></span><a href="https://www.britannica.com/science/Clostridium-tetani" class="md-crosslink ">Clostridium tetani</a></em>.</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/a-visit-with-the-word-doctor-medical-vocabulary-quiz" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/28/254328-131-8CF54640/Yorkshire-terrier-dressed-as-doctor.jpg" alt="A Yorkshire terrier dressed up as a veterinarian or doctor on a white background. (dogs)" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">A Visit with the Word Doctor: Medical Vocabulary Quiz</div> </div> </a><span class="marker MOD5 mod-inline"></span> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">The twitching of muscle fibres controlled by a single motor <a href="https://www.britannica.com/science/neuron" class="md-crosslink autoxref " data-show-preview="true">nerve cell</a>, called <span id="ref524121"></span>fasciculation, may occur in a healthy person, but it usually indicates that the muscular <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="atrophy" href="https://www.britannica.com/dictionary/atrophy" data-type="EB">atrophy</a> is due to disease of motor nerve cells in the <a href="https://www.britannica.com/science/spinal-cord" class="md-crosslink autoxref " data-show-preview="true">spinal cord</a>. Fasciculation is seen most clearly in muscles close to the surface of the skin.</p><span class="marker MOD6 mod-inline"></span> <span class="marker PREMOD7 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="2357" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/65/2565-050-72774A52/enzyme-defects-release-energy-Enzyme-muscles-glycogen.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/722004/2357"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/65/2565-050-72774A52/enzyme-defects-release-energy-Enzyme-muscles-glycogen.jpg"><img src="https://cdn.britannica.com/65/2565-050-72774A52/enzyme-defects-release-energy-Enzyme-muscles-glycogen.jpg?w=300" alt="enzyme defects affecting glycogen breakdown in muscle" data-width="1275" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/65/2565-050-72774A52/enzyme-defects-release-energy-Enzyme-muscles-glycogen.jpg" data-href="/media/1/722004/2357">enzyme defects affecting glycogen breakdown in muscle</a><span>Various enzyme defects can prevent the release of energy by the normal breakdown of glycogen in muscles. Enzymes in which defects may occur include glucose-6-phosphatase (I); lysosomal x-1,4-glucosidase (II); debranching enzyme (III); branching enzyme (IV); muscle phosphorylase (V); liver phosphorylase (VI, VIII, IX, X); and muscle phosphofructokinase (VII). Enzyme defects that can give rise to other carbohydrate diseases include galactokinase (A<sub>1</sub>); galactose 1-phosphate UDP transferase (A<sub>2</sub>); fructokinase (B); aldolase (C); fructose 1,6-diphosphatase deficiency (D); pyruvate dehydrogenase complex (E); and pyruvate carboxylase (F).</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph"><span id="ref524122"></span><a href="https://www.britannica.com/science/glycogen" class="md-crosslink " data-show-preview="true">Glycogen</a> is a storage form of carbohydrate, and its breakdown is a source of energy. Muscle weakness is found in a rare group of hereditary diseases, the <span id="ref524123"></span><a href="https://www.britannica.com/science/glycogen-storage-disease" class="md-crosslink " data-show-preview="true">glycogen-storage diseases</a>, in which various enzyme defects prevent the release of energy by the normal breakdown of glycogen in muscles. As a result, abnormal amounts of glycogen are stored in the muscles and other organs. The best-known glycogen-storage disease affecting muscles is <span id="ref524124"></span><a href="https://www.britannica.com/science/McArdle-disease" class="md-crosslink " data-show-preview="true">McArdle disease</a>, in which the muscles are unable to degrade glycogen to <a href="https://www.britannica.com/science/lactic-acid" class="md-crosslink " data-show-preview="true">lactic acid</a> on exertion because of the absence of the enzyme <span id="ref524125"></span><a href="https://www.britannica.com/science/phosphorylase" class="md-crosslink ">phosphorylase</a>. Abnormal accumulations of glycogen are distributed within muscle cells. <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="Symptoms" href="https://www.britannica.com/dictionary/Symptoms" data-type="EB">Symptoms</a> of the condition include pain, stiffness, and weakness in the muscles on exertion. McArdle disease usually begins in childhood. No specific treatment is available, and persons affected are usually required to restrict exertion to tolerable limits. The condition does not appear to become steadily worse, but serious complications may occur when the muscle protein <a href="https://www.britannica.com/science/myoglobin" class="md-crosslink " data-show-preview="true">myoglobin</a> is excreted in the urine. Other glycogen-storage diseases result from deficiency of the enzymes phosphofructokinase or acid maltase. With <span id="ref524126"></span><a href="https://www.britannica.com/science/Pompes-disease" class="md-crosslink " data-show-preview="true">acid maltase deficiency</a>, both heart and voluntary muscles are affected, and death usually occurs within a year of birth.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=black-friday-2024">Subscribe</a> </div> </div> </div> </DIV></div><span class="marker MOD7 mod-inline"></span> </section> <span class="marker h3"></span><section data-level="1" id="ref58881"> <h2 class="h1"><span id="ref524127"></span>Muscle weakness</h2> <section data-level="2" id="ref58882"> <h2 class="h2">Signs and symptoms</h2> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">Weakness is a failure of the muscle to develop an expected force. Weakness may affect all muscles or only a few, and the pattern of muscle weakness is an indication of the type of muscle disease. Often associated with muscle weakness is the wasting of affected muscle groups. A muscle may not be fully activated in weakness because of a less than maximal voluntary effort; a disease of the brain, spinal cord, or <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="peripheral" href="https://www.merriam-webster.com/dictionary/peripheral" data-type="MW">peripheral</a> nerves that interferes with proper electrical stimulation of the muscle fibres; or a defect in the muscle itself. Only when all causes have been considered can weakness be attributed to failure of the contractile machinery (i.e., the anatomy) of the muscle cell.</p><span class="marker MOD8 mod-inline"></span> <span class="marker PREMOD9 mod-inline"></span><p class="topic-paragraph">The effect of weakness in a particular muscle group depends on the normal functional role of the muscle and the degree to which force fails to develop. A weakness in muscles that are near the ends of the limbs usually results in a tendency to drop things if the <a href="https://www.britannica.com/science/arm" class="md-crosslink autoxref " data-show-preview="true">upper limb</a> is affected or in “foot drop” if the lower limbs are affected. The overall disability is not as great as weakness of more <span id="ref524128"></span>proximal (closer to the body) muscles controlling the pelvic or shoulder girdles, which hold large components of the total body mass against the force of gravity. Weakness of the proximal muscles that control the <a href="https://www.britannica.com/science/scapula" class="md-crosslink autoxref " data-show-preview="true">shoulder blade</a> (scapula), for example, results in “winging” (i.e., when the sharp inner border protrudes backward) as the arms are held outstretched. If the weakness is severe, the arms cannot be raised at all.</p><span class="marker MOD9 mod-inline"></span> </section> <section data-level="2" id="ref58883"> <h2 class="h2">Assessment</h2> <span class="marker PREMOD10 mod-inline"></span><p class="topic-paragraph">Muscle disease may be detected by assessing whether the muscle groups can withhold or overcome the efforts of the physician to pull or push or by observing the individual carrying out isolated voluntary movements against gravity or more complex and <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="integrated" href="https://www.merriam-webster.com/dictionary/integrated" data-type="MW">integrated</a> activities, such as walking. The weakness of individual muscles or groups of muscles can be quantified by using a <span id="ref524129"></span>myometer, which measures force based on a hydraulic or electronic principle. Recordings of contraction force over a period of time are valuable in determining whether the weakness is improving or worsening.</p><div class="one-good-fact-module"> </div><span class="marker MOD10 mod-inline"></span> <span class="marker PREMOD11 mod-inline"></span><p class="topic-paragraph">The <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="assessment" href="https://www.merriam-webster.com/dictionary/assessment" data-type="MW">assessment</a> of muscle weakness (and wasting) is directed toward discovering evidence of muscle inflammation or damage. These changes are discerned by blood tests or by measuring alterations of the electrical properties of contracting muscles. Another investigative tool is the muscle <span id="ref524130"></span><a href="https://www.britannica.com/science/biopsy" class="md-crosslink " data-show-preview="true">biopsy</a>, which provides muscle specimens for pathological <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="diagnosis" href="https://www.merriam-webster.com/dictionary/diagnosis" data-type="MW">diagnosis</a> and biochemical analysis. Muscle biopsies can be taken with a needle or during a surgical procedure.</p><span class="marker MOD11 mod-inline"></span> </section> </section><span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article></div> </div></div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":1,"pagesTotal":5,"pageId":722004,"pageLength":1056,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-130/js/libs/jquery-3.5.0.min.js?v=3.130.14"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-130/dist/topic-page.js?v=3.130.14' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"B","adLeg":"B","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"PAGINATED","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Muscle disease | Description, Causes, Types, & Treatment | Britannica