title: McArdle disease: a unique study model in sports medicine.
abstract: McArdle disease is arguably the paradigm of exercise intolerance in humans. This disorder is caused by inherited deficiency of myophosphorylase, the enzyme isoform that initiates glycogen breakdown in skeletal muscles. Because patients are unable to obtain energy from their muscle glycogen stores, this disease provides an interesting model of study for exercise physiologists, allowing insight to be gained into the understanding of glycogen-dependent muscle functions. Of special interest in the field of muscle physiology and sports medicine are also some specific (if not unique) characteristics of this disorder, such as the so-called 'second wind' phenomenon, the frequent exercise-induced rhabdomyolysis and myoglobinuria episodes suffered by patients (with muscle damage also occurring under basal conditions), or the early appearance of fatigue and contractures, among others. In this article we review the main pathophysiological features of this disorder leading to exercise intolerance as well as the currently available therapeutic possibilities. Patients have been traditionally advised by clinicians to refrain from exercise, yet sports medicine and careful exercise prescription are their best allies at present because no effective enzyme replacement therapy is expected to be available in the near future. As of today, although unable to restore myophosphorylase deficiency, the 'simple' use of exercise as therapy seems probably more promising and practical for patients than more 'complex' medical approaches.
authors.affiliation: Universidad Pablo Olavide, Sevilla, Spain.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Santalla
authors.forename: Gisela
authors.initials: G
authors.lastname: Nogales-Gadea
authors.forename: Niels
authors.initials: N
authors.lastname: Ørtenblad
authors.forename: Astrid
authors.initials: A
authors.lastname: Brull
authors.forename: Noemi
authors.initials: N
authors.lastname: de Luna
authors.forename: Tomàs
authors.initials: T
authors.lastname: Pinós
authors.forename: Alejandro
authors.initials: A
authors.lastname: Lucia
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D017079:Exercise Tolerance / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism*; D006012:Glycogen Storage Disease Type V / Q000503:physiopathology* / Q000628:therapy*; D006006:Glycogen Synthase / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D005082:Physical Exertion / Q000502:physiology; D012206:Rhabdomyolysis / Q000209:etiology / Q000503:physiopathology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D013178:Sports Medicine
chemical_list: D006003:Glycogen; D006006:Glycogen Synthase; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506943:ATP2A1 protein, human