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The ‘McArdle paradox’: exercise is a good advice for the exercise intolerant
  1. Alejandro Lucia1,
  2. Ros Quinlivan2,3,
  3. Andrew Wakelin4,
  4. Miguel A Martín5,6,
  5. Antoni L Andreu5,7
  1. 1European University of Madrid, Madrid, Spain
  2. 2The MRC Centre for Neuromuscular Disease, Institute of Neurology, Queen Square, London, UK
  3. 3Dubowitz Neuromuscular Centre, Great Ormond Street Hospital, London, UK
  4. 4Association for Glycogen Storage Disease (UK), London, UK
  5. 5Spanish Network for Research in Rare diseases (CIBERER), Instituto de Salud Carlos III, Spain
  6. 6Laboratorio de Enfermedades mitocondriales y neuromusculares, Instituto de Investigación Hospital 12 de Octubre (i+12), Madrid, Spain
  7. 7Departament de Patologia Mitocondrial i Neuromuscular, Hospital Universitari Vall d’Hebron, Institut de Recerca (VHIR), Universitat Autónoma de Barcelona, Barcelona, Spain
  1. Correspondence to Dr R Quinlivan, MRC Centre for Neuromuscular Diseases, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK; ros.quinlivan{at}uclh.nhs.uk

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McArdle disease (glycogen storage disease type V, OMIM database number 232600) may provide the ultimate model of exercise intolerance in humans, and thus is of great interest in the sports medicine setting. The condition is an autosomal recessive disorder of muscle glycogen metabolism originally described in 1951 by Brian McArdle.1 Patients have pathogenic mutations in both alleles of the PYGM gene, which encodes myophosphorylase, the skeletal muscle isoform of glycogen phosphorylase.2 As a result, myophosphorylase activity is totally absent. Because this enzyme initiates the breakdown of muscle glycogen leading to liberation of glucose-1-phosphate, patients are unable to obtain energy from their muscle glycogen stores. Hence this disease is arguably the paradigm of exercise intolerance in humans.2 Exercise is the trigger for symptom occurrence in McArdle patients; as such, they tend to be averse to exercise and have often been advised by clinicians to refrain from exercise.

McArdle disease and exercise

Men and women are equally affected and symptoms usually begin during childhood, typically in the school playground or physical education classes.3 The clinical presentation is dominated by exercise intolerance in the form of acute crises of early fatigue and contractures, which are often accompanied by exertional rhabdomyolysis, as indicated by marked increases in serum levels of creatine kinase (CK) activity and myoglobinuria.3 Rhabdomyolysis can sometimes be so severe as to cause acute renal failure. A typical feature of the disease is the so-called ‘second wind’ phenomenon, that is, marked improvement in the tolerance of aerobic, dynamic, large muscle mass exercise (walking …

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