McArdle disease is a rare disease of muscle metabolism. Affected people cannot use a starch-like substance called glycogen which is stored in muscle and used for energy at the beginning of activity and during strenuous exercise. The effects of the condition are fatigue and cramping within a few minutes of starting an activity, which can potentially lead to acute muscle damage. After about seven or eight minutes of exercise the muscle can start to use alternative sources of energy from fats and sugars supplied from the liver and so the symptoms ease. This phenomenon is called the 'second wind'. In healthy people, aerobic training is known to improve the ability of muscle to burn fats for energy during exercise. In theory then, aerobic training could be beneficial to people with McArdle disease, as their muscles might be trained to use fats earlier and more efficiently during exercise. The purpose of this review was to identify any randomised controlled trials of aerobic training and assess its effects in people with McArdle disease. There were no randomised controlled trials of aerobic training in people with McArdle disease. There were, however, three small uncontrolled studies (the largest included nine participants). The studies showed that it is possible for people with McArdle disease to undergo exercise training and there were no harmful effects. Whether or not training is beneficial for people with McArdle disease needs further investigation, with randomised controlled trials including larger numbers of people with the condition.
Evidence from non-randomised studies using small numbers of patients suggest that it would be safe and worthwhile for larger controlled trials of aerobic training to be undertaken in people with McArdle disease.
McArdle disease is a rare metabolic myopathy caused by a complete absence of the enzyme muscle glycogen phosphorylase. Affected people experience symptoms of fatigue and cramping within minutes of exercise and are at risk for acute muscle injury (rhabdomyolysis) and acute renal failure. If the first few minutes of exercise are paced, a 'second wind' will occur enabling exercise to continue. This is due to mobilisation and utilisation of alternative fuel substrates. Aerobic training appears to improve work capacity by increasing cardiovascular fitness.
To assess the effects of aerobic training in people with McArdle disease.
We searched the Cochrane Neuromuscular Disease Group Specialized Register (11 January 2011), CENTRAL (2010, Issue 4), MEDLINE (January 1966 to January 2011) and EMBASE (January 1980 to January 2011).
All randomised and quasi-randomised controlled studies of aerobic exercise training in people of all ages with McArdle disease.
Two authors identified possible studies for inclusion and assessed their methodological quality. Had more than one study of sufficient methodological quality been identified we would have undertaken a meta-analysis.
There were no randomised or quasi-randomised controlled trials of aerobic training in people with McArdle disease. However, three open studies using small numbers of participants provided some evidence that aerobic training improves fitness without adverse events in people with McArdle disease.