McArdle disease is an ultra-rare disorder of energy supply which can cause exhaustion, cramping and muscle pain in everyday activities. If activity is continued whilst in pain, muscle damage ensues with the risk of muscle breakdown (rhabdomyolysis), which can lead to acute kidney failure or compartment syndrome.

Symptoms are usually apparent before age 10 but many people do not manage to obtain a diagnosis until their thirties or even later. In middle or old age some people with McArdle disease experience fixed muscle weakness, possibly from cumulative muscle damage.

With diagnosis, correct advice on management can be followed and further problems can be avoided.  Those with McArdle disease should take regular aerobic exercise such as walking, and limit anaerobic activities such as lifting heavy weights to no more than 6 seconds at a time.