This plain language explanation of McArdle disease and its effect should help those without any medical knowledge. From children to elderly relatives, this should help them to better understand the condition.

People with McArdle’s have a problem with the use of energy in their muscles. Symptoms arise because affected people cannot use a form of sugar (called glycogen) which is stored in the muscles.


When people with McArdle‘s undertake intense activity (such as going up stairs or running for a bus) or “static” activity (like gripping to open a new jam jar, or standing on tiptoe to reach a shelf) they run out of energy and get very tired, very quickly. If they do it with maximum effort, problems arise in under 10 seconds, otherwise it may happen in 2 to 3 minutes.


Any activity which is not carefully paced can result in a tightening sensation in the muscles, and people with McArdle‘s must respond to this signal. If they do not slow down or pause for a rest for at least 30 seconds they are likely to find that the affected muscles go into a cramp. Then they MUST take a long rest, because, if they press on, the cramp will become severe and the muscle will become locked up, swollen and extremely painful. This can last for hours or even days.

It is important to avoid severe cramping for three reasons:

  • Firstly, during episodes tiny bits of broken down muscle are released into the blood which can block the kidneys. This happens only rarely but it can be life threatening and must be treated by a doctor as a matter of urgency.

  • Secondly, episodes can (very rarely) result in a muscle crisis which requires urgent surgery to correct before permanent damage is done to the muscle, nerves or even the limb.

  • Thirdly, episodes can cause a build up of muscle damage over the years and that can make activity a lot harder in later life.


It is possible for people with McArdle‘s to make activity a bit easier by learning to get into “second wind”. This is when the muscles start to make more use of other forms of energy – mainly sugar released from stores in the liver, and fat. By regularly exercising in “second wind” they can improve their body’s ability to use these energy sources, and therefore manage better with activity and exercise.


There are several things that can help people with McArdle’s:

  1. An early diagnosis and getting the right advice before a lot of damage is done.

  2. Regularly exercising in “second wind” (at least 45 minutes on 5 days each week is recommended).

  3. Avoiding, or being very careful of, intense and “static” activity.

  4. Sharing experiences with others who have McArdle’s.


You can’t catch McArdle’s – it is a genetic condition and is very rare, about 1 person in every 100,000 has it. Only about one third of these have been diagnosed, the others struggle on unrecognised. It is inherited from parents who are both carriers. They will not have any symptoms so usually will have no idea that they are carriers. Each of their children have only a 25% chance of having McArdle’s.

While all the children of people who have McArdle’s will be carriers, only if the other parent is a carrier can the children get the condition - there is then a 50% risk. As only about 1 person in every 160 is a carrier, the chance of a person with McArdle‘s person having a McArdle child is very small.



People who have been diagnosed late, sometimes after decades of manual work or pushing themselves too hard, are usually the worst affected. They may have a lot of pain, restricted abilities, weakness and many admissions to hospital.


The majority of people with McArdle‘s learn to adapt their circumstances, stay active, accommodate the condition and live relatively normal lives. An early diagnosis is a big help with that. McArdle‘s is not life threatening as long as care is taken to avoid kidney failure and to avoid risky situations, such as swimming in deep water or climbing to heights.

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What is Muscle GSD?

Human bodies make glucose from carbohydrates. Excess glucose is stored as glycogen in our muscles and liver. Muscle glycogen storage disease is when our muscles cannot convert their glycogen back into glucose to power our muscles.

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If you have another muscle GSD please contact us.

Site updated: 04/2021.

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