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Glossary of terms used in McArdle disease

You may often see or hear the following terms used in relation to McArdle disease. We have tried to provide here a layman's explanation of each term as it applies in this disease. If you would prefer more technical medical definitions please try this dictionary.


Acute renal failure
A sudden decline in kidney function. Requires urgent medical attention. In McArdle disease it can be caused by the breakdown of muscle from anaerobic activity.

Aerobic exercise
Exercise which requires oxygen to assist in converting fuel sources into energy. Walking is a good example of aerobic exercise. This is good exercise for those with McArdle disease.

Anaerobic exercise
Exercise which does not need oxygen to utilise fuel sources. Weightlifting is a good example of anaerobic exercise. This type of exercise requires the conversion of glycogen, which those with McArdle disease cannot do. Anaerobic exercise must be avoided as it is damaging to the muscles.

ATP (adenosine triphosphate)
A molecule in muscle cells which serves as an energy source for the metabolic process.

Autosomal recessive
The type of inheritance by which some genetic diseases including McArdle disease are inherited.

A type of compound, such as starches and sugars, found in food. Broken down in the body to form energy.

A condition where the muscle has fixed high resistance to movement, or spasm. It takes some hours or days for the muscle to relax again.

Creatine kinase (CK or CPK)
An enzyme which is used in the formation of ATP in muscle. People with McArdle disease tend to have a raised level of CK in their blood and this is often an early sign that something is wrong. In severely damaged muscle from excessive anaerobic activity the CK level can rise to many hundreds of times its normal level.

ECG (electrocardiogram)
A recording of the beating of the heart made by placing sensors on your chest and limbs. It is printed out as a trace or graph. There is no evidence of heart involvement in McArdle disease but an ECG is a useful general health check.

A protein which the body uses to make a chemical reaction happen. Myophosphorylase, which is missing in McArdle patients, is an enzyme.

The end product of carbohydrate metabolism and also found in certain foods such as fruit. The chief source of energy.

The form in which glucose is stored in the muscles and in the liver. It has to be converted back to glucose to be used for energy in the muscles. People with McArdle disease have large stores of glycogen in their muscles as they are unable to convert it back to glucose. Their liver stores are normal.

The conversion of glycogen and glucose, via a series of steps, finally into ATP which energises the muscle. The process does not use oxygen and is thus anaerobic. People with McArdle disease have problems with this process.

Isometric activity/exercise Muscular action in which tension is developed without contraction of the muscle. Also known as 'static' exercise as there is no movement of the muscle. For example: clenching fists, holding something up or pushing. This is the worst type of activity for McArdle people.

Lactic acid
An acid which is made as a biproduct of the muscle using carbohydrate. Normally there is a rise of lactic acid in the bloodstream on exercise, but in McArdle disease it does not rise. The lack of this rise can be a help in diagnosis.

Malignant hyperthermia
A severe form of fever caused by a reaction to certain anaesthetics and muscle relaxants. Those with McArdle disease are at an increased risk of malignant hyperthermia and should always tell their anaesthetist about their McArdle disease before having a general anaesthetic.

The process by which energy is made available for use in the body.

A very small organ within the cells of the muscle which is responsible for energy production from fuels. Through regular aerobic exercise the number of mitochondria can be increased, which boosts the aerobic capacity of the muscle.

Pain in a muscle or muscles. This the main symptom of McArdle disease.

A protein found in red skeletal muscle.

Presence of myoglobin in the urine. Muscle damage releases myoglobin into the blood and the kidneys remove it from the blood to the urine. An excessive amount of myoglobin in the blood can "block" the kidneys and cause acute renal failure.

A disease of the muscle. McArdle Disease is a myopathy.

The muscle type of phosphorylase. There are also brain and neo-natal forms.

Of the muscle and nerves. People with McArdle disease may be diagnosed and/or cared for by a neuromuscular consultant.

An enzyme used in the conversion of stored glycogen to glucose so that it can be utilised for energy.

Complex organic compunds found in the body and in foods such as meat and eggs. Consist mainly of amino acids. They serve a number of functions including as enzymes and are involved in oxygen transport and muscle contraction.

The destruction of cells in the skeletal muscles. In McArdle disease this arises from fixed spasm of the muscle caused by excessive activity such as lifting something heavy - see "anaerobic".

Last reviewed: 5 June 2012.