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Despite their best efforts, it is impossible for healthcare providers to be fully up-to-date and familiar with every condition which they deal with. Also, without having McArdle’s themselves, it is impossible for them to appreciate every nuance of the condition, especially when each McArdle person presents somewhat differently.
It is part of our mission to help inform them, and you can help.

An extensive range of publications is available from IamGSD.

Diagnosed with McArdle disease

When you finally get diagnosed with McArdle disease, there is a very high likelihood that the clinic you receive your diagnosis from has previously seen very few, if any, cases of McArdle’s. This can understandably lead to a risk of them having misconceptions about some aspects of the condition. 

The situation will no doubt improve once you are referred on to a specialist, but in the meantime it is a good idea to watch out for the possibility of one or two of the following occasional misconceptions. Every one of us can help improve understanding, to the benefit of those who come after us.

Should one of these misconceptions arise, please take a moment to politely explain the correct information.

If you are a medical professional please make sure to read our Medical Emergencies page.

 We can help by supplying your healthcare provider with copies of these booklets.
Or they can access the “Medical Overview” and the “Clinical Practice Guidelines” online.
Or PDFs can be downloaded from our Publications page.


 Watch out for these easy misconceptions which occasionally arise. It would be useful to correct them when there is an opportunity.

The misconceptions...

Putting right the misconceptions and further references.


“The problem is resolved after a brief rest.” 

A misconception of what triggers second-wind.

This arises from slightly incorrect accounts of second-wind in many research papers, or simply misconceptions of second-wind. Rest does not get us into second-wind, or we would be in second-wind before we started activity. It is activity that achieves second-wind. We need to be using the target muscles for around 6 to 12 minutes, during which time we need to respond to any muscle cramping by slowing our pace or pausing for the occasional rest, typically of 30 seconds each. Once in second-wind activity is significantly easier, but the problem is not fully resolved.


Wakelin A. Living with McArdle Disease. International Association for Muscle Glycogen Storage Disease. 2017, Second-wind – an essential tool. pp14–16. Download PDF.


The problem is exercise, so don’t exercise.” 

Not realizing that we need to exercise for aerobic fitness.

The cardinal symptom of McArdle’s is often described as “exercise intolerance”. This is well meaning but is also very misleading. Exercise is an intended and planned activity. People affected by McArdle’s can make suitable adjustments to their planning and carrying out of exercise, so as to minimize or avoid significant symptoms. There is a vastly greater risk with physical activity, especially activities of daily living which are not usually planned or accommodated. We try to use management strategies across the whole spectrum of physical activity and need to be especially attuned to the risk of externally imposed and unexpectedly intense activity, such as having to run away from danger. In fact, we need to maximize not minimize our exercise as this can be planned and managed appropriately, will boost our aerobic fitness, and even build muscle mass, both of which will ease symptoms, and reduce the risk of serious episodes.


See: 1) page 13, “Beneficial exercise” in the Medical Overview booklet; and 2) the exercise guidance in the Supplementary Material section of the Clinical Practice Guidelines booklet.


Haller RG, Wyrick P, Taivassalo T, Vissing J. Aerobic conditioning: an effective therapy in McArdle's disease. Annals of Neurology: Official Journal of the American Neurological Association and the Child Neurology Society. 2006;59(6):922-8.  Download PDF.


“Take 37g sucrose 5 minutes before exercise.” 

Incomplete reading of the research paper.

This statement has led too many people with McArdle’s to take this amount of sugar multiple times per day, with the consequences of weight gain and insulin resistance. (Some individuals consume fruit juice instead and this has the same issue.) The relevant research paper states “...restrict the use of pre-exercise sucrose to no more than a few times weekly before engaging in strenuous exercise that would otherwise promote contracture and myoglobinuria.” This might, for instance, be something like moving a piece of furniture but is more commonly likely to arise from sexual relations.


Andersen S, Haller R & Vissing J. Effect of Oral Sucrose Shortly Before Exercise on Work Capacity in McArdle Disease. Archives of Neurology. 2008;65(6):786-9.  Download PDF.


“You only need go to hospital if your urine is cola-colored.” 

Not appreciating that you may well need to go before that.

Yes, you must respond if you see cola-colored urine. However, this is not a reliable signal as there are many factors in addition to muscle damage that can affect the the color of the urine. In particular: size of the damaged muscle/s, hydration level, time since the injury, and ingestion of highly colored foods or drinks. It is much more important to consider the degree of contracture in the muscles and how the person is feeling. There is a flowchart to help you make your decision on the “Medical” menu of the IamGSD website.

For medical professionals, we have guidance on emergency treatment of rhabdomyolysis, with the risk of complications including acute renal failure and compartment syndrome. Go to Emergencies page.


When to seek urgent medical care. International Association for Muscle Glycogen Storage Disease, 2023. Access web page.


“You will get used to the pain, just push through it.” 

Not realizing that our pain is different to normal exercise pain.

There is a very common saying in exercise: “No pain, no gain”. However, in people with McArdle’s this is just not possible as our pain comes on much sooner than normal muscle pain. We have to use management techniques to keep the pain within certain limits. Otherwise it very, very quickly develops into severe pain and muscle damage. People with McArdle’s cannot push through this pain, if they try to do so the muscles end up in contracture and become immobilized. This can develop into compartment syndrome. They need to learn how to manage activity effectively, especially to minimize isometric (static) and anaerobic activity, and thus to avoid prolonged or chronic pain.


Lucia A, et al. Clinical practice guidelines for glycogen storage disease V & VII (McArdle disease and Tarui disease) from an international study group. Section 5.7 Pain management. Neuromuscular Disorders 31 (2021) 1296–1310. Download PDF.


There is no point in confirming the diagnosis as there is no treatment.” 

Not realizing that without a treatment, management is all.

There is currently no drug treatment or cure, but there is much that can be done to improve quality of life and some people with McArdle’s can become almost asymptomatic. It is vital to establish a genetically proven diagnosis. Otherwise it is very easy to confuse McArdle’s with some of the other muscle GSDs and even other metabolic disorders. The exact diagnosis is necessary to enable the most appropriate approach to the particular condition: such as exercise, diet and management techniques. In addition, having a genetic diagnosis means that the person could potentially join in studies and research projects through organizations such as the Euromac Registry and the CoRDS Registry. Go to our patient registries web page.


Lucia A, et al. Clinical practice guidelines for glycogen storage disease V & VII (McArdle disease and Tarui disease) from an international study group. Section 5.4. Information & guidance for day-to-day management. Neuromuscular Disorders 31 (2021) 1296–1310.
Download PDF.


“There is no need for a CK test, we know it will be high.” 

Not understanding that the pattern of tests can be very informative.

Baseline CK: Nearly all people with McArdle’s have a high baseline Creatine Kinase (CK), the average being around 2500 IU/L. This is their norm and compares with the top of the normal range being usually quoted as around 200 to 300 IU/L. A CK test perhaps once a year can help the person monitor how they are managing their condition. It can indicate whether improved aerobic fitness has reduced muscle damage, but equally important is to consider the person’s weight, fitness level, daily symptom burden, etc.

Serious episodes: CK will greatly increase, and usually peak at 24 hours after the incident. A CK test can help assess how bad the episode was, and a few repeated CK tests will monitor the episode to ensure that it is not ongoing or getting worse (e.g. compartment syndrome). In terms of discharge from medical care, CK may still be many times the patient's normal baseline level. More important is how the patient feels and their kidney function. Please see our guidance on emergencies.


Lucia A, et al. Clinical practice guidelines for glycogen storage disease V & VII (McArdle disease and Tarui disease) from an international study group. Section 5.3. Laboratory testing. Neuromuscular Disorders 31 (2021) 1296–1310. PDF.


“Take cornstarch regularly through the day and night” 

Confusion between muscle GSDs and hepatic GSDs.

If a healthcare provider is not familiar with GSDs, it is possible for them to not appreciate the difference between the muscle types and the hepatic (liver) types. Cornstarch is a complex carbohydrate which breaks down slowly and is therefore useful in maintaining blood glucose levels in the hepatic GSDs. However, there is no evidence that it is useful in McArdle’s and the other muscle GSDs.

Birch K. The McArdle Disease Handbook – a guide to the scientific and medical research into McArdle Disease (2011, 2015). Section 7: Dietary supplements which have been considered for McArdle’s, 7.1.4 Cornstarch. Association for Glycogen Storage Disease (UK). Download PDF.


“McArdle’s is just a syndrome.” 

Not knowing that this is long out of date.

When first described in 1951, McArdle disease was reasonably termed a syndrome – a set of signs or symptoms that occur together without an identifiable cause. By 1959 it was shown that the deficient enzyme was myophosphorylase, so it was no longer a syndrome, but a disease. By 1984 the gene encoding myophosphorylase (PYGM) was discovered, so it was then shown that McArdle’s is a genetic disease.


Schmid R, Robbins PW, and Traut RR (1959) Glycogen Synthesis in Muscle Lacking Phosphorylase. Proceedings of the National Academy of Science USA 45: 1236-1240. Access websIte.

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