Health condition
Pompe vs McArdle: exercise clues
Pompe and McArdle disease both cause exercise problems but behave differently: McArdle causes cramps at the start of activity with a second wind, while late-onset Pompe causes progressive weakness and breathing muscle involvement.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
Which gene and test confirm it, who should be tested in the family, and which specialist to see.
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McArdle: symptoms within minutes of starting exercise, relieved by brief rest, classic second wind, episodes of dark urine after exertion
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Pompe: gradually worsening limb-girdle weakness over years, difficulty with stairs and rising, breathlessness lying flat
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Both often show a raised CK - the pattern of symptoms directs the right enzyme or gene test
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Distinguishing them matters: Pompe has enzyme replacement therapy, McArdle is managed with exercise strategy
Understanding the condition
What it is and what happens next.
What causes it, how it is confirmed, and the testing and specialist routes available in the UK.
What it is and how it presents
Both conditions sit in the muscle-energy family, and both get mislabelled as unfitness or fibromyalgia, but the histories diverge cleanly. The McArdle story is dynamic: pain and stiffness arrive early in exertion, forced rest brings relief, and steady pacing unlocks a second wind. The Pompe story is degenerative: no dramatic cramps, but a slow decline in hip and shoulder strength, trouble climbing stairs, and eventually orthopnoea as the diaphragm weakens - a feature McArdle does not produce.
Testing, surveillance and specialist care
A neuromuscular or metabolic clinic can separate the two quickly: a dried blood-spot acid alpha-glucosidase assay screens for Pompe, PYGM sequencing confirms McArdle, and a forearm or cycle exercise test adds physiology where genetics is ambiguous. The distinction changes management fundamentally, since Pompe is treatable with enzyme replacement. NHS clinical genetics services carry some of the longest waits in the health service, often many months for a first appointment, whereas private genetic testing and a specialist review can typically be arranged within around two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a neuromuscular specialist or metabolic physician. Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any emergency symptoms.
Frequently asked
Common questions about Pompe vs McArdle: exercise clues.
Quick, plain-English answers to what people ask us most.
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What are Pompe disease and McArdle disease?
Both are rare inherited metabolic muscle disorders that can cause exercise-related symptoms, but they involve different enzyme deficiencies and glycogen-processing pathways, leading to somewhat different patterns of symptoms.
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How do the exercise symptoms differ between Pompe and McArdle disease?
McArdle disease classically causes early exercise intolerance with muscle pain and cramping within minutes of starting activity, often improving with a brief rest (the 'second wind' phenomenon), while Pompe disease causes more gradual, progressive muscle weakness rather than acute exercise-triggered pain.
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What causes Pompe disease?
Pompe disease results from deficiency of the enzyme acid alpha-glucosidase, causing abnormal glycogen build-up within muscle cells and progressive weakness, including of the breathing muscles.
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What causes McArdle disease?
McArdle disease is caused by deficiency of a different enzyme, myophosphorylase, needed to break down glycogen for immediate energy during exercise, causing early muscle fatigue and cramping with exertion.
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Are Pompe and McArdle disease hereditary?
Yes, both are inherited in an autosomal recessive pattern, meaning both parents typically carry one copy of the relevant faulty gene without being affected themselves.
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How are these conditions diagnosed and distinguished?
Specific blood tests measuring the relevant enzyme activity, along with genetic testing for the responsible gene mutations, distinguish between the two conditions, as the pattern of symptoms alone can sometimes overlap.
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Can Pompe or McArdle disease be treated?
Pompe disease has an available enzyme replacement therapy that can slow progression, while McArdle disease is mainly managed through exercise pacing strategies, dietary adjustments, and avoiding sudden intense exertion, as there's no specific enzyme replacement available.
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Does breathing weakness occur in both conditions?
Breathing muscle weakness is a particularly characteristic and often serious feature of Pompe disease, whereas McArdle disease doesn't typically cause this pattern of breathing muscle involvement.
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What is the 'second wind' phenomenon in McArdle disease?
This refers to the improvement in exercise tolerance that often occurs after a brief rest period during early exertion in McArdle disease, as the muscles shift to using an alternative fuel source; this specific pattern isn't seen in Pompe disease.
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When should I see a specialist, and how quickly can I be seen privately?
See a neurologist if you have unexplained exercise intolerance or progressive muscle weakness. Private specialist assessment, including relevant enzyme and genetic testing, is typically available within about two weeks, faster than standard NHS referral pathways for rare muscle conditions.