Unexplained muscle pain, cramping and tiredness in active people can be due to many conditions that affect energy production, such as anaemia, diabetes or hormone abnormalities. One rare muscle condition that affects physical performance is McArdle’s disease. What is McArdle’s disease, how do we diagnose it, and what are the management strategies?
What is McArdle’s disease?
McArdle’s disease is a rare genetic condition of the muscle caused by a deficiency in myophosphorylase, the enzyme responsible for breaking down glucose in muscle cells. Muscles struggle to obtain energy without this enzyme, particularly during intense exercise.
McArdle disease symptoms
Generally, active people experience symptoms when engaging in intense exercise or pushing beyond their limits. These symptoms include:
- Muscle fatigue, weakness, and pain occur during intensive activities such as running, cycling, or weightlifting. Muscle cramping is often a feature. These muscle symptoms are generally worse at the beginning of the exercise. Any muscle can be affected. Chronic weakness, even at rest, can develop over time and often affects the upper arm and leg muscles.
- Dark urine may occur after intensive exercise. This dark urine results from sudden muscle breakdown, also called rhabdomyolysis.
- Other atypical symptoms include difficulty chewing or swallowing, as well as sudden acute compartment syndrome.
Second wind phenomenon: What is it?
Unlike typical fatigue, individuals with McArdle’s disease often experience improved endurance after a brief rest, as the body shifts to alternative energy sources such as fatty acids and glucose.
How is McArdle’s disease diagnosed?
You should see an experienced sports medicine doctor who can assess you to determine whether you have any of the features of McArdle’s disease. Your doctor will rule out other causes of muscle pain, weakness, and fatigue.
Investigations that are used to confirm the diagnosis and exclude other causes include:
- Blood Tests
Elevated creatine kinase (CK) levels during or after activity indicate muscle damage. However, CK levels may be normal in some cases of this disease. Genetic testing for PYGM mutations can confirm the diagnosis.
- Forearm Exercise Test
This test involves measuring lactate and ammonium levels before and after a brief workout. In McArdle’s disease, lactate fails to rise, but ammonium increases, reflecting impaired glycogen breakdown.
- Muscle Biopsy
If necessary, a biopsy can identify abnormalities in the muscle tissues.
- Imaging and Nerve Studies
MRI and nerve studies can help rule out other conditions that may be causing muscle pain and weakness.
Other causes of muscle pain with exercise
- Acute muscle injury, such as a calf or quadriceps muscle tear
- Chronic exertional Compartment syndrome
- Nerve entrapments such as calf nerve pain, referred pain from the lumbar spine or inflammatory neuritis
- Medical problems such as anaemia, thyroid disease, diabetes, and iron deficiency
- Blood vessel entrapment, such as popliteal artery entrapment syndrome
Treatment for McArdle disease
While there is no cure for McArdle’s disease, active individuals can stay fit with a targeted management approach without risking complications. This disease does not have to sideline you from activity and sport.
McArdle disease diet
A few of the nutritional strategies that can improve symptoms include the following:
- Pre-Workout Carbohydrate Loading: A carb-rich snack 30 minutes before exercise can provide a quick energy boost and protect against muscle breakdown.
- Frequent Small Meals: Balanced meals with adequate protein and healthy fats support muscle repair and endurance.
- Supplementation: In some cases, creatine supplementation may improve muscle performance.
Tips to stay active with McArdle disease
Staying fit and exercising is possible with this disease. However, there are some tips to keep you active and reduce complications:
- Low-Intensity, Aerobic Activities: Walking, swimming, or cycling are safer and help build endurance over time.
- Gradual Warm-Ups: Starting slow can help activate alternative energy pathways, reducing early fatigue.
- Avoid Overexertion: High-intensity, anaerobic activities can trigger symptoms and cause muscle damage.
- Keep fit: Generally, the fitter you are, the less likely you are to develop symptoms during exercise.
- Watch for signs of excessive muscle breakdown, like extreme muscle pain or dark urine. Stay well hydrated and avoid extended endurance activities such as an Ironman or marathon. If you develop dark urine after exercise, you should seek medical attention.
Other frequently asked questions:
What is the average age of diagnosis of McArdle’s disease?
Symptoms are often overlooked, so it’s not unusual for the diagnosis to be delayed until adulthood. The average age of diagnosis is 33 years.
If an individual is diagnosed with McArdle disease, is genetic counselling recommended?
Yes. This condition is inherited as an autosomal recessive disease. The chances of a baby having the disease from affected parents are 25%, and the chance of being a carrier for the disease is 50%.
Can people lift with McArdle’s disease?
Yes. Traditionally, people with McArdle disease were told to avoid heavy-weight training. However, recent studies suggest that weight training is safe when supervised by a strength and conditioning coach.
Are there any exercises you should avoid?
Yes. According to studies, exercises that should be avoided in McArdle’s disease include the following:
- Static muscle contractions (e.g., handgrip exercises)
- Static muscle contractions or heavy loads on low muscle mass (e.g., weight lifting), unless performed under the programmed supervision of clinicians and exercise/fitness specialists.
- Dynamic exercises at a high-intensity level (e.g., competitive ball games)
- Exercises with a high involvement of eccentric (lengthening) muscle contractions (e.g., jumps)
- Very intense dynamic aerobic exercise (e.g., strenuous running, swimming, or cycling) except in very fit individuals who are well trained for the specific activity.
Final word from Sportdoctorlondon about McArdle disease
If you have unexplained muscle pain and fatigue symptoms, you should see an experienced sports medicine doctor who can assess you and investigate for muscle diseases like McArdle disease. Having McArdle disease does not have to prevent you from participating in activities. Confirming a diagnosis will help you manage your symptoms better.
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