What Is McArdle Disease?
McArdle disease is a rare inherited condition that affects how muscles produce energy during exercise. People with this disorder cannot properly break down glycogen, a stored form of sugar the body normally uses for fuel during activity.
McArdle disease is caused by changes in a gene involved in muscle energy production. The condition is inherited and usually occurs when a person receives a changed gene from both parents.
Because the muscles cannot access energy the usual way, physical activity may quickly lead to pain, fatigue, or muscle weakness. Symptoms often begin during childhood or the teenage years, though some people are not diagnosed until adulthood.
Symptoms
McArdle disease mainly affects the muscles during physical activity. Symptoms can range from mild to more severe and may vary from person to person.
Common symptoms include:
- Muscle pain during exercise
- Feeling unusually tired after starting activity
- Muscle cramps or stiffness
- Weakness with exercise
- Trouble doing intense physical activity
- Dark or cola-colored urine after strenuous exercise
- A “second-wind” feeling where exercise becomes easier after several minutes of gentle movement
In some cases, repeated muscle breakdown can lead to kidney problems. A small number of people may also develop ongoing muscle weakness later in life.
How Is It Diagnosed?
Your healthcare provider will begin by reviewing your symptoms, exercise history, and family medical history. A physical exam can help evaluate muscle strength and movement.
Testing may include:
- Blood tests to look for signs of muscle damage
- Genetic testing to identify gene changes linked to McArdle disease
- Exercise testing to measure how the muscles respond to activity
- Urine testing after muscle symptoms occur
- Imaging or muscle biopsy in certain situations
Because McArdle disease is uncommon, people are sometimes diagnosed later than expected. Evaluation by a neurologist or neuromuscular specialist may help confirm the condition.
How Is It Treated?
There is currently no cure for McArdle disease, but treatment can help manage symptoms and lower the risk of complications.
Most care plans focus on improving safe activity levels and preventing muscle injury. Treatment may include:
- Low- to moderate-intensity aerobic exercise
- Gradually warming up before activity
- Avoiding sudden strenuous exercise
- Nutrition strategies that support energy needs
- Drinking or eating carbohydrates before exercise when recommended
- Physical therapy or supervised exercise programs
- Monitoring for kidney complications after severe muscle breakdown
Some people benefit from working closely with a care team to develop a personalized activity and nutrition plan. With the right approach, many individuals can continue to stay active and improve daily function.
