What Is Muscle Atrophy?

Overview of muscle atrophy

A decrease in the size of your muscles or muscle strength may mean you have muscle atrophy. Muscle atrophy is referred to as the net loss of proteins and other components of muscle cells. It can be a result of the lack of muscle usage due to injury or illness. Additionally, damage to your nerves may also cause muscle atrophy. Muscle atrophy can be treated or managed with exercise and diet to ensure a good quality of life.

Muscles are composed of muscle fibres (muscle cells) and protein filaments.^1,2 An atrophied muscle will have a lower cellular volume and show a reduction in overall mass compared to normal muscle.³ 

Muscle atrophy is typically categorised into two groups: disuse atrophy or neurogenic atrophy, based on the cause. In disuse atrophy, a reduction or complete absence of muscle use is the main cause.⁴ However, in neurogenic atrophy, the primary cause is an injury to, or disease of the nerves outside your brain and spinal cord - also known as the peripheral nervous system (PNS).^5,6

What are the causes of muscle atrophy?

Depending on the type of muscle atrophy present, there are different causes. In healthy muscles, muscle protein synthesis and muscle protein breakdown are balanced. This means that muscle mass is maintained.

Disuse atrophy

Disuse atrophy occurs when you stop physically loading your muscles. This is because in the absence of physical stimulation, muscle protein synthesis decreases. Therefore, the rate of muscle protein breakdown is no longer countered by adequate muscle protein synthesis. This leads to muscle mass loss.

If you are in good health, you may experience disuse atrophy if you have a:⁴

• Sedentary lifestyle (a lifestyle that lacks physical activity)
• Short-term illness or a period of bed rest
• Localised limb immobilisation

Along with a decrease in muscle protein synthesis, in ageing or with disease,  inflammation can affect muscle protein breakdown. It increases the rate of muscle loss.

You might have accelerated disuse atrophy if you:⁴

• Have age-related atrophy (sarcopenia)
• Have a critical illness
• Have a major injury
• Have a chronic illness that causes you pain and/or disability  
• Are malnourished (deficient in nutrients)

Neurogenic atrophy 

In neurogenic atrophy, the nerves that stimulate your muscles are damaged. Without nerve stimulation, muscle fibres trigger muscle protein breakdown, causing the loss of muscle mass. 

The conditions that cause damage to the nerves supplying your muscles include:⁷

• Amyotrophic lateral sclerosis
• Spinal muscular atrophy
• Guillain-Barre syndrome
• Poliomyelitis

What are the symptoms and effects of muscle atrophy?

The symptoms of muscle atrophy vary between people and are often linked to the underlying cause. However, common effects include:⁸

• Gradual weakening of your muscles 
• Decrease in the size of the affected muscles, due to the loss of muscle mass
• Reduction in physical performance (you may walk slower, have frequent falls or be unable to carry out daily tasks)

Common symptoms of muscle atrophy include:

• Tremors
• Muscle cramps
• Numbness or tingling in the areas affected
• Difficulty when speaking, swallowing or breathing - if muscles in the face or throat are affected^9,10

How is muscle atrophy diagnosed?

If you have any of the symptoms found with muscle atrophy, your healthcare provider will take a full medical history and carry out a physical exam. They will also look at the size of your muscles in order to identify the areas affected. When they have completed this, they might refer you for any of the following diagnostic tests:^10,11

• Muscle strength and function tests (these assess how easily you can complete certain activities such as walking, standing up from a seated position or grip strength)
• Imaging techniques - MRI, CT or DEXA scans
• Electromyography (EMG)
• Blood tests (to detect specific markers that indicate a specific condition)

What are the health consequences of muscle atrophy?

Without treatment, muscle atrophy can have a significant effect on the quality of life. It is important that you speak to your healthcare provider about any symptoms that are stopping you from completing your normal activities or that are worrying you. 

You may find that muscle atrophy:^{9, 10}

• Impacts your mobility and daily activities
• Increases your risk of injuries
• Affects how quickly you feel fatigued
• Reduces your independence 
• Reduces the quality of your life and how you feel in yourself

Treatment and management of muscle atrophy

The treatment or management plan created by your healthcare provider will depend on the underlying cause and type of muscle atrophy you have. If you have disuse atrophy due to injury or a sedentary lifestyle, the muscle atrophy will likely be reversible. Whereas, with neurogenic atrophy, nerve damage is not reversible - it cannot be cured and can only be managed.

Treatment and management options include:^{7,11,12,13,14,15}

Physical therapy and exercise:

1. Resistance training
2. Strength training
3. Endurance exercise

Nutritional interventions:

1. Increasing dietary protein
2. Prescription supplements (e.g. protein, leucine (an amino acid), creatine, and vitamin D)

Medications and therapies:

1. NSAIDs (e.g. ibuprofen)
2. Condition-specific medications
3. Electrical muscular stimulation (EMS)

Assistive devices and mobility aids

How is muscle atrophy prevented?

In most cases, muscle atrophy is an unavoidable consequence of an injury or medical condition. However, the severity and risk can be reduced via protective measures and preventative actions such as:¹⁶

• Regular physical exercise
• Eating a balanced diet with adequate protein intake
• Reducing your injury risk
• Managing any underlying health conditions that either directly cause muscle atrophy or prevent you from regular physical activity or adequate nutrition

FAQs

How long does it take for muscle atrophy to occur?

Depending on your age, physical activity level and the cause of your atrophy, the time it takes for muscle atrophy to occur differs. Gradual muscle mass loss is a natural part of ageing, with a 3-8% reduction in muscle mass every 10 years after the age of 30.¹⁷ With limb immobilisation, strength can be lost within a week of stopping movement.¹⁸ If you have neurogenic atrophy, the rate of muscle loss will be determined by disease progression.

How long will it take to reverse my muscle atrophy?

If you have disuse atrophy, your muscle mass and strength can be restored via physical therapy and changes to your diet. The time it takes to recover will depend on your age, overall fitness and the amount of muscle atrophy.⁴ It is easy to become demotivated if you do not see instant results through physical therapy. However, keeping consistent is the best way to return to full health.

When should I see a doctor?

If you are feeling weaker than normal or have difficulty completing your normal daily activities, speak to your healthcare provider. This is so they can start investigating the cause and help restore your strength. They may do this by creating an exercise or nutrition plan to support you.. 

Summary

Muscle atrophy is characterised by a decrease in muscle size and strength, caused by too little physical activity or an underlying medical condition. Disuse atrophy is common with injury or short-term illness that prevents you from exercising or eating well. This type of atrophy can be reversed through physical therapy and proper nutrition. Neurogenic atrophy is caused by irreversible nerve damage and can be managed with different treatments and therapies. It is important that you speak to your healthcare provider about any difficulties you may have to maintain your quality of life.