Dominic Stone
Muscle atrophy, or muscle wasting, is the loss of skeletal muscle mass. It can be caused by a variety of factors, including immobility, aging, malnutrition, medications, injuries, or diseases that impact the musculoskeletal or nervous system. The primary cause is often attributed to inactivity, where the body breaks down unused muscles to conserve energy. This can occur during periods of illness, injury, or bed rest, leading to muscle disuse and atrophy. The symptoms and progression of muscle atrophy depend on the underlying cause, and treatment options vary accordingly. Physical therapy, exercise, and proper nutrition are commonly recommended to slow or reverse muscle atrophy, but in some cases, it may be irreversible. Understanding the factors contributing to muscle atrophy is crucial for maintaining muscle health and preventing potential disabilities associated with muscle weakness.
| Characteristics | Values |
|---|---|
| Primary Cause | Inactivity or lack of physical activity |
| Other Causes | Ageing, malnutrition, medications, injury, disease, bed rest, nerve damage, genetics, inflammation of muscles, etc. |
| Symptoms | Reduced muscle mass, muscle weakness, pain, paralysis, etc. |
| Treatments | Physical therapy, functional electrical stimulation, proper nutrition, anabolic agents, etc. |
| Reversibility | Can be reversed with activity, proper diet, exercise, and treatment for the underlying condition |
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What You'll Learn
Inactivity and immobility
The time it takes for muscles to atrophy varies depending on the muscle group and the health of the individual. For example, lower body muscles show signs of atrophy faster, within a week. However, the effects of inactivity and immobility on muscle atrophy can be slowed or reversed through physical activity and exercise. Resistance exercises, in particular, have been shown to be beneficial in reducing muscle atrophy, especially in older adults. Functional electrical stimulation (FES) is another effective treatment for muscle atrophy caused by inactivity and immobility. This technique uses electrical impulses to stimulate muscle contraction in affected muscles.
In addition to exercise, proper nutrition is crucial to preventing and treating muscle atrophy. A diet that provides sufficient calories, protein, and other nutrients that promote muscle development can help slow or reverse atrophy. This is especially important in cases of malnutrition, which can lead to muscle wasting and atrophy. Adequate nutrition can help the body build and retain muscle mass.
In some cases, muscle atrophy due to inactivity and immobility can be unavoidable, such as during the recovery period from an illness or injury. In these situations, it is essential to prioritize rest and recovery while also maintaining some form of physical activity within one's capabilities. This may include bed exercises or physical therapy techniques to prevent muscle wasting.
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Malnutrition and inadequate nutrition
Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, ageing, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Malnutrition-related muscle atrophy may develop as a result of medical conditions that impair the body's ability to absorb nutrients. Diets low in lean protein, fruits, and vegetables can impair muscle growth or maintenance.
Malnutrition, frequently seen in older patients, can lead to changes in body composition, resulting in functional impairment and poor clinical outcomes. Nutritional status is typically evaluated using the Global Leadership Initiative on Malnutrition (GLIM) criteria. In older patients, malnutrition can lead to a decline in mid-thigh muscle cross-sectional area (CSA), an increase in the risk of falls and fractures, a lower quality of life, and higher morbidity and mortality.
The co-occurrence of malnutrition and physical inactivity, both prevalent in older individuals, may speed up the process of muscle atrophy, leading to sarcopenia and adverse health outcomes. Sarcopenia is age-related muscle atrophy and can be slowed by exercise. Malnutrition-related muscle atrophy can be treated with dietary changes or supplements, regular exercise, and proper nutrition.
Inadequate nutrition can cause muscle atrophy, and this may be due to a lack of calories and protein. Adequate calories and protein are crucial to prevent muscle atrophy. Protein needs may vary depending on metabolic factors and disease state, so high-protein supplementation may be beneficial. Supplementation of protein or branched-chain amino acids, especially leucine, can provide a stimulus for muscle synthesis and inhibit protein breakdown.
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Age, genetics, and nerve damage
Genetics play a crucial role in spinal muscular atrophy, a genetic disorder characterized by muscle weakness and wasting. This condition arises from the loss of specialized nerve cells called motor neurons, which are responsible for muscle movement. Spinal muscular atrophy encompasses several types, differing in age of onset and severity. Type 0, the rarest and most severe form, manifests before birth, with affected infants exhibiting joint deformities, extremely weak muscle tone, and respiratory muscle weakness. Type I, or Werdnig-Hoffmann disease, is the most common form, with muscle weakness evident at birth or within the first few months of life. Children with Type I often struggle with head control, sitting, and swallowing. Type II, or Dubowitz disease, develops in children between 6 and 12 months of age, causing muscle weakness and tremors. Type III, or Kugelberg-Welander disease, typically affects individuals after early childhood, resulting in muscle weakness and difficulty with walking and climbing stairs over time. Type IV is rare and usually begins in early adulthood, leading to mild to moderate muscle weakness, tremors, and breathing problems.
Nerve damage can also induce muscle atrophy, as observed in animal studies. Experiments on rats revealed that chronic nerve constriction led to substantial muscle loss, particularly in the sciatic nerve-innervated muscles, with a 66% decrease in TA mass and a 50% reduction in EDL mass after 28 days. Histological analysis indicated signs of necrotizing myopathy, regenerating fibers, and atrophy. Nerve damage caused a decrease in fiber diameter across all three fiber types, with type 2b fibers showing the most significant atrophy. Despite the muscle loss, nerve damage-induced atrophy was accompanied by elevated myofibrillar protein synthesis rates, contrary to the initial hypothesis of decreased MPS rates.
Muscle atrophy due to nerve damage is also associated with diseases such as muscular dystrophy, myopathies, and injuries or diseases impacting the nervous system, including spinal cord injuries and strokes. These conditions can cause muscle weakness and wasting, contributing to muscle atrophy.
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Diseases and injuries
Muscle atrophy is the wasting or thinning of muscle mass. It can be caused by a wide range of injuries or diseases that impact the musculoskeletal or nervous system. The hallmark sign of muscle atrophy is the loss of lean muscle mass. The predominant symptom is increased weakness, which may result in difficulty or inability in performing physical tasks depending on which muscles are affected.
Diseases that primarily affect the muscles, such as polymyositis (an autoimmune inflammatory disease), muscular dystrophy, or myopathies, can cause atrophy. Diseases that rob the muscles of energy, like cancer and malnutrition, are other causes. In addition, mitochondrial dysfunction affects muscle tissue regulation and can lead to skeletal muscle atrophy.
Neurogenic atrophy is caused by an injury or disease affecting nerves that connect to the muscles. When these nerves are damaged, they can't trigger the muscle contractions needed to stimulate muscle activity. When your muscles don't contract, your body breaks them down, causing a decrease in size and strength. Diseases and conditions that can affect these nerves include amyotrophic lateral sclerosis (ALS), multiple sclerosis, carpal tunnel syndrome, and spinal cord injury.
The amount of time it takes for muscles to atrophy depends on age, fitness level, and the cause of atrophy. If muscle atrophy is due to disuse (physiologic), the process can start within two to three weeks of not using the muscles. However, neurogenic muscle atrophy may develop sooner depending on the health condition. For example, a study in the Journal of Rehabilitation Medicine found that older men who did eight weeks of strength training lost about 25% of their muscle gains after they stopped training for just two weeks.
Treatment for muscle atrophy depends on the underlying cause but often includes exercise and adequate nutrition. Physical therapy, strength training, and targeted mitochondrial therapy can also help.
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Treatments: exercise, nutrition, and therapy
Muscle atrophy, or the wasting and thinning of muscle mass, can be treated through a combination of exercise, nutrition, and therapy. The type of treatment recommended by a healthcare provider will depend on the underlying cause of the atrophy.
Exercise
Physiologic atrophy, caused by the disuse of muscles, can be reversed through regular exercise. This includes low-impact exercises that target the affected muscles, such as water exercises, resistance exercises, weightlifting, and stair climbing. The intensity of the exercises should gradually increase over time. Even those who cannot actively move certain joints can benefit from exercises using braces or splints.
Nutrition
Inadequate nutrition can cause muscle atrophy, and malnutrition-related atrophy can be treated with a healthy diet and nutritional supplements. A diet rich in lean protein, fruits, and vegetables is essential for muscle growth and maintenance.
Therapy
Physical therapy is the leading treatment option for muscle atrophy. It involves specific stretches and exercises to prevent immobility and promote muscle healing. Electrical stimulation, or functional electrical stimulation (FES), is a type of physical therapy that uses electrical impulses to stimulate muscle contraction. Ultrasound therapy is another non-invasive procedure that uses sound waves to aid in muscle healing.
The time it takes to recover from muscle atrophy depends on the type of atrophy and its severity. Physiologic atrophy is usually reversible but can take several months or longer to fully recover muscle strength.
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Frequently asked questions
Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system.
Studies have shown that within a week there are molecular signs of atrophy. Depending on the muscle group, the time varies, with lower body muscles showing signs of atrophy quicker (7-8 days).
The primary cause of muscle atrophy is physical inactivity. If a person does not use a particular muscle, the body eventually breaks it down to conserve energy. Muscle atrophy can also be caused by inadequate nutrition, age, genetics, and certain medications.
Muscle atrophy can be treated through regular exercise, proper nutrition, and physical therapy. Functional electrical stimulation (FES) is another effective treatment for muscle atrophy.
The symptoms of muscle atrophy vary widely depending on the cause and severity of muscle loss. Symptoms include reduced muscle mass, muscle weakness, and pain.
