What Is Muscle Weakness?
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Medically reviewed by Amy Kwan, PT
Muscle weakness occurs when your body isn't able to contract your muscles properly, leading to reduced strength in one or more of your muscles. In most cases, muscle weakness happens because of an underlying health condition. But aging also plays a factor. In fact, about 5% of adults in the U.S. aged 60 years and above experience muscle weakness.
If your muscles feel weak, it's important to see your healthcare provider for diagnosis and treatment. If left untreated, muscle weakness can make it difficult to perform daily activities and may also cause other symptoms. Your exact treatment plan will depend on the underlying condition that's causing your muscle weakness and the severity of your symptoms.
Symptoms of Muscle Weakness
Muscle weakness can lead to a wide range of symptoms that may range from mild to severe. A few mild symptoms include:
Trouble gripping things with your hands
Changes in finger movements
Difficulty walking
Loss of muscle coordination
But, serious symptoms can also occur, such as:
Inability to walk or run
Trouble getting up from a sitting or lying down position
Cramping or stiffness
Muscle pain or numbness
Unintentional weight loss
Difficulty breathing
Irregular heart rate
Why Do Your Muscles Feel Weak?
Several things that can cause your muscles to feel weak—ranging from underlying health conditions, infections, and lifestyle habits.
Neurological Disorders
Several neurological disorders can lead to muscle weakness. These include:
Amyotrophic lateral sclerosis (ALS): Previously known as Lou Gehrig's disease, this condition affects the motor neurons that control voluntary muscle movement in your brain. Degeneration and death of the motor neurons eventually cause the muscle to weaken, leading to difficulty in performing daily activities such as walking, talking, and other actions.
Cerebral palsy: Cerebral palsy is a condition that occurs due to abnormal brain development or damage to a developing brain. People with cerebral palsy often experience muscle weakness and have difficulty maintaining posture and balance.
Guillan-Barré syndrome: This is a neurological condition where the immune system attacks a part of the peripheral nervous system. As a result of this attack, muscle weakness can occur. Severe cases of the condition can even lead to paralysis where you cannot use some or all of your muscles.
Multiple sclerosis: Multiple sclerosis is a condition that happens when your nerve cells in the brain or spinal cord lose myelin—a layer of proteins and phospholipids that coats your nerve cells and helps them function properly. This can interrupt the flow of nerve impulses in your body, and eventually lead to improper functioning of the muscles.
Lambert-Eaton myasthenic syndrome (LEMS): This condition is an autoimmune disorder that occurs when your immune system attacks calcium channels on the nerve endings that play a key role in the release of acetylcholine (a type of neurotransmitter that plays a role in muscle movement). This often results in low levels of acetylcholine which leads to abnormal muscle contractions and causes muscle weakness.
Myasthenia gravis: This autoimmune condition causes the immune system to attack healthy cells or proteins in your body. Myasthenia gravis can cause muscle weakness because of an interruption in the communication between your nerves and muscles.
Endocrine Disorders
Your endocrine system is responsible for regulating your hormones. If you have any of the following hormonal conditions, muscle weakness may occur:
Addison’s disease: This condition causes damage to your adrenal glands—which are glands that help produce hormones to regulate metabolism, blood pressure, and immune system functioning. Low levels of these hormones can cause muscle weakness.
Hypothyroidism and hyperthyroidism: When you have hypothyroidism, your thyroid gland doesn't make enough thyroid hormone. But hyperthyroidism occurs when your thyroid gland produces too much thyroid hormone. Any dysfunction in your thyroid hormone production may increase your risk of muscle weakness, among other muscle and bone-related symptoms.
Cushing's syndrome: A condition that occurs when your body produces too much cortisol—a hormone that plays an important role in your body's response to stress. High levels of cortisol can cause significant muscle weakness.
Infections
Infections with certain bacteria, viruses, or fungi may also lead to muscle weakness. These infections may include:
Streptococcus (commonly known as strep)
Staphylococcus aureus (commonly known as staph)
Mycobacterium spp.
Klebsiella spp.
Escherichia coli
Candida spp.
Aspergillus spp.
Influenza A and B viruses
Adenovirus
Dengue virus
West Nile virus
Hepatitis B and C viruses
Other Causes
The following factors can also increase your risk of muscle weakness:
Electrolyte imbalance
History of stroke, anemia, cancer, or sarcopenia
Older age
Nutritional deficiencies
Genetic factors
Certain medications such as statins, glucocorticoids, and fluoroquinolones
Excessive alcohol consumption
When to Contact a Healthcare Provider
You may want to consult with your healthcare provider if you are experiencing:
Sudden onset of muscle weakness that is not associated with any other symptoms
Difficulty performing daily activities such as walking, climbing stairs, or moving your limbs
Muscle weakness on only one side of the body
Persistent muscle weakness that worsens over time
During your appointment, your healthcare providers may ask about your personal or family medical and your symptoms—such as when your symptoms started, how severe they are, and how often you're experiencing them. They can also use certain tests to make a proper diagnosis, such as:
Blood tests: Blood tests such as creatine kinase tests can help identify diseases that may be affecting the muscles. Some blood tests can also detect metabolic abnormalities, the presence of infections, and genetic disorders.
Ultrasonography: A muscle ultrasound can help identify neurological disorders that may have led to muscle weakness.
Magnetic resonance imaging (MRI): MRI is also an effective tool to detect whether specific neurological conditions are responsible for muscle weakness.
Electromyography: This test measures the electrical activity of your muscles and can help your provider understand the functioning of your muscles and nerves.
Muscle biopsy: A muscle biopsy involves collecting a sample of tissues from specific muscles and observing the samples under a microscope. In some cases, this test can help diagnose the underlying cause of muscle weakness.
Treatment
Your healthcare provider can recommend a treatment plan based on the severity of your symptoms and the potential underlying cause of your muscle weakness. Treatment options may include:
Physical therapy to strengthen your muscles and improve mobility
Medications
Dietary changes to improve nutritional deficiencies
Surgery, which is usually only an option for severe cases of muscle weakness that don't improve with other treatments
How to Manage Muscle Weakness
Fortunately, there are some ways you can manage and prevent muscle weakness on your own. Consider trying the following strategies:
Moving your body through physical activity each day
Incorporating strength-training exercises into your gym routine
Eating a diet high in protein
Drinking plenty of water
Warming up and cooling down before and after exercises
Being careful while lifting heavy objects
A Quick Review
Muscle weakness is common and can occur due to a variety of underlying causes, such as health conditions, infections, and lifestyle habits. Anyone can develop muscle weakness, but people of older age are especially at risk. If you're experiencing weak muscles, it's best to speak with your healthcare provider to identify the causes of muscle weakness. They can properly test and diagnose you and come up with a treatment plan that can help keep your symptoms at bay.
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