Muscle weakness is when your muscles can’t function at their usual capacity. This is common and is usually not a concern. Depending on the cause, muscle weakness might affect your shoulders, legs, face, arms, hips, or other body parts.
Everyday causes of muscle weakness include:
- excessive movement, such as exercise, walking long distances, or physical labor
- fatigue or a lack of sleep
- a recent viral or bacterial infection that’s left you feeling weak
In other cases, muscle weakness may signal a health condition, such as multiple sclerosis (MS), chronic fatigue syndrome (CFS), or a hormone imbalance.
If you’re concerned about new, sudden, or persistent muscle weakness, consider talking with a doctor. They can assess your symptoms and suggest the most appropriate treatments or remedies.
1. Excessive movement
The first cause a healthcare professional will rule out is muscle fatigue.
You might have noticeably weaker muscles after starting a new exercise regime or returning to exercise after spending time sedentary, such as when recovering from an illness.
Healthcare professionals will also rule out whether you’re experiencing pain-related movement problems with usual muscle strength, rather than true muscle weakness.
If they rule out these factors, they may test your muscle strength using an objective tool called the Medical Research Council Muscle Scale. Depending on the results, they may recommend further diagnostic tests.
2. Age-related muscle weakness
Everyone begins to lose muscle mass and strength as they get older, starting as early as age 30 years. This is a typical bodily process.
Muscle strength reduces more quickly in some people, known as sarcopenia. This affects an estimated 10% to 20% of older adults.
Symptoms of sarcopenia include:
- muscle weakness
- falling
- walking slowly
- perceived muscle wasting
- having difficulty doing usual daily tasks
Getting more exercise, especially strength training, and following a protein-rich diet can help with these symptoms.
3. Vitamin and mineral deficiencies
Some vitamin deficiencies and mineral deficiencies can cause muscle weakness.
For example, a 2018 case study reports that vitamin D deficiency can lead to proximal muscle weakness, which means weakness near the center of the body, and an increased risk of falls.
Other vitamin deficiencies linked with muscle weakness include:
- calcium deficiency (hypocalcemia)
- potassium deficiency (hypokalemia)
- iron deficiency (anemia)
- vitamin B12 deficiency
If you suspect a vitamin deficiency, consider asking a doctor for blood tests. Taking vitamin supplements is a common and effective treatment option.
4. Chronic fatigue syndrome
People with CFS — also known as myalgic encephalomyelitis (ME) or ME/CFS — experience extreme fatigue after small amounts of activity. The US Institute of Medicine published a report in 2015 renaming CFS as systemic exertion intolerance disease (SEID). Therefore, some institutions refer to the condition as SEID.
The Centers for Disease Control and Prevention (CDC) report that up to 2.5 million people in America may have CFS.
This fatigue may feel like muscle weakness, though the muscles themselves haven’t lost strength. People with CFS may have difficulty maintaining muscle tone as they aren’t able to do as much physical activity.
Research from 2016 says there is increasing evidence that abnormalities in the muscle’s biochemistry, such as acid buildup, may play a major role in fatigue associated with CFS.
Other symptoms of CFS include:
- difficulty sleeping
- problems with thinking and memory
- symptoms worsening when standing or sitting up
- pain, such as muscle aches, headaches, or joint pain
- a sore throat
- digestive issues, including irritable bowel syndrome
There’s no specific treatment for CFS, but over-the-counter painkillers, healthy sleep habits or sleep medication, and mental health treatments can help.
5. Multiple sclerosis
MS is an autoimmune condition where your body attacks healthy nerve fibers. Nearly 1 million people in the United States live with MS.
Muscle weakness is a common symptom of MS. This may be because you’re moving around less due to pain and fatigue, which means your muscles lose strength. It could also result from damage to the nerve fibers in the spinal cord or brain.
You may feel muscle weakness all over your body or specific body parts, including the arms, hands, legs, feet, facial muscles, and muscles that help you talk or swallow. It can also affect bladder control.
Other symptoms of MS include:
- tingling
- numbness
- memory problems
- mood changes
- fatigue
- pain
Treatment for MS aims to slow the disease course and prevent symptom relapse. A doctor may prescribe medications and rehabilitation methods.
6. Hormonal causes
Various hormonal conditions can cause muscle weakness, including:
Diabetes is another hormonal condition that can affect your muscles. Diabetic neuropathy may affect the nerves that control movement, leading to muscle weakness. If you have diabetes, taking diabetes medication can help with symptoms and complications.
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