Muscle Weakness and Muscle Fatigue

Diagnosing Muscle Weakness and Muscle Fatigue

Muscle weakness, also called myasthenia gravis in extreme cases, is a decrease of strength in one or more muscles. It is a symptom, not a disease, which is common in many muscular, neurological, and metabolic disorders. Muscle weakness may occur in just one muscle or all of the muscles, depending on the cause. It may be accompanied by muscle pain, atrophy, muscle cramps, or other symptoms.

If you are experiencing sudden muscle weakness, especially in one side of the body, you may be experiencing a stroke and should seek immediate medical help.

Muscle Weakness and Muscle Fatigue  

It is important to understand that muscle weakness and muscle fatigue are not the same thing.

  • Muscle weakness refers to a lack of physical muscle strength—an inability to move the arms, legs, or other muscles. The patient may still be able to make the muscles function, though he or she may experience muscle pain while doing so.
  • Muscle fatigue refers to a lack of energy. It may be a result of poor sleep, overwork, worry, boredom, or a lack of exercise. It can also be caused by illness, certain medications, or medical treatments such as chemotherapy. Finally, muscle fatigue can also be caused by neurological disorders such as depression and anxiety.

Both muscle weakness and muscle fatigue are symptoms, not diseases. Like anything else, the symptom must be evaluated in combination with other symptoms in order for the cause to be determined.


Muscle pain and weakness have a very wide variety of causes. The most common causes can include:

There are also many less common, but still possible, causes. Though rare, these include:

It is also possible that the muscle weakness is a result of a less dangerous condition, such as the flu or even the common cold. Certain medications and outside substances can also cause sudden muscle weakness.


Like leg weakness, arm weakness may simply be a result of overall muscle weakness throughout the body. Again, like leg weakness, arm weakness may simply be a perception of the patient, and not an indication of true muscle loss in the area.

However, arm weakness can also be a symptom of more dangerous conditions. It might be caused by injury to the arm; infection of the arm, muscular wasting from certain muscular disorders; nerve damage or compression at the vertebral column, or certain hereditary conditions. It may also be caused by temporary infections, such as the common cold.

The most potentially life-threatening cause of sudden arm weakness is stroke. If you are suddenly unable to move an arm, especially on only one side of the body, you may be experiencing a stroke and should seek emergency medical help immediately.

In some cases, weak arms may also occur from disuse. If this is the case, physical therapy may help to improve your arm weakness. An arm or elbow compression sleeve can also provide support and strength to the affected area as it recovers.

If your arm weakness is persistent or causes you significant pain, you should seek prompt medical care from a licensed physician. Over-the-counter pain medications, ice, rest, and wearing a compression sleeve can all help reduce your arm pain and weakness until your appointment.


Leg weakness can be either limited to the legs, or exist as part of a generalized feeling of weakness throughout the body. Often, patients who feel tired or ill perceive that they are experiencing muscle weakness, but there is no true loss of muscle function.

However, a sudden weakness in the legs can also be a sign of a stroke, which occurs when the brain is deprived of oxygen. If you have experienced sudden leg weakness accompanied by loss of vision, double vision, blurred vision, paralysis, severe headache, loss of bowel control, fainting, or any change in your level of consciousness, you may be experiencing a stroke and should seek immediate medical attention. 

Leg weakness may also be caused by sciatica, a condition that occurs when the spinal cord nerves are pinched or compressed as they exit the spine through the vertebrae of the backbone.

Another potential cause of weak leg muscles is a neuromuscular disease such as myasthenia gravis, an autoimmune disorder that causes muscle weakness. It could also be caused by multiple sclerosis, a disease that affects the brain and spinal cord and causes problems with coordination and balance.

If, however, your leg weakness has been gradual, speak to a physician to determine the correct cause. Over-the-counter pain relievers, ice, rest, and elevation can all help reduce your discomfort until your appointment. Wearing a leg compression sleeve can also help to alleviate your pain or discomfort.

These products are designed to help relieve pain and discomfort from Muscle Weakness: