Weakness and fatigue are
terms that are often used as if they mean the same thing. But in fact they
describe two different sensations. It is important to know exactly what you
mean when you say "I feel weak" or "I am fatigued" because it can help you and
your doctor narrow down the possible causes of your symptoms.
- Weakness is a lack of physical or muscle strength and the feeling
that extra effort is required to move your arms, legs, or other muscles. If
muscle weakness is the result of pain, the person may be able to make muscles
work, but it will hurt.
- Fatigue is a feeling of tiredness or exhaustion or a need to rest
because of lack of energy or strength. Fatigue may result from overwork, poor sleep, worry, boredom, or lack of exercise. It is a symptom that may be caused by illness, medicine, or medical treatment such as chemotherapy. Anxiety or depression can also cause fatigue.
Both weakness and fatigue are symptoms, not diseases. Because
these symptoms can be caused by many other health problems, the importance of
weakness and fatigue can be determined only when other symptoms are
General weakness often occurs after you have
done too much activity at one time, such as by taking an extra-long hike. You
may feel weak and tired, or your muscles may be sore. These sensations usually
go away within a few days.
In rare cases, generalized muscle
weakness may be caused by another health problem, such as:
- A problem with the minerals (electrolytes) found naturally in the body, such as low
levels of potassium or sodium.
- Infections, such as a urinary tract infection or a respiratory infection.
- Problems with the thyroid gland, which
regulates the way the body uses energy.
- A low thyroid level (hypothyroidism) can cause fatigue, weakness, lethargy,
weight gain, depression, memory problems, constipation, dry skin, intolerance
to cold, coarse and thinning hair, brittle nails, or a yellowish tint to the
- A high thyroid level (hyperthyroidism) can cause fatigue, weight loss,
increased heart rate, intolerance to heat, sweating, irritability, anxiety,
muscle weakness, and thyroid enlargement.
- Guillain-Barré syndrome, a rare nerve
disorder that causes weakness in the legs, arms, and other muscles and that can
progress to complete
- Myasthenia gravis, a rare, chronic disorder that causes weakness and rapid muscle
Muscle weakness that is slowly getting worse requires a
visit to a doctor.
Sudden muscle weakness and loss of function in
one area of the body can indicate a serious problem within the brain (such as a
transient ischemic attack) or
spinal cord or with a specific nerve in the body.