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.
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.
Fatigue is a feeling of tiredness,
exhaustion, or lack of energy. You may feel mildly fatigued because of
overwork, poor sleep, worry, boredom, or lack of exercise. Any illness, such as
a cold or the flu, may cause fatigue, which usually goes away as the illness
clears up. Most of the time, mild fatigue occurs with a health problem that
will improve with home treatment and does not require a visit to a
A stressful emotional situation may also cause fatigue.
This type of fatigue usually clears up when the
stress is relieved.
Many prescription and
medicines can cause weakness or fatigue. The use or
abuse of alcohol, caffeine, or illegal drugs can cause fatigue.
visit to a doctor usually is needed when fatigue occurs along with more serious
symptoms, such as increased breathing problems,
signs of a serious illness, abnormal bleeding, or unexplained weight loss or
Fatigue that lasts longer than 2 weeks usually requires a
visit to a doctor. This type of fatigue may be caused by a more serious health
problem, such as:
A decrease in the amount of oxygen-carrying
substance (hemoglobin) found in red blood cells (anemia).
disorders, such as
diabetes, in which sugar (glucose) remains in the
blood rather than entering the body's cells to be used for
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 skin.
A high thyroid level
(hyperthyroidism) can cause fatigue, weight loss, increased heart rate,
intolerance to heat, sweating, irritability, anxiety, muscle weakness, and
Kidney disease and liver disease, which cause
fatigue when the concentration of certain chemicals in the blood builds up to
If fatigue occurs without an
obvious cause, it is important to evaluate your mental health. Fatigue is a
common symptom of mental health problems, such as
depression. Fatigue and depression may become so
severe that you may consider suicide as a way to end your pain. If you think
your fatigue may be caused by a mental health problem, see your doctor.
Neurological symptoms—which may be
signs of a problem with the nervous system—can affect many body functions.
Symptoms may include:
Numbness, weakness, or lack of movement in your
face, arm, or leg, especially on only one side of your body.
Trouble seeing in one or both eyes.
Confusion or trouble understanding simple statements.
Problems with balance or coordination (for example, falling down
or dropping things).
Heartbeat changes can include:
A faster or slower heartbeat than is normal for
you. This would include a pulse rate of more than 120 beats per minute (when
you are not exercising) or less than 50 beats per minute (unless that is normal
A heart rate that does not have a steady
Symptoms of serious illness in a baby
may include the following:
The baby is limp and floppy like a rag doll.
The baby doesn't respond at all to being held, touched, or talked
The baby is hard to wake up.
Symptoms of a heart attack may
Chest pain or pressure, or a strange feeling in the chest.
Nausea or vomiting.
Pain, pressure, or a
strange feeling in the back, neck, jaw, or upper belly, or in one or both
shoulders or arms.
Lightheadedness or sudden
A fast or irregular heartbeat.
The more of these symptoms you have, the more likely it is that
you're having a heart attack. Chest pain or pressure is the most common
symptom, but some people, especially women, may not notice it as much as other
symptoms. You may not have chest pain at all but instead have shortness of breath, nausea, numbness,
tingling, or a strange feeling in your chest or other areas.
Many prescription and nonprescription drugs can cause
weakness and fatigue. A few examples are:
blood pressure medicines.
Statin medicines for high
Seek Care Now
Based on your answers, you may need care right away. The problem is likely to get worse without medical care.
Call your doctor now to discuss the symptoms and
arrange for care.
If you cannot reach your doctor or you don't have
one, seek care in the next hour.
You do not need to call an
You cannot travel safely either by driving
yourself or by having someone else drive you.
You are in an area
where heavy traffic or other problems may slow you down.
Change in Heartbeat
Make an Appointment
Based on your answers, the problem may not improve without medical
Make an appointment to see your doctor in the
next 1 to 2 weeks.
If appropriate, try home treatment while you
are waiting for the appointment.
If symptoms get worse or you have
any concerns, call your doctor. You may need care sooner.
If you have generalized weakness
and fatigue along with other symptoms, evaluate those symptoms. Home treatment
for your other symptoms usually will improve your weakness and fatigue. Mild
generalized weakness and fatigue that occur with a
viral illness usually improve with the following home
Get extra rest while you are ill. Let your
symptoms be your guide.
If you have a cold, you may be able to stick
to your usual routine and just get some extra sleep.
If you have
the flu, you may need to spend a few days in bed.
Return to your usual activities slowly to avoid
prolonging the fatigue.
How this information was developed to help you make better health decisions.