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Weakness and Fatigue


  • Weakness means decreased muscle strength.
  • Paralysis means severe loss of strength. The child can't move a part of the body.
  • Fatigue means feeling very tired and needing extra rest. Muscle strength is normal.

Symptoms of Weakness (loss of strength)

  • True weakness always interferes with function. Once a child is walking, weakness is seen more in the legs than the arms. Reason: muscle strength is needed for normal walking.
  • Leg Weakness. This is what you will see. Examples: trouble standing, walking, climbing stairs, getting off the floor, running and jumping. If severe, the child can't stand or walk.
  • Arm Weakness. This is what you will see. Examples: trouble feeding one's self, writing/drawing/typing, combing or washing the hair. Other children have trouble lifting objects above the head, turning door knobs or buttoning shirts. If the weakness is severe, the child starts dropping objects.
  • Face Weakness. Weak face muscles cause droopy eyelids or trouble moving the eyes. A droopy face or crooked smile may also occur. You might notice trouble sucking, swallowing or speaking.
  • Weakness in Babies. In infants not yet walking, you will see the loss of motor milestones (loss of normal development). These include new trouble turning over, sitting, crawling, and pulling up. In the early months, you will see the loss of head support, reaching or kicking. A weak cry or suck also may be seen.

Causes of New Onset Muscle Weakness

  • Most causes of new onset muscle weakness are serious. True weakness points to diseases of the spinal cord or its nerves. Nerves carry messages from the spinal cord to the muscles in the arms and legs. Diseases that cause muscle weakness are very rare.
  • Most children with new onset weakness need special tests to make the right diagnosis. If the weakness gets worse, most children need to be admitted to the hospital.

Specific Causes of New Onset Muscle Weakness

  • Polio is a severe spinal cord disease that causes paralysis. It is prevented by the polio virus vaccine. Polio is almost wiped out in the entire world. There have been no cases in the US since 1979. Now, it only occurs in 2 countries.
  • Acute Flaccid Myelitis (AFM) is a rare infection of the spinal cord. It acts like polio did. It causes sudden onset of arm or leg weakness in one or more places. The main cause has been an enterovirus. There has been a rise in cases since 2014.
  • West Nile Virus myelitis. See the Mosquito Bite care guide for details. Also acts like polio did.
  • Guillain-Barre syndrome is a severe nerve weakness that starts in the feet and moves up the body over several days. It affects the same parts on both sides of the body. It can follow some viral infections.
  • Tick paralysis is a rare problem from a tick that has been attached for 5 or more days. Often it is hidden in the hair. Once the tick is removed, the weakness clears. It takes a few hours to a day.
  • Poisoning. Some types of poisoning can cause weakness, often with confusion.
  • Viral myositis. Muscle pain in the leg muscles is seen with some viral infections, such as influenza. The pain can make some children not want to walk. This is different than weakness. The muscle pain lasts a few days to a week.

When To Call

Call 911 Now

  • Hard to wake up or to keep awake. Exception: child needs normal sleep.
  • Awake but can't move
  • Trouble breathing or slow, weak breathing
  • Followed a head or neck injury
  • You think your child has a life-threatening emergency

Go to ER Now

  • Can't stand or walk
  • Confused or not alert when awake
  • Doesn't make eye contact or respond when awake
  • Crooked smile (weakness of 1 side of the face)
  • Not able to pass urine
  • Stiff neck (can't move neck normally)
  • Severe headache

Call Doctor or Seek Care Now

  • All other children with new onset of weakness
  • New onset of unsteady walking
  • Your child looks or acts very sick
  • You think your child needs to be seen, and the problem is urgent

Contact Doctor Within 24 Hours

  • Weakness is a chronic problem and getting worse
  • Fever present more than 3 days with fatigue (tires easily but no weakness)
  • You think your child needs to be seen, but the problem is not urgent

Contact Doctor During Office Hours

  • Weakness is a chronic problem and not getting worse
  • Fatigue (tires easily but no weakness) lasts more than 2 weeks
  • Delays in motor development (sitting, crawling, walking)
  • You have other questions or concerns

Self Care at Home

  • Normal fatigue during a short-term illness (tires easily and needs more rest, but no true weakness)
  • Normal fatigue after hard work or sports

Care Advice

What You Should Know About Normal Fatigue (feeling very tired) When Sick:

  • Children who are sick are often less active.
  • They become easily tired and need extra rest. They take extra naps and sleep longer hours for many days. As long as your child is alert when awake, extra sleeping is normal.
  • This is different than the normal fatigue from exercise. Examples are a soccer game, manual labor or a long hike. This type of fatigue does not last long. It responds to a good night's sleep.
  • Sick children also are less hungry for meals but like to drink fluids. As long as they stay hydrated, this is normal.
  • Here is some care advice that should help.

Trust Your Child to Choose the Right Activity Level:

  • When they are awake, most sick kids want to watch TV. Some want to play with their toys. A few may want to play outside. That's also fine.
  • If they are feeling badly, they may just want to rest. They may prefer to stay in bed or on the sofa for a day or two.
  • As long as they are alert and able to walk normally, this is normal.

Avoid Trying to Force Bed Rest When Awake:

  • Most children sleep extra hours when they are sick with any infection. Their body tells them how much sleep they need. Getting enough sleep helps them fight the infection. Let them choose the amount.
  • Trying to force extra bed rest is not helpful for common childhood illness.
  • It doesn't reduce symptoms.
  • It doesn't help the body heal faster.
  • It doesn't shorten how long the illness lasts.
  • It doesn't prevent complications.
  • Bed rest also can't be enforced in children who don't want it.
  • An old myth was that sick children must stay in bed until their fever is gone. This is not true.

Return to School:

  • Your child can go back to school after the fever is gone and the fatigue is mild.
  • Your child should also feel well enough to join in normal activities.

What to Expect:

  • Being very tired during the first 2 or 3 days of an infection is normal.
  • Energy is often back to normal within 7 days.
  • After a major sickness like mono, it may take 2 weeks.

Call Your Doctor If:

  • Weakness (loss of muscle strength) occurs
  • Fever lasts more than 3 days
  • Extra sleepiness lasts more than 1 week
  • Fatigue (very tired) lasts more than 2 weeks
  • You think your child needs to be seen
  • Your child becomes worse


Barton Schmitt MD, FAAP
Disclaimer: this health information is for educational purposes only. You, the reader, assume full responsibility for how you choose to use it.
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