Muscle weakness on one side of the body and what causes it

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Hemiparesis is partial weakness on one side of the body. It can affect either the left or right side of the body. The weakness may involve the arms, hands, legs, face or a combination. About 80% of stroke survivors experience hemiparesis, making it one of the most common effects of a stroke.

People who have hemiparesis are still able to move the affected side of the body, but with limited strength. One side of the body may become completely weak, and this condition is called hemiplegia.

Hemiparesis Symptoms

Laura Porter / Verywell


The most obvious symptom of hemiparesis is the partial paralysis of one side of the body. Symptoms correspond to the side of the brain or spine that has been damaged.

An injury to the left side of the brain typically results in weakness on the right side of the body. An injury to the right side of the brain typically results in weakness on the left side of the body.

Depending on the type of spine injury and the level of injury within the spine, hemiparesis may involve the same side of the body as the spine injury or may involve the opposite side.

Some symptoms of hemiparesis include the following:

  • Inability to maintain balance
  • Difficulty walking
  • Inability to grasp objects
  • Decreased precision in movement
  • Muscle fatigue
  • Lack of coordination
  • Leaning to one side while standing, walking or sitting
  • Loss of bowel or bladder control


In addition to stroke, hemiparesis can be caused by a number of other medical conditions. The most common causes of hemiparesis are the following:

  • Stroke
  • Multiple sclerosis
  • Traumatic injury: May affect the brain, spine or nerves
  • Congenital medical conditions such as cerebral palsy that are present from birth
  • Spine disease
  • A tumor of the brain or spine
  • Infection of the brain, spine or meninges
  • Psychological and psychiatric conditions (can cause temporary weakness)
  • Postictal paralysis: Temporary weakness after a seizure
  • Inflammatory and autoimmune conditions


If you complain of any symptoms of hemiparesis, your healthcare provider will do a physical examination. It can be difficult to determine whether your symptoms are the result of weakness, pain, or another cause.

The physical examination includes a test of your reflexes, sensation, and strength. Your healthcare provider will rate your strength on a scale of 1-5. This rating can also help when the same healthcare provider or other healthcare providers assess your strength at a later time, as it can be used as a comparison.

Muscle Strength Rating Scale

The rating scale for muscle strength is as follows:

  • 0/5: No movement
  • 1/5: Mild muscle twitching
  • 2/5: Movements from side to side, but cannot lift the arm or leg up against gravity
  • 3/5: Can move up against gravity, but not against any force, such as mild pushing by the examiner
  • 4/5: Can move against force, such as pushing by the examiner, but not with normal expected strength
  • 5/5: Can move against force with expected strength

Diagnosis of the cause of hemiparesis can also be confirmed with imaging studies, which may include the following:


Treatment of hemiparesis is first directed towards targeted treatment of the cause, whether the cause is a stroke, a brain tumor, or an infection, etc. The goal of long-term treatment of hemiparesis is to strengthen motor skills and coordination and to improve your ability to manage everyday activities.


Physical and occupational therapy are important in the recovery of hemiparesis. Therapy may include the use of electrical stimulation to the brain, imagery, and the use of assistive devices such as a cane, walker or wheelchair.

Modifications to the home may need to be made to accommodate and help increase mobility. Some of the modifications may include:

  • Grab bars
  • Ramps
  • Raised toilet seats
  • A bench in the tub
  • Non-slip adhesive strips in the bathtub
  • Electric toothbrushes
  • Electric razors

Fortunately, hemiparesis is not a progressive condition unless there is evidence of an aggressive, growing brain tumor.

A Word From Verywell

Hemiparesis is a common manifestation of neurological disease. Most often affecting the arms, legs, or both, hemiparesis makes it difficult to maintain a normal level of independent daily activities, and it is one of the leading causes of disability

Stroke is the most common cause of hemiparesis, and that is why stroke prevention is an important part of healthy living that everyone should know about.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Cogollor JM, Rojo-Lacal J, Hermsdörfer J, et al. Evolution of cognitive rehabilitation after stroke from traditional techniques to smart and personalized home-based information and communication technology systems: literature reviewJMIR Rehabil Assist Technol. 2018;5(1):e4. doi:10.2196/rehab.8548

  2. American Stroke Association. Hemiparesis. Updated April 8, 2019.

  3. Weiss TC. Hemiparesis - types, treatment, facts and information. Disabled World. Updated January 17, 2017.

  4. Naqvi U, Sherman Al. Muscle strength grading. Treasure Island, FL: StatPearls Publishing. Updated July 1, 2019.