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 may involve the arms, hands, legs, face, neck, or trunk. or a combination.

Stroke is the most common cause of hemiparesis; about 80% of stroke survivors experience it.A stroke occurs when brain cells are damaged due to insufficient blood and oxygen supply. People who have hemiparesis are still able to move the affected side of the body, but with limited strength.

This article will explore additional causes of hemiparesis, its common symptoms, and the treatment and recovery process.

Hemiparesis Symptoms

Laura Porter / Verywell


Hemiparesis is a common result of injuries or disease of the nervous system, which includes the brain, spinal cord, and nerves. In addition to stroke, hemiparesis can be caused by a number of other medical conditions:

  • Traumatic brain injury, such as from a fall, sports injury, or car accident
  • Arthritis-related changes or trauma that affects the spinal cord or spinal motor nerves
  • A tumor, or abnormal growth of tissue, of the brain or spinal cord
  • Autoimmune disorders in which the immune system attacks the nervous system, such as multiple sclerosis (MS)
  • Medical conditions that are present from birth, such as cerebral palsy, affect the ability to walk and move
  • Infection of the brain, spinal cord, or meninges (protective tissue that covers the brain and spinal cord)
  • Postictal paralysis, which is temporary weakness after a seizure
  • Psychological and psychiatric conditions that can cause temporary weakness


Hemiparesis is weakness of one side of the body. Symptoms correspond to the side of the brain or spinal cord 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 spinal cord injury and the level of injury within the spinal cord, hemiparesis may involve the same side of the body as the spinal cord injury or may involve the opposite side.

Consequences of hemiparesis also can include:

  • 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

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.


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

One side of the body may become completely weak; this condition is called hemiplegia.

Diagnosis of the cause of hemiparesis or hemiplegia can also be confirmed with imaging of the brain or spine and may include:

  • Computerized tomography (CT) scan, which uses multiple X-rays and a computer to get three-dimensional view
  • Magnetic resonance imaging (MRI), which uses a magnetic field and computer to get two- or three-dimensional images

Treatment and Recovery

Treatment of hemiparesis is first directed towards targeted treatment of the cause, whether it's a stroke, brain tumor, infection, or another condition.

The goal of long-term treatment of hemiparesis is to strengthen motor skills and coordination and to improve your ability to manage everyday activities. Recovery and partial recovery from hemiparesis is possible with rehabilitation and therapy.

Therapy and Rehabilitation

Physical and occupational therapy are often important in the short-term and long-term recovery process. It can help stroke survivors regain movement even years after the stroke.

Therapy and rehabilitation may include:

  • Modified constraint-induced therapy (mCIT), a practice of using the weakened part of the body and limiting use of the unaffected side of the body
  • Electrical stimulation, which involves placing small electric pads on weakened muscles to give an electric charge that forces the muscle to contact
  • Cortical stimulation, which sends electrical currents to the brain during exercises
  • Mental imaginary, which involved dedicated visualization practices where you imagine you're moving the weakened side of the body
  • Assistive devices, such as braces, canes, walkers, and wheelchairs and practicing activities using these devices

Home Modifications

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


Hemiparesis is a weakness of one side of the body that can make mobility and everyday activities difficult. It commonly occurs due to injuries or conditions that affect the nervous system, and the most common cause is stroke.

Therapy and rehabilitation are an important part of the recovery process and can help with strength and mobility improvements over time.

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. Weiss TC. Hemiparesis - types, treatment, facts and information. Disabled World.

  3. American Stroke Association. Hemiparesis.

  4. Naqvi U, Sherman Al. Muscle strength grading. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.

By Jose Vega MD, PhD
Jose Vega MD, PhD, is a board-certified neurologist and published researcher specializing in stroke.