Cerebral palsy (CP) affects far more than movement. The underlying brain injury disrupts signals to muscles throughout the body, and over time those disrupted signals create a cascade of effects on bones, joints, digestion, breathing, and energy levels. An estimated 5 million children under five worldwide have CP, making it the most common motor disability in childhood. Here’s how it changes the body, system by system.
How CP Changes Muscles and Muscle Tone
The core problem in cerebral palsy is that a brain injury, usually occurring before or during birth, sends abnormal signals to the muscles. Most children with CP have the spastic type, where muscle stiffness increases in proportion to how fast a limb is moved. This velocity-dependent stiffness is why a child’s arm or leg may feel loose when moved slowly but locks up with quicker movement. Other children have low muscle tone (hypotonia), which makes their limbs feel floppy, or involuntary movements that are harder to control.
Over time, the affected muscles undergo changes at the cellular level that go well beyond simple “tightness.” The individual muscle fibers become overstretched and fewer in number, reducing the muscle’s force-generating capacity to roughly 17 to 48 percent of what a typical muscle can produce. Connective tissue and fat infiltrate the muscle, replacing functional tissue. These internal changes, combined with muscle growth that can’t keep pace with bone growth, eventually cause permanent shortening called contractures. Once a contracture develops, the joint it crosses loses range of motion regardless of how much stretching you do, because the problem is structural, not just a matter of tone.
Bone and Joint Complications
Because muscles pull on bones as a child grows, abnormal muscle forces gradually reshape the skeleton. The hip joint is especially vulnerable. In children with CP who cannot walk independently, the ball of the hip is progressively pulled out of its socket by tight or imbalanced muscles around the joint. Clinicians track this using a measurement called migration percentage, which captures how much of the femoral head sits outside the hip socket. Once that number crosses 30 percent, the hip is considered “at risk” and needs close monitoring. Without intervention, the joint can fully dislocate, causing significant pain and making sitting difficult.
The spine is also affected. Poor trunk muscle control and asymmetric muscle pull can lead to scoliosis, particularly in children who spend most of their time in a wheelchair. A curved spine doesn’t just limit posture. It compresses the lungs on one side, which compounds the breathing problems described below. Over a lifetime, abnormal loading on joints also accelerates arthritis, especially in the hips, knees, and ankles.
Breathing and Lung Health
Respiratory illness is the leading cause of hospitalization and the most common cause of early death in people with severe CP. Several factors converge to make the lungs vulnerable. Poor postural control and spinal deformity restrict how far the chest wall can expand, physically limiting lung capacity. A weak cough, caused by the same muscle coordination problems that affect the limbs, means mucus sits in the airways instead of being cleared. That retained mucus breeds chronic inflammation and recurrent infections.
On top of this, many people with CP aspirate, meaning food, liquid, or saliva enters the airway instead of the stomach. The motor control issues that cause difficulty walking also affect the lips, tongue, and throat muscles involved in swallowing. Repeated aspiration leads to a specific type of lung infection called aspiration pneumonia, which can become a recurring problem throughout life.
Swallowing, Digestion, and Nutrition
Swallowing difficulties affect a large proportion of people with CP. In one study, nearly 65 percent of children with CP experienced “false routes” during swallowing, where food or drink entered the wrong passage, particularly while drinking liquids. This makes mealtimes slow, exhausting, and sometimes dangerous. Children who struggle to swallow often take in too few calories, leading to chronic undernutrition that further weakens muscles and bones.
Gastroesophageal reflux, where stomach acid flows back into the esophagus, adds another layer of difficulty. Reflux causes discomfort that can make a child refuse food entirely, and repeated vomiting means even successfully swallowed nutrients are lost. Constipation is also strikingly common, affecting more than half of children with CP in study populations. Reduced physical activity, low fluid intake, and impaired coordination of the muscles lining the gut all contribute. Together, these digestive problems create a cycle where poor nutrition worsens muscle weakness, which in turn makes feeding harder.
Vision, Hearing, and Communication
Because CP originates from a brain injury, the sensory processing areas of the brain can be affected alongside the motor areas. About 1 in 10 people with CP has a severe vision impairment. The most common form is cortical visual impairment, where the eyes themselves may work fine but the brain has trouble interpreting what they see. This can look like difficulty tracking moving objects, problems with depth perception, or inconsistent visual responses depending on fatigue or the complexity of a scene.
Hearing loss also occurs at higher rates than in the general population, particularly when CP results from prematurity or newborn jaundice. Speech is often affected as well, not because of intellectual disability but because the same muscle coordination problems that affect limbs also affect the small, precise muscles of the mouth, tongue, and vocal cords. The resulting speech pattern, called dysarthria, can range from mildly slurred to unintelligible, even when the person’s language comprehension and cognitive ability are fully intact.
Energy Expenditure and Fatigue
People with CP use dramatically more energy to do everyday tasks. According to the National Institute of Neurological Disorders and Stroke, people with CP may use up to five times the energy of their peers just to walk and move around. Research comparing adults with spastic CP to healthy controls confirmed significantly higher oxygen consumption during walking, with those who have involvement in both legs (spastic diplegia) paying the steepest energy cost.
This means that what looks like a short walk across a room can be the metabolic equivalent of a brisk jog for someone without CP. The result is chronic fatigue that accumulates over years. Many adults with CP describe hitting a wall in their 30s or 40s, where activities they managed in their twenties become unsustainable. This is part of a recognized pattern called post-impairment syndrome, a combination of pain, fatigue, and progressive weakness driven by decades of compensatory movement, repetitive strain on joints, and early-onset arthritis.
How Severity Varies Across the Spectrum
CP exists on a wide spectrum. The Gross Motor Function Classification System (GMFCS) divides mobility into five levels, and where a person falls on this scale largely predicts which secondary complications they’ll face. At Level I, children walk without restrictions but may struggle with advanced motor skills like running or jumping. At Level V, independent movement is extremely limited even with assistive technology, and the person depends on others for nearly all positioning and transport.
Children at GMFCS Levels IV and V face the highest risk of hip displacement, scoliosis, respiratory complications, and swallowing difficulties. But even those at milder levels experience the energy penalty, joint wear, and pain that accumulate over a lifetime of moving with altered mechanics. The brain injury itself doesn’t worsen over time, but its effects on the growing and aging body very much do, which is why proactive monitoring of hips, spine, nutrition, and lung health matters at every stage of life.