A possible cause of sudden muscle weakness in one or both legs is stroke, which is a potentially fatal condition that reduces oxygen supply to the brain, states Healthgrades. Other potential causes of leg weakness include sciatica, injury, neuromuscular diseases, toxins and medications.
Some people experience weakness throughout the body, including the legs, whereas others develop weakness in either or both legs, notes Healthgrades. In some cases, muscle weakness results from tiredness and does not indicate an underlying condition.
Sudden leg weakness is typically a symptom of stroke, especially if it occurs on a single side of the body or manifests along with other severe symptoms, such as vision loss or changes, a numb sensation, paralysis or intense headache, says Healthgrades. Symptoms of stroke also include high fever, inability to urinate, loss of bowel control, fainting and lethargy. To prevent severe complications, a person should contact a health care professional immediately if any of these signs and symptoms occur.
Leg weakness is a common symptom of spinal conditions, such as arthritis of the spine, herniated disc and spinal cord injury, according to Healthgrades. People with spinal conditions typically experience pain, numbness, burning or a tingling feeling in the area of the affected nerve. Individuals who have a sprain, strain, fractured bone, or other bone, muscle or joint injury also suffer leg weakness.