Common causes of muscle weakness in the legs include sciatica and stroke, according to Healthgrades. Lack of leg strength is also characteristic of diseases like multiple sclerosis and myasthenia gravis.
The sciatic nerve extends from the lower back down each leg, MedlinePlus explains. If the nerve is damaged or pinched, sciatica develops. Its other symptoms include pain along one side, numbness and difficulty walking. Sciatica is sometimes caused by a slipped disc, tumor or pelvic injury.
Sudden leg weakness, especially if it is limited to one side of the body, is a potential sign of stroke, warns Healthgrades. In stroke cases, weakness often occurs with blurred or double vision, numbness, paralysis, incontinence, fainting or severe headache.
Leg weakness is an early symptom of multiple sclerosis, WebMD states. This is sometimes accompanied by balance problems, numbness and fatigue that make walking challenging. Other initial signs of MS include blurred or double vision, poor coordination, tingling sensations and difficulty thinking.
Myasthenia gravis is an autoimmune disease that affects muscle control throughout the body, the Muscular Dystrophy Association reports. Typically, muscles in the face, neck and jaw are affected first. Limb weakness occurs as the disease progresses. When muscles tire, controlling them is more difficult. Rest reduces symptoms.