Causes of weakness in legs

Weakness in the legs can be caused by many conditions and diseases. Weakness means there is less strength in the muscles than there should be. Some people mistake fatigue as weakness, but technically in the medical world, they aren't the same.

People with the flu or cancer, for example, may say they feel weak when they're referring to sluggishness. Weakness in the legs is a symptom of injuries, neuromuscular diseases, toxins and metabolic diseases.

Addison's Disease

Addison's disease is a hormonal disorder that causes muscle weakness, fatigue, weight loss, darkening of the skin and low blood pressure. Men and women can get it, not matter what their age. It occurs when your adrenal glands fail to make enough cortisol and perhaps aldosterone. Symptoms tend to start slowly. In addition to the physical changes noted above, people with Addison's disease can also be irritable and depressed.

Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS), better known as Lou Gehrig's disease, is a motor neuron disease that progresses very fast. There is no cure, and ALS is eventually fatal. ALS targets and attacks the neurons in your brain, spinal cord and brainstem that control voluntary muscles. The upper and lower motor neurons die off and stop sending signals to your muscles. This causes the muscles to become weak, atrophy and twitch. All muscles are vulnerable to ALS. Patients can no longer move their legs, arms and body and eventually lose the ability to breathe.

Multiple Sclerosis

Multiple sclerosis (MS) causes the degeneration of the central nervous system's nerves. In addition, the myelin, which insulates the nerves, disappears. This causes the electrical impulses along the nerves to slow down because they are damaged. As this continues, the basic functions controlled by your nervous system start to deteriorate. Seeing, talking, writing, walking and memory become difficult. Early symptoms of MS include muscle weakness, difficulties with balance, muscle numbness or fatigue, and vision problems.

Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth disease (CMT) is a very common inherited neurological disorder. It's named after the doctors who identified it in the 1800s. CMT makes up several conditions that affect your peripheral nerves, which are outside the spinal cord and brain. CMT affects sensory and motor nerves. It's common to experience weakness in your lower leg muscles or foot. This can cause a high-stepped walk or a foot drop, along with frequent falls or tripping. The small muscles in your feet are so weak, there may be deformities such as hammertoes or high arches. The lower part of the legs also lose muscle mass, so they take on a skinny appearance. As CMT progresses, hands may start to feel weak and muscles may atrophy.


Polymyositis is a muscle disease in which the fibres become inflamed. It's not known how it's caused, but the white blood cells suddenly invade the muscles, especially the ones in the torso or trunk. This causes weakness that fluctuates between remission and severe flareups. The most common symptom at the onset of the disease is weakness of the muscles closest to the trunk. They begin to lose power and atrophy. Climbing stairs, standing up and lifting can be very difficult.

Back Problems

It's not uncommon for leg or foot pain to be caused by an issue in the lower back. The nerves in the back may be compressed or under pressure. This doesn't necessarily cause pain in the back, but instead the pain and weakness show up in the lower extremities. That's because the nerves travel down the legs. Leg pain and its symptoms are usually referred to as sciatica. Common descriptions of leg pain include a heavy feeling or weakness that conflicts with movement. You may feel like you need to drag your leg. Legs move much slower than they used to, especially when climbing stairs.