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What are Common Causes of Left Arm Weakness?

By Paul Woods
Updated Mar 03, 2024
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Weakness and tenderness in the left arm can be caused by a number of different things, but injury, muscle strain, and illness tend to be the most common. People who experience weakness in only one arm should usually have the problem diagnosed by a medical expert, since this sort of isolation is often a sign that something isn’t right. The problem isn’t always serious, but fixing things before they get worse is one of the best ways for people to stay healthy. Left side weakness that isn’t treated can cause strain and fatigue in the muscles on the right side that are working harder to compensate, which often only compounds pain and discomfort.


Left arm weakness is often a consequence of some sort of injury. Any time a person breaks a bone in their left arm, wrist, or hand, for instance, he or she may feel fatigue or tingling as the body responds to the trauma. Cuts and lacerations can be causes, too, and even deep bruises can cause temporary weakness.

Sprains to the wrist and elbow have similar effects. Sprains occur when a ligament is forced to stretch beyond what is normal, and the muscular tissue gets injured as a result. In some cases a pinched nerve, which is when one of the nerves leading to the arm or hand gets twisted or “pinched” between muscles and tendons, can also result in weakness or numbness. Sprains and pinched nerves often go away on their own, but both require a period of rest for the affected area. In more serious cases some sort of rehabilitative therapy may be needed to make sure feelings of weakness don’t recur.

Weakness is often also a fairly normal part of recovering from an arm injury. Part of this owes to the actual healing process, as bone regrowth and muscle regeneration takes a lot of energy. It can also result from lack of use, as the arm may lose strength from inactivity during the more “quiet” time of recuperation.


Some normal activities, repeated again and again, can over time cause left arm weakness as well. One of the best-known repetitive-use conditions is carpal tunnel syndrome, which results from overuse of the joint supports around the wrists. People who spend a lot of time with their wrists at an “engaged” angle are most at risk for carpal tunnel; when the syndrome happens on only one side, it’s usually a result of using one hand or wrist more frequently than the other. Checkers and store clerks who constantly scan things across a barcode machine with one hand are just one example.

Tendinitis, which is overuse of the tendons supporting joints, may also be to blame. This condition can occur in the elbow, shoulder, or wrist, and usually results in a loss of strength in the arm as a whole. People can get tendinitis from repeated motion, like swinging a golf club or tennis racket, as well as from a sudden spike in muscle dependence. Someone who is normally pretty sedentary but who spends an entire day lifting heavy boxes might grow weak in their left arm as a consequence of overuse, for instance.

Illnesses and Disease

Many medical conditions can have left arm weakness as a primary or secondary symptom. Among the most critical is cardiac arrest, more commonly known as a heart attack, where acute chest pain and pressure in the chest often are accompanied by weakness in the left arm. Bursitis is another common cause that occurs when the bursae, which are compartments filled with fluid that provide padding around joints, become inflamed. This causes swelling and discomfort, and can also lead to numbness and weakness in one or both arms. Any disease or illness that causes inflammation, including the common flu, can have this effect on the arms, though most of the time these hit both together.

Degenerative conditions like Multiple Sclerosis may also lead a person to feel weakness in one arm. It is not uncommon for the sensation to switch periodically from one arm to the other, or from the arms to the legs; weakness in these cases often comes and goes as patients experience flare-ups.

Calcium deposits on the bones of the left arm or wrist can also be a cause, as can cysts and tumors; various cancers of the blood and bone can lead to weakness, too, if they are situated near a major nerve center. Major growths are usually visible on the surface of the arm, but not always. By the time something is apparent under the skin it has usually been growing for some time, which often means that it is more serious.

Prevention and Treatment

Most medical experts recommend that people come in for an evaluation if they experience weakness that lasts for more than a day or two, or any time weakness is accompanied by pain or swelling. A workup can rule out anything serious while helping form a plan of care for whatever the underlying ailment actually is.

Preventing weakness in the first place is usually a matter of playing it safe when it comes to exertion, and making sure to take rests when doing strenuous activity. There are many different ways to treat weakness depending on its cause. Protective braces can be used to minimize damage from things like repetitive use injury, and slings can help stabilize sprained or strained muscles; painkillers and muscle relaxant drugs might also be helpful, depending on the circumstances.

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Discussion Comments
By julies — On Sep 20, 2012

I slipped on the stairs and ended up having a bad sprain in my left arm. The easiest thing would have been to not do any exercises to strengthen the muscle, but I knew this would only be worse in the long run.

I didn't realize a sprain could cause so much pain, and I had some numbness in my left hand and arm for quite a while after I fell. At least I knew the reason for the numbness, and knew that if I did the right exercises, it would heal like it was supposed to.

By sunshined — On Sep 19, 2012

I work as a hair dresser and have developed carpal tunnel in my left wrist and arm. I am left handed and this is the hand and arm that is affected the most. There are many days that I have left arm weakness and numbness and am having more trouble doing my job.

I am planning on having surgery to correct this, but have also been thinking about a different line of work. I am on my feet all day long and this is hard on my feet and legs as well.

Most people I know have had good results with carpal tunnel surgery, but I think I would have even better results if I didn't go back to doing what caused it in the first place. Some days I wake up and don't have any pain or weakness in my arm, and other days it bothers me all day long.

By honeybees — On Sep 19, 2012

My mom had a stroke that affected the entire left side of her body and has left her with left arm weakness and numbness. She can do a few things with her left arm, but there isn't much strength there.

At least she is right handed, so she is used to doing most things with her right hand. She has gone through a lot of physical therapy and has improved quite a bit, but I doubt she will gain full recovery of her left arm.

By golf07 — On Sep 18, 2012

I broke my left arm one year when we were skiing and I had pain and weakness in my left arm for a long time after that. Even several years later, I don't have the strength in my left arm that I have in my right arm.

I wasn't very good about doing exercises to strengthen the muscles in my arm as it was healing. If I try to lift something with my left arm, or try to lift weights, there is a significance difference between my left arm and right arm.

Even though the break was temporary, my left arm has really never been the same since then. I no longer have the pain, but some of the weakness is still there.

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