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Loss of Strength / Weakness
Weakness refers to loss of muscle strength where people can't move a muscle normally despite trying as hard as they can. However, the term is often misused when people with normal muscle strength say they feel weak when they feel tired or when their movement is limited because of pain or joint stiffness.

For a person to intentionally move a muscle (called a voluntary muscle contraction), the brain must generate a signal that travels a pathway from:
The brain
Through nerve cells in the brain stem and spinal cord
Through nerves from the spinal cord to the muscles (called peripheral nerves)
Across the connection between nerve and muscle (called a neuromuscular junction)

Also, the amount of muscle tissue must be normal, and the tissue must be able to contract in response to the signal from the nerves. Therefore, true weakness results only when one part of this pathway (brain, spinal cord, nerves, muscles, or the connections between them) is damaged or diseased.

Weakness may develop suddenly or gradually. Weakness may affect all of the muscles in the body (called generalized weakness) or only one part of the body. For example, depending on where the spinal cord is damaged, spinal cord disorders may cause weakness only of the legs.

Symptoms depend on which muscles are affected, like when weakness affects muscles of the chest, people may have difficulty breathing or when weakness affects muscles that control the eyes, people may have double vision. Complete muscle weakness causes paralysis. People may have other symptoms depending on what is causing the weakness. Weakness is often accompanied by abnormalities in sensation, such as tingling, a pins-and-needles sensation, and numbness.

Muscle weakness is very common in multiple sclerosis (MS) and can occur in any part of the body. It can range from specific parts that are always tired or become tired easily to your entire body. You can have a great nights rest and when you awaken, you feel as if you just ran a marathon or stayed up all night. There are many factors that can be causing this but the end result is that you are "wiped out" from the start of the day. When you are already tired, it becomes very difficult to stay active or even exercise. Just remember that you have to work hard and stay going because either you use it or loose it.

Causes of Weakness

Because malfunction in the same part of the signal pathway causes similar symptoms regardless of cause, the many causes of muscle weakness are usually grouped by the location of the cause. That is, causes are grouped as those that affect the brain, spinal cord, peripheral nerves, muscles, or connections between nerves and muscles. However, some disorders affect more than one location.

Causes differ depending on whether weakness is generalized or affects only specific muscles. The most common causes of generalized weakness are:
A decrease in general physical fitness (called deconditioning), which may result from illness and/or a decrease in physical reserves (frailty), such as muscle mass, bone density, and the heart's and lungs' ability to function, especially in older people
Loss of muscle tissue (wasting or atrophy) due to long periods of inactivity or bed rest, as occurs in an ICU
Damage to nerves due to a severe illness or injury, such as severe or extensive burns
Certain muscle disorders, such as those due to a low level of potassium (hypokalemia), consumption of too much alcohol, or use of corticosteroids
Drugs used to paralyze muscles, like those to keep people from moving during surgery or while on a ventilator

The most common causes of weakness in specific muscles are:
Strokes (the most common cause of weakness affecting one side of the body)
A pinched nerve, as occurs in carpal tunnel syndrome
A ruptured or herniated disk in the spine
Pressure on or compression of the spinal cord, as can result from cancer that has spread to the spinal cord
Multiple sclerosis

Many people report weakness when their problem is actually fatigue. Common causes of fatigue include a severe illness, cancer, a chronic infection (such as HIV infection, hepatitis, or mononucleosis), heart failure, anemia, chronic fatigue syndrome, fibromyalgia, mood disorders (such as depression), and MS.

Managing Weakness

The first step in managing weakness effectively is to determine what is most likely causing it.
Deconditioning of muscles results from lack of use. Often in MS, due to fatigue, pain, imbalance, or other symptoms, a person's overall activity level is reduced. Lack of activity will cause the muscles affected by MS, as well as those that are not affected by the disease, to become weak. For this type of weakness, progressive resistive exercise with weights can be very effective. A physical therapist can recommend a weight-training program that fits abilities and limitations.
Damage to the nerve fibers (demyelination) in the spinal cord and brain that stimulate the muscles can also cause weakness. The muscles are not receiving the nerve impulses they require in order to work effectively – which often results in a reduction in endurance. Because the source of this type of weakness is impaired nerve conduction, weight training to strengthen the affected muscles isn't effective and may even increase feelings of weakness and fatigue. The recommended strategy is to maintain the tone of those muscles that are not receiving adequate nerve conduction with regular use, while working to strengthen the surrounding muscles that are receiving adequate conduction. A physical therapist can work to identify the sources of your weakness and recommend appropriate strategies to manage them.

Weakness in the legs, ankles and feet can interfere with walking. Management strategies to address walking problems include exercise, assistive devices and medication. Weakness in the upper body and arms can interfere with activities of daily living and self-care. Occupational or physical therapists can recommend appropriate exercises for your arms and hands, as well as tools and devices to assist with activities in the home and at work.

Many will lose muscle strength in the arms and legs as the disease progresses. Muscle weakness can involve the extremities (arms and legs) on one side of the body (hemiparesis), both legs (paraparesis), or all four extremities (quadraparesis). Muscles in the affected area may tighten (spasticity) and contract spontaneously (spasm or clonus). The loss can range from reduced dexterity to paralysis of an arm or leg. The loss of muscle strength occurs not only in the for of relapses, but also as a gradual process without recovery. Depending on the severity, an assistive devise may be required.

Respiration

Respiration or breathing is primarily under the control of the autonomic nervous system (ANS) which is the part of the central nervous system (CNS) that controls vital functions such as heartbeat and respiration without conscious thought. It's unusual for MS to affect the ANS and therefore uncommon for breathing problems to occur in MS as a direct result of loss of autonomic control. If breathing problems occur suddenly, it's imperative to see your doctor immediately or go to the emergency room since this may indicate infection or some other problem.

Weakness of the ventilatory muscles can begin early in the disease. In MS, the most common cause of respiratory problems is loss of muscle strength and endurance. Just as a person can experience muscle weakness in the arms or legs, weakness can occur in the ventilatory muscles of the chest and abdomen that are involved in breathing. Just like weakness in the other parts of the body, weakness of the ventilatory muscles can begin to occur early in the disease course and gradually worsen over time.

Certain medications may also contribute to respiratory problems such as tranquilizers, muscle relaxants, and opioid analgesics, can depress breathing. The use of these medications should be carefully monitored in anyone with a history of respiratory distress or swallowing problems.

Respiratory changes can also contribute to other problems. People with weakened ventilatory muscles have to work harder to inhale and exhale. This extra effort can be quite tiring, particularly for people who already experience a significant amount of MS fatigue. Respiratory problems can also interfere with the process of speech and voice production making it much more difficult and tiring for people to carry on a conversation or speak loudly enough to be heard.

Testing Muscle Strength

First, doctors try to determine whether people are weak or simply tired. If people are weak, doctors then determine whether the weakness is severe enough or worsening quickly enough to be life threatening.

In people with weakness, the following symptoms are cause for concern:
Weakness that develops over a few days or less
Difficulty breathing
Difficulty raising the head while lying down
Difficulty chewing, talking, or swallowing
Loss of the ability to walk

Doctors test muscle strength by asking the person to push or pull against resistance or to do maneuvers that require strength, such as walking on the heels and tiptoes or rising from a chair. Sometimes weakness is evident when a person uses one limb more than another (for example, when swinging the arms while walking or when holding the arms up with the eyes closed). Knowing which body parts are weak (the pattern of weakness) can help doctors identify what the problem is.

Bladder and Bowel
MS can involve the nerves responsible for involuntary actions of the bladder and intestines. Those with MS may often have constipation and urinary retention. These symptoms may lead to other complications, such as infections of the bladder, kidney, or blood. Dysfunction in the workings of the bladder or bowels occurs in up to 80% of people with MS.

Bladder dysfunction in MS happens when nerve signals to the bladder and urinary sphincter (the muscles surrounding the opening to the bladder) are blocked or delayed because of lesions on the spinal cord. The dysfunction can be for two reasons: the bladder is spastic, so it isn’t holding the urine, or the bladder isn’t emptying all the way, because the sphincter is spastic (contracting when it's supposed to be relaxing to let out the urine, or vice versa).

If bladder dysfunction is left untreated, it can cause permanent damage to the urinary tract. This happens when there's incomplete emptying of the bladder and urine is retained, resulting in both urinary tract infections and formation of stones from minerals which collect. Constantly leaking urine can result in skin breakdown and infection. In addition, bladder dysfunctions often result in people avoiding socializing and restricting their normal daily activities.

Bladder symptoms can appear as:

Hesitancy

There is an urge to urinate, but it takes a long time to begin to urinate or it's difficult to keep the urine flowing. Sometimes, the attempt is even "dry," meaning no urine is released at all.

Urgency

The need to urinate comes on suddenly and strongly and may be accompanied by an uncomfortable "full" feeling in the bladder.

Frequency

There's a need to urinate much more often than usual. This often happens at night, causing sleep disturbances.

Incontinence

This can either feel like a sudden urge to urinate, followed by the flow starting immediately before there's a chance to react, or dribbling or leaking with no warning or sensation.

Bowel symptoms usually manifest as constipation, although diarrhea and incontinence can also occur. Many of these types of symptoms can be managed with medications, combined with modifications in diet, fluid intake and habits. Dysfunction occurs in almost two thirds of patients during the disease course.