1.0 Introduction

Muscle weakness (myasthenia, asthenia or muscular debility) happens when your full effort does not produce a normal muscle contraction or movement, and can range from a brief bout of weakness to paralysis. It is sometimes referred to as reduced muscle strength, muscular weakness, and weak muscles.

Whether you are ill or you simply need rest, short-term muscle weakness will happen to nearly everyone at some point. A tough workout will exhaust your muscles until you have given them sufficient chance to recover with rest, for example.

However, if you develop persistent muscle weakness, or muscle weakness with no apparent cause or normal explanation, it may be a sign of an underlying health condition.

Voluntary muscle contractions are usually generated when your brain sends a signal through your spinal cord and nerves to a muscle. If your brain, nervous system, muscles, and/or the connections between them are injured or affected by disease, your muscles may not contract normally. This can produce muscle weakness.

It is important to remember that muscles fatigue extraordinarily fast and become less powerful. When muscles cannot move or exert force – or only to a limited extent – they are weak. This can lead to once simple tasks becoming much harder.

More than an inconvenience, muscle weakness has a domino effect on an individual’s health. It slows metabolism (how fast your body burns energy), puts more pressure on joints, hurts posture, throws us off balance, and limits our mobility.

With this in mind, it is important to understand the potential causes of muscle weakness.

It is important to note that this article contains only general information and must not be used for self-diagnosis or self-treatment, and does not replace appropriate medical advice.

Consequently, if you are suffering from muscle weakness seek medical advice so that the cause(s) of the weakness can be determined to enable targeted and tailored treatment and therapy.

2.0 What is Muscle Weakness?

The term muscle weakness can be used to describe several different things – having a wide range of meanings, including tiredness, reduced power and failure to work at all.

Muscles weakness can be categorised as follows:

• Primary or true muscle weakness;
• Muscle tiredness; and
• Muscle fatigability.

The difference between these three types of muscle weakness is often vague and you can have more than one of them. You can also progress from one to another.

However, working out which one is the main problem can help medical professionals work out what is causing it. This is because some conditions tend to cause one type of weakness rather than another.

2.1 What is Primary or True Muscle Weakness?

This manifests itself as an inability to perform what you want to do with a muscle, even the first time you try. There is a reduction in the force which the muscle can exert, however hard you try.

When this kind of weakness occurs the muscles are often floppier than usual and reduced in bulkiness. It can happen, for example, following stroke. The weakened muscles cannot move the usual load, meaning a real change in muscle power.

Diagnosing true weakness requires an examination with a medical professional.

2.2 What is Muscle Tiredness?

This is sometimes called asthenia (i.e. lack or loss of strength). It is a sense of weariness or exhaustion that you feel when using the muscle.

The muscle is not genuinely weaker, it can still do its job but it takes you more effort to manage it. This type of weakness is often seen in people who have chronic fatigue syndrome, sleep disorders, depression, and chronic heart, lung, and kidney disease.

It may be due to a reduction in the speed with which the muscle can get its energy supply.

2.3 What is Muscle Fatigability?

Some muscle tiredness is mainly muscle ‘fatigability’ – the muscle starts off normally but tires very quickly and takes longer to recover than normal.

This often goes with muscle tiredness but is particularly seen in some uncommon conditions such as myasthenia gravis and myotonic dystrophy.

However, the lack of use of certain muscles from these conditions may progress to true muscle weakness.

3.0 What are the Potential Causes of Muscle Weakness?

Muscle weakness has a variety of causes, some being more common than others, and includes (not an exhaustive list):

• Lack of use.
  • Lack of muscle fitness (deconditioning) is one of the most common causes of muscle weakness.
  • It may occur as a result of an inactive (sedentary) lifestyle.
• Age.
  • As we age, our muscles tend to lose strength and bulk and they become weaker.
  • Regular exercise can ameliorate some of the effect.
• Pregnancy.
  • During and just after pregnancy, high levels of steroids in the blood, together with a tendency to be lacking in iron (anaemia), can cause a feeling of muscle tiredness.
  • This is normal in pregnancy and whilst some exercise is still sensible, when pregnant you need to be particularly careful when exercising.
  • Remember you are carrying a weight on the front.
  • This can lead to lower back pain if you do not adapt what you do to take account of your altered posture.
• Overexertion and injury.
  • Ranging from aching muscles to rupture of a muscle fibre, for example due to sports.
• Wrong or unhealthy diet.
  • Usually from a lack of minerals and/or vitamins.
• Accidents or disorders weakening the individual’s body, confining them to bed and causing immobility.
  • For example stroke, infections or injury of the cruciate ligament in the knee, meniscus, spinal disk and back problems, hip surgery.
• Denervation can cause muscle atrophy due to non-use.
  • For example incomplete tetraplegia or peripheral nerve damage (after accident, surgery).
• Psychological disorders.
  • For example depression and anxiety.
  • Anxiety and depression are both conditions which tend to cause a sense of tiredness and ‘fatigability’ rather than true weakness.
• Myositis.
  • Soreness of voluntary muscle due to inflammation.
• Neuromuscular disorders.
  • Muscle disorders such as muscular dystrophy.
  • Neural disorders such as polyneuropathy, Parkinson’s disease, multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS).
• Carpal tunnel syndrome.
  • Compression of a nerve in the wrist.
• Autoimmune diseases, such as Graves’ disease, Guillain-Barre syndrome, and Myasthenia gravis pseudoparalytica (abnormal muscle weakness, autoimmune disorder – disturbed signal transmission between muscle and nerve).
• Certain sleep disorders.
• Thyroid conditions, such as hypothyroidism and hyperthyroidism.
• Electrolyte imbalances, such as hypokalaemia (potassium deficiency), hypomagnesaemia (magnesium deficiency), and hyperkalaemia (elevated calcium in your blood).
• Peripheral neuropathy.
  • A disease or degenerative state of the peripheral nerves in which motor, sensory, or vasomotor nerve fibers may be affected and which is marked by muscle weakness and atrophy, pain, and numbness.
• Stroke.
• Herniated disc.
• Chronic fatigue syndrome (CFS).
• Hypotonia (a lack of muscle tone that is usually present at birth).
• Peripheral neuropathy, a type of nerve damage.
• Neuralgia.
  • Acute paroxysmal pain radiating along the course of one or more nerves usually without demonstrable changes in the nerve structure.
• Polymyositis or chronic muscle inflammation.
  • Polymyositis is an inflammatory muscle disease of unknown cause that affects muscles and chiefly skeletal muscles and is characterised especially by weakness of the muscles (such as those of the shoulder, neck, or hip) closest to the trunk.
• Prolonged bed rest or immobilisation.
• A weak heart that pumps too little oxygen-rich blood to the muscles.
• Alcoholism.
  • This can cause alcoholic myopathy: a disorder of muscle tissue or muscles.

3.1 Viruses and Infections

Infections and illnesses are amongst the most common causes of temporary muscle fatigue, and is usually through muscle inflammation. Even though recovery is usual, if inflammation is severe (such as a bad bout of influenza), the weakness can last quite a while.

Muscle weakness can also be caused by complications from certain viruses and infections, including:

• Polio.
• West Nile virus.
• Rheumatic fever.
• Botulism, a rare and serious illness caused by Clostridium botulinum bacteria, can also lead to muscle weakness.

3.2 Drugs and Medication

Prolonged use of certain drugs may also result in muscle weakness, including:

• Statins and other lipid-lowering agents.
• Antiarrhythmic drugs, such as amiodarone (Pacerone) or procainamide.
• Corticosteroids, such as prednisone.
• Colchicine (Colcrys, Mitigare), which is used to treat gout.
• Some antibiotics (including ciprofloxacin and penicillin).
• Anti-inflammatory painkillers (such as naproxen and diclofenac).
• Long-term use of prescribed oral steroids also causes muscle weakness and wasting.
  • This is an expected side-effect which anyone on long-term treatment is likely to experience.
  • It is one of the reasons medical professionals try to avoid putting patients on long-term steroids if possible.
• Less commonly-used medicines which can cause muscle weakness and damage to muscles include:
  • Some heart medicines (for example, amiodarone).
  • Chemotherapy medicines.
  • Anti-HIV medications.
  • Interferon which is used in some cancers and for multiple sclerosis (MS).
  • Medicines used to treat an overactive thyroid.

4.0 How to Work Out (Diagnose) the Underlying Cause of the Muscle Weakness

If you experience muscle weakness for which there is no apparent/normal explanation, make an appointment with a medical professional.

As part of an examination (including a full medical history and physical evaluation), you will be asked about your muscle weakness, including:

• How long you have had it.
• Was there an obvious cause, such as a high impact injury (for example a fall, collision, accident or sports trauma)?
• Muscle(s) that have been affected.
• Is it getting worse, better, or staying the same.
• Are you taking any medication?
• Are you losing or gaining weight.
• Have you been experiencing dizziness?
• Family medical history.
• Symptoms such as:
  • Tenderness over the muscles;
  • Tremors;
  • Loss of strength;
  • Loss of motion (such as lifting hand over head height or rotation of the spine);
  • Muscle wastage/decrease in size.
  • Reduced/diminished reflex or absence/loss of reflex.
  • Senses.
  • Muscle tone.
  • Pain (such tingling or burning sensation).

If needed, one or more tests will be performed, including:

• CT scans or MRI to examine the inner structures of your body.
• Nerve tests to assess how well your nerves are working.
• Testing your balance and co-ordination.
• Electromyography (EMG) to test the nerve activity in your muscles.
• Blood tests (complete blood count, CBC) to check for signs of infection or other conditions (including abnormalities of hormones, salts, and blood cells).
• A muscle biopsy to see whether the muscles themselves show signs of inflammation or damage.
  • A biopsy is a procedure where a small sample is taken to look at under the microscope.
• Chemistry, EKG and chest X-ray.

The pattern and severity of weakness, associated symptoms, medication use, and family history help the medical professional to determine the cause of your weakness.

In the physical examination, the medical professional should objectively note down your loss of strength, conduct a neurological survey and search for patterns of weakness and other abnormalities.

5.0 What Treatment will I receive for my Muscle Weakness?

Once the medical professional has determined the cause of your muscle weakness, they will recommend appropriate treatment. The treatment plan will depend on the underlying cause of the muscle weakness, as well as the severity of symptoms.

As such there are a range of treatment options for the various condition that cause muscle weakness, including:

• Rest and recuperation:
  • Muscle weakness due to overexertion can usually be resolved with adequate rest, with muscle strength usually returning by itself.
  • Regular exercise builds up and strengthens muscles.
  • Following a progressive training programme can reduce the incidence of overexertion.
  • Chronic overexertion can lead to injury which may then require the skills of a physiotherapist.
• Physiotherapy (PT):
  • Physiotherapists (such as Sports or Occupational Therapists) can suggest exercises to improve your quality of life if you have conditions such as MS or ALS. For example, a physical therapist might suggest progressive resistive exercise to help someone with MS strengthen muscles that have become weak from lack of use. For someone with ALS, a physical therapist might recommend stretching and range of motion (ROM) exercises to prevent muscle stiffness.
  • Occupational therapists can advise on a range of exercises to strengthen your muscles, usually dealing with workplace causes of muscle weakness.
  • PT’s will recommend regular exercises – with or without equipment, assistive devices and/or tools – to help with day-to-day or workplace activities.
  • PT’s can recommend exercises to address weakness in one side of your body and help with motor skills.
• Electrotherapy:
  • Muscles atrophy when they are inactive, such as in cases of illness, after accidents or immobility.
  • This process can be delayed, stopped and muscles strengthened with electrically induced pulses.
  • Endurance, blood flow and mobility are also improved. Electrical signals help strengthen the muscles by causing them to contract.
  • The electrical signals triggering muscle contraction are transmitted to the muscle from the device via electrodes attached to the skin.
  • Decreasing muscle strength during immobilisation (e.g. postoperatively) and muscular imbalance are avoided.
  • Prophylaxis and therapy of muscular atrophies with electrostimulation can help avoid orthopaedic secondary injuries and shorten the period of inpatient treatment.
  • The efficiency of electrotherapy has been proven in several studies.
  • Electrotherapy should be used regularly, and application is very easy and ideal for home use.
  • Individuals can use some electrotherapy devices at home according to their medical professional’s instructions.
• Medication:
  • Over-the-counter (OTC) pain relievers, such as ibuprofen or acetaminophen, can help manage pain associated with conditions such as peripheral neuropathy, CFS, and Neuralgia.
  • Thyroid hormone replacement is used to treat hypothyroidism.
    • Standard treatment usually involves taking levothyroxine (Levoxyl, Synthroid), which is a synthetic thyroid hormone.
• Dietary Changes:
  • Changing your diet can help remedy electrolyte imbalances.
  • Take supplements such as calcium, magnesium oxide, or potassium oxide depending on your individual needs.
• Surgery:
  • Surgery may be used to treat certain conditions, such as a herniated disc or hyperthyroidism.

5.1 Symptoms versus Disorder

If muscle weakness is caused by one of the below, treatment may alleviate the symptoms but not the cause of the disorder.

• Accident or surgery.
  • For example cruciate ligament (knee), meniscus, shoulder, hip, spinal disk and back problems, or peripheral nerve damage and incomplete tetraplegia leading to denervation;
• Disorder, for example after stroke.
• Is a symptom of a neural and muscular disorder (e.g. multiple sclerosis).

6.0 Recognising Muscle Weakness as an Emergency

There are times when muscle weakness can be a sign of something very serious, such as a stroke.

If you experience any of the following symptoms, call the emergency services immediately:

• Sudden onset of muscle weakness.
• Sudden numbness or loss of feeling.
• Sudden difficulty moving your limbs, walking, standing, or sitting upright.
• Sudden difficulty smiling or forming facial expressions.
• Sudden confusion, difficulty speaking, or trouble understanding things.
• Chest muscle weakness resulting in difficulties breathing.
• Loss of consciousness.

7.0 Summary

There are many possible causes of muscle weakness, ranging from common to rare, serious to minor, temporary to permanent.

Fortunately, most cases of muscle weakness which lack obvious cause are reversible. However, muscle weakness is rarely the only sign of serious underlying disease.

If you have persisting muscle weakness, particularly if it severe, localised, painful or present for more than two to three weeks, you should visit a medical professional.

Once they have talked to you about your symptoms, they will be able to offer some guidance as to the likely cause. They will also be able to tell you if there are any serious concerns about your symptoms and will be able to refer you for further testing if required and to a physiotherapist.