The term muscle weakness
can be used to describe several different things.
Muscle weakness is a
lack of muscle strength. The causes are many and can be divided into conditions
that have either true or perceived muscle weakness.
Causes of muscle pain
fall into a few general groups, as follows: injury or overuse; stress;
autoimmune disease; neurological and muscle disorders; infection; obstructed
blood flow, or drug side effects.
Muscle weakness is
commonly due to lack of exercise, ageing, muscle injury or pregnancy. It can also
occur with long-term conditions such as diabetes or heart disease. There are
many other possible causes, which include stroke, multiple sclerosis,
depression, fibromyalgia and chronic fatigue syndrome (ME).
1) 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. If muscles are not used
then the fibres within the muscles are partially replaced with fat. Muscle
wasting will eventually occur: muscles become less chunky and more floppy. Each
fibre is just as strong but there aren’t so many of them and they don’t
contract so effectively.
Muscle power is
greatest and recovery times are shortest in our 20s and 30s. This is why most
great athletes are in this age range. However, building of muscles through
regular exercise can be done at any age. Many successful long-distance runners
are aged over 40. Muscle tolerance for prolonged activity such as marathon
running remains high for longer than the powerful, short-burst activities like
sprinting.
2) Ageing
As we age, our muscles
tend to lose strength and bulk and they become weaker.. However, exercise is
still beneficial and it is still possible to increase muscle power and strength
with a careful and safe exercise routine. Injury recovery times are much longer
with great age, balance is often impaired and thinner bones are easily broken.
So, supervision is sensible, especially at first.
3) Infections
Infections and
illnesses are amongst the most common causes of temporary muscle fatigue. This
is usually through muscle inflammation.. They include flu (influenza),
glandular fever (Epstein-Barr virus), HIV, Lyme disease and hepatitis C. Other
less common causes, in the UK at least, are tuberculosis (TB), malaria,
syphilis, polio and dengue fever.
4) 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.
5) Persistent
(chronic) diseases:
Many chronic diseases
commonly cause muscle weakness. In some conditions this is due to reduced blood
and nutrient supply to muscles:
Peripheral arterial
disease: this is caused by narrowing of the arteries, usually due to the
build-up of cholesterol. It's linked to smoking and diet.
ü Diabetes:
this can cause weakness and loss of fitness. Having raised blood sugar levels
(and sometimes altered salt levels) puts muscles at a disadvantage too and they
don't perform so well. In addition, as diabetes progresses, the blood supply to
small nerves is lost.
ü Heart
disease - particularly heart failure: this can cause easy tiring of the muscles
through a reduction in blood supply at times of high demand. This is because
the heart is unable to keep up with the increased requirements of the exercising
muscles, as it can't pump blood as effectively as it should.
ü Chronic
lung disease: lung conditions such as chronic obstructive pulmonary disease
(COPD) cause a reduction in the ability of the body to take in oxygen. Muscles
require a fast supply of oxygen from the blood, particularly when exercising.
Reduction in oxygen intake leads to easy tiring.
ü Chronic
kidney disease: Kidney disease also causes a build-up of poisonous substances
(toxins) in the blood because the poorly functioning kidneys process these
toxins more slowly. This can lead to true muscle weakness as well as muscle
tiredness.
ü Anaemia:.
Anaemia often 'creeps' on quite slowly, so that significant muscle tiredness
and breathlessness develop before the condition is diagnosed.
ü Anxiety:
generalised tiredness can be caused by anxiety. This is due to overactivity of
the body’s adrenaline (epinephrine) system.
ü Depression:
general weariness and a feeling of generalised tiredness can also be caused by
depression.
6) Muscle
damage through injury
There are many ways in
which your muscles can be directly damaged. The most obvious is injury or
trauma such as sporting injuries, pulls and sprains. In any muscle injury,
bleeding from damaged muscle fibres occurs inside the muscle, followed by
swelling and inflammation. This makes the muscle less strong and also painful
to use. Localised pain is the primary symptom but weakness also results.
7) Medicines
Many medicines can
cause muscle weakness and muscle damage as a side-effect or an allergic
reaction. Usually this begins as tiredness or fatigue. It can progress to
permanent changes if the medicines are not stopped.
8) Other
substances
Prolonged use of
alcohol can cause weakness of shoulder and hip muscles.Smoking can indirectly
weaken muscles. Smoking causes narrowing of the arteries, leading to peripheral
arterial disease.
Cocaine misuse causes
marked muscle weakness, as can other drugs of abuse.
9) Sleep
disorders
Problems that disturb
or reduce sleep lead to a generalised increase in tiredness, including muscle
'fatigability'. This can include:
·
Pure insomnia.
·
Anxiety.
·
Depression.
·
Chronic pain.
·
Restless legs syndrome.
·
Shift work.
·
The presence of small
babies who don't sleep through the night.
·
Uncommon causes of
muscle weakness
10) Chronic
fatigue syndrome (CFS)
CFS is sometimes
triggered by certain viral infections such as glandular fever (Epstein-Barr
virus) and flu (influenza) but it is poorly understood. Muscles are not
inflamed but tire very easily.
11) Fibromyalgia: the
muscles also become very tender to touch and they tire extremely easily. They
are not usually wasted and can demonstrate normal (although uncomfortable)
strength on formal testing. People with fibromyalgia tend to complain more of
the pain than the tiredness or weakness.
11) Underactive thyroid (hypothyroidism)
In this condition a
shortage of thyroid hormone leads to generalised tiredness. In untreated
hypothyroidism, muscle degeneration and wasting can develop. This can be severe
and difficult to reverse. Hypothyroidism is a common condition but it is
usually picked up early and treated before long-lasting muscle problems can
result.
12) Electrolyte
disorders and lack of fluid in the body (dehydration)
Problems of the balance
of salts in the body, including dehydration through not drinking enough, cause
muscle tiredness. This may be severe in extreme cases, such as dehydration
during a marathon. Muscles work less well when there is an imbalance in the
salts in the blood.
13) Conditions
of muscle inflammation
Inflammatory diseases
of muscle typically affect older adults and include conditions such as
polymyalgia rheumatica (muscles of the shoulders and thighs become tender and
weak), polymyositis and dermatomyositis.
Conditions of
generalised tissue inflammation such as systemic lupus erythematosus and rheumatoid
arthritis can cause muscle weakness. In a small proportion of cases of
rheumatoid arthritis, muscle weakness and tiredness may be the only sign of the
disease for some considerable time.
14) Cancers:
Cancers can cause
muscle damage directly but the presence of cancer anywhere in the body can also
cause generalised muscle tiredness. In advanced disease, general weight loss
will also lead to true muscle weakness. Muscle weakness is not usually the
first sign of a cancer but occurs later in the condition.
15) Nerve
conditions which damage muscles:
Conditions affecting
nerves tend to lead to true muscle weakness. This is because if the nerve to a
muscle fibre stops working, the muscle fibre can’t work either and it will
become floppy and eventually shrivel.
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