
- "Asthenia" redirects here. The tortrix moth genusGenusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
is nowadays considered a junior synonym of EpinotiaEpinotiaEpinotia is a very large genus of tortrix moths . It belongs to the tribe Eucosmini of subfamily Olethreutinae.-Species:166 species of Epinotia were considered valid as of 2009...
.
Weakness is a symptom represented, medically, by a number of different conditions, including: lack of muscle strength, malaise
, dizziness
, or fatigue. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy
and inflammatory myopathy
.
All cruelty springs from weakness.
Although men are accused of not knowing their own weakness, yet perhaps few know their own strength. It is in men as in soils, where sometimes there is a vein of gold which the owner knows not of.
As you simplify your life, the laws of the universe will be simpler; solitude will not be solitude, poverty will not be poverty, nor weakness weakness.
Credulity is the man's weakness, but the child's strength.
Do you really think it is weakness that yields to temptation? I tell you that there are terrible temptations which it requires strength, strength and courage to yield to.
Get it into your head once and for all, my simple and very fainthearted fellow, that what fools call humanness is nothing but a weakness born of fear and egoism; that this chimerical virtue, enslaving only weak men, is unknown to those whose character is formed by stoicism, courage, and philosophy.
I believe the most solemn duty of the American president is to protect the American people. If America shows uncertainty and weakness in this decade, the world will drift toward tragedy. This will not happen on my watch.
If thou wouldn't conquer thy weakness thou must not gratify it.
If we resist our passions, it is more due to their weakness than our strength.
Insincerity is always weakness; sincerity even in error is strength.
- "Asthenia" redirects here. The tortrix moth genusGenusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
is nowadays considered a junior synonym of EpinotiaEpinotiaEpinotia is a very large genus of tortrix moths . It belongs to the tribe Eucosmini of subfamily Olethreutinae.-Species:166 species of Epinotia were considered valid as of 2009...
.
Weakness is a symptom represented, medically, by a number of different conditions, including: lack of muscle strength, malaise
, dizziness
, or fatigue. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy
and inflammatory myopathy
. It occurs in neuromuscular junction
disorders, such as myasthenia gravis
.
Definition
Weakness describes a number of symptoms, including: loss of muscle strength, malaise, dizziness
or fatigue. The term can be divided into two other more specific states, true weakness and perceived weakness.
- True weakness (or neuromuscular) describes a condition where the force exerted by the muscles is less than would be expected, for example muscular dystrophyMuscular dystrophyMuscular dystrophy is a group of muscle diseases that weaken the musculoskeletal system and hamper locomotion. Muscular dystrophies are characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue.In the 1860s, descriptions of boys who...
.
- Perceived weakness (or non-neuromuscular) describes a condition where a person feels more effort than normal is required to exert a given amount of force but actual muscle strength is normal, for example chronic fatigue syndromeChronic fatigue syndromeChronic fatigue syndrome is the most common name used to designate a significantly debilitating medical disorder or group of disorders generally defined by persistent fatigue accompanied by other specific symptoms for a minimum of six months, not due to ongoing exertion, not substantially...
.
In some conditions, such as myasthenia gravis
muscle strength is normal when resting, but true weakness occurs after the muscle has been subjected to exercise. This is also true for some cases of CFS, where objective post-exertion muscle weakness with delayed recovery time has been measured and is a feature of some of the published definitions.
Asthenia
Asthenia (Greek: ασθένεια, lit. lack of strength but also disease) is a medical term referring to a condition in which the body lacks or has lost strength either as a whole or in any of its parts. It denotes symptoms of physical weakness and loss of strength
. General asthenia occurs in many chronic wasting diseases (such as anemia and cancer), sleep disorders or chronic disorders of the heart, lungs or kidneys, and is probably most marked in diseases of the adrenal gland. Asthenia may be limited to certain organs or systems of organs, as in asthenopia
, characterized by ready fatiguability. Asthenia is also a side effect of some medications and treatments, such as Ritonavir
(a protease inhibitor
used in HIV
treatment), vaccines such as the HPV vaccine Gardasil
and fentanyl patches (an opioid
used to treat pain).
Differentiating between psychogenic (perceived) asthenia and true asthenia with muscular weakness
is often difficult, and in time apparent psychogenic asthenia accompanying many chronic disorders is seen to progress into a primary weakness.
Differential diagnosis
Weakness can be central, neural and peripheral. Central muscle weakness manifests as an overall, bodily or systemic, sense of energy deprivation, and peripheral weakness manifests as a local, muscle-specific incapacity to do work. Neural weakness can be both central and peripheral.Central
The central component to muscle fatigue is generally described in terms of a reduction in the neuraldrive or nerve-based motor command to working muscles that results in a decline in the force output. It has been suggested that the reduced neural drive during exercise may be a protective mechanism to prevent organ failure if the work was continued at the same intensity. The exact mechanisms of central fatigue are unknown although there has been a great deal of interest in the role of serotonergic pathways.
Neural
Nerves are responsible for controlling the contraction of muscles, determining the number, sequence and force of muscular contraction. Most movements require a force far below what a muscle could in potential generate, and barring pathology
nervous fatigue is seldom an issue. For extremely powerful contractions that are close to the upper limit of a muscle's ability to generate force, nervous fatigue can be a limiting factor in untrained individuals. In novice strength trainers
, the muscle's ability to generate force is most strongly limited by nerve’s ability to sustain a high-frequency signal. After a period of maximum contraction, the nerve’s signal reduces in frequency and the force generated by the contraction diminishes. There is no sensation of pain or discomfort, the muscle appears to simply ‘stop listening’ and gradually cease to move, often going backwards. As there is insufficient stress on the muscles and tendons, there will often be no delayed onset muscle soreness
following the workout. Part of the process of strength training is increasing the nerve's ability to generate sustained, high frequency signals that allow a muscle to contract with their greatest force. It is this neural training that causes several weeks worth of rapid gains in strength, which level off once the nerve is generating maximum contractions and the muscle reaches its physiological limit. Past this point, training effects increase muscular strength through myofibrilar or sarcoplasmic hypertrophy and metabolic fatigue becomes the factor limiting contractile force.
Peripheral
Peripheral muscle fatigue during physical work is considered an inability for the body to supply sufficient energy or other metabolites to the contracting muscles to meet the increased energy demand. This is the most common case of physical fatigue—affecting a national average of 72% of adults in the work force in 2002. This causes contractile dysfunction that is manifested in the eventual reduction or lack of ability of a single muscle or local group of muscles to do work. The insufficiency of energy, i.e. sub-optimal aerobic metabolism, generally results in the accumulation of lactic acid
and other acid
ic anaerobic metabolic by-products in the muscle, causing the stereotypical burning sensation of local muscle fatigue, though recent studies have indicated otherwise, actually finding that lactic acid is a source of energy.
The fundamental difference between the peripheral and central theories of muscle fatigue is that the peripheral model of muscle fatigue assumes failure at one or more sites in the chain that initiates muscle contraction. Peripheral regulation is therefore dependent on the localised metabolic chemical conditions of the local muscle affected, whereas the central model of muscle fatigue is an integrated mechanism that works to preserve the integrity of the system by initiating muscle fatigue through muscle derecruitment, based on collective feedback from the periphery, before cellular or organ failure occurs. Therefore the feedback that is read by this central regulator could include chemical and mechanical as well as cognitive cues. The significance of each of these factors will depend on the nature of the fatigue-inducing work that is being performed.
Though not universally used, ‘metabolic fatigue’ is a common alternative term for peripheral muscle weakness, because of the reduction in contractile force due to the direct or indirect effects of the reduction of substrates or accumulation of metabolites within the muscle fiber. This can occur through a simple lack of energy to fuel contraction, or interference with the ability of Ca2+ to stimulate actin
and myosin
to contract.
Lactic acid
It was once believed that lactic acidbuild-up was the cause of muscle fatigue. The assumption was lactic acid had a "pickling" effect on muscles, inhibiting their ability to contract. The impact of lactic acid on performance is now uncertain, it may assist or hinder muscle fatigue.
Produced as a by-product of fermentation
, lactic acid can increase intracellular acidity of muscles. This can lower the sensitivity of contractile apparatus to Ca2+ but also has the effect of increasing cytoplasm
ic Ca2+ concentration through an inhibition of the chemical pump
that actively transports
calcium out of the cell. This counters inhibiting effects of K+ on muscular action potentials. Lactic acid also has a negating effect on the chloride ions in the muscles, reducing their inhibition of contraction and leaving potassium ions as the only restricting influence on muscle contractions, though the effects of potassium are much less than if there were no lactic acid to remove the chloride ions. Ultimately, it is uncertain if lactic acid reduces fatigue through increased intracellular calcium or increases fatigue through reduced sensitivity of contractile proteins to Ca2+.
Associated conditions
Many different conditions can cause weakness. In 2010 DiagnosisProlisted 464 possible cause. True weakness may be due to problems with the nerves, neuromuscular junction
or with muscles.
- Amyotrophic lateral sclerosisAmyotrophic lateral sclerosisAmyotrophic lateral sclerosis , also referred to as Lou Gehrig's disease, is a form of motor neuron disease caused by the degeneration of upper and lower neurons, located in the ventral horn of the spinal cord and the cortical neurons that provide their efferent input...
- BotulismBotulismBotulism also known as botulinus intoxication is a rare but serious paralytic illness caused by botulinum toxin which is metabolic waste produced under anaerobic conditions by the bacterium Clostridium botulinum, and affecting a wide range of mammals, birds and fish...
- Centronuclear myopathy
- Myotubular myopathy
- Muscle AtrophyMuscle atrophyMuscle atrophy, or disuse atrophy, is defined as a decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle. When a muscle atrophies, this leads to muscle weakness, since the ability to exert force is related to mass...
- SarcopeniaSarcopeniaSarcopenia is the degenerative loss of skeletal muscle mass and strength associated with aging...
- DysautonomiaDysautonomiaDysautonomia is a broad term that describes any disease or malfunction of the autonomic nervous system. This includes postural orthostatic tachycardia syndrome , inappropriate sinus tachycardia , vasovagal syncope, mitral valve prolapse dysautonomia, pure autonomic failure, neurocardiogenic...
- Charcot-Marie-Tooth
- HypokalemiaHypokalemiaHypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
- Motor neurone diseaseMotor neurone diseaseThe motor neurone diseases are a group of neurological disorders that selectively affect motor neurones, the cells that control voluntary muscle activity including speaking, walking, breathing, swallowing and general movement of the body. They are generally progressive in nature, and can cause...
- Muscular dystrophyMuscular dystrophyMuscular dystrophy is a group of muscle diseases that weaken the musculoskeletal system and hamper locomotion. Muscular dystrophies are characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue.In the 1860s, descriptions of boys who...
- Myotonic dystrophyMyotonic dystrophyMyotonic dystrophy is a chronic, slowly progressing, highly variable inherited multisystemic disease. It is characterized by wasting of the muscles , cataracts, heart conduction defects, endocrine changes, and myotonia. Myotonic dystrophy can occur in patients of any age...
- Myasthenia gravisMyasthenia gravisMyasthenia gravis is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatiguability...
- Progressive muscular atrophyProgressive muscular atrophyProgressive muscular atrophy is a rare subtype of amyotrophic lateral sclerosis or motor neurone disease which affects only the lower motor neurones. PMA is thought to account for around 4% of all ALS/MND cases...
- Spinal muscular atrophySpinal muscular atrophySpinal Muscular Atrophy is a neuromuscular disease characterized by degeneration of motor neurons, resulting in progressive muscular atrophy and weakness. The clinical spectrum of SMA ranges from early infant death to normal adult life with only mild weakness...
- Cerebral palsyCerebral palsyCerebral palsy is an umbrella term encompassing a group of non-progressive, non-contagious motor conditions that cause physical disability in human development, chiefly in the various areas of body movement....
- Infectious mononucleosisInfectious mononucleosisInfectious mononucleosis is an infectious, widespread viral...
- Herpes zosterHerpes zosterHerpes zoster , commonly known as shingles and also known as zona, is a viral disease characterized by a painful skin rash with blisters in a limited area on one side of the body, often in a stripe...
- Vitamin D deficiency
- FibromyalgiaFibromyalgiaFibromyalgia is a medical disorder characterized by chronic widespread pain and allodynia, a heightened and painful response to pressure. It is an example of a diagnosis of exclusion...
- Celiac disease
- Hypercortisolism (Cushing's syndromeCushing's syndromeCushing's syndrome is a hormone disorder caused by high levels of cortisol in the blood. This can be caused by taking glucocorticoid drugs, or by tumors that produce cortisol or adrenocorticotropic hormone or CRH...
) - Hypocortisolism (Addison's diseaseAddison's diseaseAddison’s disease is a rare, chronic endocrine disorder in which the adrenal glands do not produce sufficient steroid hormones...
) - Primary hyperaldosteronism (Conn's syndromeConn's syndromePrimary aldosteronism, also known as primary hyperaldosteronism, is characterized by the overproduction of the mineralocorticoid hormone aldosterone by the adrenal glands., when not a result of excessive renin secretion. Aldosterone causes increase in sodium and water retention and potassium...
) - Ehlers-Danlos syndromeEhlers-Danlos syndromeEhlers–Danlos syndrome is a group of inherited connective tissue disorders, caused by a defect in the synthesis of collagen . The collagen in connective tissue helps tissues to resist deformation...
- DiarrheaDiarrheaDiarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
- McArdle's Disease
- Ross River FeverRoss River FeverRoss River Fever is a mosquito-borne infectious disease caused by infection with the Ross River virus. The illness is typically characterised by an influenza-like illness and polyarthritis...
- Barmah Forest Fever
Pathophysiology
Muscle cells work by detecting a flowof electrical impulses from the brain
, which signals them to contract
through the release of calcium
by the sarcoplasmic reticulum. Fatigue (reduced ability to generate force) may occur due to the nerve, or within the muscle cells themselves. New research from scientists at Columbia University suggests that muscle fatigue is caused by calcium leaking out of the muscle cell. This makes less calcium available for the muscle cell. In addition, the Columbia researchers propose that an enzyme activated by this released calcium eats away at muscle fibers.
Substrates
within the muscle generally serve to power muscular contractions. They include molecules such as adenosine triphosphate
(ATP), glycogen
and creatine phosphate
. ATP binds to the myosin
head and causes the ‘ratchetting’ that results in contraction according to the sliding filament model
. Creatine phosphate stores energy so ATP can be rapidly regenerated within the muscle cells from adenosine diphosphate
(ADP) and inorganic phosphate ions, allowing for sustained powerful contractions that last between 5–7 seconds. Glycogen is the intramuscular storage form of glucose
, used to generate energy quickly once intramuscular creatine stores are exhausted, producing lactic acid
as a metabolic byproduct. Contrary to common belief, lactic acid accumulation doesn't actually cause the burning sensation we feel when we exhaust our oxygen and oxidative metabolism, but in actuality, lactic acid in presence of oxygen recycles to produce pyruvate in the liver, which is known as the Cori cycle.
Substrates produce metabolic fatigue by being depleted during exercise, resulting in a lack of intracellular energy sources to fuel contractions. In essence, the muscle stops contracting because it lacks the energy to do so.