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{{redirect|Exhaustion|other uses|Exhaust}}
{{Redirect|Fatigue (physical)|material fatigue|Fatigue (material)}}
{{SignSymptom infobox |
Name = Fatigue |
ICD10 = {{ICD10|R|53||r|50}} |
ICD9 = {{ICD9|780.7}} |
ICDO = |
OMIM = |
DiseasesDB = 30079 |
MedlinePlus = |
eMedicineSubj = |
eMedicineTopic = |
MeshName = Fatigue |
MeshNumber = C23.888.369 |
}}
The word '''''fatigue''''' is used in everyday living to describe a range of afflictions, varying from a general state of '''lethargy''' to a specific work-induced burning sensation within one's muscles. Physiologically, "fatigue" describes the inability to continue functioning at the level of one's normal abilities<ref>{{cite journal |author=Gandevia SC |title=Some central and peripheral factors affecting human motoneuronal output in neuromuscular fatigue |journal=Sports medicine (Auckland, N.Z.) |volume=13 |issue=2 |pages=93-8 |year=1992 |pmid=1561512 |doi=}}</ref><ref>{{cite journal |author=Hagberg M |title=Muscular endurance and surface electromyogram in isometric and dynamic exercise |journal=Journal of applied physiology: respiratory, environmental and exercise physiology |volume=51 |issue=1 |pages=1-7 |year=1981 |pmid=7263402 |doi=}}</ref><ref>{{cite journal |author=Hawley JA, Reilly T |title=Fatigue revisited |journal=Journal of sports sciences |volume=15 |issue=3 |pages=245-6 |year=1997 |pmid=9232549 |doi=}}</ref> due to an increased [[perception]] of effort.<ref>{{cite journal |author=Enoka RM, Stuart DG |title=Neurobiology of muscle fatigue |journal=J. Appl. Physiol. |volume=72 |issue=5 |pages=1631-48 |year=1992 |pmid=1601767 |doi=}}</ref> Fatigue is [[wiktionary:ubiquitous|ubiquitous]] in everyday life, but usually becomes particularly noticeable during heavy [[physical exercise|exercise]].
Fatigue has two known forms; one manifests as a local, muscle-specific incapacity to do work, and the other manifests as an overall, bodily or systemic, sense of energy deprivation. Due to these two divergent facets of fatigue symptoms, it has been proposed to look at the causes of fatigue from "central" and "peripheral" perspectives.<ref>{{cite journal |author=Gandevia SC, Enoka RM, McComas AJ, Stuart DG, Thomas CK |title=Neurobiology of muscle fatigue. Advances and issues |journal=Adv. Exp. Med. Biol. |volume=384 |issue= |pages=515-25 |year=1995 |pmid=8585476 |doi=}}</ref><ref>{{cite journal |author=Kent-Braun JA |title=Central and peripheral contributions to muscle fatigue in humans during sustained maximal effort |journal=European journal of applied physiology and occupational physiology |volume=80 |issue=1 |pages=57-63 |year=1999 |pmid=10367724 |doi=}}</ref>
Fatigue can be dangerous when performing tasks that require constant concentration, such as driving a [[vehicle]]. When a person is sufficiently fatigued, he or she may experience [[sleep deprivation|microsleeps]] (loss of concentration). However, objective cognitive testing should be done to differentiate the neurocognitive deficits of brain disease from those attributable to tiredness.
The sense of fatigue is believed to originate in the [[reticular activating system]] of the lower brain. [[Musculoskeletal system|Musculoskeletal]] structures may have co-evolved with appropriate brain structures so that the complete unit functions together in a constructive and adaptive fashion.<ref>{{cite book |author=Edelman, Gerald Maurice |title=The remembered present: a biological theory of consciousness |publisher=Basic Books |___location=New York |year=1989 |pages= |isbn=0-465-06910-X |oclc= |doi=}}</ref> The entire systems of muscles, joints, and [[wiktionary:proprioceptive|proprioceptive]] and [[wiktionary:kinesthetic|kinesthetic]] functions plus parts of the brain evolve and function together in a unitary way).<ref>{{cite book |author=Kelso, J. A. Scott |title=Dynamic patterns: the self-organization of brain and behavior |publisher=MIT Press |___location=Cambridge, Mass |year=1995 |pages= |isbn=0-262-61131-7 |oclc= |doi=}}</ref>
==Types==
There are two main types of fatigue: central and peripheral.
* ''Central Fatigue'' The central component to fatigue is generally described in terms of a reduction in the [[nervous system|neural]] drive or nerve-based motor command to working muscles that results in a decline in the force output.<ref>{{cite journal |author=Gandevia SC |title=Spinal and supraspinal factors in human muscle fatigue |journal=Physiol. Rev. |volume=81 |issue=4 |pages=1725-89 |year=2001 |pmid=11581501 |doi=}}</ref><ref>{{cite journal |author=Kay D, Marino FE, Cannon J, St Clair Gibson A, Lambert MI, Noakes TD |title=Evidence for neuromuscular fatigue during high-intensity cycling in warm, humid conditions |journal=Eur. J. Appl. Physiol. |volume=84 |issue=1-2 |pages=115-21 |year=2001 |pmid=11394239 |doi=}}</ref><ref>{{cite journal |author=Vandewalle H, Maton B, Le Bozec S, Guerenbourg G |title=An electromyographic study of an all-out exercise on a cycle ergometer |journal=Archives internationales de physiologie, de biochimie et de biophysique |volume=99 |issue=1 |pages=89-93 |year=1991 |pmid=1713492 |doi=}}</ref> 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.<ref>{{cite journal |author=Bigland-Ritchie B, Woods JJ |title=Changes in muscle contractile properties and neural control during human muscular fatigue |journal=Muscle Nerve |volume=7 |issue=9 |pages=691-9 |year=1984 |pmid=6100456 |doi=10.1002/mus.880070902}}</ref><ref>{{cite journal |author=Noakes TD |title=Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic performance |journal=Scandinavian journal of medicine & science in sports |volume=10 |issue=3 |pages=123-45 |year=2000 |pmid=10843507 |doi=}}</ref> The exact mechanisms of central fatigue are unknown although there has been a great deal of interest in the role of serotonergic pathways.<ref>{{cite journal |author=Davis JM |title=Carbohydrates, branched-chain amino acids, and endurance: the central fatigue hypothesis |journal=International journal of sport nutrition |volume=5 Suppl |issue= |pages=S29-38 |year=1995 |pmid=7550256 |doi=}}</ref><ref>Newsholme, E. A., Acworth, I. N., & Blomstrand, E. 1987, 'Amino acids, brain neurotransmitters and a functional link between muscle and brain that is important in sustained exercise', in G Benzi (ed.), Advances in Myochemistry, Libbey Eurotext, London, pp. 127-133.</ref><ref>{{cite journal |author=Newsholme EA, Blomstrand E |title=Tryptophan, 5-hydroxytryptamine and a possible explanation for central fatigue |journal=Adv. Exp. Med. Biol. |volume=384 |issue= |pages=315-20 |year=1995 |pmid=8585461 |doi=}}</ref>
* ''Peripheral Fatigue'' Fatigue during physical work is considered an inability for the body to supply sufficient energy 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 [[cellular respiration|aerobic metabolism]], generally results in the accumulation of [[lactic acid]] and other [[acid|acidic]] anaerobic metabolic by-products in the muscle, causing the stereotypical burning sensation of local muscle fatigue.
The fundamental difference between the peripheral and central theories of fatigue is that the peripheral model of 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 fatigue is an integrated mechanism that works to preserve the integrity of the system by initiating 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.
Fatigue is typically the result of [[labour (economics)|work]]ing, mental [[Stress (medicine)|stress]], [[jet lag]] or active [[recreation]], and also [[boredom]], [[disease]] and [[Sleep deprivation|lack of sleep]]. It may also have chemical causes, such as [[poison]]ing or [[mineral]] or [[vitamin]] deficiencies.
Although chronic (meaning of six months or more duration) fatigue is a symptom of nearly 30 different diseases, post exertional fatigue, also known as [[exercise intolerance]], is rare and is primarily found in organic brain diseases, [[mitochondrial disease]] and [[neuromuscular disease]]. Impaired exercise tolerance however, is a common symptom, often found in those taking medications such as [[beta blocker]] treatment for high blood pressure. <ref>{{cite web|url=http://www.just2tired.com/labels/fatigue-due-to-medication.html|title=Fatigue caused by medications}}</ref>
==Associated conditions==
{{incomplete-list}}
*[[Addison's disease]]
*[[AIDS]]
*[[Anemia]]
*[[Anorexia Nervosa]]
*[[Anxiety]] or [[Panic disorder|Panic Disorder]]
*[[Arthritis]]
*[[ATRT]] - Brain Cancer
*[[Autoimmune disease]]
*[[B12 Deficiency]]
*[[Cancer Syndrome]]
*[[Chemical dependency]]
*[[Chronic fatigue syndrome]] (CFS)
*[[Clinical depression]]
*[[Congestive Heart Failure]]
*[[Crohn's disease|Crohn's Disease]]
*[[Diabetes mellitus|Diabetes]]
*[[Endometriosis]]
*[[Fibromyalgia]]
*[[Hemochromatosis]]
*[[HIV]]
*[[Hyperthyroidism]]/[[Graves disease|Graves' Disease]]
*[[Hyperparathyroidism]]
*[[Hypothyroidism]]/[[Hashimoto's Thyroiditis]]
*[[Idiopathic Hypersomnia]]
*[[Lead poisoning]]
*[[Leukemia]] or [[Lymphoma]]
*[[Lupus erythematosus]]
*[[Lyme disease]]
*[[Interstitial Cystitis]]
*[[Medications]]
*[[Mitral valve prolapse]]/[[Mitral regurgitation]]
*[[Mononucleosis]]
*[[Multiple sclerosis]]
*[[Muscular Dystrophy]]
*[[Myasthenia gravis]]
*[[Parkinson's disease]]
*[[Pernicious anemia]]
*[[Pneumonia]]
*[[Pregnancy]]
*[[Primary Biliary Cirrhosis]] (PBC)
*[[Reyes Syndrome]]
*Certain [[medications]], e.g. [[lithium salt]]s, [[ciprofloxacin]]
*[[Sinusitis]]
*[[Sleep deprivation]]
*[[Sleep disorders]], e.g. [[insomnia]], [[obstructive sleep apnea]], or [[narcolepsy]]
*[[Starvation]]
*[[Ulcerative colitis]]
*[[Wegener's granulomatosis]]
==See also==
*[[Somnolence]]
*[[Insomnia]]
*[[Combat stress reaction]] (Battle fatigue)
*[[Malaise]]
*[[Asthenia]]
*[[Paresis]]
*[[Debility]]
*[[Muscle weakness]]
*[[Muscle fatigue]]
*[[Infectious mononucleosis]]
*[[Celiac]] disease (gluten sensitivity)
==References==
{{Reflist|2}}
==External links==
* [http://www.nlm.nih.gov/medlineplus/ency/article/003088.htm NIH/Medline]
* [http://www.cancer.gov/cancertopics/pdq/supportivecare/fatigue/patient National Cancer Institute]
{{Symptoms and signs}}
[[Category:Exercise physiology]]
[[Category:Symptoms]]
[[de:Müdigkeit]]
[[es:Fatiga]]
[[fr:Fatigue (physique)]]
[[he:עייפות]]
[[nl:Vermoeidheid]]
[[fi:Väsymys]]
[[sq:Lodhja (trupore)]]
[[yi:מיעדקייט]]
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