{
  "id": "fatigue",
  "title": "Fatigue",
  "lang": "en",
  "source_lang": "en",
  "summary": "Fatigue is a subjective, persistent sense of low energy and reduced drive, physical, mental or both, which may reflect normal exertion or an underlying condition.",
  "category": "health",
  "subcategory": "diseases",
  "type": "concept",
  "aliases": [
    "tiredness",
    "weariness",
    "exhaustion",
    "lethargy"
  ],
  "generated_at": "2026-10-09",
  "model": "pro/claude-haiku-5-5",
  "url": "https://aiwiki.page/en/fatigue/",
  "translations": {
    "zh-Hans": {
      "url": "https://aiwiki.page/zh/fatigue/",
      "json": "https://aiwiki.page/zh/fatigue.json"
    }
  },
  "sections": [
    {
      "heading": "",
      "text": "Fatigue is a subjective sense of diminished energy and drive that can be physical, mental, or both. In medicine it is usually treated as a symptom rather than a disease, and numerous medical conditions include it among their accompanying features. It is a frequent reason for consultation in primary care, and it can erode performance at work as well as family and social relationships (it negatively affects work performance, family life, and social relationships). Clinicians distinguish ordinary, self-limiting tiredness from persistent fatigue that interferes with daily life."
    },
    {
      "heading": "Definition and terminology",
      "text": "One common clinical wording describes it as a struggle to begin and sustain activity, accompanied by a wish to rest. In everyday speech, the terms fatigue, sleepiness, tiredness, lacking energy, and exhaustion are used interchangeably. The research literature is less tolerant of this looseness: the definition of fatigue varies greatly across studies, partly because the phenomenon draws on psychosocial and behavioral processes and so resists a single precise definition.\n\nBecause the experience is internal, assessment is difficult. Fatigue can be highly subjective, since patients differ in what they consider fatigue and how they describe it, and few methods exist to objectively confirm it or grade its severity."
    },
    {
      "heading": "Types and classification",
      "text": "A common scheme sorts fatigue into fatigue secondary to other medical conditions, physiologic fatigue, or chronic fatigue. Physiologic fatigue arises when routines of exercise, sleep, diet or other activity are disturbed without an underlying disease, and it resolves with rest (an imbalance in the routines of exercise, sleep, diet, or other activity that is not caused by an underlying medical condition and is relieved with rest). Fatigue linked to another illness may persist for a month or more, though it usually resolves within six months (it may last one month or longer, but it generally lasts less than six months).\n\nChronic fatigue is characterized by a different pattern. One classification describes it as chronic, or pathological, occurs after modest effort and continues despite rest. Thresholds vary between sources: some describe extreme tiredness that often persists for 2 to 4 weeks or longer as clinically significant, while others reserve the term \"chronic\" for longer durations.\n\nReported figures put the share of Americans whose fatigue disrupts ordinary life at about 20%."
    },
    {
      "heading": "Physiological basis",
      "text": "Fatigue is not a single mechanism. In skeletal muscle, it appears as the transient decrease in performance capacity of muscles, usually evidenced by a failure to maintain or develop a certain expected force or power. Researchers commonly divide the phenomenon into two components: \"peripheral fatigue\" is typically used to describe force reductions due to processes distal to the neuromuscular junction, whereas those due to processes within motoneurons and the central nervous system are commonly known as \"central fatigue.\"\n\nThe peripheral component is linked to local muscle conditions. Peripheral fatigue originates in the muscle and is attributed to factors such as energy depletion, accumulation of metabolic byproducts, and impaired calcium handling, which directly affect muscle contraction efficiency. Energy depletion here refers largely to the consumption of ATP and stored fuels. The central component, by contrast, involves a reduction in voluntary activation of muscles, stemming from alterations in neurotransmitter levels and neural drive from the central nervous system. Its relative importance depends on the task: central fatigue, preponderant during long-duration, low-intensity exercises, may involve a drop in the central command.\n\nSome physiological responses to sustained exertion can either add to fatigue or offset it, and this principle applies to both peripheral and central processes (responses to sustained exercise can either contribute to, or compensate for, fatigue)."
    },
    {
      "heading": "Causes and associated conditions",
      "text": "The differential diagnosis of fatigue includes lifestyle issues, physical conditions, mental disorders, and treatment side effects. Among the frequently implicated factors are overexertion, deconditioning, viral illness, upper respiratory tract infection, anemia, lung disease, medications, cancer, and depression. In many cases, however, the cause is unknown.\n\nInfections are a notable example, including infectious diseases and the prolonged symptoms that can follow a pandemic infection. Sleep disruption and depression both appear repeatedly in clinical assessments.\n\nFatigue is especially prominent in oncology. Fatigue is the most prevalent cancer-related symptom and has a significant adverse impact on patients' functional ability and quality of life. The disease itself contributes: cancer places excess demands on the body's resources for cell repair and uncontrolled growth, with metabolite accumulation causing fatigue. Treatments add to the burden, as its association with treatment modalities like chemotherapy and radiotherapy makes it very common. In one study of patients receiving chemotherapy with or without radiation, 17% of respondents met criteria for cancer-related fatigue.\n\nIn older adults, fatigue is an important component of frailty syndrome, and it has been associated with falls, functional decline and higher mortality. Occupational factors also matter: work schedule, shift work, and poor sleep quality are other causes of fatigue."
    },
    {
      "heading": "Evaluation and diagnosis",
      "text": "Evaluation begins with history. A complete history of the fatigue covers sleep timing and quality, whether the person wakes refreshed, exercise habits, and recent stressors such as changes in relationships, work, school, or living arrangements.\n\nThe pattern of symptoms carries diagnostic information. Fatigue that worsens with activity and lessens with rest suggests a general medical condition, whereas fatigue that is present constantly and does not lessen with rest, particularly with occasional bursts of energy, may indicate a mental health condition.\n\nPhysical examination and medication review are standard. The doses and scheduling of prescribed and over-the-counter medications should be reviewed. Examination may reveal lymphadenopathy (indicating tumor spread or recurrence), cardiac murmurs (endocarditis), goiter (thyroid hormone imbalance), edema (heart failure, liver disease, or malnutrition), poor muscle tone (advancing neurologic condition), and neurologic abnormalities, each pointing toward particular secondary causes.\n\nLaboratory testing has limited yield. Results of laboratory studies affect management in only 5 percent of patients, and if initial results are normal, repeat testing is generally not indicated. Screening questionnaires are used for comorbid problems: physicians should use validated screening tools to rule out comorbid sleep, mood, and substance use disorders. Measurement approaches include self-report surveys, physiological markers, and performance assessments, and in oncology short instruments such as the Brief Fatigue Inventory are considered practical for routine use."
    },
    {
      "heading": "Chronic fatigue syndrome",
      "text": "Chronic fatigue syndrome (CFS), also called myalgic encephalomyelitis (ME/CFS), is one of the best-known forms of prolonged fatigue. It is a complex, chronic condition marked by persistent, debilitating fatigue that is not alleviated by rest and often worsens with physical or mental exertion. Related symptoms include cognitive impairments, post-exertional malaise, muscle and joint pain, sleep disturbances, and immune system dysfunction.\n\nDiagnosis is difficult. Diagnosing CFS/ME is challenging due to the absence of definitive biomarkers, the overlap of symptoms with other conditions, and the lack of standardized diagnostic criteria. Criteria have changed over time. Earlier research criteria, the Fukuda criteria, required at least six months of severe chronic fatigue not due to exertion or other illness, plus at least four of eight listed symptoms. The criteria currently recommended in the United States are the 2015 Institute of Medicine/National Academy of Medicine criteria, which require a substantial reduction in pre-illness activities lasting more than 6 months, with post-exertional malaise and unrefreshing sleep, plus at least one of cognitive impairment or orthostatic intolerance.\n\nSources differ on whether the diagnosis is one of exclusion. One account holds that it is a clinical diagnosis that can be made only when other disease processes are excluded. Another states that diagnosis of ME/CFS is based on positive signs and symptoms and is therefore not a diagnosis of exclusion.\n\nThe heterogeneity of the condition is also debated. Different CFS criteria may at best be diagnosing a spectrum of disease severities and at worst different CFS phenotypes or even different diseases. The cause remains unknown, and the illness carries stigma. For management, the guidelines cited by the AAFP recommend that persons diagnosed with chronic fatigue syndrome should be evaluated and treated for comorbidities, such as sleep disturbance, depression, and pain. Cognitive behavior therapy and graded exercise therapy have been shown to improve fatigue, work and social adjustment, anxiety, and postexertional malaise. Graded exercise therapy remains contested, particularly by patients who report worsening after exertion, and the appropriateness of this approach is still debated."
    },
    {
      "heading": "Management of fatigue more broadly",
      "text": "Where a cause can be identified, treating it is the preferred route, although treatment of cause is not possible in all cases. Both nonpharmacologic and pharmacologic strategies for the management of fatigue are used. Drugs targeting inflammatory signalling are an active area of research: therapeutic agents targeting cytokine load are in early stages of study and available results are not favorable."
    },
    {
      "heading": "Related usage",
      "text": "The word has a distinct meaning in materials engineering, where fatigue describes progressive damage and eventual failure of a material under repeated loading, often at stresses below its static strength. Mental fatigue, a reduction in sustained cognitive performance, is studied separately in psychology and neuroscience."
    }
  ],
  "links": [
    "energy",
    "adenosine-triphosphate",
    "infectious-disease",
    "pandemic",
    "depression",
    "psychology",
    "neuroscience"
  ],
  "sources": [
    {
      "title": "What Are Signs of Fatigue? Causes & Treatment",
      "url": "https://www.emedicinehealth.com/fatigue/article_em.htm"
    },
    {
      "title": "Fatigue: An Overview",
      "url": "https://www.aafp.org/afp/2008/1115/p1173"
    },
    {
      "title": "Fatigue - Special Subjects - Merck Manual Professional Edition",
      "url": "https://www.merckmanuals.com/professional/special-subjects/nonspecific-symptoms/fatigue"
    },
    {
      "title": "Fatigue - an overview",
      "url": "https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/fatigue"
    },
    {
      "title": "Fatigue in Exercise",
      "url": "https://coachsci.sdsu.edu/csa/vol65/asmussen.htm"
    },
    {
      "title": "Recovery of central and peripheral neuromuscular fatigue after exercise",
      "url": "https://journals.physiology.org/doi/full/10.1152/japplphysiol.00775.2016"
    },
    {
      "title": "Central and Peripheral Fatigue",
      "url": "https://link.springer.com/chapter/10.1007/978-3-031-47065-3_9"
    },
    {
      "title": "Neuromuscular fatigue in healthy muscle: Underlying factors and adaptation mechanisms - ScienceDirect",
      "url": "https://www.sciencedirect.com/science/article/pii/S1877065711000029"
    },
    {
      "title": "Fatigue and cancer: causes, prevalence and treatment approaches",
      "url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2409868/"
    },
    {
      "title": "Fatigue in Cancer: A Review of Literature",
      "url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2886215/"
    },
    {
      "title": "Fatigue in Adults: Evaluation and Management",
      "url": "https://www.aafp.org/afp/2023/0700/fatigue-adults"
    },
    {
      "title": "Fatigue Monitoring Using Wearables and AI: Trends, Challenges, and Future Opportunities",
      "url": "https://arxiv.org/pdf/2412.16847"
    },
    {
      "title": "Chronic Fatigue Syndrome: Diagnosis, Treatment, and Future Direction",
      "url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11526618/"
    },
    {
      "title": "Are current chronic fatigue syndrome criteria diagnosing different disease phenotypes?",
      "url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5650174/"
    },
    {
      "title": "Diagnosis and Management of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome - Mayo Clinic Proceedings",
      "url": "https://www.mayoclinicproceedings.org/article/s0025-6196(23)00402-0/fulltext"
    },
    {
      "title": "Chronic Fatigue Syndrome - Special Subjects - Merck Manual Professional Edition",
      "url": "https://www.merckmanuals.com/professional/special-subjects/chronic-fatigue-syndrome/chronic-fatigue-syndrome"
    },
    {
      "title": "Chronic Fatigue Syndrome: Diagnosis and Treatment",
      "url": "https://www.aafp.org/afp/2012/1015/p741"
    },
    {
      "title": "Chronic Fatigue Syndrome: Diagnosis, Treatment, and Future Direction - PMC",
      "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC11526618/"
    }
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/"
}