Physical fatigue

Physical fatigue, or muscle fatigue, is the temporary physical inability of a muscle to perform optimally. The onset of muscle fatigue during physical activity is gradual, and depends upon an individual’s level of physical fitness, and also upon other factors, such as sleep deprivation and overall health. It can be reversed by rest.

Muscle strength testing can be used to determine the presence of a neuromuscular disease, but cannot determine its etiology. Additional testing, such as electromyography, can provide diagnostic information, but information gained from muscle strength testing alone is not enough to diagnose most neuromuscular disorders.

Musculoskeletal structures may have co-evolved with their corresponding brain structures in a way that allows them to adapt to environmental conditions (e.g.—proprioception).

Chronic fatigue

Prolonged fatigue is defined as fatigue persisting for at least one month. Chronic fatigue is defined as fatigue persisting for at least six consecutive months. Chronic fatigue may be either “persistent” or “relapsing.” Chronic fatigue is a non-specific symptom. It can occur in patients suffering from any of the following conditions:

Autoimmune diseases such as celiac disease, multiple sclerosis, and spondyloarthropathy
Blood disorders such as anemia and hemochromatosis
Cancer, in which case it is called cancer fatigue
Chronic fatigue syndrome (CFS)
Drug abuse including alcohol abuse[
Depression and other mental disorders that feature depressed mood
Eating disorders, which can produce fatigue due to inadequate nutrition
Endocrine diseases like diabetes mellitus and hypothyroidism
Gulf War Syndrome
Heart disease
Irritable Bowel Syndrome
Inborn errors of metabolism such as Fructose malabsorption.
Liver failure
Infectious diseases such as infectious mononucleosis.
Leukemia or lymphoma
Lyme disease
Neurological disorders such as narcolepsy, Parkinson’s disease and post-concussion syndrome
Physical trauma and other pain-causing conditions, such as arthritis
Sleep deprivation or sleep disorders
Uremia, which is caused by kidney disease