Fatigue (also called exhaustion, lethargy, languidness, languor, lassitude, and listlessness) is a weariness caused by exertion. It can describe a range of afflictions, varying from a general state of lethargy to a specific work-induced burning sensation within oneâ€™s muscles. It can be both physical and mental. Physical fatigue is the inability to continue functioning at the level of oneâ€™s normal abilities. It is ubiquitous in everyday life, but usually becomes particularly noticeable during heavy exercise. Mental fatigue, on the other hand, rather manifests in somnolence.
Fatigue is considered a symptom, as opposed to a medical sign, because it is reported by the patient instead of being observed by others.
Physical fatigue or muscle weakness (or â€œlack of strengthâ€) is a direct term for the inability to exert force with oneâ€™s muscles to the degree that would be expected given the individualâ€™s general physical fitness. A test of strength is often used during a diagnosis of a muscular disorder before the etiology can be identified. Such etiology depends on the type of muscle weakness, which can be true or perceived as well as central or peripheral. True weakness is substantial, while perceived rather is a sensation of having to put more effort to do the same task. On the other hand, central muscle weakness is an overall exhaustion of the whole body, while peripheral weakness is an exhaustion of individual muscles.
In addition to physical, fatigue also includes mental fatigue, not necessarily including any muscle fatigue. Such a mental fatigue, in turn, can manifest itself both as somnolence (decreased wakefulness) or just as a general decrease of attention, not necessarily including sleepiness. It may also be described as more or less decreased level of consciousness. In any case, this can be dangerous when performing tasks that require constant concentration, such as driving a vehicle. For instance, a person who is sufficiently somnolent may experience microsleeps. However, objective cognitive testing should be done to differentiate the neurocognitive deficits of brain disease from those attributable to tiredness
Fatigue is typically the result of working, mental stress, overstimulation and understimulation, jet lag or activerecreation, depression, and also boredom, disease and lack of sleep. It may also have chemical causes, such as poisoning or mineral or vitamin deficiencies. Massive blood loss frequently results in fatigue.
The sense of fatigue is believed to originate in the reticular activating system of the lower brain. Musculoskeletal structures may have co-evolved with appropriate brain structures so that the complete unit functions together in a constructive and adaptive fashion. The entire system of muscles, joints, and proprioceptive and kinesthetic functions plus parts of the brain develop and function together in a unitary way.