Fatigue, definition

Dalakas MC, Mock V, Hawkins MJ. Fatigue Definitions, mechanisms, and paradigms for study. Semin Oncol 1998 25(Suppl l) 48-53. 

Chaffin, D. B. (1973), Localized Muscle Fatigue—Definition and Measurement, Journal cf Occupational Medicine, Vol. 15, p. 346. 

Fracture Mechanics. Linear elastic fracture mechanics (qv) (LEFM) can be appHed only to the propagation and fracture stages of fatigue failure. LEFM is based on a definition of the stress close to a crack tip in terms of a stress intensification factor K, for which the simplest general relationship is... 

Various materials (e.g., metal, plastics, or rubber) are used to make the flexing elements in these couplings. The use of the couplings is governed by the operational fatigue limits of these materials. Practically all metals have fatigue limits that are predictable, therefore, they permit definite boundaries of operation to be established. Elastomers such as plastic or rubber, however, usually do not have a well-defined fatigue limit. Their service life is determined primarily by conditions of installation and operation. 

In human exercise physiology, fatigue is often defined as an inability of a muscle or a group of muscles to sustain the required or expected force (Edwards, 1981). This definition is very applicable for the study of factors limiting dynamic or isometric exercise in intact organisms at varying intensities. 

In conclusion, it is apparent that the lack of definitive methods for assessment of free radicals in muscle and other tissues inhibits clear conclusions to be drawn concerning the relevance (or lack of relevance) of these substances in muscle pathology. In particular, the relevance of free radicals to the deficits in muscle function (fatigue and damage), which occur with exercise, is still unclear despite extensive study. This and other areas require much further examination. 

Desire. I should recognize it for what it is. No good pretending. Some trick of fatigue or grief or delayed shock or affection. Desire. No less but no more. Definitely no more. 

CDC Case Definition An illness characterized by acute or insidious onset of fever, night sweats, undue fatigue, anorexia, weight loss, headache, and arthralgia. Laboratory criteria for diagnosis is (1) isolation of Brucella species from a clinical specimen or (2) fourfold or greater rise in Brucella agglutination titer between acute- and convalescent-phase serum specimens obtained >2 weeks apart and studied at the same laboratory or (3) demonstration by immunofluorescence of Brucella species in a clinical specimen. 

Although fatigue is common and everyone knows what it is, it is difficult to define. One definition is the inability to maintain the required power output . Fatigue can be divided into two classes, peripheral and central. Peripheral fatigue arises within the muscle whereas central fatigue arises within the brain or the motor nerves. Although fatigue affects most people at some time in their life, there is no acceptable biochemical mechanism(s) to explain it. There are, however, several hypotheses. 

IDLH Immediately Dangerous to Life and Health. The OSHA definition for IDLH is the maximum concentration of contaminant from which one can escape in 30 minutes without suffering irreversible health effects or escape-impairing effects such as dizziness, fatigue, impaired judgement, or slowing. Based on human and animal studies IDLH may be considered the LOEL (lowest observable effect level) or 500 x PEL if no other data are available or any concentration... 

The Firestone flexometer method in D623 is not very specific. The standard test pieces are in the shape of a frustum of a rectangular pyramid but the use of any suitable shape is permitted when cut from products. The apparatus operates at 800 cycles/min and a range of compression loads and amplitudes of oscillation are possible, but no particular conditions are specified. The test piece is fatigued until a definite, but unspecified, decrease in the height of the test piece is reached, which is supposed to represent the onset of internal porosity. Parameters such as temperature rise and changes in compression are reported. 

Tyres are very definitely fatigued during use and, as mentioned for fabric/rubber adhesion above, it is very important to carry out dynamic tests to assess bond efficiency. Methods have not apparently been standardised but a variety of procedures have been reported71 79 Some workers have used the same or a similar test piece as in static tests and applied a cyclic tensile stress or strain, whilst others have used some form of fatigue tester operating in compression/shear to repeatedly stress or strain cord/rubber composite, or even to flex samples in the form of a belt. Khromov and Lazareva80 describe a method using test pieces cut from tyres. 

Fukuda K, Straus SE, Hickie I, Sharpe MC, Dobbins JG, Komaroff A. The chronic fatigue syndrome a comprehensive approach to its definition and study. International Chronic Fatigue Syndrome Study Group. Ann Intern Med 1994 121 953-959. 

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