For me there are (atleast) two different types of fatigue. The two are closely related and have only a few differences but those cause a very unique physical experience in each case.

  • Physical Fatigue: Basically, what you feel after being out all night on a saturday night. It does not involve any degree of stress but there is a real heaviness and need to sleep for a very long time. One feels detached and pensive towards their surroundings.
  • Emotional Fatigue: Is created when one retains a great deal of stress from their day. Can also be caused by the aftermath of a great deal of anxiety or other strong negative emotion. A headache or muscle tension may be present. The need to sleep is even more intense then with physical fatigue. The ability to reason is impaired and one will sleep a half-sleep such that the mind is resting and the body is merely going through the motions.
Hmmm, Waterhouse seems to have forgotten Mental Fatigue. When you're really pushing the brain neurons to fire for long periods, such as finding a logic error in a program (even worse: machine code), you can easily experience this malady. I think a few folks get this every so often while posting nodes on E2. If there's a particular word that would fit perfectly for your writeup, and you spend 45 minutes pushing words through your mental thesaurus until you find it, you can experience mental fatigue.

Some symptoms of mental fatigue include posting a random nodeshell rescue GTKY writeup in the midst of hypertechnical factuals, getting sudden almost painful cravings for coffee that has boiled off half of the water (and thus concentrating the life-giving caffeine), and sudden cranial explosions similar to the movie Scanners.

Fatigue, the ayurvedic approach.

A stress-driven body and mind is the major cause of fatigue, for many people this is a normal state of living in today's hectic world. Most people have lost touch with the normal experience of "calm energy," which is a state of low tension and high energy that allows for optimism, confidence, and the stamina necessary to enjoy success, love and happiness.

What causes fatigue ?

According to ayurveda, fatigue is caused by overuse, misuse or no use of the mind, emotions or body,

Misuse is doing something that is against your nature. If you are an honest person, and you find yourself in a situation where you feel pressured to lie or cheat, that misuse of your mental faculties could cause you to feel fatigued.

An example of physical misuse is knowing that a physical task is beyond your capability, but doing it anyway. Or perhaps your heart is very tender, and you are surrounded by people who are habitually angry -- an example of emotional misuse.

Even lack of use can cause fatigue.
Use it or lose it applies not only to the body, but to the brain and emotions as well.

The first step in correcting fatigue is to determine the cause. You can ask yourself if your fatigue is caused by physical, mental or emotional factors. And is it caused by overuse, misuse or lack of use?

Once you know which behavior is causing the fatigue, you must, of course, stop that behavior. Become familiar with your stress-point and your own level of comfort. The solution to the problem of fatigue is found in one simple sentence: proper use of the mind, body and emotions.

The three doshas and fatigue.

There is a relationship between the three doshas and the three main types of fatigue. Mental fatigue is associated with an imbalance in vata dosha, emotional fatigue is caused by an imbalance in pitta dosha, and physical fatigue is caused by an imbalance in kapha dosha.

Ama (impurities caused by undigested food) is a major cause of all three types of fatigue. To avoid all types of fatigue, avoid leftovers, fast foods, foods grown with chemical fertilizers or sprayed with pesticides, or packaged, canned, frozen or processed foods.

Try the following recommendations for each type of fatigue:

For mental fatigue:
 * Vata-pacifying diet and daily routine.
 * Go to bed early, avoid mental work right before bed.

For emotional fatigue:
 * Pitta-pacifying diet and daily routine.
 * Never skip meals.

For physical fatigue:
 * Kapha-pacifying diet and daily routine.
 * Reduce ama and drink enough throughout the day.

Depending on your mind-body type and imbalances, you may be more susceptible to certain types of fatigue.

Two final points of advice for dealing with fatigue: cut back on coffee, cola, caffeinated teas, etc. And do not take sleeping pills, this allows your body to reestablish a natural rest and activity cycle.

Second, schedule enough rest each day. The human nervous system and body is not designed for a constant diet of tension, pressure, speed and excitement. It must have adequate rest to permit natural regeneration and recuperation, and to experience "calm energy" and joy.
Materials fatigue is the process by which materials fail or fracture when subjected to repetitive stress / strain. Fatigue failures are normally studied in the context of modern or manufactured materials, however the concepts apply to natural materials and fibers as well.

History The mechanism of fatigue was first studied when early railroad car or engine axles failed unexpectedly. Engineers of the time had a good understanding of simple stress failures however the resulting designs did not take into account the then unknown mechanisms of fatigue failure.

Mechanisms When metals are stressed the lattice structure deforms along slippage planes. Within the elastic limit, most of slippage is fully recovered on unloading. However under cyclic deformations some of the slippages are permanent and these begin to form microscopic cracks.

These small cracks can act as both stress concentrations and to effect stress relief, depending on the details of design and loading. At the micro-level stress cracks develop low pH at the crack-tip which acts to accelerate crack growth and is a factor in accelerating fatigue rate in aqueous, saline or corrosive environments.

Design implications

Many structural metals (iron, steel, titanium exhibit a distinct 'endurance limit' which is a level of cyclic stress which can continue for an infinite number of cycles without causing failure. Some materials (e.g. aluminum, magnesium) do not have a fixed endurance limit and will eventually fail at any level of repeated stress, no matter how low. Generally where there is a known endurance limit, if a structure survives one million cycles, it will last indefinitely.

The study of fatigue is a substantial branch of materials science. Because most reciprocating or rotating machinery sees well over a million cycles in many modes the economics of understanding fatigue are compelling.

Historically, when fatigue was not well understood, many catastrophic failures resulted, including for example early iron and steel ships sometimes broke in half due to repetitive stresses due to wave and storm motions.

Today many large structures such as bridges are inspected for fatigue cracks. In situations where it is not practical to completely prevent fatigue failure, the designer must accommodate the anticipate crack growth rate, crack-size and ensure that the inspection plan will find fatigue cracks at or above the critical size for the design.

High-stress, low weight components, such as engine connecting rods must be produced and maintained without transverse scratches, which will induce early failure by creating a stress concentration where a fatigue crack will be initiated at a lower level than in a smooth surface.

The fatigue endurance of critical components may also be increased by creating residual stress in the surface of the part. Usually this is accomplished by bead blasting the surface, which leaves the surface in a state of residual compressive stress. By pre-stressing in compression, the effective tension stress in the surface is reduced.

Fa*tigue" (?), n. [F., fr. fatiguer to fatigue, L. fatigare; cf. L. affatim sufficiently.]

1.

Weariness from bodily labor or mental exertion; lassitude or exhaustion of strength.

2.

The cause of weariness; labor; toil; as, the fatigues of war.

Dryden.

3.

The weakening of a metal when subjected to repeated vibrations or strains.

Fatigue call Mil., a summons, by bugle or drum, to perform fatigue duties. -- Fatigue dress, the working dress of soldiers. -- Fatigue duty Mil., labor exacted from soldiers aside from the use of arms. Farrow. -- Fatigue party, a party of soldiers on fatigue duty.

 

© Webster 1913.


Fa*tigue", v. t. [imp. & p. p. Fatigued (?); p. pr. & vb. n. Fatiguing, n.] [Cf. F. fatiguer. See Fatigue, n.]

To weary with labor or any bodily or mental exertion; to harass with toil; to exhaust the strength or endurance of; to tire.

Syn. -- To jade; tire; weary; bore. See Jade.

 

© Webster 1913.

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