While different studies have produced variable results about the effects of fatigue inducing elements in flight performance and aviation errors, yet there is on the whole general agreement among researchers that fatigue is negative factor in aviation, particularly when it comes to military operations. "Despite the mixed findings, there is agreement on the importance of adequate sleep management and sleep logistics for military troops in wartime (Johnson & Naitoh, 1974; Naitoh et al., 1986; Nicholson & Stone, 1987). (ibid)

Researchers also point out that the varying results obtained from studies are related to and dependent on the type of experiments and the situations in which the testing takes place. They note that the best data and sources of information on the true effects of fatigue are often taken from actual combat situations and conditions; while many state that the results from simulations and laboratory experiments do not produce an accurate picture of the reality of fatigue and fatigue-induced errors in aviation. (ibid)

Many studies on fatigue focus on the effects on the body and the physiological implications of flying at high altitudes; as well as the way that this effects the inducement of bodily fatigue. A recent study on aviation fatigue states that, "exhaustion among flight crew is a significant but often underreported problem in civilian and military air operations.

As many as eight per cent of all plane crashes and near-misses in both civilian and military aviation are the result of pilot fatigue." ("One in Twelve Plane," 2005, p. 26)

The study looked at the results of investigations into accidents involving passenger aircraft over the past 30 years, records of crashes by U.S. Army, Navy and Air Force planes in peacetime, and war operations such as Desert Storm." Report author John Caldwell, of the U.S. Air Force Research Laboratory in San Antonio, Texas, says more effort must be made by airlines to ensure crew get enough sleep between flights."

Fatigue can result from facing stressful situations in difficult conditions for long periods of time, a situation that many Air Force pilots face in combat situations. Besides these factors, fatigue can result from and be complicated by physiological disruptions in the body "clock " and timing mechanisms. Sleep deprivation has been shown to be one of the central facets in the impacts on fatigue, especially under stressful conditions. This type of situation is obviously a central concern for the Air Force, and various methods including GO Pills have been used as a means of alleviating the problem. (Brown, L. 2003) However, there are many other strategies that can be implemented and which will be discussed in this section.

The exact nature of fatigue is a contentious issue among many researchers. There is considerable debate as to the interrelationship between the different types and definitions of fatigue that have to be taken into account. The studies of fatigue are essentially concerned with various manifestations of the phenomenon. These include changes in the level of aviation performance which are expressed in the decreased capacity for work. This is usually referred to as objective fatigue. This muscular fatigue is measured by the use of the finger ergograph. (Bartley, Chute & Ivy, 1947, p. 7)

Secondly there is physiological fatigue which refers to "...the physiological changes due to the chemical products of fatigue" and the metabolic rate of energy consumption which "... measures this real basis of physical fatigue and also mental fatigue in so far as it can be determined physiologically." (ibid) the third working definition of fatigue that is recognized is more psychological and relates to ennui or weariness and boredom. (ibid) All of these various definitions of fatigue are not mutually excusive have to be considered in the overall assessment of the effects of aviation fatigue.

Studies of fatigue have dealt the problem from three quite different angles. Some have defined fatigue in terms of the subjectively observed feelings of fatigue as these show themselves in ennui, boredom, dissatisfaction with the task, and feelings of bodily weariness and an unpleasant affective tone. All these can be grouped under the term Subjective Fatigue. Others have been concerned with changes in the level of performance or output as a result of continuous work. This can be called Objective Fatigue. Still others have taken the position that physiological changes within the organs constitute the real basis of fatigue, and that the term should be applied to them. This can be spoken of as Physiological Fatigue.

The problem with the measurement and assessment of fatigue in terms of these three central...

This has led to the following assessment of fatigue.
If any two of these three variables were correlated with one another the problem would be simplified, but as a matter of fact, each one is to a certain extent independent of every other. Neither subjective feeling nor output is highly correlated with physiological condition; nor are subjective feeling and output closely related. Output has a much less rapid decrement than subjective feeling. As a result of these discrepancies some psychologists, notably Muscio and Watson, have argued that the term fatigue is essentially ambiguous and should be eliminated from discussions of work and fatigue. (ibid)

In the light of the above view it seems obvious that each type of fatigue and its variables will have to be considered both in isolation as well as in conjunction with one another in order for the comprehensive picture of fatigue to emerge.

Flying at high altitudes is a central factor which affects the pilot and can lead to the physiological symptoms of fatigue. In investigating the effects of altitude on body functioning we first must understand what is defined as high altitude and then observe the important changes that occur in the internal environment of the human body. Exposure to changes in altitude has a profound effect on the human body. External conditions inhibit the body to provide sufficient oxygen for cellular respiration, causing the body to go into a state of homeostasis in an attempt to maintain life.

The effects of high altitude on the human body is hypoxia, hyperventilation, changes in lung volume, changes in pulmonary diffusing capacity, changes in number of red blood cells, changes in hemoglobin concentration, and changes in cardiac output. The human body is also prone to high altitude stress which includes effects like increased secretion of ADH, redistribution of body fluids, and impairment of mental reactions.

Human Ecology)

The relationship between altitude and fatigue as a result of the decrease in oxygen intake has been associated with symptoms of fatigue.

Generally the human body acclimatizes to high altitudes and begins to function differently to compensate for the change in atmospheric gases. Yet, the performance of body systems may decline rapidly and if prolonged and may be fatal. In order to sustain life the human body must absorb oxygen; it also expels carbon dioxide from the body. With an increase in elevation, the body is forced to adjust in order to provide adequate oxygen needed for internal respiration. One of the major effects that the body experiences when there is a reduction of oxygen is known as hypoxia.

The condition the body experiences when there is less oxygen available in the air, as at high altitude, is known as hypoxia. The condition in which the arterial blood contains lower than normal partial pressure of oxygen is sometimes known as hypoxemia. "The condition the body experiences when there is less oxygen available in the air, as at high altitude, is known as hypoxia. The condition in which the arterial blood contains lower than normal partial pressure of oxygen is sometimes known as hypoxemia." (Deitz & Thoms, 1991, p. 32)

Normal symptoms of acclimatization to altitude include increased heart and exhalation rates to rid the body of the increased amounts of carbon dioxide being inhaled; Increased bladder activity caused by increased levels of sodium bicarbonate due to the higher than normal levels of carbon dioxide in the bloodstream; Insomnia; Slight swelling of the feet and knees; and Breathlessness; and fatigue. "As a result of the lack of oxygen the muscles quickly become tired. Muscle glycogen, the muscles' energy store, decreases." (Clarke, 2003) Other symptoms are also indicative of symptoms related to extreme fatigue and can seriously impair an aviator's judgment.

In war and operational situations there are many stressful aspects that are often labeled as fatigue. This particularly refers to the syndrome of chronic nervous fatigue in pilots in operational conditions and relates to the more psychological aspects of fatigue. Researcher's state that this understanding of fatigue in military personnel is known as aeroneurosis, as described in a study by Armstrong.

The symptoms he described are more or less identical with those of the syndrome variously called "situational neurosis," "chronic exhaustion state," "anxiety state," "anxiety neurosis," or "chronic nervous exhaustion." We use the term chronic exhaustion state because we do not believe the functional disturbances encountered in a pilot…