This is sourced from Naval Strike and Air Warfare Center; ??Performance Maintenance during continuous flight operations;?? published 01 Jan 2000; and from USAF School of Aerospace Medicine; ??Warfighter endurance management during continuous flight and ground operations??; published January 2003;

Before we start, we’ll need a couple of definitions. Continuous Operations: Operations that extend over 24 hours at a normal rate. Each individual works a usual amount of hours, and is relieved at the end of a shift to return later. As the operation runs round-the-clock an individual will work different hours which may conflict with circadian rhythms, and disrupt sleep patterns. Sustained Operations: Involve continuous performance longer than 24 hours. Work is continued until a goal is reached. Sleep deprivation is common. Prevalent in ground warfare.

After a night without sleep mental and motor skill performance degrades to that of an individual who is considered to be legally drunk, (i.e. blood alcohol content (BAC) of 0.10 %). Even 18 hours of wakefulness equates to BAC of 0.05%.

Sleep cannot be stored up prior to a continuous or sustained operation. Sleep loss, circadian rhythm disruption and hard work combine to produce fatigue. Fatigue is not due to lack of motivation or attitude. Fatigue needs to be managed.

The planning and organisation required prior to the start of an operation may mean a team is already tired. This is referred to as preload.

Prior experience with sleep loss does not provide training to maintain performance. Resistance to fatigue varies between individuals.

Combat naps, the military equivalent of a power nap, help to maintain performance. After a power nap, individuals may experience 5 – 20 minutes of sleep inertia characterized by confusion and sluggishness. Taking more naps (practicing) appears to reduce this problem. During sustained or continuous operations, power naps should be encouraged and sometimes mandated. Power naps should last less than 40 minutes from the time one begins to attempt sleep to the time of awakening. It is designed to be too short to allow the individual to enter slow wave sleep (SWS) and yet still get a brief, hopefully restorative, nap. The first SWS epoch occurs within about 60 minutes. Research suggests that these naps can provide between 2 to 4 hours of useful physical and mental activity, for about 2-3 days, sometimes longer. After a few days however, cumulative sleep debt would be overwhelming.

A short sleep is best when more time is available for rest during a mission but not enough for a full sleep. Short sleeps are recommended to be at least 3-4 hours in duration. They are designed to allow the individual to progress through and avoid the SWS epochs. These sleep periods can maintain useful waking performance levels for 4-10 hours and perhaps longer. Although few studies have been done, anecdotal military evidence suggests that 3-4 hour naps can maintain crews for 4-5 days before sleep debt becomes overwhelming.

The minimum amount of sleep required to maintain performance during sustained operations is 4 – 5 hours per day. Fragmented sleep is less effective.

A ‘normal’ sleep is generally accepted as being 8 hours. Whatever the length of sleep, it should occur in 90 – 100 minute increments to avoid awakening during the deeper stages of sleep. This will minimize sleep inertia. Sleep should occur at the same time every day (including weekends), in a dedicated, quiet and dark place.

Sleeping more than 10 hours may cause sleep drunkenness and should be discouraged, even after a period of sleep deprivation.

There are numerous cyclic body rhythms in humans that collectively are described as circadian rhythms. Isolated from all external clues, humans seem to operate on a 25 hour cycle. External clues such as light and darkness (the most powerful cues), sleep, meals, social activities and clocks, reset the biological clock daily.

On an average circadian cycle, performance peaks between 12:00 and 21:00 hours (normally around 16:00), and falls to a minimum between 03:00 and 06:00 hours.

Continuous or sustained operations, trans-meridian travel (jet lag) and sleep deprivation all force the rhythmic systems of the body to re-adapt. They become out of phase with local time and with each other. Some phases will be delayed and others advanced. Seven continuous days of shift work are required to adjust the body temperature cycle. A single period of night work, or seven in a row, is more easily tolerated than three of four consecutive nights (which starts the process of circadian desynchronisation). If a round-the-clock operation is needed teams should specialise in either days or nights.

Extroverts, younger people, and those living on a more regimented schedule tend to have an easier time adjusting. As a general rule the body will adapt 40 minutes/day when traveling east and 60 minutes/day when traveling west. Westward travel requires lest time to acclimate. Bright lights maintain alertness and are a strong factor in accelerating circadian adaption.

It is easiest to initiate sleep twice a day; in the early afternoon and just before normal sleep time. Alcohol, while initially relaxing, significantly worsens the duration and quality of sleep. Caffeine interferes with sleep, and prevents effective napping. A nap or short sleep is most effective during the low point of the circadian cycle (03:00 – 06:00 hours).

Fatigue is both physical and mental. Physical aspects involve a loss of the power of muscles and sensors to respond. Mental fatigue includes the subjective feeling of weariness followed by worsening performance of cognitive tasks. This subjective sense of fatigue is the first indicator that people are getting tired. A useful external indicator is that the fatigued person loses their sense of humour.

During the Falklands conflict sedatives were used by the British to regulate sleep for pilots. Amphetamines were used by the British and Germans in WWII. During Vietnam both the American Air Force and Navy made amphetamines available to aviators. Intermittently since Vietnam up through Desert Storm the Air Force has used both amphetamines and sedatives in selected aircraft for specific missions. A combination of dextro-amphetamine (Dexedrine) and scopalomine are used by the Navy and NASA to combat motion sickness.

5mg of dextro-amphetamine (Dexedrine) help maintain alertness without causing other changes in mood and perception. 200mg caffeine compares favorably to amphetamine in improving cognitive performance but is less effective in maintaining alertness. 5mg of Dexedrine can be taken every 2 hours if required; dose should not exceed 30mg per 24 hour period.

Benzodiazepines produce the ‘most natural’ quality of sleep, and are used as sleep initiators. 5mg of zolpidem (Ambien) or 15mg of temazepam (Restoril) is used as an aide to sleep. A 7 – 8 hour period of restriction from higher cognitive activities is needed after taking this medication. No more than 10mg of zolpidem or 15mg of temazepam can be taken per 24 hour period.

Medication should be tested prior to it being needed, to allow individuals to adapt and gain familiarity with it. The Navy states that the use of stimulants or sedatives is appropriate only in combat or during exceptional circumstances of operational necessity.