What is Circadian Rhythms ?

Apart from the alternation between wakefulness and sleep, man has other internal
cycles, such as body temperature and hunger/eating. These are known as circadian
rhythms as they are related to the length of the day.

Basically , Circadian rhythms are physiological and behavioural functions and processes in the body
that have a regular cycle of approximately a day (actually about 25 hours in man).

Although, circadian rhythms are controlled by the brain, they are influenced and

synchronised by external (environmental) factors such as light. 

An example of disrupting circadian rhythms would be taking a flight that crosses time 

zones. This will interfere with the normal synchronisation with the light and dark (day/

night). This throws out the natural link between daylight and the body’s internal clock, 

causing jet lag, resulting in sleepiness during the day, etc. Eventually however, the 

circadian rhythm readjusts to the revised environmental cues.

circadian rhythm for body temperature. This pattern is very

robust, meaning that even if the normal pattern of wakefulness and sleep is disrupted

(by shift work for example), the temperature cycle remains unchanged. Hence, it can

be seen that if you are awake at 4-6 o’clock in the morning, your body temperature is

in a trough and it is at this time that is hardest to stay awake. Research has shown

that this drop in body temperature appears to be linked to a drop in alertness and

performance in man. 

Although there are many contributory factors, it is noteworthy that a number of major 

incidents and accidents involving human error have either occurred or were initiated in the 

pre-dawn hours, when body temperature and performance capability are both at their 

lowest

The engineer’s performance at this ‘low point’ will be improved if he is well rested,

feeling well, highly motivated and well practised in the skills being used at that point.