The body changes during the day much as the tide of the ocean. At some times of the day the body is more alert than others and consequently can be the cause of injuries. These different alert periods are also known as circadian rhythms. These physiological rhythms change the heart rate, body temperature, blood pressure and hormonal fluctuations. These changes are at their apex between Noon and 6 PM. Their Low point is usually between 3 AM and 6 AM, which is usually when most people are sleeping. Given this information it is obvious that a person performing shift work may become less productive in the beginning of their shift change until their body catches up with their work routine. It is best not to have short shift work periods such as one week for one eight hour shift and after one week shift to the second eight hours, etc. This period of time is much too short for the body to become accustomed to the various three shifts of a 24-hour period. If one shift lasts for one week the workers body may take until Thursday or Friday to become accustomed by that time the hours of the shift will change i.e. Monday through Friday 8 AM to 4 PM then the next week 4 PM to midnight and the third shift midnight to 8 AM. Each of these shifts requires acclimation of the worker. Females have another cycle that they must contend with on a monthly basis. The menstrual cycle of the female worker usually plays an important part even if not formally acknowledged. This period typically has a cycle of 28 days that is divided into five phases the premenstrual and menstrual phase is probably the most important when relating to strenuous or hazardous working conditions.
Concepts in Human Factors Engineering is a series containing eleven articles:
While determining and considering these various circadian phases one must also allow for adjustments if justified. Individuals are not all the same and consequently will not be affected the same by short or long work shifts. As previously mentioned short shifts are not as stabilizing as longer shifts, for example the shift of
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