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Capacity Building
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Mindset
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Shift Schedules
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Circadian Rhythms
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Chronotype Test
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Determine Your Chronotype
To determine your own circadian rhythm pattern or chronotype, complete our online morningness-eveningness assessment known as the M-E Scale.
What is a Chronotype?
Chronotype is the scientific name for your individual circadian rhythm pattern. There is considerable research to document that chronotype is a key factor in determining shiftwork tolerance, and a critical element in the selection of effective individual shiftwork readiness or lifestyle adjustment strategies. Humans have been defined in terms of three major circadian types or chronotypes, using measures such as the Horne-Ostberg Morningness-Eveningness Scale, a subjective instrument that has been correlated with body temperature and other physiological factors. The three types are "morning," "evening" and "indifferent" or "mid-range". The first two categories each represent approximately 15% to 20% of the human population and the "indifferent" or "mid-range" category applies to the majority (60% to 70%) of humans.
Larks, Owls and Shiftwork
A morning-type individual, or "lark", is defined as one whose circadian rhythms are skewed about two to three hours earlier than the norm for the human population as a whole. That is, larks naturally awaken between 4:00 a.m. and 6:00 a.m. and are ready for sleep by 8:00 p.m. to 10:00 p.m. To a lark, midnight is perceived as the middle of the night. Conversely, an evening-type individual, or "owl", is defined as one whose circadian rhythms are skewed about two to three hours later than the norm. That is, owls naturally awaken between 8:00 a.m. and 10:00 a.m. and do not find themselves feeling sleepy until the midnight-to-2:00 a.m. time frame. The traditional 8-hour evening shift is a perfect physiological fit for this "owl" population, even though social strains may occur.
Studies comparing the tolerance of larks and owls for a night-shift assignment have found that morning types are more sensitive to delays in night sleep. Moreover, their sleep duration during a morning sleep is shorter, and they show a greater decrease in indicators of fitness after night work. Morning-type individuals also report less satisfaction with night work, indicating that there can be attitudinal challenges among "larks" assigned to the night shift.
Shiftwork Adjustment Strategies
Considerations of circadian or biological type as a predictor of shiftwork success must be tempered, however, with some findings about long-term adjustment to shiftwork. A five-year study of the health and psychosocial effects of shiftwork found that morning-type individuals initially had more difficulty with work schedules involving night work. Then, data gathered at the end of this 5-year study period indicated that there were a higher proportion of "owls" and "indifferent" types in the unstable or maladjusted group, and a higher proportion of morning types or "larks" in the stable or adjusted group (Kundi, et. al., 1985).
This longitudinal research has demonstrated that the early onset of difficulties among shiftworkers, and especially "larks", can act as a signal that targeted strategies must be used to cope with shift-related challenges. Unfortunately, the initial absence of such problems in "owls" often reduces their motivation to develop effective coping mechanisms. So, these "owls" develop one or more of the common effects of shiftwork, all because they were not intentional in selecting and implementing effective coping strategies.
As the research makes clear, chronotype can help you adjust to shiftwork. But, no matter what your chronotype may be, shiftwork adjustment has to be an active, intentional process—not a passive one—if it is to be successful.
Learn your chronotype -->
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