Topic 2 - Biological Rhythms Flashcards
Circadian Rhythms
Biological cycles that occur naturally around once a day, such as the sleep/wake cycle
Phase delay
You delay the time when you go to sleep (ie. staying up later)
Phase Advance
You bring forward the time that you go to sleep (ie. going to sleep earlier).
Key Research
Czseisler et al (1982) - Rotating shift work schedules that disrupt sleep are improved applying circadian principles.
Background
The human sleep-wake cycle has evolved to fit our plannet’s 24hr day night cycle schedule. Employers with 24hr operations require employees to violate circadian principles.
Aims
To investigate the effects of taking the properties of the human circadian systems into account in the design of work schedules.
Samples
Great Salt Lake Minerals and Chemical Corp.
Utah
Potash Production
8hr phase advance shift system
153 Male Employees - 85 on rotating
Inital Self-Report
Questionaire
Rotating shift workers experienced more problems with insomnia
29% had fallen asleep at work
90% complained shifts changed too much
81% took 2-4 days to adjust after each change
Procedure
The 85 were split into two groups;
- All were changed to a phase delay pattern
- 33 continued to rotate shifts once a week
- 52 rotated shifts every 21 days
After 3 months of this new system, a questionaire was sent out to gain worker feedback
After 9 months, a productivity analysis was taken.
Results
Significantly more workers preferred the new phase delay.
Only 20% of people complained that shifts changed too often (21 day group).
Improved health index scores (21 days group)
Staff turnover dropped
Potash harvesting/productivity increased.
Conclusion
Work schedules that rotate by phase delay with an extended interval between each rotation are most compatible with human circadian timing. Work schedules must account for circadian rhythms.
Endogenus Factors
Internal forces which determine circadian rhythms eg. internal ‘body clock’.
Exogenous Factors
External factors which determine circadian rhythms eg. light
Siffre
Lived 400ft below below the surface in a cave for 2 months. This was in a completely dark environment
His body went through the sleep/wake cycle every 24.5 hrs rather than the day/night cycle of 24 hrs.
This suggests the internal body clock is independent from the day/night cycle.
Preckel et al
272 students in 9th + 10th grade at 5 German high schools.
Lark - Sleep before 11pm, Wake before 8am
Owl - Sleep after 11pm, Wake after 8am
Students were given a chronotype indicator (owl or lark)
Being an owl was harmful to GPA
School should start later for Owls.
