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Shift Lag: The time it takes to adjust. Disrupting Biological/ circADIAN Rhythms: Shift Work. Aims To know the effects of shift work upon EP’s and EZ’s To know the key study of Czeisler (1982) To understand the effects of a phase delay system in shift work

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disrupting biological circadian rhythms shift work

Shift Lag:

The time it takes to


Disrupting Biological/circADIAN Rhythms: Shift Work


To know the effects of shift work upon EP’s and EZ’s

To know the key study of Czeisler (1982)

To understand the effects of a phase delay system in shift work

To be able to explain the role of melatonin on biological adjustment

To be able to evaluate research on disruptions to biological rhythms

key concepts
Key concepts
  • SCN disruption
  • EP and EZ De-synchronisation
  • 12000 Lux artificial Light is best
  • Individual differences (unhappy and happy)
  • Czeisler’s research
  • Accidents that justify research
  • Influence of Day time Sleep
  • Phototherapy
  • Melatonin

Shift work patterns involve dividing the day into three eight hour shifts



4:00pm-12:00 am

shift work
Shift work
  • Shift work patterns involve dividing the day into three eight hour shifts
        • 12:00 - 8:00 am
        • 8:00 am - 4:00 pm
        • 4:00 pm -12:00 am
  • Therefore leading to the disruption of the EP’s and EZ’s.
  • There is usually a shift change each week, and Jet Lag studies show us that this is not long enough time for resynchronisation to complete. Therefore workers are in a chronic state of Jet Lag impairing performance and increasing stress.
  • When we are working out of phase with our biological clocks our performance is reduced, we are less attentive and slower to respond.
  • Disasters examples
  • Two problems arise with shift work
    • The need to maintain a 24 hour that is out of sync with the world and
    • The demands of a changing shift pattern
human error and shift work
Human error and shift work
  • Negative effects
    • e.g. decreased attention
    • slowing of reasoning skills
    • impaired reaction could have serious consequences on the ability to do work or drive safely.

Possible justification for animal research

Practical application of Psychology in the real world

sleep deprivation studies
Sleep deprivation studies
  • Peter Tripp
  • Randy Gardner

If the question asks for disruption of biorhythms you can discuss sleep deprivation, shift work, jet lag and SAD and DSPS

  • The specification states that you need to know about disruption of biological rhythms… clearly suggesting more than one.  The two obvious ones suggested above are the effects shift work and of jet lag.  However, SAD is a disrupted biorhythm that can be seen as either circadian or infradian so can also be discussed in a question on disruption of rhythms. 
  • However, a much richer vein of material would be a discussion of the effects of sleep deprivation studies, covered in the sleep section.  Work by Dement, Jouvet, Rechtschaffen, Huber-Weidman  and the case studies of Randy Gardner and Peter Tripp look at the effects of disrupting the stages of sleep (ultradian) and the sleep-wake cycle (circadian).
the need to maintain a 24 hour that is out of sync with the world
The need to maintain a 24 hour that is out of sync with the world
  • People who are working shifts are often sleep deprived because they find it hard to sleep with there is light outside and its noisy
  • The social constraints may tempt workers to stay awake when they should be sleeping
seo et al 2000 older shift workers
Seo et al (2000) older shift workers
  • Found that older shift workers had less total sleep time because they woke up early.
  • To solve the problem of being woken by daylight, shift workers are recommended to use thick curtains or blackout blinds.
  • Shifts workers tend to be awake late evening and/or early morning and sleep during the day. Unless workers succeed in resetting their biological clocks they experience sleepiness at work and insomnia at home.
  • This is more severe when shifts change often and they move against the clock.
  • After a shift change people take a week to adapt to the new regime, during which they are less productive as they are operating during their body’s night clock and restless when they should be sleeping.
czeisler et al 1990
Czeisler et al (1990)
  • Czeisler et al (1990) believes that shift work environments that are warm and dimly lit are counter productive. So, they compared the rate of adaptation of two groups of ppts to an imposed shift change by asking them to report to the laboratory during the night and sleep at home during the day.
    • The control group worked during the night in ordinary indoor lights of about 150 lux.
    • The experimental group worked under bright illumination of 7000-12000 lux, equivalent to early morning light.
    • The experimental group were also asked to stay in complete darkness from 9am to 5pm, whilst the controls were given no specific instructions.
  • The resetting of the biological clocks were monitored by measuring body temperature, which varies rhythmically.
    • After 6 days the experimental group had all shifted the low point of the circadian temperature rhythm by 10 hours,
    • the controls 1 hour.
    • Bright lighting in the work place seems to be key to helping workers to adapt to new shifts so that they are alert at work and sleep well during the day. Even in this situation adaptation can take up to 4 days, so workers who change shift every week would spend most of their time desynchronised .
treatments for jet lag and shift work
treatments for Jet Lag and Shift Work

Boivin et al (1996) put 31 male participants on an inverted sleep pattern (so they were awake at night and slept during the day) for three days.  Each day when they woke they were sat in front of dim lights for 5 hours and then placed in one of four conditions: Very bright light, Bright light ,Ordinary room light , Continued dim light. Core body temperature was recorded and used as a measure of how well they were adapting to the new rhythm. After three days: Group 1 had advanced by five hours (they were adapting to the new pattern best) Group 2 had advanced by three hours. Group 3 had advanced by one hour. Group 4 had drifted backwards by one hour (were failing to show any signs of adapting).


Artificial light can help us adapt our bio rhythms to suit the environment, however, brighter light is even more effective. Clearly, this useful in the workplace to help shift workers to adapt to changing sleep-wake cycles. 

Shift work

circadian rhythms that adapt more slowly cope best with shift lag jet lag
Circadian rhythms that adapt more slowly cope best with Shift Lag/Jet lag

Other individual differences: ………………………….


daytime sleep problems for shift workers
Daytime sleep problems for Shift workers
  • Insomnia
  • Temptations
  • Less quality and quantity
  • Tiredness
  • Social isolation
  • Divorce


answer the following questions from eysenck p 86 87 176 177
Answer the following questions from Eysenck p.86-87/176-177
  • Describe the findings and significance of the Moore-Ede (1993) research. ($77Billion, accidents, medical expense)
  • Describe the shift work patterns as suggested by Monk and Folkard (1983). (RapidCircadian maintained, Slow)
  • What has been suggested as a method of rapidly resetting biological rhythms? (Bright light substitute)
  • Explain the findings of Dawson and Campbell’s (1991) research. (bright light 4 hours helped ppts to work better)
  • Describe Czeisler’s (1982) suggestions.
  • Evaluate research into disrupting biological rhythms.
czeisler et al 1982 utah chemical plant

Extend Rotation Length! 7-21

Czeisler et al.(1982) Utah chemical plant
  • Czeisler et al (1982) carried out a study in a Utah chemical plant, where there was a high incidence of health, sleep and stress problems reported by staff who were on short rotation shifts.
  • Czeisler persuaded the company to change to a phase delay system (moving a shift forward each time) and to increase shift rotation from 7 to 21 days, allowing for more adjustment. Consequently, 9 months later worker satisfaction and factory output both increased.

Phase Delay


research findings
Research findings
  • A significant strength of this research is the consistent evidence that disrupting biological rhythms has a negative impact upon cognitive and emotional well being. Leading at times to serious consequences.
  • For example, Czeisler et al (1982) found out that there was a high incidence of health, sleep and stress problems reported by staff who were on short rotation shifts.
methodological issues
Methodological Issues
  • A Further strength of this research area is that the evidence is generated from field studies that have high validity.
  • However, an unavoidable limitation is the inability to control for confounding variables, such as personality and individual differences.
  • Therefore, it proves to be more difficult to reach complete conclusions about the causal influences in any resulting behaviour.
real life significance
Real life significance
  • This area of study has huge application in the real world. Although many of these studies show the negative consequences of disrupting biological rhythms, many people who carry out shift work do not suffer from cognitive impairment, (lack of attention or concentration ) or any negative effects on their emotional well being.
  • This demonstrates clearly the remarkable ability of our biological rhythms to adapt to changing environmental circumstances.

Different Recommendations

Less fluctuations (non-fluctuating shifts)

cause less disruption to the SCN

dawson and campbell
Dawson and Campbell
  • It might help if shift workers reset their biological clocks as quickly as possible. Bright lights as a substitute to daylight has proven effective in resetting the biological clock.
  • Dawson and Campbell exposed workers to a 4 hour pulse of very bright light which appeared to help them work better.
ways to lessen the effects
Ways to lessen the effects
  • Monk and Folkard (1983) identified two major types of shiftwork:
    • Rapidly rotating the shifts (weekly)
    • Slowly rotating the shifts (monthly)
  • There are problems with both shift work systems. However rapidly rotating may be more beneficial. They allow the workers to maintain a fairly consistent circadian rhythm. Whereas, slowly rotating shifts can cause harmful effects by causing major changes to individuals circadian rhythms.

Fast rotation = less disruption and less social isolation; more consistent Circadian activity

rapid is best
Rapid is best
  • On the other hand, research has found that it takes people about a week before their circadian rhythms have adjusted to a new sleep/wake cycle, so one might expect slow rotation would be better. Rapid rotation means that your rhythms are always disrupted.
task 7 choosing treatments
Task 7: Choosing Treatments

Shift Work

Jet Lag

Imagine you are an occupational psychologist and have been asked to work with nurses to help them deal with the effects of shift work. After reading your notes on this topic and the information on page 176 in Eysenck and 8/9 in the complete companion

What recommendations would you make?

Imagine you are an occupational psychologist and have been asked to work with a flight crew to help them deal with Jet Lag. After reading your notes on this topic and the information on page 175/176 in Eysenck and 8/9 in the complete companion

What recommendations would you make?

treatments for jet lag and shift work2
treatments for Jet Lag and Shift Work

Melatonin helps Jet/Shift lag because it binds to neurone receptor sites on the SCN, altering their activity, resetting the biological clock.

Takahashi (2002) found that Melatoninspeeds up the resynchronisation process after an 11 hour flight.

Sharkey (2001) Melatoninspeeds up biological adjustment to shift patterns, and increased sleep time during non-work periods.

Herxheimer and Petrie (2001) reviewed 10 studies and found that where melatonin was taken near to bedtime, it was remarkably effective. However, if taken at the wrong time of day it may actually delay adaptation



  • If you take 0.5mg of melatonin you will fall asleep earlier and wake earlier (phase advance). This is called phase advance because we advance the sleep phase (sooner).
  • If we are exposed to bright light in the evening, the opposite occurs: we sleep and wake later – phase delay.
    • Phase advance – early bird – Older people
    • Phase delay – owl – Teenagers/young adults

AO2/3: Individual differences

  • Biological rhythms play an important role in our sleep and wake cycle, as well as our cognitive and emotional preoccupations
  • Pineal gland, and suprachiasmatic nucleus relate endogenous pacemakers to exogenous zeitgebers
  • Disruption of biological rhythms bear catastrophic consequences

This is the consequence of Disrupting

Circadian Rhythms

Less REM

Less DEEP sleep


The brighter the light

The greater the adaptation

Cause 1: sleep deprivation

Causality can

Not be


Cause 2: Circadian

Rhythm/SCN disruption

10,000 lux

Black out blinds

The brighter the light

The greater the Circadian shift

24 marks
24 marks
  • Describe and evaluate research and or theories into biological rhythms (24 marks)
  • Write up a report discussing research into circadian rhythms (8m).
  • Describe the human endogenous pacemaker (biological clock) in control of the sleep wake cycle (6m).
  • What application to the real world has biological rhythm research got? (4m)
  • Explain individual difference effects on Circadian Rhythm research (8m)
  • Discuss research and explanations of the disruption to Circadian rhythms (16m) AO2/3 Evaluation/commentary
  • Jet lag example
  • SCN disruption
  • Jet lag research
  • Individual differences
  • Shift work example
  • Czeilser Utah
  • Czeilser 1990
  • Melatonin treatments (x3)
  • Justification of animal research
  • Animal research
  • Real world application