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Bio. rhythms are cyclical changes in the way bio. systems behave. They are driven by pur body's internal 'clocks' called endogenous pacemakers (e.g. SCN) but exogenous factors(e.g. light, time, social cues) also have an influence --> We need to respond to environ. changes to function - not every part responds quickly = de-synchronisation--> Two most common types: jet lag & shift work

Shift work - pattern of working during the night & sleep during day so out of sync w/influence of zeitgebers --> Shift works leads to:

 Decreased alertness .. 'circadian trough' ..midnight-4am when cortisol & body temp. lowest

Sleep deprivation - daytime diff. to sleep (noise/daylight) ..typically 2 hours shorter than normal nocturnal sleep; REM in particular affected --> Lack of sleep makes coping w/circadian trough diff.

KNUTSSON - shiftworkers for 15+yrs 3x likely as non-shiftworker to heart disease --> MARTINO - suggests could be due to direct effect of desynchronisation of rhythms or indirect such as sleep deprivation

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H/W  shift work effects not just due to disruption of bio. rhythms (REDUCTIONISM) --> i.e. lack of sleep associated with having to go to bed at unusual times/ lack of time socialising --> SOLOMON 60% divorce rate among night shift workers

Research has shown that:

  • rotating shifts disruptive (GOLD)- Shifts at set time are better.. but even then having days off will cause disruption
  • shifts involving phase delay less damaging to health --> BAMBRA further suggests that change in shift every 3-4days is better than 7days
  • very bright artificial lighting (10000 lux) shown by BOIVIN +ve effect on advancing circadian rhythm of 31 males --> Even ordinary lighting had effect (but not dim lighting) --> further SUPPORT GRONFIER: entrained circadian rhythms.. 24 hrs..bright light pulses

Jet travel and jet lag

We arent equipped to cope w/sudden changes in bio. rhythms - reflected by 'jet lag' (symptoms: fatigue, nausea, disorientation, insomnia) when travelling long distances...

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Disruption III

..very quickly --> advised to take 1 day to adjust to each hr of time change

RECHT SUPPORTING evidence for jet lag: US baseball team --> performance affected by 3hr time change across US --> More wins (44%) = EAST to WEST .. b/c phase delay.. longer day --> More losses = WEST to EAST .. phase advance.. day started earlier --> Field study = evidence high ecological validity H/W ONLY generalisable to baseball player

Melatonin 'miracle cure' for shift lag & jet lag --> hormone naturally occuring in sleep-wake cycle can be artificially taken at bed-time to help re-synch body clock --> Shown to work but must taken at right time at correct dosage

ALSO not eating then eating to fit new time zone helps

INDIVIDUAL DIFF: to which people are affected by shift work or jet lag --> H/W majority cope well

RESEARCH METHODO.: lab expts=variables isolated high internal validity H/W lacks ecological validity of real experience of shift work etc.

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disruption IV

REAL WORLD APPLICATION: useful to industry - accidents workplace occur night - we know circadian trough exists interventions put in place to help workers alert at diffic. time --> reducing effects of disruption of bio. rhythms = saved lives, improved labour productivity & safety

Most evidence based on biological factors (REDUCTIONISM) --> H/W all objective scientific data, found again and again =reliable --> H/W interaction of bio. factors & other factors such as INDIVID DIFF. & influence of external/social cues (e.g. food) need to be studied --> Furthermore, explanations could be argued DETERMINISTIC imlpies individ. cannot control jet lag effect etc .. clearly evidence that individ. behaviour (i.e. changing eating patterns) influence how badly sufer jet lag

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