A03 Biological Rhythms: Circadian Rhythms

• Practical application to shift work

  Knowledge of circadian rhythms has given researchers better understanding of the adverse consequences that occur due to their disruption (desynchronisation). For example, night workers in shift work experience a period of decreasing concentration around 6 am (a circadian trough) where mistakes/accidents are more likely to occur.
• Shift work and poor health (Practical application to shift work)

  Research also found association between shift work and poor health because shift workers are three times more likely to develop heart disease due to stress of poor quality sleepo during the day. Thus, there are economic implications in terms of how to manage worker productivity.
• Practical application to drug treatments

  Circadian rhythms co-ordinate a number of the body's basic processes such as heart rate , digestion and hormone levels. This therefore has an effect on pharmacokinetics, the action of drugs on the body and how well they are absorbed and distributed.
• Circadian peak times (Practical application to drug treatments)


  Research into circadian rhythms revealed that there are peak times during the day/night where drugs are most likely to be effective which led to the development of guidelines to do with drug timing with medications: like anticancer and respiratory drugs.
• Use of case studies and small samples

  People involved may not be representative of the wider population and limits the extent of meaningful generalisation.
• Siffre's most recent case study (Use of case studies and small samples)

  Siffre,aged 60, in his most recent cave study, observed his endogenous pacemaker ticked more slowly than when he was younger. Even when the same person is involved, there are factors that vary which may prevent general conclusions from being drawn.
• Poor control in studies

  Ppts still had access to aritificial light. For example, Siffre turned on a lamp when he woke up until he went to bed. It was assumed that the light would have no effect on the free-running circadian rhythms but Czeisler adjusted his ppts' circadian rhythms from 22 hours to 28 using a dim light.
• Individual differences


  Individual cycles can vary from 13 to 65 hours complicating the generalisation of the findings.
• Duffy et al study (Individual differences)

  Revealed some displayed a natural preferance for going to sleeping and waking up early (called Larks) while there were ppts who preffered the opposite (called Owls). Also there is an age difference in sleep/wake cycles.d