Circadian, infradian and ultradian rhythms

Cricadian rhythms are biological cycles lasting around 24 hours facilitated by time checks and regular events such as meal times, and controlled by an endogenous pacemaker working as a 'body clock' Sleep-wake cycle

• Siffre (1972) sixth months in a cave with no times, settling into a sleep-wake cycle of 25-30 hours
• Aschoff and Weber (1965) found that participants in a bunker with no natural light settled into a sleep-wake cycle of 25-27 hours, implying that endogenous pacemakers exert a strong influence on circadian rythms.

Infradian rythms are biological cycles lasting more then 24 hours controlled by the hypothalamus…