Biological rhythms

Biological rhythm = Any change in a biological activity that repeats periodically, e.g, daily, monthly, annually.

There are 4 types:
Ultradian - less than 24 hrs
Circadian - 24 hrs
Infradian - More than 24 hrs
Circannual - Yearly

ULTRADIAN
(less than 24 hours) Friedman and Fisher in 1967 studied people in luxorious isolation who did not have any time cues. For example, food, drink and cigarettes were available at any time.  They found BRAC (basic rest activity cycle) followed 90 minute cycle over 6 hours.
Furthermore - Stages of sleep -

INFRADIAN
(longer than 24 hrs) Russel et al studied into womens menstrual cycles which are controlled by hormones released in the pituitary gland. Used 2 separate groups of females and wiped sweat on the upper lips of the other. He found that their menstrual cycles synchronised which may link EZ's in the form of pheromones. Additionally, when several women live together and do not take oral contraceptives it is known they tend to menstuate at the same time every month.
Men have monthly cycles too - Emspon 1977 - used 21 male ppts and their body temp/alerness was measured from 49-102 days. Found there was a 20 day cycle.

CIRCANNUAL
(yearly) SAD - season affective disorder) In winter we are more depressed, over eat and sleep due to high melatonin and reduced serotonin as…