Biological rhythms: Infradian and ultradian rhythms


Infradian rhythms: 

A type of biological rhythm that can take longer than a day to complete (frequency of less than 1 cycle in 24 hours) 

e.g.menstrual cycle 

- Governed by monthly changes in hormone levels which regulates ovulation.

The cycle if referred to as the time between the first day of the women's period, when the womb lining is shed, and a day before her next period. 

- Typically takes 25 days to complete (24- 35 days is normal).

- During each cycle- rising levels of hormone oestrogen causes ovary to develop an egg and release it (ovulation). 

- After ovulation, hormone progesterone helps the womb lining thicken and prepares for pregnancy.  

- If pregnancy does not occur- egg absorbed into the body, womb lining sheds. (bleeding- period). 

                                                                  Research study 

Menstrual cycle said to be endogenous (caused by internal influences). However, some studies suggest that it could be exogenous (caused by outside- environmental influences) such as the cycles of other women. 

Kathleen method and study


  • How menstrual cycle may synchronize as a result of other femles pheromones. McClintock involved 29 women with history of irregular periods.
  • Took samples of pheromones from 4 women at different stages of their menstraul cycles via cotton pad that the women wore on their armpits for 8hrs.
  • Pads treated


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