11. Infradian rhythms

What are infradian rhythms?

cycles that occur for longer than 24hrs. They could be weekly, monthly or annual cycles. e.g. menstrual cycle

General outline of an average menstrual cycle

The cycle begins from the first day of a woman’s period, when the womb lining is shed, to the day before her next period. The average cycle takes 28 days to complete, however this varied in every woman and can be anywhere between 21 days and 35 days. Menstruation lasts on average 5 days and ovulation is 14 days into the cycle.

What hormones are involved in the menstrual cycle?

Progesterone, oestrogen, FSH, LH

follicle stimulating hormone (FSH)

• role

• peak

• where is it released from?

• stimulates follicles to release egg.

• Peak at day 14 (ovulation).

• Released from pituitary gland

luteinising hormone (LH)

• role

• peak

• where is it released from?

• Triggers ovulation. Tells ovary what hormones to release.

• Peak at ovulation, day 14.

• Released from pituitary gland

progesterone

• role

• peak

• where is it released from?

• Maintenance and growth of uterus lining- increases womb lining, getting the womb ready for pregnancy.

• After ovulation, progesterone increases in preparation for the possible development of an embryo.

• released from ovaries

oestrogen

• role

• peak

• where is it released from?

• Triggers ovulation and helps with uterus lining

• Highest around half way through the cycle, during ovulation.

• released from ovaries

what happens if pregnancy doesn’t occur?

The egg is absorbed back into the body, the lining of the womb sheds, and this is the menstrual flow.

Menstrual cycle- exogenous zeitgebers. McClintock and Stern

• Aim

• Participants

• IV

• DV

• method

• results

• conclusions

• Aim- to show that the menstrual cycle is influenced by pheremonal secretions from other women.

• 29 women in total, uni students, no birth control

• IV- donor pheromones of someone who was about to ovulate or someone had ovulated

• DV- affect on length of cycle

• pheromones gathered from 9 women at various stages of the cycle- cotton pads placed under armpit for 8 hrs to ensure pheromones were picked up. Odour of pads rubbed upon upper lip of 20 other women (experimental group). On day 1- pads from start of cycle applied. On day 2- pads from day 2 etc.

• Results:

  1. Cycle shortens if inhaled secretions from women about to ovulate

  2. Cycle lengthened if inhaled from women who had already ovulated

  3. 68% of women had changes to cycle which brought them closer to their ‘odour donor’

• Supports role of exogenous zeitgebers and explains why some women who live together have synchronised cycles

AO3- methodological limitations in synchronisation studies

P- many limitations with synchronisation studies

E- numerous factors other than pheromones that could change a woman’s cycle, e.g. stress, diet, exercise etc that may act as confounding variables. Furthermore, small sample size and all students so can’t generalise

E- women self-reported about their own cycles. Recent replication of the research between women’s cycles in close proximity has failed to find evidence of menstrual synchrony suggesting reduced reliability

AO3- evolutionary approach

P- evolutionary psychologists suggest a possible reason for women’s menstrual cycles synchronising is that it provides an evolutionary advantage for groups of women

E- women who ovulate at same time likely to give birth at same time. the synchronisation of pregnancies means that childcare can be shared among multiple mothers who have children at the same time. this is due to a number of reasons I.e. women lactating at the same time, the release of oxytocin- mothers are able to bond to babies, more likely to want to care for another child

E-BUT it can also be argued that women becoming pregnant at the same time would put a strain on resources in a pre-industrialised society which would limit not enhance survival

L- therefore raises questions about whether would actually be an evolutionary advantage BUT perhaps

AO3- applications

P- there are many positive impacts of the increasing understanding of the menstrual cycle

E- it has led to improved training schedules for sportswomen.

E- during the follicular phase- high oestrogen=good for HIIT, quicker recovery and more motivated. When strength training is performed more frequently in follicular phase and less in luteal phase strength gains increase from 14-40% compared to when it is evenly distributed

during the luteal phase- high oestrogen and progesterone- high core temperature- feel warmer during exercise. Metabolism is also faster- use fat faster. Lower intensity aerobic training is more suitable. Also can relieve anxiety and promote good sleep- increases recovery.

L- shows positive applications for women from having increased understanding of the menstrual cycle