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Females

The Biology of the Menstrual Cycle

In the fifth resource in a series, the Welsh Institute of Performance Science’s Natalie Brown explains a typical or natural menstrual cycle and the signs of an irregular cycle

The menstrual cycle occurs due to changes in hormone levels in the body. Hormones are chemical messengers that interact between the brain and the ovaries, and there are four hormones involved in the control of the menstrual cycle. Of those four, two are released from the brain (Lutenising Hormone and Follicle-stimulating Hormone) and cause oestrogen and progesterone to be increased or decreased in the ovaries.

The fluctuations in oestrogen and progesterone cause the release of an egg and the lining of the uterus to build up in preparation to receive a fertilised egg. If the egg is not fertilised, levels of both hormones decrease and cause the lining of the uterus to break down causing menses (a period). This process repeats on average every 28 days (range of 21-35 days is normal) with day 1 of the cycle being the first day of bleeding. 

Periods begin for girls between the ages of 8 and 15; most commonly at the age of 12.

Key Terms

  • Follicular Phase (pre-ovulation): from the first day of the period to ovulation. Oestrogen begins to rise as the egg is prepared to be released.
  • Ovulation: when the egg is released from the ovary, mid-cycle (approximately 14 days after the last period in a 28-day cycle). Oestrogen is at its peak before and then drops shortly after the egg is released.
  • Luteal Phase: between ovulation and menstruation, oestrogen increases for a second time and progesterone is at its highest before both hormones decline rapidly if the egg is not fertilised.
  • Menstruation: the period when the uterus lining sheds, lasting between three and seven days. Levels of oestrogen and progesterone are low.

Basic facts about the menstrual cycle:

  • The menstrual cycle starts with the first day of the period (the bleed) and the cycle begins again when the next period starts.
  • Hormones interact between the brain and the ovaries causing maturation of the ovaries and release of the egg.
  • The menstrual cycle is much more than a period, affecting the digestive system, emotions, mental health, energy levels, and causing bloating, anxiety, cramps in the stomach and headaches, among others.

Key Points

The menstrual cycle lasts 21 – 35 days, but this may change and vary when periods first start for approximately the first 2 years (known as menarche), lasting up to 45 days. After this, periods should be regular and any variation may be caused by the negative effect of physical or mental stress, training and diet. Periods should be regular and are an important sign of female health. 

The process of ovulation provides the body with the much-needed hormones: oestrogen and progesterone. In addition to their function in fertility, they also influence bone density, metabolism, sleep quality, emotions, moods and mental health, all of which can impact on training and performance.

In this video, Natalie Brown answers the question: 'What is considered to be a typical menstrual cycle?'

Typical symptoms experienced across phases of the menstrual cycle

In this video, Natalie Brown discusses athletes’ experiences of period symptoms and how it makes them feel in relation to sport.

Opportunity to reflect

Were you aware of these menstrual cycle symptoms and if any females you coach experience any of these?

Atypical menstrual cycles

The menstrual cycle is a sign of short- and long-term good health in females.

Factors influencing menstrual cycle regularly include: 

  • hormonal contraceptives
  • age
  • diet
  • exercise
  • energy balance
  • pregnancy
  • medical conditions
  • stress
  • sleep
  • travel.

Menstrual cycles are considered irregular under these circumstances:

Menstrual cycles can also be atypical in the case of:

  • excessively painful periods
  • no ovulation
  • heavy menstrual bleeding.

In this video, Natalie Brown answers the question: 'What is considered atypical in relation to the menstrual cycle?'

More from Natalie Brown

This is the fifth resource in a series on menstrual health developed with Natalie Brown

READ THE FULL SERIES

Related Resources

  • The Menstrual Cycle: Female Athletes' Experiences and Perceptions

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  • Menstrual Cycles and Participation

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  • Understanding the Impact of Menstruation on Performance

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