Transcript

SIMON REA

The figure here shows a typical menstrual cycle of 28 days, although the cycle can last between 21 and 35 days and can be even longer in teenagers. So these 28 days are broken down into two phases. The first half of the cycle is called the follicular phase, and the second half the luteal phase.

There are four points in the cycle where hormones are at significantly different levels. Day one of the cycle is the first day of the menstrual bleeding, or when the period starts. And during the period, both of the hormones, oestrogen and progesterone, are at their lowest levels.

Oestrogen, which is shown in light blue on the figure, we can see how and it’s low initially. And then around about day 5 to 7, its levels start to rise up to a peak around day 12 before dropping off, and then it rises again a little bit towards the end of the cycle. So its profile goes from low, to high, to medium.

On the other hand, progesterone, which is shown in dark blue on the figure, is low for the whole of the first half of the cycle. But it rises after ovulation, around day 14, up to a peak towards the end of the cycle. So its profile goes low, to medium, to high. And then towards the end of the cycle, levels of both hormones start to fall off quite significantly.

This pattern is really important, as changes in each hormone can make the athlete feel differently and also produce different physiological responses in the body. Oestrogen is regarded as a feel-good hormone, as it increases the levels of another hormone, serotonin, which makes us feel good. And this can improve confidence, mood, and general wellbeing. It can also increase the motivation to exercise and has physiological effects, such as protecting against muscle damage, reducing inflammation in the body, and speeding up recovery time.

Now, because of these benefits, as oestrogen rises to its peak in the first half of the cycle, the physiological environment is considered most favourable for strength training and high-intensity exercise. A small number of studies have shown that if strength training is performed more frequently in the first half of the cycle and less frequently in the second half, the adaptations to this training are between 13% and 20% greater than if strength training is spaced more evenly across the cycle.

In the second half of the cycle where progesterone dominates, the serotonin levels start to drop. And this can for some people cause a change in mood, with the athlete becoming quieter and more introspective. At this point, it can become more difficult to build muscle and develop strength as progesterone, which is a catabolic hormone, meaning that it breaks down muscle. Also, the body is less able to use carbohydrate as a fuel for exercise. And this means that it can become harder to work at higher intensities.

And the body’s core temperature is raised by up to half a degree during the second half of the cycle. But this hasn’t shown to have any significant affect on heat tolerance during exercise. The drop in serotonin can also cause brain fog. And spatial awareness can be affected, which can make coordinated activities more difficult.

However, progesterone does have a big benefit, as it has a calming effect on the brain, meaning that athletes may feel less anxious and may sleep better. At the end of the cycle, the fall in levels of both hormones is the cause of many symptoms, which can be reported during this time, including pain, muscle pain, tiredness, increased anxiety, and irritability. And these symptoms can make training more challenging.