Menstruation happens to half the population, and enables the continuation of the human race, so it’s time we got comfortable talking about it!
Almost 95% of all females report some kind of menstrual cycle-related symptoms and 67% of female athletes believe these symptoms impair their athletic performance.
Throughout the menstrual cycle, women are exposed to constantly changing female steroid hormone profiles.
The follicular phase, (week 1 and 2), starts at the first day of your period and ends with the release of an egg, (ovulation). In the early phase, oestrogen and progesterone are low. Oestrogen begins to increase halfway through the follicular phase to reach a peak in the late phase with a sharp drop just prior to ovulation.
Following ovulation, both oestrogen and progesterone increase until a plateau is reached during the middle of the luteal phase, (week 3 and 4). In the late luteal phase both oestrogen and progesterone decrease again.
Some women, particularly recreational runners can experience an ovulation, (the lack of the release of an egg), and luteal phase deficient cycles. These cycles are characterised by low progesterone concentration during the second half of the cycle. They also demonstrate a high level of inconsistency from one cycle to the next. Changes in menstrual function, are not necessarily related to changes in bleeding patterns. These ovulatory disturbances often remain unperceived by apparently regularly menstruating women and is a common cause of infertility.
But do these changes in hormone profile over the menstrual cycle have an impact on exercise performance?
The current literature suggests that the fluctuations in female hormones through the cycle do not affect muscle strength or fatiguability.
Basal body temperature is increased during the luteal phase in most women who experience regular menstrual cycles. It is increased by 0.3-0.5 degrees celsius after ovulation and remains elevated throughout the luteal phase of the cycle. At the onset of menstruation, body temperature decreases to previous levels and remains at this level throughout the follicular phase. This increase in resting body temperature during mid-luteal phase remains elevated throughout exercise and/or heat stress.
This increase in basal body temperature may result in an increase thermoregulatory and cardiovascular strain and as such, may have a negative effect on prolonged exercise performance during the luteal phase of the menstrual cycle. There are some studies that show an increased cardiovascular strain during the luteal phase.
If it is assumed there is a critical core temperature limit for exercise performance, then elevated body temperature during the luteal phase will be a disadvantage and will limit time to exhaustion in the heat.
The practical take home message for regularly menstruating female endurance athletes in particular is to adjust the competition and training schedule to the menstrual cycle where the conditions are expected to be hot and humid. However, there does not need to be an adjustment where the contractile characteristics and VO2max are the greatest performance determinants.
For the every day exerciser, it may be worth tracking where in your cycle you are, especially when considering training or playing sport in the heat and humidity. This is not to say that it is unsafe to do so, but rather to manage your body temperature by exercising in the cooler part of the day, or where that is impossible, manage heat symptoms with ice, cold drinks and appropriate clothing.
Written by Simonne Reynolds (nee Spooner) FACP
Specialist Sports Physiotherapist
Director Spooner Specialist Physiotherapy