I’ve been wanting to write a post about how the menstrual cycle can affect running performance for a while now, but I’ve been putting it off because it’s a little uncomfortable isn’t it? However, our bodies and our hormones really affect our performance, and every woman should take into account her own personal cycle when planning training and reviewing performance.

I should probably say here that I am not medically trained, and the following observations are simply my own experiences and based on my own research. Everybody is different, so keep a diary and figure out what works for you.

It probably helps to understand the menstrual cycle first. The first day of the cycle is the first day of bleeding, which can last anywhere between around 3 and 7 days. The follicular phase (of which bleeding is a part) lasts around 14 days, sometimes longer, and leads up to the ovaries releasing an egg (ovulation) which begins with a surge in oestrogen and lutenizing hormone. The following 14 days is called the luteal phase, where oestrogen is at its highest, which has been noted can hinder performance.

I’ve been tracking my running performance for almost a year now, and how it fluctuates according to where I am in my cycle, and I’ve noticed some patterns:

  • The first two weeks of my cycle (the follicular phase) I can run fast for less effort. I generally set PBs during this time, even on the first day of my period, and plan in my races accordingly. Some women tell me they can’t run during their period, but for me, I feel at my strongest and fastest. My heart rate is lower despite running faster than normal. I have a feeling that a lot of women don’t like running during their period because they may be bleeding heavily, and they may be suffering cramps, but actually exercise can help reduce period pain and those feel-good endorphins are a great mental boost. I’m lucky not to have cramping, and I love that I feel super-powered at running during my period.
  • During ovulation I generally feel a bit icky, I get pain, and it’s during that fortnight leading up to my next period that my performance tends to decline. I slow down, my legs feel heavier, and I seem to hit zones 4 and 5 when running at or near to my aerobic threshold (i.e. a tempo run) where I would usually be in zone 3 during the follicular phase. I usually do longer runs here as my endurance doesn’t suffer, but I do find it tougher. The few days before my period, I feel like I’m terrible at running. The simple (scientific) explanation here is that during this luteal phase, increased oestrogen promotes fat utilisation because the body wants to spare glycogen. What does this mean for performance? Simply that the female runner should take on extra carbohydrate for additional energy while training during this phase. Low blood sugar during this phase can result in decreased lactate threshold levels, which explains why I can’t run as fast as usual. Women are also slower to begin to sweat during this luteal phase, which makes it harder for the body to regulate temperature during exercise, and a lower plasma volume means blood flow is slower, which consequently contributes to a slower recovery too. It seems that taking on extra sodium before exercise during this phase could also help aid fluid balance and endurance. How incredible that hormones can have such an impact on our performance two weeks every month!
  • There seems to be a mistruth that a woman’s iron levels drop during her period but actually this drop has been shown to not be significant enough to affect performance. However, if you do suffer from heavy periods, do check with your doctor about whether a supplement may be appropriate. Running can affect iron levels in general – men too! – as iron can be lost through sweat, and the gastrointestinal tract. There is also a theory that the simple act of footstrike can cause iron loss – so it’s worth looking into iron supplementation, particularly if you have been feeling more tired than normal lately.

In summary, my advice would be to keep a diary of your menstrual cycle and your running performance to find a pattern and help to plan your race diary. I would recommend planning your races for when you are on your period, or during the follicular phase. And get your iron levels tested frequently. Be careful of high-intensity training during the luteal phase, and plan in more recovery time too.

What are your experiences of training at different stages of your menstrual cycle?