Have you noticed that sometimes your run feels amazing, like you could fly, and the next week the same workout feels sluggish and exhausting? Ever wondered why?

As women, we are all well aware of the changes that our bodies go through with our menstrual cycles. As runners, it’s especially important to pay attention to what is going on with our bodies and how it can affect our running performance. Every woman’s response to hormone levels is different and it can be hard to predict the optimal time for hard workouts and racing. We are hoping that the following information can help you navigate your training schedule within your cycle.

There are two phases in a woman’s cycle: the follicular phase – days 1-14 – begins with the start of your period, and the luteal phase – days 15-28 – begins with ovulation. During the follicular phase, estrogen levels rise, and progesterone levels are decreased. During the luteal phase, your estrogen levels are lowered and progesterone rises. 

Both of these hormones have an affect on a runner’s physiology. Estrogen affects a lot of things. A normal level of estrogen can promote bone density, so as estrogen levels decrease, so does bone strength. This is why women post menopause can be more susceptible to osteoporosis. Estrogen can also affect lung function, body temperature control, plasma volume in your blood, and hydration and fluid retention. Estrogen can also promote muscle glycogen, which is the process that the body absorbs carbohydrates for fuel. All of these factors are important for runners, so it’s a good idea to pay attention to them during your cycle. 

Here’s what happens to your body during each phase and what it could mean for your running performance. 

During the follicular phase, estrogen is increased. Your lung function may be higher during this phase, so you may be able to breathe easier during this phase. Your metabolism is affected as well. Higher estrogen promotes increased muscle glycogen. This means that during this phase your primary source of fuel is carbohydrates. It’s important to replenish, maybe even increase, your carb intake during this phase because your glycogen metabolism is increased. You might notice feeling more heavy, sluggish and bloated during the first several days of the follicular phase. 

During the luteal phase, estrogen levels drop and progesterone increases. Progesterone stimulates breathing and elevates heart rate, which can make the same workout feel more labored during this phase.  Body temperature levels are also elevated during this phase, so it can be difficult to regulate in hot weather. You may also sweat more during this phase, so make sure you are replenishing your electrolytes, especially during this phase. Additionally, blood sugar levels can decrease during the luteal phase, which means the level of lactate also decreases. This means that your lactate threshold runs may need to be performed at a higher intensity during the luteal phase. During this phase, your body’s metabolism has a greater reliance on fat and tends to save glycogen, so fatigue can possibly be delayed during longer, harder runs.

It’s important to keep in mind that intense workouts and reduced caloric intake can affect hormone balance and can cause an irregular cycle or amenorrhea (absence of a period). As you continue and progress with your training, it’s important to adjust your nutrition accordingly to accommodate the demand placed on your body. 

As you can see, there can be arguments made for racing and running hard during either phase. What’s important is that you listen to your body and become aware of how it reacts to the training and your cycle and make adjustments accordingly. My personal experience is that mid-follicular phase (around day 5-6) seems to be my peak performance time. Others have reported having better performance mid-luteal phase. My suggestion is to pay attention, maybe even keep a log for a month or two, paying attention to your heart rate, fatigue levels, how you feel, nutrition and hydration and plan your races accordingly.

Run like a girl!