How the Menstrual Cycle Impacts Running—and What You Can Do About It

For trail runners, the menstrual cycle is a classic catch-22.

The prolonged absence of a menstrual cycle could indicate a relative energy deficiency from inadequate diet, excessive exercise or a combination of both. (It could also warrant a trip to the local pharmacy for a pregnancy test.)

Meanwhile, a normal menstrual cycle indicates health and hormonal synergy, but running in certain phases of the menstrual cycle can be a pain in the rear (or, more accurately, a pain in the front).

Here’s a rundown of how the hormonal fluctuations of the menstrual cycle can impact your running, as well as strategies for optimizing performance.

1. Body Temperature

The Science

Progesterone, the hormone that dominates the luteal phase—the phase of the menstrual cycle between ovulation and menstruation; see sidebar at article’s end for a complete description of the different phases—increases basal body temperature by an average of 0.4 degrees Fahrenheit.

Research studies have shown that in the middle of the luteal phase, increased body temperature can hurt performance, especially during prolonged exercise in hot, humid climates (like Western States, Badwater or the Vermont 100).

Think of the body as having a thermostat like a fancy car, with a built-in default setting. Your body turns on its air conditioning (i.e., starts sweating) when you have reached a designated temperature above the default setting.

However, if the air conditioning is not strong enough or if the environmental temperature is extra high, the body temperature will continue to rise until performance is decreased.

The menstrual cycle affects the thermostat, raising the default setting at which the body starts cooling itself and making athletes more susceptible to performance impacts. In some circumstances, the temperature can even climb until heat exhaustion occurs.

RELATED: How The Menstrual Cycle And Birth Control Can Affect Runners

Optimizing Performance

Let’s be real, if you are lucky enough to get into Western States, you are not going to drop just because you are in your luteal phase. Studies have shown that various forms of pre-cooling, especially cold-water immersion and crushed-ice ingestion, before an event can improve endurance performance. These techniques could be especially important for women in the luteal phase.

However, pre-cooling alone won’t cut it in longer races like Western States. Practice cooling throughout the race by having cooling tools prepared at each aid station, such as arm sleeves to pack with ice and neck bandanas to dip in cold water. And use every stream crossing for some extra cold-water immersion!

2. Metabolism and Nutrition

The Science

Estrogen plays a role in metabolism by increasing fat utilization and decreasing utilization of stored carbohydrates, while progesterone increases the breakdown of proteins.

What does this mean in the context of the menstrual cycle? During the luteal phase, and particularly the mid-luteal phase, when estrogen levels are high, the body is not as capable of utilizing stored carbohydrates. This makes supplemental carbohydrates all the more important, to avoid low blood sugar.

Progesterone is also high in the luteal phase, so it is essential to concentrate on protein intake to promote recovery.

Optimizing Performance

Focus on carbohydrate consumption in order to hit higher intensity levels in racing and training.

In this phase, “first breakfast” before a run becomes just as important as “second breakfast” after the run. A banana (31 grams of carbohydrates) or oatmeal (54 grams of carbohydrates per half cup) are ideal pre-run, “first breakfast” choices.

For fueling while running, Dr. Stacy Sims, the co-founder of Osmo Nutrition and author of ROAR, a physiology-based training and nutrition book for women, recommends 2.5 food calories per kilogram of bodyweight per hour of activity in the mid-luteal phase. If you like breaking it down in terms of carbohydrates, she recommends consuming approximately 40 to 45 grams of carbs per hour.

Finally, post-run nutrition in the mid-luteal phase should incorporate both protein and carbohydrates. Dr. Sims recommends 20 to 30 grams of protein and 8 to 10 grams of carbs within 30 minutes of training. My favorite post-run “second breakfast” is Greek yogurt with a handful of cereal, and coffee.

3. Premenstrual Symptoms

The Science

Despite the frequency of the term “PMS,” only 20 to 30 percent of women have premenstrual syndrome, characterized by consistent emotional and physical symptoms that interfere with their daily life.

Premenstrual symptoms, on the other hand, are more ubiquitous, affecting approximately 80 percent of women. These symptoms include bloating, abdominal cramps, breast tenderness, food cravings, fatigue, mood swings and insomnia; they start at some point in the luteal phase (days 15 to 28) and generally resolve themselves once menstrual flow starts.

Although the science of premenstrual symptoms and PMS is complex and not entirely clear, there are some well-tested methods for alleviating symptoms.

Optimizing Performance

If we were playing Family Feud, bloating and abdominal cramping would easily top the list of trail runners’ most bothersome premenstrual symptoms. Through some simple techniques, it is easy to reduce and even prevent these symptoms.

RELATED: How Women Athletes’ Nutritional Needs Differ From Mens’

First, understand safe techniques while training or racing. Many runners use over-the-counter pain medications such as non-steroidal anti-inflammatory drugs(NSAIDs)—which include aspirin, ibuprofen and naproxen—to manage premenstrual symptoms. NSAIDs inhibit hormones that regulate blood flow to the kidneys, and ultrarunners who may be running for several hours (or days) have an increased risk of kidney damage with NSAID use.

Midol is another commonly used over-the-counter drug for menstrual cramp relief that comes in different formulations. (Check the components, as some formulations contain NSAIDs.) For some runners, Tylenol 8-hour Controlled Release Tablets can be helpful when used in moderation (excessive use can cause liver damage) as they have a different mechanism of action than NSAIDs.

One of the best tips for staving off bloating and abdominal cramping is to avoid alcohol while symptomatic—so hold off on that post-run shower beer. Instead, hydrate with plenty of water.

Studies have also shown that some premenstrual symptoms are related to poor dietary habits and low magnesium levels. Runners with premenstrual symptoms should consider consuming foods that are high in magnesium, like spinach, black beans, avocado, dark chocolate and pumpkin seeds. (Put them together for an interesting salad—or dessert, depending on the ratio of chocolate to everything else.)

Putting It All Together

Female runners vary in their exact menstrual timeline and their symptoms from month to month. It can be helpful to include menstrual cycle details in a training log (although maybe not in the comment section in Strava) to find patterns in performance.

Most runners feel best on days 5 to 14 and 17 to 20 of their menstrual cycle, when estrogen and progesterone are lowest and glycogen stores are readily available. These days are a great time to race or plan a key workout.

Generally, during the luteal phase, focus on cooling and carbohydrate supplementation, and avoid NSAIDs during any part of the menstrual cycle when you will be exercising vigorously.

The rest of the time, focus on treating your symptoms with these techniques, keeping in mind that your performance shouldn’t be impacted too much as long as you adjust fueling and cooling accordingly.

Armed with this information, if you still feel like your menstrual cycle abnormally influences your race or training performance, or if you feel that your premenstrual symptoms are interfering with your daily life, you should consider scheduling an appointment with your doctor.

The Phases of the Menstrual Cycle

The natural menstrual cycle—defined here as the first day of one period to the first day of the next period—can vary from runner to runner. Although I outline a 28-day cycle with five days of menstrual flow, it’s considered normal for an adult cycle to span anywhere from 21 to 35 days with two to seven days of menstrual flow.

Some runners may choose to take an oral contraceptive pill (OCP) or have an intrauterine device (IUD) placed, which can influence the timing of the menstrual cycle and can alter associated symptoms. There are several important concepts that runners should understand before choosing an OCP, IUD or other contraceptive. (I will discuss OCPs and running performance in a future article.)

Here’s a quick outline of the menstrual cycle:

The Follicular Phase

Timeline: Average is days 1-14, with variations that span 11-21 days.

Hormones: The follicular phase begins on day one with the onset of menstrual flow. Menstrual flow occurs when estrogen and progesterone levels drop from the previous cycle, which causes the lining of the uterus to shed. After menstrual flow stops, estrogen levels begin to slowly rise, while progesterone levels remain low.

Overall: A follicle will mature into an egg.

Symptoms: Possible menstrual cramps during the first few days of menstrual flow.

The Ovulatory Phase

Timeline: Average is day 14, but depends on the length of the follicular phase.

Hormones: Rising estrogen causes a rise in luteinizing hormone and a mature egg is released from the ovary.

Overall: If you are considering pregnancy, alert your (training) partner!

Symptoms: Some women may feel lower abdominal pain for a couple minutes to a few hours. If you want to sound fancy at a dinner party, the pain is called mittelschmerz, a German word meaning “middle pain.”

RELATED: When Should You Skip A Run?

The Luteal Phase

Timeline: Average is days 15-28, with variations that span 10-16 days.

Hormones: Progesterone levels rise after ovulation and remain high throughout most of this phase. Estrogen levels initially drop after ovulation, but then start to slowly rise. If the egg is not fertilized, estrogen and progesterone levels drop, menstrual flow starts and the luteal phase ends.

Overall: The uterine lining becomes thicker to prepare for possible pregnancy.

Symptoms: RAWRRR! This effect can be classified as a premenstrual symptom. Premenstrual symptoms occur 1-2 weeks before menstrual flow and can cause bloating, abdominal cramps, appetite changes, mood swings, depression, and insomnia.

Megan Roche is a fourth-year Stanford Medical student, a four-time USATF trail national champion and a member of Nike Trail Elite and Team Clif Bar. Follow Megan’s training on Strava here and follow her on Twitter here.