Periods get a bad rap. At best, they’re a monthly annoyance for the better part of four decades. And at worst, they can have dramatic, negative effects on everyday living, fertility struggles, and even athletic performance.

But a period—the menstruation phase of the female body’s cycle—is a sign that your body is functioning the way it should, explains Dr Stacy Sims, a female athletic performance physiologist. Although it may not feel like your period is doing you any favours that’s not actually the case, Sims tells Runner’s World. Exercising during your period can offer some surprising advantages for your fitness.

Let’s take a look at how you can use your menstruation cycle to your training advantage.

From a physiological standpoint, the first two days of the cycle actually lend themselves to harder training and better recovery, Sims says.

What is the menstrual cycle, exactly?
Sims explains that there are four phases of the reproductive cycle: menstruation, follicular, ovulation, and luteal. Fluctuating hormones define the different phases of the cycle.

Flashback to middle school health class: A period, or menstruation, is the shedding of uterine lining if an egg was not fertilized.
Unless you’re super in tune with your body, you may only recognise the menstruation phase thanks to cramping, bleeding, and in some cases, mood swings. “Unfortunately, around 35 to 40 percent of women suffer heavy menstrual bleeding,” Sims says, noting they may also experience severe cramps that keep them bedridden.

Even if you don’t notice the hormonal changes that come with other phases of your cycle, there’s often a lot going on in the body.

The phases of menstruation
Sims breaks down each phase of the cycle:

Menstruation phase: The bleeding phase is day one of your cycle, when estrogen and progesterone hormones drop, and there’s an inflammatory response from the uterine shedding. From a physiological standpoint, the first two days of the cycle actually lend themselves to harder training and better recovery, Sims says.

“Although women have historically thought they can’t do much [during their period], that they’re delicate flowers, that’s not true,” she says. On the contrary, it’s a good time to race or do HIIT workouts.

Follicular phase: The follicular phase, the longest phase of the cycle, is marked by the pituitary gland releasing a hormone, called follicle-stimulating hormone. That’s the hormone that (as the name implies) stimulates the follicles, which contain eggs in your ovaries to mature. Similar to the menstruation phase, your core body temperature is lower during this phase.

“During the follicular phase there’s a decrease in your core temperature compared with the luteal phase, so you might have better heat tolerance,” Sims explains. This makes the follicular phase another ideal time to hit the starting line or kick up your training in the gym.

Ovulation phase: Following the follicular phase is ovulation, when your body is preparing for an egg to be fertilized, and your levels of estrogen and progesterone increase. This phase only lasts for about 12 to 24 hours. It also marks the end of the follicular phase and beginning of the luteal phase.

Luteal phase: Finally, there’s the luteal phase, during which many women will experience premenstrual symptoms (PMS). There might be more inflammation during this phase because the body wants to avoid attacking a (potentially) fertilised egg, Sims explains.

How should you adjust your training to your menstrual cycle if you want to get the most out of your workouts?
For starters, know that consistent training is always key. You can work out at any time of your cycle and if you do so on the regular, you’ll gain benefits. But, if you want to get more in tune with your body and train to when you’re feeling your best (or when your body is primed for more intense workouts), it’s smart to get to know your cycle.

Before you menstruate — that is, during the luteal phase — your hormones increase, there’s a drop in your plasma volume (so your blood gets thicker), you have less sodium in your system, your core temperature increases, and you might feel fatigued, explains Professor Caroline Apovian, professor of medicine at Harvard Medical School and co-director of the Center for Weight Management and Wellness at Brigham and Women’s Hospital. This all contributes to those PMS symptoms women often experience.

During the luteal phase, research has shown — surprisingly to many — that thanks to high levels of estrogen and progesterone, things like endurance, static strength endurance (measured on a grip strength meter), VO2 max, and maximal endurance performance can be diminished.

A small study published in the Journal of Sports Medicine and Physical Fitness in 2020, analysing info from 10 trained female runners, found that running economy — how efficiently a runner can use oxygen during exercise — was worse during the mid-luteal phase, compared to other phases of the cycle, which can affect training and performance.

These findings contradict what nearly 50 percent of elite athletes perceive: that performance is negatively affected during menstruation. In fact, once you start bleeding is an ideal time to push your training and even schedule a goal race.

“This is when your body is at its strongest,” Apovian tells Runner’s World. “Your estrogen and progesterone drop, and that’s when you’re stronger during workouts.”

When estrogen and progesterone levels are low (like in the menstrual phase and early follicular phase), Sims explains, women can access carbohydrates more easily, which means they can hit higher-intensity workouts more easily. Core body temps are also down during this time, too, by as much as one degree Fahrenheit, which helps promote heat tolerance. “The body is also more resilient to stress, from a physiological and psychological standpoint,” Sims adds.

This is the time, Apovian says, to go hard on the road and in the weight room. “As you start bleeding, you have more ability to do intense weight lifting,” she says, noting that strength training is incredibly important for women to improve bone density.

Not only are women’s bodies primed for harder workouts and better recovery during their periods, but the immune system is more resilient to bacteria and viruses, Sims explains. “Your body is like, ‘Boom! We didn’t get pregnant. We’re ready to take over the world,” she says.

In addition to the body being better equipped to tackle tough workouts during menstruation, women may also see more robust responses to exercise, Sims says, thanks to that improved resilience and decreased inflammation.

“We are looking at maximising training stress to maximise adaptations,” Sims says. “Sure, women can do high intensities whenever they want, but they won’t necessarily get the same stimulus when the [progesterone and estrogen] sex hormones are elevated.”

Exercise physiologist Dr Alyssa Olenick, agrees women can gain benefits from training during the follicular phase — but smart training programmes performed any time throughout the month will yield advantages, she notes.

“There might be a slight benefit at this time with some early data suggesting more muscle or strength gains with higher volume during the follicular phase versus the luteal phase,” she tells Runner’s World via e-mail. But, she notes, there are only a few studies on this and they don’t compare it to training throughout the month, but rather to other phases of the cycle. That’s why we need more research on this—and on training for endurance throughout the menstrual cycle.

She goes on to say there isn’t any data to say that high-intensity exercise during the luteal phase is bad for you.

Sims says that someone doesn’t have to put a complete pause on training during her luteal phase when she might feel a little off. Instead, it’s more about being aware of what’s going on, which can help put training highs and lows into perspective. “Physiologically there might be something going on that’s making those intervals harder,” she says. “Or that hot yoga class is harder because you have less heat tolerance.”

What’s the best way to track your cycle?
To get more in tune with your cycle so you can better plan and make the most of your workouts — or simply recognize the link between your cycle and how you feel during your workouts — the best way to learn is to take notes.

There are several apps that are designed to help, including Clue or Flo. The more information you share with these tracking apps, the more personalized feedback they give. You can also track the days of your cycle and how you’re feeling on the calendar app on your phone or a tried-and-true paper journal.

“Women need to be able to find their own patterns,” Sims says. “They might feel fine on day five but flat on day six. Tracking can help women dial in their training to make the most of the [hormone fluctuation].”

An important note: Sims emphasises the importance of tracking individual cycles and for women to understand their own highs and lows. “It would be a significant misstep to tell women they can’t train when they feel great,” Sims says. In other words, even if experts suggest your workouts could be better during the menstrual and follicular phases of your cycle, if you find yourself feeling energised and ready to tackle a tough interval and tempo workout during the other phases — get after it.

What if you’re on hormonal birth control?
Women who are on hormonal birth control do not get a normal period, Sims emphasises, noting it’s a “huge misconception.” Unless women are using an intrauterine device (IUD), hormonal birth control down-regulates the natural ovarian hormones and the cycle is regulated by hormones not created by the body (called exogenous hormones).

“The bleed [women experience] is withdrawal bleed from the hormones, which is not representative of what is happening in the body,” Sims says.

This said, Sims points out that during the first five or so days of the active birth control pill, women can recover well and hit high intensities, similarly to the natural follicular phase.

“But for each subsequent day on the hormones, recovery and the ability for intensity decreases, with the lowest [ability to recover] occurring in the last week of the active pills,” she says.

Olenick points out that the menstrual cycle research as it relates to training does not apply to women on hormonal birth control in the same way, so it’s tough to offer concrete guidelines to this population.

Should you adjust your nutrition during your cycle?
There’s no question that proper nutrition can improve performance and recovery. It also can help improve various symptoms that come with the menstruation cycle, including fatigue and cramping.

Apovian and Sims stress how crucial hydration is during menstruation thanks to fluid loss. That means during intense training cycles, you’ll want to (and should) drink even more.

Protein is also incredibly important, throughout the cycle, and especially during the luteal phase. Sims says we need about 12 percent more protein during this time because our bodies are building tissue.

Carbohydrates are also key during the luteal phase, she says, because our bodies have a harder time accessing them. She recommends at least 45 percent to 50 percent of daily calories from carbs — the typical recommendation by the USDA, but the key is to avoid skimping on carbs during this time.

Runners also need to be cognisant about their iron needs during the menstruation phase, especially, due to blood loss. For those who don’t get enough iron, researchers think performance might actually be worse in the early follicular phase because of iron-deficiency anaemia in those with heavy periods. That’s because iron is a key component of red blood cells, which transport oxygen to the muscles. Without adequate iron, runners can’t use their aerobic pathways effectively, therefore making your miles feel harder.

Female athletes tend to have lower levels of not only iron, but vitamin D and calcium, which are crucial for bone health. These are important to get into your diet throughout your cycle.

The bottom line on exercising during your period
“Having your period is a sign of health,” Sims says. “If your cycle is regular, your endocrine system is healthy. Your body has enough calories and resilience to stress to exist. When you see changes in your cycle, that’s an early red flag and [lets us] pull back to prevent injury and overtraining.”

Although science backs up the fact that women can perform better during their periods, they can perform well across the entire cycle, Olenick says, pointing out that nutrition strategies can help mitigate declines during certain parts of the cycle (like more protein during the luteal phase to boost recovery, for example).

At the end of the day, the key to unlocking the power of your period is to understand your body. Although cycles, hormones, and energy levels vary from person to person, honing in on your own will help you adjust training and racing — and maybe help you understand why your body might need to back off from training for a day or week. With this knowledge, just like dialled-in nutrition, sleep, stretching, and mileage, your period becomes another piece of the training and racing puzzle.

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