11 things you need to know about exercising on your period

Here's a fact that will surprise you: You can stop worrying about having your period on race day. Everyone worries about having their period for a big event, but in reality, your hormones are favorable for performance once your period starts. Remember Paula Radcliffe broke the world record for the fastest marathon in Chicago in 2002 while she had menstrual cramps!

It makes sense, if you think about it. Once you’re in the clear of the possibility of pregnancy, the body goes into a more relaxed mode and all those energy systems used in the high-hormone phase are at your disposal for exertion. Same goes for the low-hormone phase that follows your period. As ironic as it may seem, your exercise physiology is most like a man's during your period and the days that follow. And guess what? You're stronger, too.

More: How to Eliminate PMS From Your Life Forever

So whether you're working out, training, or racing, it will feel easier when you're in the low-hormone phase of your cycle, which starts the first day of menstrual bleeding. Though there are very few specific studies on performance throughout the menstrual cycle, one study conducted on swimmers found that the women clocked their fastest times during menstruation and their slowest during the premenstrual period.

That doesn't mean you're doomed if a key event lands on a high-hormone day. Research shows that key performance indicators such as max VO2 and lactate threshold (the point at which your muscles start to burn) remain constant throughout your cycle, so you can still score a personal best even with PMS in endurance sports. However, if you play stick-and-ball sports, such as soccer and lacrosse, you may notice a downtick in performance during this time.

More: 6 Estrogen Hormone Therapy Options Explained

I'd be lying if I said that exercise won't feel harder during those high-hormone days before your period. And there's no doubt that it can mess with your performance. The natural fluctuations of these powerful biochemical messengers impact your exercise metabolism, the fuels that you burn and spare, your plasma volume levels (which are needed to sweat), how well you tolerate heat, moods, and much more. Here are some of the "girl things" that can happen, especially as those hormone levels rise, and how best to control them:

1. It's harder to make muscle. 
The upsurge in estrogen and progesterone in women has a profound effect on muscle-cell turnover and protein synthesis. What I mean by this is that estrogen turns down the anabolic or growing capacity of the muscle and progesterone turns up the catabolism or breakdown of muscle tissue, which makes it more difficult to access amino acids. As a result, you have higher rates of muscle breakdown during hard efforts. It's simply harder for us to make and maintain muscle when these hormones are high.

2. Metabolism and cravings change. 
Where's the chocolate? Actually, pass the chips and anything else that's sweet and starchy while you're at it. Why? For one, estrogen reduces your carb-burning ability, likely to help you save those limited glycogen stores in case of pregnancy, famine, and emergency, while it increases fat burning and fatty acid availability. This is great for endurance activities, but you'll need to eat more carbs for high-intensity activity.

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3. You may be bloated.
You may start to feel belly bloat and your clothes may feel a bit tight in the days before your period because high estrogen and progesterone affect the hormones that regulate the fluid in your body. Estrogen increases the expression of a hormone called vasopressin (also known as arginine vasopressin or AVP) that is responsible for retaining water and constricting blood vessels. Meanwhile, progesterone competes for the same receptor site as another fluid regulatory hormone called aldosterone (responsible for retaining sodium), which means less aldosterone is released. This sets off another chain of events that ultimately leads to a reduction in blood volume (due to less total-body sodium retention) and therefore a reduction in cardiac output and blood pressure.

4. Heat feels hotter.
Progesterone elevates your core temperature, so you'll feel hotter to begin with. On top of that, lower blood volume during high-hormone days means it's harder for your body to sweat and cool itself. To compensate for the shift in core temperature and body water, it's important to do some PMS pregaming and start drinking before you begin your workout—especially if you're exercising in the heat.

More: How Severe PMS Threatens Your Health

5. Prepare for cramping.
The lining of your uterus doesn't just shed itself. The process is driven by the release of hormone-like chemicals called prostaglandins, which make your uterus contract and expel its lining. This can be an uncomfortable if not downright painful process. The best way to mitigate this is to do some preplanning. In the 5 to 7 days before your period starts, you can reduce the effect of cramp-causing chemicals (specifically PE-2, an estrogen-mediated prostaglandin) by taking magnesium, omega-3 fatty acids, and low-dose 80-milligram aspirin. Yes, it has to be aspirin, not ibuprofen or another nonsteroidal anti-inflammatory drug (NSAID), because aspirin suppresses the production of prostaglandins irreversibly, whereas other NSAIDs are reversible. Try this yoga routine to also help ease cramps.

6. Headaches can happen. 
Some women suffer menstrual headaches, particularly migraines, when estrogen levels shift. The best way to head off these headaches is to stay hydrated and eat more nitric oxide (NO)–rich foods, such as beets, pomegranate, watermelon, and spinach in the days leading up to the start of your period. The NO-rich foods will promote dilation and help reduce the severity of the shift.

7. Playing the field is trickier. Spatial cognition, which you use to locate teammates on the field or to identify and hit your target in sports such as golf or tennis, is strongest during menstruation and lowest during the midluteal or high-hormone phase. Testosterone has a strong positive influence on this ability.

8. GI issues may occur. 
Many women report having GI issues such as gas and diarrhea when their periods start. This has less to do with estrogen and progesterone (though progesterone, and to a small effect estrogen, slows the contractility of the smooth muscle of the digestive tract) and more with the prostaglandins that cause the uterine contractions and shedding.

9. May notice mood swings and lost mojo.
My coauthor, Selene Yeager, told me she wants to burn down the house about one day a month. Another client talks about how she feels like her world is crashing in. During a recent ride with a pro sprinter, she confided that the day or two before her period, "I feel like a newbie on my bike. Head's foggy. Body is bloated and unresponsive. It's really great, let me tell you." Getting more branched-chain amino acids (especially leucine) can help mitigate some of these unpleasant effects. Leucine crosses the blood-brain barrier, slows down the effect of serotonin, and fends off central nervous system fatigue.

10. Watch out for heavy bleeding.
If you have heavy periods, you're at higher risk of becoming anemic because your body may not be able to pump up your blood-iron stores fast enough to keep pace with your blood loss. Your risk is even greater if you are an athletic woman, since you have more muscle stress, damage, and inflammation from high levels of cortisol following hard efforts.

11. Keep a journal.
These days my clients are all about tracking every little move. They have activity trackers and sleep monitors and apps that help them analyze every morsel they put into their mouths. Yet I'm surprised how few women make note of their menstrual cycle and how they feel during it. Start now. As you train through several cycles, pay attention to how your body reacts and responds to training during each phase. It'll help you identify when you’re strongest and when you need to put in a little extra work for the performance you want.

This article originally appeared on RodaleWellness.com.