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Like most women, I have a love-hate relationship with my period. On one hand, my monthly visitor is notoriously inconvenient, often showing up just with plenty of cramps and headaches in tow. On the other hand, I realize that my period’s extreme punctuality each month is a good indicator that all is working properly with my lady parts.

For me, missing a period is not something that happens . . . ever. My cycle is so annoyingly regular, you can set a clock by it. So you can imagine my sudden panic when one day, about eight months ago, my little friend didn’t show up for her monthly visit. 

After a mild anxiety attack, two pregnancy tests, and a trip to the doctor, I finally discovered the culprit – exercise.

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Yes, it turns out that, for some women, starting an intense new workout routine like marathon training or weightlifting (which I had just done) for the first time can produce stress hormones, the same way that a big move, new job, or tough break-up sometimes does. When this stress affects your brain and causes your menstrual cycle to stop, it's called hypothalamic amenorrhea.

“This particular area of the brain, the hypothalamus, is where a lot of the hormones for your period are regulated," ob-gyn Alyssa Dweck, MD, said in an interview with Shape. "The hypothalamus is very affected by stress.” She also explained that nature has a way of protecting you from getting pregnant if your body is under a high amount of stress. “Your body prevents ovulation so you don’t have a lot of estrogen, don’t build a big uterine lining, and then don't get a period." 

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So does this mean you should stop your sweat sessions at the gym? Not necessarily. While some women do end up noticing changes in their menstrual cycle after adopting exercise, others don't. DIana Ramo, MD/OBGYN, Co-Chair, The National Preconception Health and Health Care Initiative (PCHHC), explains that it all has to do with how each individual responses to stress. And if you do happen to experience any shifts, things should go back to normal once your body has adapted, which typically happens within one to three cycles.  

That's what happened with me — though my period was thrown off for one cycle after adding weightlifting to my exercise routine three to four times a week, it has since been its normal, very punctual self, even sometimes sparing me of the cramps and headaches I used to experience in the past. 

In fact, according to Dr. Thomas Hyde, a sports chiropractor physician and co-author of Conservative Management of Sports Injuries, exercise can, in many cases, make your period easier to deal with. “Moderate physical activity may actually improve various severe side effects of menstruation – including uterine cramping, vomiting, nausea and back pain —that occur in approximately 50 percent of women,” he told Livestrong.com.

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Just try not to overdo it. “Very strenuous exercise or what is required for athletic competition is not healthy,” fertility specialist Dr. Katherine Dale told Vivala. “It increases natural testosterone in women, and suppresses estrogen and progesterone,” which can affect your thyroid and increase your risk of having a miscarriage. 

So while you shouldn’t necessarily be intimidated by strenuous exercise, it might be a good idea to check in with your doctor before you start training for a triathlon, especially if this sort of routine is brand new for you. 

"Listen to your body," advises Ramos. "Ease into the workouts." She also reminds women that workouts don't have to be crazy strenuous. In fact, she notes that a simple walk (on a regular basis, of course) is enough to make a big difference in our health.