Working out regularly affects all aspects of your life in a positive way. It keeps your heart healthy, improves flexibility and strength in your muscles, improves your blood pressure and blood circulation, gives you energy, helps you maintain a healthy weight, can prevent injuries or alleviate chronic pain, and can even make you have a better night's sleep.
Exercise can even help you when you have your period. You may not have a ton of energy to do what you normally do, but a little moderate exercise can actually alleviate cramps (dysmenorrhea) and bloating. The blood circulating through your body can also relieve headaches, and the release of endorphins can help you get rid of your cranky or depressed mood. I find that exercising can also curb my insatiable cravings for junk food.
Some women can stop getting their periods (called amenorrhea), and exercise can have something to do with that. If you are exercising excessively or obsessively, and have a lower percentage of body weight than is normal for your height (possibly from anorexia), your body could go into rescue mode. Working out takes a ton of energy, so in order for your body to keep up, it will begin to shut down unnecessary functions to use what little energy it has to keep your basic life functions going.
Since menstruation is not vital to your life, its purpose is to reproduce, your body will turn off the function to save energy. The good news is that usually when you begin cutting down on the exercise, and your body gets the nutrition and calories it needs, your periods should come back.
Likewise, if your body fat percentage is much higher than the normal level for your height (obesity), periods can also stop. Losing weight can help bring periods back.
Fit's Tips: Exercise and body weight aren't the only things that can affect your cycle, and a missing period isn't a disease, it's a symptom. If you are suffering from irregular or missed periods, make an appointment with your gynecologist so they can help you figure out how to get your period back.