Exercise and your menstrual cycle

Exercise and your menstrual cycle

What you need to know from Women’s Sports Medicine at TRIA

Active and athletic women can experience irregularities in their menstrual cycle (period), which are related to exercise. Irregularities may mean not starting your period, or having your periods stop or become longer or shorter. Read this information to learn more about how exercise can affect your period and when to follow up with your clinician.

What is a typical menstrual cycle?

The menstrual cycle is the hormonal cycle a woman’s body goes through to prepare for pregnancy. A menstrual cycle starts the first day of your first period and lasts until the first day of your next period. Most girls get their first period around 12 years old, but any time between 8 and 15 is normal. First periods usually start for girls about 2 years after developing breasts and pubic hair. The average menstrual cycle lasts 28 days but can occur within 21 to 45 days. On average, women lose 2 to 3 tablespoons of blood during their period. Women continue to have a menstrual cycle until menopause. Menopause is the lack of a menstrual cycle for 12 months in a row. Menopause occurs for most women between 45 and 55 years old.

What is considered an irregular period?

The most common type of irregular period due to exercise is amenorrhea. Amenorrhea occurs when either you:

  • Have not had your first period by 15 years old (called primary amenorrhea).
  • Miss a period for at least 3 months in a row (called secondary amenorrhea).

Among women in general, amenorrhea occurs in 2 to 5 percent of women. Among athletes, amenorrhea occurs in as many as 69 percent of dancers and 65 percent of distance runners.

What causes amenorrhea?

Active and athletic women who are training hard for their sport can struggle to fuel their body (eat enough calories) for the amount of activity they are doing. This is one aspect of the female athlete triad, which is a group of interrelated conditions active women can experience.

An energy deficit (not having enough energy) can occur if you use up more calories with exercise than you take in. This energy deficit causes weight loss and hormonal changes that can change normal periods. Energy deficits may be done on purpose due to disordered eating behaviors. These behaviors may include focusing on eating only “healthy foods,” eating “clean” or eating very few calories to decrease body weight.

How to know if you are fueling your body correctly

Many active and athletic women think they’re eating enough calories. But they likely are not if they have an irregular period or no period. Having a period regularly can be a good sign that you’re taking in enough energy to meet your body’s demands. Using a calorie-counting app (on a smartphone or tablet computer) is not a good way to estimate your energy needs. Calorie-counting apps can underestimate or overestimate the actual amount of energy your body needs.

Health effects of irregular periods

Exercise can help promote good bone health. Irregular periods, however, can affect bone growth. Not having a period for more than 6 months, or having cycles longer than 34 days, can cause bone loss. The amount of bone loss depends on the amount of time you have irregular periods over your lifetime.

Bone stress fractures are also more common in active and athletic women who have irregular periods. Be aware that birth control (hormonal types) can hide irregular periods. Before starting birth control to help have regular periods, talk to your clinician about your diet and exercise.

Problems with your period

If you experience any of the following problems with your period, contact your clinician.

  • You haven’t had your first period by 15 years old.
  • You haven’t had a period for 3 or more months in a row.
  • Your periods are lasting longer than usual or more than 7 days.
  • You’re experiencing heavy bleeding with your periods, which requires changing a menstrual pad or tampon every 1 to 2 hours.
  • Your periods are very painful.

Tracking your menstrual cycle

Tracking your menstrual cycle can be an important part of training for your sport. That’s because the hormonal changes you experience throughout your period can change what your body needs to perform at its best. Plus, tracking your period can also help you spot irregularities. Consider using a calendar or app on your smartphone or tablet computer to help you keep an eye on your cycle and identify any irregularities.

For more information

Office of Women’s Health