Last month, on the day my period started, I had a few cramps, felt a little bloated, was slightly irritable, and noticed a lovely little pimple just to the left of center on my forehead. On most days, making all that go away (except the pimple) would be as easy as going out for a run. But on that day, lacing up my sneakers was too daunting. I felt exhausted, and gearing up for a workout seemed incredibly difficult. So I skipped the run—and didn’t feel better until the next day.

Why So Tired?

I didn’t think much about why I felt too tired to exercise that day, but if you have ever experienced something similar, there may be an explanation. A study from the University of Adelaide in Australia suggests that the phenomenon is quite real and probably related to hormone levels, which vary dramatically throughout the course of the menstrual cycle.

According to the study of young, sedentary women, exercise is most difficult from ovulation to the before the menstrual period starts. During this time, 2 of the principle menstrual cycle hormones, estrogen and progesterone, are low.

Researchers believed that the low hormone levels may cause exercise to be more difficult. They suggested that when these hormone levels are low, women may depend greater on fats than carbs as an energy source. This can contribute to muscle soreness and premature fatigue.

Testing Their Theory

In the study, a group of women went through the same exercises at different points during their menstrual cycles. Although the women completed the same exercise test in both phases of the menstrual cycle, the exercise test conducted at the beginning of the month took longer to complete and the women reported feeling more physically and mentally fatigued at this time point.

Exercise Could Help (If You Weren’t So Tired)

While hormone levels may lead to difficulty with exercise during the menstrual period, exercise is a good remedy for the symptoms many women encounter before and during their periods. Exercise can improve your mood, increase your metabolism, and help reduce bloating. In addition, the American College of Obstetricians and Gynecologists advises women to exercise to help alleviate menstrual cramps.

According to the 2008 Physical Activity Guidelines for Americans, all adults need at least 150 minutes of moderate intensity aerobic physical activity each week, which amounts to 30 minutes a day.

What About Your Diet?

Looking at your diet may be one way to increase energy. Eat a healthy, well-balanced diet. It should be rich in fruits and vegetables. Drink plenty of fluids. Also, limiting salt may help reduce bloating and limiting caffeine might help with irritability.

There are also nutritional supplements that may help with premenstrual syndrome symptoms:

  • Calcium can reduce pain, cramping, and mood swings
  • Magnesium can reduce headache, fluid retention, and mood changes
  • Vitamin E can help with breast tenderness
  • Talk to your doctor before you begin taking any vitamins or supplements.

    Medication May Help

    Every woman's menstrual cycle is different. Track your symptoms over time to learn your specific patterns and share them with your doctor if you are concerned.